SpringCloud 源码系列（5）—— 负载均衡 Ribbon（下）

SpringCloud 源码系列（4）—— 负载均衡 Ribbon（上）

SpringCloud 源码系列（5）—— 负载均衡 Ribbon（下）

五、Ribbon 核心接口

前面已经了解到 Ribbon 核心接口以及默认实现如何协作来查找要调用的一个实例，这节再来看下各个核心接口的一些特性及其它实现类。

1、客户端配置 — IClientConfig

IClientConfig 就是管理客户端配置的核心接口，它的默认实现类是 DefaultClientConfigImpl。可以看到在创建 IClientConfig 时，设置了 Ribbon 客户端默认的连接和读取超时时间为 1 秒，例如读取如果超过1秒，就会返回超时，这两个一般需要根据实际情况来调整。、

 1 @Bean
 2 @ConditionalOnMissingBean
 3 public IClientConfig ribbonClientConfig() {
 4     DefaultClientConfigImpl config = new DefaultClientConfigImpl();
 5     // 加载配置
 6     config.loadProperties(this.name);
 7     // 连接超时默认 1 秒
 8     config.set(CommonClientConfigKey.ConnectTimeout, DEFAULT_CONNECT_TIMEOUT);
 9     // 读取超时默认 1 秒
10     config.set(CommonClientConfigKey.ReadTimeout, DEFAULT_READ_TIMEOUT);
11     config.set(CommonClientConfigKey.GZipPayload, DEFAULT_GZIP_PAYLOAD);
12     return config;
13 }

CommonClientConfigKey 这个类定义了 Ribbon 客户端相关的所有配置的键常量，可以通过这个类来看有哪些配置。

  1 public abstract class CommonClientConfigKey<T> implements IClientConfigKey<T> {
  2
  3     public static final IClientConfigKey<String> AppName = new CommonClientConfigKey<String>("AppName"){};
  4
  5     public static final IClientConfigKey<String> Version = new CommonClientConfigKey<String>("Version"){};
  6
  7     public static final IClientConfigKey<Integer> Port = new CommonClientConfigKey<Integer>("Port"){};
  8
  9     public static final IClientConfigKey<Integer> SecurePort = new CommonClientConfigKey<Integer>("SecurePort"){};
 10
 11     public static final IClientConfigKey<String> VipAddress = new CommonClientConfigKey<String>("VipAddress"){};
 12
 13     public static final IClientConfigKey<Boolean> ForceClientPortConfiguration = new CommonClientConfigKey<Boolean>("ForceClientPortConfiguration"){}; // use client defined port regardless of server advert
 14
 15     public static final IClientConfigKey<String> DeploymentContextBasedVipAddresses = new CommonClientConfigKey<String>("DeploymentContextBasedVipAddresses"){};
 16
 17     public static final IClientConfigKey<Integer> MaxAutoRetries = new CommonClientConfigKey<Integer>("MaxAutoRetries"){};
 18
 19     public static final IClientConfigKey<Integer> MaxAutoRetriesNextServer = new CommonClientConfigKey<Integer>("MaxAutoRetriesNextServer"){};
 20
 21     public static final IClientConfigKey<Boolean> OkToRetryOnAllOperations = new CommonClientConfigKey<Boolean>("OkToRetryOnAllOperations"){};
 22
 23     public static final IClientConfigKey<Boolean> RequestSpecificRetryOn = new CommonClientConfigKey<Boolean>("RequestSpecificRetryOn"){};
 24
 25     public static final IClientConfigKey<Integer> ReceiveBufferSize = new CommonClientConfigKey<Integer>("ReceiveBufferSize"){};
 26
 27     public static final IClientConfigKey<Boolean> EnablePrimeConnections = new CommonClientConfigKey<Boolean>("EnablePrimeConnections"){};
 28
 29     public static final IClientConfigKey<String> PrimeConnectionsClassName = new CommonClientConfigKey<String>("PrimeConnectionsClassName"){};
 30
 31     public static final IClientConfigKey<Integer> MaxRetriesPerServerPrimeConnection = new CommonClientConfigKey<Integer>("MaxRetriesPerServerPrimeConnection"){};
 32
 33     public static final IClientConfigKey<Integer> MaxTotalTimeToPrimeConnections = new CommonClientConfigKey<Integer>("MaxTotalTimeToPrimeConnections"){};
 34
 35     public static final IClientConfigKey<Float> MinPrimeConnectionsRatio = new CommonClientConfigKey<Float>("MinPrimeConnectionsRatio"){};
 36
 37     public static final IClientConfigKey<String> PrimeConnectionsURI = new CommonClientConfigKey<String>("PrimeConnectionsURI"){};
 38
 39     public static final IClientConfigKey<Integer> PoolMaxThreads = new CommonClientConfigKey<Integer>("PoolMaxThreads"){};
 40
 41     public static final IClientConfigKey<Integer> PoolMinThreads = new CommonClientConfigKey<Integer>("PoolMinThreads"){};
 42
 43     public static final IClientConfigKey<Integer> PoolKeepAliveTime = new CommonClientConfigKey<Integer>("PoolKeepAliveTime"){};
 44
 45     public static final IClientConfigKey<String> PoolKeepAliveTimeUnits = new CommonClientConfigKey<String>("PoolKeepAliveTimeUnits"){};
 46
 47     public static final IClientConfigKey<Boolean> EnableConnectionPool = new CommonClientConfigKey<Boolean>("EnableConnectionPool") {};
 48
 49     /**
 50      * Use {@link #MaxConnectionsPerHost}
 51      */
 52     @Deprecated
 53     public static final IClientConfigKey<Integer> MaxHttpConnectionsPerHost = new CommonClientConfigKey<Integer>("MaxHttpConnectionsPerHost"){};
 54
 55     /**
 56      * Use {@link #MaxTotalConnections}
 57      */
 58     @Deprecated
 59     public static final IClientConfigKey<Integer> MaxTotalHttpConnections = new CommonClientConfigKey<Integer>("MaxTotalHttpConnections"){};
 60
 61     public static final IClientConfigKey<Integer> MaxConnectionsPerHost = new CommonClientConfigKey<Integer>("MaxConnectionsPerHost"){};
 62
 63     public static final IClientConfigKey<Integer> MaxTotalConnections = new CommonClientConfigKey<Integer>("MaxTotalConnections"){};
 64
 65     public static final IClientConfigKey<Boolean> IsSecure = new CommonClientConfigKey<Boolean>("IsSecure"){};
 66
 67     public static final IClientConfigKey<Boolean> GZipPayload = new CommonClientConfigKey<Boolean>("GZipPayload"){};
 68
 69     public static final IClientConfigKey<Integer> ConnectTimeout = new CommonClientConfigKey<Integer>("ConnectTimeout"){};
 70
 71     public static final IClientConfigKey<Integer> BackoffInterval = new CommonClientConfigKey<Integer>("BackoffTimeout"){};
 72
 73     public static final IClientConfigKey<Integer> ReadTimeout = new CommonClientConfigKey<Integer>("ReadTimeout"){};
 74
 75     public static final IClientConfigKey<Integer> SendBufferSize = new CommonClientConfigKey<Integer>("SendBufferSize"){};
 76
 77     public static final IClientConfigKey<Boolean> StaleCheckingEnabled = new CommonClientConfigKey<Boolean>("StaleCheckingEnabled"){};
 78
 79     public static final IClientConfigKey<Integer> Linger = new CommonClientConfigKey<Integer>("Linger"){};
 80
 81     public static final IClientConfigKey<Integer> ConnectionManagerTimeout = new CommonClientConfigKey<Integer>("ConnectionManagerTimeout"){};
 82
 83     public static final IClientConfigKey<Boolean> FollowRedirects = new CommonClientConfigKey<Boolean>("FollowRedirects"){};
 84
 85     public static final IClientConfigKey<Boolean> ConnectionPoolCleanerTaskEnabled = new CommonClientConfigKey<Boolean>("ConnectionPoolCleanerTaskEnabled"){};
 86
 87     public static final IClientConfigKey<Integer> ConnIdleEvictTimeMilliSeconds = new CommonClientConfigKey<Integer>("ConnIdleEvictTimeMilliSeconds"){};
 88
 89     public static final IClientConfigKey<Integer> ConnectionCleanerRepeatInterval = new CommonClientConfigKey<Integer>("ConnectionCleanerRepeatInterval"){};
 90
 91     public static final IClientConfigKey<Boolean> EnableGZIPContentEncodingFilter = new CommonClientConfigKey<Boolean>("EnableGZIPContentEncodingFilter"){};
 92
 93     public static final IClientConfigKey<String> ProxyHost = new CommonClientConfigKey<String>("ProxyHost"){};
 94
 95     public static final IClientConfigKey<Integer> ProxyPort = new CommonClientConfigKey<Integer>("ProxyPort"){};
 96
 97     public static final IClientConfigKey<String> KeyStore = new CommonClientConfigKey<String>("KeyStore"){};
 98
 99     public static final IClientConfigKey<String> KeyStorePassword = new CommonClientConfigKey<String>("KeyStorePassword"){};
100
101     public static final IClientConfigKey<String> TrustStore = new CommonClientConfigKey<String>("TrustStore"){};
102
103     public static final IClientConfigKey<String> TrustStorePassword = new CommonClientConfigKey<String>("TrustStorePassword"){};
104
105     // if this is a secure rest client, must we use client auth too?
106     public static final IClientConfigKey<Boolean> IsClientAuthRequired = new CommonClientConfigKey<Boolean>("IsClientAuthRequired"){};
107
108     public static final IClientConfigKey<String> CustomSSLSocketFactoryClassName = new CommonClientConfigKey<String>("CustomSSLSocketFactoryClassName"){};
109      // must host name match name in certificate?
110     public static final IClientConfigKey<Boolean> IsHostnameValidationRequired = new CommonClientConfigKey<Boolean>("IsHostnameValidationRequired"){};
111
112     // see also http://hc.apache.org/httpcomponents-client-ga/tutorial/html/advanced.html
113     public static final IClientConfigKey<Boolean> IgnoreUserTokenInConnectionPoolForSecureClient = new CommonClientConfigKey<Boolean>("IgnoreUserTokenInConnectionPoolForSecureClient"){};
114
115     // Client implementation
116     public static final IClientConfigKey<String> ClientClassName = new CommonClientConfigKey<String>("ClientClassName"){};
117
118     //LoadBalancer Related
119     public static final IClientConfigKey<Boolean> InitializeNFLoadBalancer = new CommonClientConfigKey<Boolean>("InitializeNFLoadBalancer"){};
120
121     public static final IClientConfigKey<String> NFLoadBalancerClassName = new CommonClientConfigKey<String>("NFLoadBalancerClassName"){};
122
123     public static final IClientConfigKey<String> NFLoadBalancerRuleClassName = new CommonClientConfigKey<String>("NFLoadBalancerRuleClassName"){};
124
125     public static final IClientConfigKey<String> NFLoadBalancerPingClassName = new CommonClientConfigKey<String>("NFLoadBalancerPingClassName"){};
126
127     public static final IClientConfigKey<Integer> NFLoadBalancerPingInterval = new CommonClientConfigKey<Integer>("NFLoadBalancerPingInterval"){};
128
129     public static final IClientConfigKey<Integer> NFLoadBalancerMaxTotalPingTime = new CommonClientConfigKey<Integer>("NFLoadBalancerMaxTotalPingTime"){};
130
131     public static final IClientConfigKey<String> NFLoadBalancerStatsClassName = new CommonClientConfigKey<String>("NFLoadBalancerStatsClassName"){};
132
133     public static final IClientConfigKey<String> NIWSServerListClassName = new CommonClientConfigKey<String>("NIWSServerListClassName"){};
134
135     public static final IClientConfigKey<String> ServerListUpdaterClassName = new CommonClientConfigKey<String>("ServerListUpdaterClassName"){};
136
137     public static final IClientConfigKey<String> NIWSServerListFilterClassName = new CommonClientConfigKey<String>("NIWSServerListFilterClassName"){};
138
139     public static final IClientConfigKey<Integer> ServerListRefreshInterval = new CommonClientConfigKey<Integer>("ServerListRefreshInterval"){};
140
141     public static final IClientConfigKey<Boolean> EnableMarkingServerDownOnReachingFailureLimit = new CommonClientConfigKey<Boolean>("EnableMarkingServerDownOnReachingFailureLimit"){};
142
143     public static final IClientConfigKey<Integer> ServerDownFailureLimit = new CommonClientConfigKey<Integer>("ServerDownFailureLimit"){};
144
145     public static final IClientConfigKey<Integer> ServerDownStatWindowInMillis = new CommonClientConfigKey<Integer>("ServerDownStatWindowInMillis"){};
146
147     public static final IClientConfigKey<Boolean> EnableZoneAffinity = new CommonClientConfigKey<Boolean>("EnableZoneAffinity"){};
148
149     public static final IClientConfigKey<Boolean> EnableZoneExclusivity = new CommonClientConfigKey<Boolean>("EnableZoneExclusivity"){};
150
151     public static final IClientConfigKey<Boolean> PrioritizeVipAddressBasedServers = new CommonClientConfigKey<Boolean>("PrioritizeVipAddressBasedServers"){};
152
153     public static final IClientConfigKey<String> VipAddressResolverClassName = new CommonClientConfigKey<String>("VipAddressResolverClassName"){};
154
155     public static final IClientConfigKey<String> TargetRegion = new CommonClientConfigKey<String>("TargetRegion"){};
156
157     public static final IClientConfigKey<String> RulePredicateClasses = new CommonClientConfigKey<String>("RulePredicateClasses"){};
158
159     public static final IClientConfigKey<String> RequestIdHeaderName = new CommonClientConfigKey<String>("RequestIdHeaderName") {};
160
161     public static final IClientConfigKey<Boolean> UseIPAddrForServer = new CommonClientConfigKey<Boolean>("UseIPAddrForServer") {};
162
163     public static final IClientConfigKey<String> ListOfServers = new CommonClientConfigKey<String>("listOfServers") {};
164
165     private static final Set<IClientConfigKey> keys = new HashSet<IClientConfigKey>();
166
167     // ...
168 }

进入到 DefaultClientConfigImpl，可以看到 CommonClientConfigKey 中的每个配置都对应了一个默认值。在加载配置的时候，如果用户没有定制配置，就会使用默认的配置。

  1 public class DefaultClientConfigImpl implements IClientConfig {
  2
  3     public static final Boolean DEFAULT_PRIORITIZE_VIP_ADDRESS_BASED_SERVERS = Boolean.TRUE;
  4
  5     public static final String DEFAULT_NFLOADBALANCER_PING_CLASSNAME = "com.netflix.loadbalancer.DummyPing"; // DummyPing.class.getName();
  6
  7     public static final String DEFAULT_NFLOADBALANCER_RULE_CLASSNAME = "com.netflix.loadbalancer.AvailabilityFilteringRule";
  8
  9     public static final String DEFAULT_NFLOADBALANCER_CLASSNAME = "com.netflix.loadbalancer.ZoneAwareLoadBalancer";
 10
 11     public static final boolean DEFAULT_USEIPADDRESS_FOR_SERVER = Boolean.FALSE;
 12
 13     public static final String DEFAULT_CLIENT_CLASSNAME = "com.netflix.niws.client.http.RestClient";
 14
 15     public static final String DEFAULT_VIPADDRESS_RESOLVER_CLASSNAME = "com.netflix.client.SimpleVipAddressResolver";
 16
 17     public static final String DEFAULT_PRIME_CONNECTIONS_URI = "/";
 18
 19     public static final int DEFAULT_MAX_TOTAL_TIME_TO_PRIME_CONNECTIONS = 30000;
 20
 21     public static final int DEFAULT_MAX_RETRIES_PER_SERVER_PRIME_CONNECTION = 9;
 22
 23     public static final Boolean DEFAULT_ENABLE_PRIME_CONNECTIONS = Boolean.FALSE;
 24
 25     public static final int DEFAULT_MAX_REQUESTS_ALLOWED_PER_WINDOW = Integer.MAX_VALUE;
 26
 27     public static final int DEFAULT_REQUEST_THROTTLING_WINDOW_IN_MILLIS = 60000;
 28
 29     public static final Boolean DEFAULT_ENABLE_REQUEST_THROTTLING = Boolean.FALSE;
 30
 31     public static final Boolean DEFAULT_ENABLE_GZIP_CONTENT_ENCODING_FILTER = Boolean.FALSE;
 32
 33     public static final Boolean DEFAULT_CONNECTION_POOL_CLEANER_TASK_ENABLED = Boolean.TRUE;
 34
 35     public static final Boolean DEFAULT_FOLLOW_REDIRECTS = Boolean.FALSE;
 36
 37     public static final float DEFAULT_PERCENTAGE_NIWS_EVENT_LOGGED = 0.0f;
 38
 39     public static final int DEFAULT_MAX_AUTO_RETRIES_NEXT_SERVER = 1;
 40
 41     public static final int DEFAULT_MAX_AUTO_RETRIES = 0;
 42
 43     public static final int DEFAULT_BACKOFF_INTERVAL = 0;
 44
 45     public static final int DEFAULT_READ_TIMEOUT = 5000;
 46
 47     public static final int DEFAULT_CONNECTION_MANAGER_TIMEOUT = 2000;
 48
 49     public static final int DEFAULT_CONNECT_TIMEOUT = 2000;
 50
 51     public static final Boolean DEFAULT_ENABLE_CONNECTION_POOL = Boolean.TRUE;
 52
 53     @Deprecated
 54     public static final int DEFAULT_MAX_HTTP_CONNECTIONS_PER_HOST = 50;
 55
 56     @Deprecated
 57     public static final int DEFAULT_MAX_TOTAL_HTTP_CONNECTIONS = 200;
 58
 59     public static final int DEFAULT_MAX_CONNECTIONS_PER_HOST = 50;
 60
 61     public static final int DEFAULT_MAX_TOTAL_CONNECTIONS = 200;
 62
 63     public static final float DEFAULT_MIN_PRIME_CONNECTIONS_RATIO = 1.0f;
 64
 65     public static final String DEFAULT_PRIME_CONNECTIONS_CLASS = "com.netflix.niws.client.http.HttpPrimeConnection";
 66
 67     public static final String DEFAULT_SEVER_LIST_CLASS = "com.netflix.loadbalancer.ConfigurationBasedServerList";
 68
 69     public static final String DEFAULT_SERVER_LIST_UPDATER_CLASS = "com.netflix.loadbalancer.PollingServerListUpdater";
 70
 71     public static final int DEFAULT_CONNECTION_IDLE_TIMERTASK_REPEAT_IN_MSECS = 30000; // every half minute (30 secs)
 72
 73     public static final int DEFAULT_CONNECTIONIDLE_TIME_IN_MSECS = 30000; // all connections idle for 30 secs
 74
 75     protected volatile Map<String, Object> properties = new ConcurrentHashMap<String, Object>();
 76
 77     protected Map<IClientConfigKey<?>, Object> typedProperties = new ConcurrentHashMap<IClientConfigKey<?>, Object>();
 78
 79     private static final Logger LOG = LoggerFactory.getLogger(DefaultClientConfigImpl.class);
 80
 81     private String clientName = null;
 82
 83     private VipAddressResolver resolver = null;
 84
 85     private boolean enableDynamicProperties = true;
 86     /**
 87      * Defaults for the parameters for the thread pool used by batchParallel
 88      * calls
 89      */
 90     public static final int DEFAULT_POOL_MAX_THREADS = DEFAULT_MAX_TOTAL_HTTP_CONNECTIONS;
 91     public static final int DEFAULT_POOL_MIN_THREADS = 1;
 92     public static final long DEFAULT_POOL_KEEP_ALIVE_TIME = 15 * 60L;
 93     public static final TimeUnit DEFAULT_POOL_KEEP_ALIVE_TIME_UNITS = TimeUnit.SECONDS;
 94     public static final Boolean DEFAULT_ENABLE_ZONE_AFFINITY = Boolean.FALSE;
 95     public static final Boolean DEFAULT_ENABLE_ZONE_EXCLUSIVITY = Boolean.FALSE;
 96     public static final int DEFAULT_PORT = 7001;
 97     public static final Boolean DEFAULT_ENABLE_LOADBALANCER = Boolean.TRUE;
 98
 99     public static final String DEFAULT_PROPERTY_NAME_SPACE = "ribbon";
100
101     private String propertyNameSpace = DEFAULT_PROPERTY_NAME_SPACE;
102
103     public static final Boolean DEFAULT_OK_TO_RETRY_ON_ALL_OPERATIONS = Boolean.FALSE;
104
105     public static final Boolean DEFAULT_ENABLE_NIWS_EVENT_LOGGING = Boolean.TRUE;
106
107     public static final Boolean DEFAULT_IS_CLIENT_AUTH_REQUIRED = Boolean.FALSE;
108
109     private final Map<String, DynamicStringProperty> dynamicProperties = new ConcurrentHashMap<String, DynamicStringProperty>();
110
111     public Boolean getDefaultPrioritizeVipAddressBasedServers() {
112         return DEFAULT_PRIORITIZE_VIP_ADDRESS_BASED_SERVERS;
113     }
114
115     public String getDefaultNfloadbalancerPingClassname() {
116         return DEFAULT_NFLOADBALANCER_PING_CLASSNAME;
117     }
118
119     public String getDefaultNfloadbalancerRuleClassname() {
120         return DEFAULT_NFLOADBALANCER_RULE_CLASSNAME;
121     }
122
123     public String getDefaultNfloadbalancerClassname() {
124         return DEFAULT_NFLOADBALANCER_CLASSNAME;
125     }
126
127     public boolean getDefaultUseIpAddressForServer() {
128         return DEFAULT_USEIPADDRESS_FOR_SERVER;
129     }
130
131     public String getDefaultClientClassname() {
132         return DEFAULT_CLIENT_CLASSNAME;
133     }
134
135     public String getDefaultVipaddressResolverClassname() {
136         return DEFAULT_VIPADDRESS_RESOLVER_CLASSNAME;
137     }
138
139     public String getDefaultPrimeConnectionsUri() {
140         return DEFAULT_PRIME_CONNECTIONS_URI;
141     }
142
143     public int getDefaultMaxTotalTimeToPrimeConnections() {
144         return DEFAULT_MAX_TOTAL_TIME_TO_PRIME_CONNECTIONS;
145     }
146
147     public int getDefaultMaxRetriesPerServerPrimeConnection() {
148         return DEFAULT_MAX_RETRIES_PER_SERVER_PRIME_CONNECTION;
149     }
150
151     public Boolean getDefaultEnablePrimeConnections() {
152         return DEFAULT_ENABLE_PRIME_CONNECTIONS;
153     }
154
155     public int getDefaultMaxRequestsAllowedPerWindow() {
156         return DEFAULT_MAX_REQUESTS_ALLOWED_PER_WINDOW;
157     }
158
159     public int getDefaultRequestThrottlingWindowInMillis() {
160         return DEFAULT_REQUEST_THROTTLING_WINDOW_IN_MILLIS;
161     }
162
163     public Boolean getDefaultEnableRequestThrottling() {
164         return DEFAULT_ENABLE_REQUEST_THROTTLING;
165     }
166
167     public Boolean getDefaultEnableGzipContentEncodingFilter() {
168         return DEFAULT_ENABLE_GZIP_CONTENT_ENCODING_FILTER;
169     }
170
171     public Boolean getDefaultConnectionPoolCleanerTaskEnabled() {
172         return DEFAULT_CONNECTION_POOL_CLEANER_TASK_ENABLED;
173     }
174
175     public Boolean getDefaultFollowRedirects() {
176         return DEFAULT_FOLLOW_REDIRECTS;
177     }
178
179     public float getDefaultPercentageNiwsEventLogged() {
180         return DEFAULT_PERCENTAGE_NIWS_EVENT_LOGGED;
181     }
182
183     public int getDefaultMaxAutoRetriesNextServer() {
184         return DEFAULT_MAX_AUTO_RETRIES_NEXT_SERVER;
185     }
186
187     public int getDefaultMaxAutoRetries() {
188         return DEFAULT_MAX_AUTO_RETRIES;
189     }
190
191     public int getDefaultReadTimeout() {
192         return DEFAULT_READ_TIMEOUT;
193     }
194
195     public int getDefaultConnectionManagerTimeout() {
196         return DEFAULT_CONNECTION_MANAGER_TIMEOUT;
197     }
198
199     public int getDefaultConnectTimeout() {
200         return DEFAULT_CONNECT_TIMEOUT;
201     }
202
203     @Deprecated
204     public int getDefaultMaxHttpConnectionsPerHost() {
205         return DEFAULT_MAX_HTTP_CONNECTIONS_PER_HOST;
206     }
207
208     @Deprecated
209     public int getDefaultMaxTotalHttpConnections() {
210         return DEFAULT_MAX_TOTAL_HTTP_CONNECTIONS;
211     }
212
213     public int getDefaultMaxConnectionsPerHost() {
214         return DEFAULT_MAX_CONNECTIONS_PER_HOST;
215     }
216
217     public int getDefaultMaxTotalConnections() {
218         return DEFAULT_MAX_TOTAL_CONNECTIONS;
219     }
220
221     public float getDefaultMinPrimeConnectionsRatio() {
222         return DEFAULT_MIN_PRIME_CONNECTIONS_RATIO;
223     }
224
225     public String getDefaultPrimeConnectionsClass() {
226         return DEFAULT_PRIME_CONNECTIONS_CLASS;
227     }
228
229     public String getDefaultSeverListClass() {
230         return DEFAULT_SEVER_LIST_CLASS;
231     }
232
233     public int getDefaultConnectionIdleTimertaskRepeatInMsecs() {
234         return DEFAULT_CONNECTION_IDLE_TIMERTASK_REPEAT_IN_MSECS;
235     }
236
237     public int getDefaultConnectionidleTimeInMsecs() {
238         return DEFAULT_CONNECTIONIDLE_TIME_IN_MSECS;
239     }
240
241     public VipAddressResolver getResolver() {
242         return resolver;
243     }
244
245     public boolean isEnableDynamicProperties() {
246         return enableDynamicProperties;
247     }
248
249     public int getDefaultPoolMaxThreads() {
250         return DEFAULT_POOL_MAX_THREADS;
251     }
252
253     public int getDefaultPoolMinThreads() {
254         return DEFAULT_POOL_MIN_THREADS;
255     }
256
257     public long getDefaultPoolKeepAliveTime() {
258         return DEFAULT_POOL_KEEP_ALIVE_TIME;
259     }
260
261     public TimeUnit getDefaultPoolKeepAliveTimeUnits() {
262         return DEFAULT_POOL_KEEP_ALIVE_TIME_UNITS;
263     }
264
265     public Boolean getDefaultEnableZoneAffinity() {
266         return DEFAULT_ENABLE_ZONE_AFFINITY;
267     }
268
269     public Boolean getDefaultEnableZoneExclusivity() {
270         return DEFAULT_ENABLE_ZONE_EXCLUSIVITY;
271     }
272
273     public int getDefaultPort() {
274         return DEFAULT_PORT;
275     }
276
277     public Boolean getDefaultEnableLoadbalancer() {
278         return DEFAULT_ENABLE_LOADBALANCER;
279     }
280
281
282     public Boolean getDefaultOkToRetryOnAllOperations() {
283         return DEFAULT_OK_TO_RETRY_ON_ALL_OPERATIONS;
284     }
285
286     public Boolean getDefaultIsClientAuthRequired(){
287         return DEFAULT_IS_CLIENT_AUTH_REQUIRED;
288     }
289
290
291     /**
292      * Create instance with no properties in default name space {@link #DEFAULT_PROPERTY_NAME_SPACE}
293      */
294     public DefaultClientConfigImpl() {
295         this.dynamicProperties.clear();
296         this.enableDynamicProperties = false;
297     }
298
299     /**
300      * Create instance with no properties in the specified name space
301      */
302     public DefaultClientConfigImpl(String nameSpace) {
303         this();
304         this.propertyNameSpace = nameSpace;
305     }
306
307     public void loadDefaultValues() {
308         putDefaultIntegerProperty(CommonClientConfigKey.MaxHttpConnectionsPerHost, getDefaultMaxHttpConnectionsPerHost());
309         putDefaultIntegerProperty(CommonClientConfigKey.MaxTotalHttpConnections, getDefaultMaxTotalHttpConnections());
310         putDefaultBooleanProperty(CommonClientConfigKey.EnableConnectionPool, getDefaultEnableConnectionPool());
311         putDefaultIntegerProperty(CommonClientConfigKey.MaxConnectionsPerHost, getDefaultMaxConnectionsPerHost());
312         putDefaultIntegerProperty(CommonClientConfigKey.MaxTotalConnections, getDefaultMaxTotalConnections());
313         putDefaultIntegerProperty(CommonClientConfigKey.ConnectTimeout, getDefaultConnectTimeout());
314         putDefaultIntegerProperty(CommonClientConfigKey.ConnectionManagerTimeout, getDefaultConnectionManagerTimeout());
315         putDefaultIntegerProperty(CommonClientConfigKey.ReadTimeout, getDefaultReadTimeout());
316         putDefaultIntegerProperty(CommonClientConfigKey.MaxAutoRetries, getDefaultMaxAutoRetries());
317         putDefaultIntegerProperty(CommonClientConfigKey.MaxAutoRetriesNextServer, getDefaultMaxAutoRetriesNextServer());
318         putDefaultBooleanProperty(CommonClientConfigKey.OkToRetryOnAllOperations, getDefaultOkToRetryOnAllOperations());
319         putDefaultBooleanProperty(CommonClientConfigKey.FollowRedirects, getDefaultFollowRedirects());
320         putDefaultBooleanProperty(CommonClientConfigKey.ConnectionPoolCleanerTaskEnabled, getDefaultConnectionPoolCleanerTaskEnabled());
321         putDefaultIntegerProperty(CommonClientConfigKey.ConnIdleEvictTimeMilliSeconds, getDefaultConnectionidleTimeInMsecs());
322         putDefaultIntegerProperty(CommonClientConfigKey.ConnectionCleanerRepeatInterval, getDefaultConnectionIdleTimertaskRepeatInMsecs());
323         putDefaultBooleanProperty(CommonClientConfigKey.EnableGZIPContentEncodingFilter, getDefaultEnableGzipContentEncodingFilter());
324         String proxyHost = ConfigurationManager.getConfigInstance().getString(getDefaultPropName(CommonClientConfigKey.ProxyHost.key()));
325         if (proxyHost != null && proxyHost.length() > 0) {
326             setProperty(CommonClientConfigKey.ProxyHost, proxyHost);
327         }
328         Integer proxyPort = ConfigurationManager
329                 .getConfigInstance()
330                 .getInteger(
331                         getDefaultPropName(CommonClientConfigKey.ProxyPort),
332                         (Integer.MIN_VALUE + 1)); // + 1 just to avoid potential clash with user setting
333         if (proxyPort != (Integer.MIN_VALUE + 1)) {
334             setProperty(CommonClientConfigKey.ProxyPort, proxyPort);
335         }
336         putDefaultIntegerProperty(CommonClientConfigKey.Port, getDefaultPort());
337         putDefaultBooleanProperty(CommonClientConfigKey.EnablePrimeConnections, getDefaultEnablePrimeConnections());
338         putDefaultIntegerProperty(CommonClientConfigKey.MaxRetriesPerServerPrimeConnection, getDefaultMaxRetriesPerServerPrimeConnection());
339         putDefaultIntegerProperty(CommonClientConfigKey.MaxTotalTimeToPrimeConnections, getDefaultMaxTotalTimeToPrimeConnections());
340         putDefaultStringProperty(CommonClientConfigKey.PrimeConnectionsURI, getDefaultPrimeConnectionsUri());
341         putDefaultIntegerProperty(CommonClientConfigKey.PoolMinThreads, getDefaultPoolMinThreads());
342         putDefaultIntegerProperty(CommonClientConfigKey.PoolMaxThreads, getDefaultPoolMaxThreads());
343         putDefaultLongProperty(CommonClientConfigKey.PoolKeepAliveTime, getDefaultPoolKeepAliveTime());
344         putDefaultTimeUnitProperty(CommonClientConfigKey.PoolKeepAliveTimeUnits, getDefaultPoolKeepAliveTimeUnits());
345         putDefaultBooleanProperty(CommonClientConfigKey.EnableZoneAffinity, getDefaultEnableZoneAffinity());
346         putDefaultBooleanProperty(CommonClientConfigKey.EnableZoneExclusivity, getDefaultEnableZoneExclusivity());
347         putDefaultStringProperty(CommonClientConfigKey.ClientClassName, getDefaultClientClassname());
348         putDefaultStringProperty(CommonClientConfigKey.NFLoadBalancerClassName, getDefaultNfloadbalancerClassname());
349         putDefaultStringProperty(CommonClientConfigKey.NFLoadBalancerRuleClassName, getDefaultNfloadbalancerRuleClassname());
350         putDefaultStringProperty(CommonClientConfigKey.NFLoadBalancerPingClassName, getDefaultNfloadbalancerPingClassname());
351         putDefaultBooleanProperty(CommonClientConfigKey.PrioritizeVipAddressBasedServers, getDefaultPrioritizeVipAddressBasedServers());
352         putDefaultFloatProperty(CommonClientConfigKey.MinPrimeConnectionsRatio, getDefaultMinPrimeConnectionsRatio());
353         putDefaultStringProperty(CommonClientConfigKey.PrimeConnectionsClassName, getDefaultPrimeConnectionsClass());
354         putDefaultStringProperty(CommonClientConfigKey.NIWSServerListClassName, getDefaultSeverListClass());
355         putDefaultStringProperty(CommonClientConfigKey.VipAddressResolverClassName, getDefaultVipaddressResolverClassname());
356         putDefaultBooleanProperty(CommonClientConfigKey.IsClientAuthRequired, getDefaultIsClientAuthRequired());
357         // putDefaultStringProperty(CommonClientConfigKey.RequestIdHeaderName, getDefaultRequestIdHeaderName());
358         putDefaultBooleanProperty(CommonClientConfigKey.UseIPAddrForServer, getDefaultUseIpAddressForServer());
359         putDefaultStringProperty(CommonClientConfigKey.ListOfServers, "");
360     }
361 }

也可以在配置文件中定制配置，例如配置超时和重试：

 1 # 全局配置
 2 ribbon:
 3   # 客户端读取超时时间
 4   ReadTimeout: 3000
 5   # 客户端连接超时时间
 6   ConnectTimeout: 3000
 7   # 默认只重试 GET，设置为 true 时将重试所有类型，如 POST、PUT、DELETE
 8   OkToRetryOnAllOperations: false
 9   # 重试次数
10   MaxAutoRetries: 1
11   # 最多重试几个实例
12   MaxAutoRetriesNextServer: 1
13
14 # 只针对 demo-producer 客户端
15 demo-producer:
16   ribbon:
17     # 客户端读取超时时间
18     ReadTimeout: 5000
19     # 客户端连接超时时间
20     ConnectTimeout: 3000

2、均衡策略 — IRule

IRule 是最终选择 Server 的策略规则类，核心的接口就是 choose。

 1 public interface IRule{
 2
 3     // 选择 Server
 4     public Server choose(Object key);
 5
 6     // 设置 ILoadBalancer
 7     public void setLoadBalancer(ILoadBalancer lb);
 8
 9     // 获取 ILoadBalancer
10     public ILoadBalancer getLoadBalancer();
11 }

Ribbon 提供了丰富的负载均衡策略，我们也可以通过配置指定使用某个均衡策略。下面是整个Ribbon提供的 IRule 均衡策略。

3、服务检查 — IPing

IPing 是用于定期检查 Server 的可用性的，它只提供了一个接口，用来判断 Server 是否存活：

1 public interface IPing {
2
3     public boolean isAlive(Server server);
4 }

IPing 也提供了多种策略可选，下面是整个 IPing 体系结构：

4、获取服务列表 — ServerList

ServerList 提供了两个接口，一个是第一次获取 Server 列表，一个是更新 Server 列表，其中 getUpdatedListOfServers 会每被 Loadbalancer 隔 30 秒调一次来更新 allServerList。

 1 public interface ServerList<T extends Server> {
 2
 3     public List<T> getInitialListOfServers();
 4
 5     /**
 6      * Return updated list of servers. This is called say every 30 secs
 7      * (configurable) by the Loadbalancer's Ping cycle
 8      */
 9     public List<T> getUpdatedListOfServers();
10 }

ServerList 也提供了多种实现，ServerList 体系结构如下：

5、过滤服务 — ServerListFilter

ServerListFilter 提供了一个接口用来过滤出可用的 Server。

1 public interface ServerListFilter<T extends Server> {
2
3     public List<T> getFilteredListOfServers(List<T> servers);
4 }

ServerListFilter 体系结构如下：

6、服务列表更新 — ServerListUpdater

ServerListUpdater 有多个接口，最核心的就是 start 开启定时任务调用 updateAction 来更新 allServerList。

 1 public interface ServerListUpdater {
 2
 3     /**
 4      * an interface for the updateAction that actually executes a server list update
 5      */
 6     public interface UpdateAction {
 7         void doUpdate();
 8     }
 9
10     /**
11      * start the serverList updater with the given update action
12      * This call should be idempotent.
13      */
14     void start(UpdateAction updateAction);
15 }

默认有两个实现类：

7、负载均衡器 — ILoadBalancer

ILoadBalancer 是负载均衡选择服务的核心接口，主要提供了如下的获取Server列表和根据客户端名称选择Server的接口。

 1 public interface ILoadBalancer {
 2
 3     // 添加Server
 4     public void addServers(List<Server> newServers);
 5
 6     // 根据key选择一个Server
 7     public Server chooseServer(Object key);
 8
 9     // 获取存活的Server列表，返回 upServerList
10     public List<Server> getReachableServers();
11
12     // 获取所有Server列表，返回 allServerList
13     public List<Server> getAllServers();
14 }

ILoadBalancer 的体系结构如下：

8、Ribbon 相关配置类

从前面一直看下来，可以发现有很多与 Ribbon 相关的配置类，这里总结下与 Ribbon 相关的配置类，看每个配置类的配置顺序，以及都主要配置了哪些东西。

① 首先是Eureka客户端配置类 EurekaClientAutoConfiguration，这个自动化配置类主要配置了 Ribbon 所需的 EurekaClient。

 1 @Configuration(proxyBeanMethods = false)
 2 @EnableConfigurationProperties
 3 @ConditionalOnClass(EurekaClientConfig.class)
 4 @ConditionalOnProperty(value = "eureka.client.enabled", matchIfMissing = true)
 5 @ConditionalOnDiscoveryEnabled
 6 @AutoConfigureBefore({ NoopDiscoveryClientAutoConfiguration.class,
 7         CommonsClientAutoConfiguration.class, ServiceRegistryAutoConfiguration.class })
 8 @AutoConfigureAfter(name = {
 9         "org.springframework.cloud.netflix.eureka.config.DiscoveryClientOptionalArgsConfiguration",
10         "org.springframework.cloud.autoconfigure.RefreshAutoConfiguration",
11         "org.springframework.cloud.netflix.eureka.EurekaDiscoveryClientConfiguration",
12         "org.springframework.cloud.client.serviceregistry.AutoServiceRegistrationAutoConfiguration" })
13 public class EurekaClientAutoConfiguration {
14     // ....
15 }

② 接着是Ribbon自动化配置类 RibbonAutoConfiguration，这个类主要配置了如下类：

• SpringClientFactory：管理 Ribbon 客户端上下文。
• LoadBalancerClient：负载均衡客户端，默认实现类为 RibbonLoadBalancerClient（实际是在 RibbonClientConfiguration 中配置的）。
• PropertiesFactory：用于判断配置文件中是否自定义了核心接口的实现类，如 NFLoadBalancerClassName、NFLoadBalancerPingClassName 等。
• RibbonApplicationContextInitializer：开启饥饿配置的时候，用这个类来在启动时初始化 Ribbon 客户端上下文。

 1 package org.springframework.cloud.netflix.ribbon;
 2
 3 @Configuration
 4 @Conditional(RibbonAutoConfiguration.RibbonClassesConditions.class)
 5 @RibbonClients
 6 // 在 EurekaClientAutoConfiguration 之后配置
 7 @AutoConfigureAfter(name = "org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration")
 8 // 在 LoadBalancerAutoConfiguration、AsyncLoadBalancerAutoConfiguration 之前配置
 9 @AutoConfigureBefore({ LoadBalancerAutoConfiguration.class, AsyncLoadBalancerAutoConfiguration.class })
10 @EnableConfigurationProperties({ RibbonEagerLoadProperties.class, ServerIntrospectorProperties.class })
11 public class RibbonAutoConfiguration {
12
13     @Autowired(required = false)
14     private List<RibbonClientSpecification> configurations = new ArrayList<>();
15
16     @Autowired
17     private RibbonEagerLoadProperties ribbonEagerLoadProperties;
18
19     @Bean
20     public HasFeatures ribbonFeature() {
21         return HasFeatures.namedFeature("Ribbon", Ribbon.class);
22     }
23
24     @Bean
25     @ConditionalOnMissingBean
26     public SpringClientFactory springClientFactory() {
27         SpringClientFactory factory = new SpringClientFactory();
28         factory.setConfigurations(this.configurations);
29         return factory;
30     }
31
32     @Bean
33     @ConditionalOnMissingBean(LoadBalancerClient.class)
34     public LoadBalancerClient loadBalancerClient() {
35         return new RibbonLoadBalancerClient(springClientFactory());
36     }
37
38     @Bean
39     @ConditionalOnClass(name = "org.springframework.retry.support.RetryTemplate")
40     @ConditionalOnMissingBean
41     public LoadBalancedRetryFactory loadBalancedRetryPolicyFactory(final SpringClientFactory clientFactory) {
42         return new RibbonLoadBalancedRetryFactory(clientFactory);
43     }
44
45     @Bean
46     @ConditionalOnMissingBean
47     public PropertiesFactory propertiesFactory() {
48         return new PropertiesFactory();
49     }
50
51     @Bean
52     @ConditionalOnProperty("ribbon.eager-load.enabled")
53     public RibbonApplicationContextInitializer ribbonApplicationContextInitializer() {
54         return new RibbonApplicationContextInitializer(springClientFactory(), ribbonEagerLoadProperties.getClients());
55     }
56 }

③ 接着是负载均衡器配置类 LoadBalancerAutoConfiguration，这个类主要是创建了负载均衡拦截器 LoadBalancerInterceptor，并添加到 RestTemplae 的拦截器中。

 1 package org.springframework.cloud.client.loadbalancer;
 2
 3 @Configuration(proxyBeanMethods = false)
 4 @ConditionalOnClass(RestTemplate.class)
 5 @ConditionalOnBean(LoadBalancerClient.class)
 6 @EnableConfigurationProperties(LoadBalancerRetryProperties.class)
 7 public class LoadBalancerAutoConfiguration {
 8
 9     @LoadBalanced
10     @Autowired(required = false)
11     private List<RestTemplate> restTemplates = Collections.emptyList();
12
13     @Autowired(required = false)
14     private List<LoadBalancerRequestTransformer> transformers = Collections.emptyList();
15
16     // 对 RestTemplate 定制化
17     @Bean
18     public SmartInitializingSingleton loadBalancedRestTemplateInitializerDeprecated(
19             final ObjectProvider<List<RestTemplateCustomizer>> restTemplateCustomizers) {
20         return () -> restTemplateCustomizers.ifAvailable(customizers -> {
21             for (RestTemplate restTemplate : LoadBalancerAutoConfiguration.this.restTemplates) {
22                 for (RestTemplateCustomizer customizer : customizers) {
23                     customizer.customize(restTemplate);
24                 }
25             }
26         });
27     }
28
29     @Bean
30     @ConditionalOnMissingBean
31     public LoadBalancerRequestFactory loadBalancerRequestFactory(LoadBalancerClient loadBalancerClient) {
32         return new LoadBalancerRequestFactory(loadBalancerClient, this.transformers);
33     }
34
35     @Configuration(proxyBeanMethods = false)
36     @ConditionalOnMissingClass("org.springframework.retry.support.RetryTemplate")
37     static class LoadBalancerInterceptorConfig {
38
39         // 创建 RestTemplate 拦截器
40         @Bean
41         public LoadBalancerInterceptor ribbonInterceptor(LoadBalancerClient loadBalancerClient,
42                                                          LoadBalancerRequestFactory requestFactory) {
43             return new LoadBalancerInterceptor(loadBalancerClient, requestFactory);
44         }
45
46         @Bean
47         @ConditionalOnMissingBean
48         public RestTemplateCustomizer restTemplateCustomizer(final LoadBalancerInterceptor loadBalancerInterceptor) {
49             return restTemplate -> {
50                 List<ClientHttpRequestInterceptor> list = new ArrayList<>(
51                         restTemplate.getInterceptors());
52                 list.add(loadBalancerInterceptor);
53                 restTemplate.setInterceptors(list);
54             };
55         }
56
57     }
58 }

④ 之后是默认的 Ribbon 客户端配置类 RibbonClientConfiguration，这个类主要配置了 Ribbon 核心接口的默认实现。

• IClientConfig：Ribbon 客户端配置类，默认实现是 DefaultClientConfigImpl。
• IRule：负载均衡策略规则组件，默认实现是 ZoneAvoidanceRule。
• IPing：判断 Server 是否存活，默认实现是 DummyPing，永远都是返回 true。
• ServerList：获取 Server 的组件，默认实现类为 ConfigurationBasedServerList，从配置文件获取。
• ServerListUpdater：Server 列表更新组件，默认实现类为 PollingServerListUpdater。
• ServerListFilter：过滤可用的 Server 列表，默认实现类为 ZonePreferenceServerListFilter。
• RibbonLoadBalancerContext：负载均衡客户端。
• RetryHandler：重试处理器，默认实现类为 DefaultLoadBalancerRetryHandler。

  1 package org.springframework.cloud.netflix.ribbon;
  2
  3 @SuppressWarnings("deprecation")
  4 @Configuration(proxyBeanMethods = false)
  5 @EnableConfigurationProperties
  6 @Import({ HttpClientConfiguration.class, OkHttpRibbonConfiguration.class,
  7         RestClientRibbonConfiguration.class, HttpClientRibbonConfiguration.class })
  8 public class RibbonClientConfiguration {
  9     public static final int DEFAULT_CONNECT_TIMEOUT = 1000;
 10     public static final int DEFAULT_READ_TIMEOUT = 1000;
 11     public static final boolean DEFAULT_GZIP_PAYLOAD = true;
 12
 13     @RibbonClientName
 14     private String name = "client";
 15
 16     @Autowired
 17     private PropertiesFactory propertiesFactory;
 18
 19     @Bean
 20     @ConditionalOnMissingBean
 21     public IClientConfig ribbonClientConfig() {
 22         DefaultClientConfigImpl config = new DefaultClientConfigImpl();
 23         config.loadProperties(this.name);
 24         config.set(CommonClientConfigKey.ConnectTimeout, DEFAULT_CONNECT_TIMEOUT);
 25         config.set(CommonClientConfigKey.ReadTimeout, DEFAULT_READ_TIMEOUT);
 26         config.set(CommonClientConfigKey.GZipPayload, DEFAULT_GZIP_PAYLOAD);
 27         return config;
 28     }
 29
 30     @Bean
 31     @ConditionalOnMissingBean
 32     public IRule ribbonRule(IClientConfig config) {
 33         if (this.propertiesFactory.isSet(IRule.class, name)) {
 34             return this.propertiesFactory.get(IRule.class, config, name);
 35         }
 36         ZoneAvoidanceRule rule = new ZoneAvoidanceRule();
 37         rule.initWithNiwsConfig(config);
 38         return rule;
 39     }
 40
 41     @Bean
 42     @ConditionalOnMissingBean
 43     public IPing ribbonPing(IClientConfig config) {
 44         if (this.propertiesFactory.isSet(IPing.class, name)) {
 45             return this.propertiesFactory.get(IPing.class, config, name);
 46         }
 47         return new DummyPing();
 48     }
 49
 50     @Bean
 51     @ConditionalOnMissingBean
 52     @SuppressWarnings("unchecked")
 53     public ServerList<Server> ribbonServerList(IClientConfig config) {
 54         if (this.propertiesFactory.isSet(ServerList.class, name)) {
 55             return this.propertiesFactory.get(ServerList.class, config, name);
 56         }
 57         ConfigurationBasedServerList serverList = new ConfigurationBasedServerList();
 58         serverList.initWithNiwsConfig(config);
 59         return serverList;
 60     }
 61
 62     @Bean
 63     @ConditionalOnMissingBean
 64     public ServerListUpdater ribbonServerListUpdater(IClientConfig config) {
 65         return new PollingServerListUpdater(config);
 66     }
 67
 68     @Bean
 69     @ConditionalOnMissingBean
 70     public ILoadBalancer ribbonLoadBalancer(IClientConfig config,
 71             ServerList<Server> serverList, ServerListFilter<Server> serverListFilter,
 72             IRule rule, IPing ping, ServerListUpdater serverListUpdater) {
 73         if (this.propertiesFactory.isSet(ILoadBalancer.class, name)) {
 74             return this.propertiesFactory.get(ILoadBalancer.class, config, name);
 75         }
 76         return new ZoneAwareLoadBalancer<>(config, rule, ping, serverList,
 77                 serverListFilter, serverListUpdater);
 78     }
 79
 80     @Bean
 81     @ConditionalOnMissingBean
 82     @SuppressWarnings("unchecked")
 83     public ServerListFilter<Server> ribbonServerListFilter(IClientConfig config) {
 84         if (this.propertiesFactory.isSet(ServerListFilter.class, name)) {
 85             return this.propertiesFactory.get(ServerListFilter.class, config, name);
 86         }
 87         ZonePreferenceServerListFilter filter = new ZonePreferenceServerListFilter();
 88         filter.initWithNiwsConfig(config);
 89         return filter;
 90     }
 91
 92     @Bean
 93     @ConditionalOnMissingBean
 94     public RibbonLoadBalancerContext ribbonLoadBalancerContext(ILoadBalancer loadBalancer,
 95             IClientConfig config, RetryHandler retryHandler) {
 96         return new RibbonLoadBalancerContext(loadBalancer, config, retryHandler);
 97     }
 98
 99     @Bean
100     @ConditionalOnMissingBean
101     public RetryHandler retryHandler(IClientConfig config) {
102         return new DefaultLoadBalancerRetryHandler(config);
103     }
104
105     @Bean
106     @ConditionalOnMissingBean
107     public ServerIntrospector serverIntrospector() {
108         return new DefaultServerIntrospector();
109     }
110 }

⑤ Ribbon Eureka 自动化配置类 RibbonEurekaAutoConfiguration，判断是否启用 Ribbon Eureka，并触发 EurekaRibbonClientConfiguration 配置类。

 1 package org.springframework.cloud.netflix.ribbon.eureka;
 2
 3 @Configuration(proxyBeanMethods = false)
 4 @EnableConfigurationProperties
 5 @ConditionalOnRibbonAndEurekaEnabled
 6 @AutoConfigureAfter(RibbonAutoConfiguration.class)
 7 @RibbonClients(defaultConfiguration = EurekaRibbonClientConfiguration.class)
 8 public class RibbonEurekaAutoConfiguration {
 9
10 }

⑥ 默认启用 Ribbon Eureka 的情况下，会使用 Ribbon Eureka 客户端配置类 EurekaRibbonClientConfiguration：

• IPing：替换了默认实现类 DummyPing，改为 NIWSDiscoveryPing，通过判断 InstanceInfo 的状态是否为 UP 来判断 Server 是否存活。
• ServerList：替换了默认的实现类 ConfigurationBasedServerList，改为 DomainExtractingServerList，实际是 DiscoveryEnabledNIWSServerList，从 EurekaClient 获取 Server 列表。

 1 package org.springframework.cloud.netflix.ribbon.eureka;
 2
 3 @Configuration(proxyBeanMethods = false)
 4 public class EurekaRibbonClientConfiguration {
 5
 6     private static final Log log = LogFactory.getLog(EurekaRibbonClientConfiguration.class);
 7
 8     @Value("${ribbon.eureka.approximateZoneFromHostname:false}")
 9     private boolean approximateZoneFromHostname = false;
10     @RibbonClientName
11     private String serviceId = "client";
12     @Autowired(required = false)
13     private EurekaClientConfig clientConfig;
14     @Autowired(required = false)
15     private EurekaInstanceConfig eurekaConfig;
16     @Autowired
17     private PropertiesFactory propertiesFactory;
18
19     public EurekaRibbonClientConfiguration() {
20     }
21
22     public EurekaRibbonClientConfiguration(EurekaClientConfig clientConfig,
23             String serviceId, EurekaInstanceConfig eurekaConfig,
24             boolean approximateZoneFromHostname) {
25         this.clientConfig = clientConfig;
26         this.serviceId = serviceId;
27         this.eurekaConfig = eurekaConfig;
28         this.approximateZoneFromHostname = approximateZoneFromHostname;
29     }
30
31     @Bean
32     @ConditionalOnMissingBean
33     public IPing ribbonPing(IClientConfig config) {
34         if (this.propertiesFactory.isSet(IPing.class, serviceId)) {
35             return this.propertiesFactory.get(IPing.class, config, serviceId);
36         }
37         NIWSDiscoveryPing ping = new NIWSDiscoveryPing();
38         ping.initWithNiwsConfig(config);
39         return ping;
40     }
41
42     @Bean
43     @ConditionalOnMissingBean
44     public ServerList<?> ribbonServerList(IClientConfig config, Provider<EurekaClient> eurekaClientProvider) {
45         if (this.propertiesFactory.isSet(ServerList.class, serviceId)) {
46             return this.propertiesFactory.get(ServerList.class, config, serviceId);
47         }
48         DiscoveryEnabledNIWSServerList discoveryServerList = new DiscoveryEnabledNIWSServerList(
49                 config, eurekaClientProvider);
50         DomainExtractingServerList serverList = new DomainExtractingServerList(
51                 discoveryServerList, config, this.approximateZoneFromHostname);
52         return serverList;
53     }
54 }

⑦ 各个配置类所属模块

spring-cloud-netflix-eureka-client：

• org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration
• org.springframework.cloud.netflix.ribbon.eureka.RibbonEurekaAutoConfiguration
• org.springframework.cloud.netflix.ribbon.eureka.EurekaRibbonClientConfiguration

spring-cloud-netflix-ribbon：

• org.springframework.cloud.netflix.ribbon.RibbonAutoConfiguration
• org.springframework.cloud.netflix.ribbon.RibbonClientConfiguration

spring-cloud-commons：

• org.springframework.cloud.client.loadbalancer.LoadBalancerAutoConfiguration

六、Ribbon HTTP客户端组件

1、Java HTTP 组件库

① HTTP 组件库

首先简单了解下常用的 Java HTTP 组件库，Ribbon 中通过不同的配置便可以启用某个 HTTP 组件来进行服务间的通信。

Java 中的 HTTP 组件库，大体可以分为三类：

• JDK 自带的标准库 HttpURLConnection
• Apache HttpComponents HttpClient
• OkHttp

HttpURLConnection 发起 HTTP 请求最大的优点是不需要引入额外的依赖，但是 HttpURLConnection 封装层次太低，使用起来非常繁琐。支持的特性太少，缺乏连接池管理、域名机械控制，无法支持 HTTP/2等。

Apache HttpComponents HttpClient 和 OkHttp 都支持连接池管理、超时、空闲连接数控制等特性。OkHttp 接口设计更友好，且支持 HTTP/2，Android 开发中用得更多。

② 超时重试配置

先给 demo-consumer 中添加如下默认配置，即读取、连接超时时间设置为 1 秒，这也是默认值。然后重试次数为1，重试一个Server。后面基于这些配置来验证Ribbon HTTP客户端的超时和重试。

 1 ribbon:
 2   # 客户端读取超时时间
 3   ReadTimeout: 1000
 4   # 客户端连接超时时间
 5   ConnectTimeout: 1000
 6   # 默认只重试 GET，设置为 true 时将重试所有类型，如 POST、PUT、DELETE
 7   OkToRetryOnAllOperations: false
 8   # 重试次数
 9   MaxAutoRetries: 1
10   # 最多重试几个实例
11   MaxAutoRetriesNextServer: 1

然后 demo-producer 的接口休眠3秒，造成网络延迟的现象，并且 demo-producer 启两个实例。

1 @GetMapping("/v1/uuid")
2 public ResponseEntity<String> getUUID() throws InterruptedException {
3     String uuid = UUID.randomUUID().toString();
4     logger.info("generate uuid: {}", uuid);
5     Thread.sleep(3000);
6     return ResponseEntity.ok(uuid);
7 }

2、Ribbon 默认使用 HttpURLConnection

① Ribbon 默认的 HTTP 组件

在不添加其它配置的情况下，我们来看下 Ribbon 默认使用的 HTTP 组件是什么。

首先通过之前的分析可以知道，默认情况下，LoadBalancerAutoConfiguration 配置类会向 RestTemplate 添加 LoadBalancerInterceptor 拦截器。然后在 RestTemplate 调用时，即在 doExecute 方法中，创建 ClientHttpRequest 时，因为配置了拦截器，所以 ClientHttpRequestFactory 就是 InterceptingClientHttpRequestFactory，而且创建 InterceptingClientHttpRequestFactory 传入的 ClientHttpRequestFactory 默认是父类的 SimpleClientHttpRequestFactory。

 1 protected <T> T doExecute(URI url, @Nullable HttpMethod method, @Nullable RequestCallback requestCallback,
 2         @Nullable ResponseExtractor<T> responseExtractor) throws RestClientException {
 3     //...
 4     ClientHttpResponse response = null;
 5     try {
 6         // 创建 ClientHttpRequest
 7         ClientHttpRequest request = createRequest(url, method);
 8         if (requestCallback != null) {
 9             requestCallback.doWithRequest(request);
10         }
11         // ClientHttpRequest 发起请求
12         response = request.execute();
13         handleResponse(url, method, response);
14         return (responseExtractor != null ? responseExtractor.extractData(response) : null);
15     }
16     catch (IOException ex) {
17         // ...
18     }
19     finally {
20         if (response != null) {
21             response.close();
22         }
23     }
24 }
25
26 protected ClientHttpRequest createRequest(URI url, HttpMethod method) throws IOException {
27     // getRequestFactory 获取 ClientHttpRequestFactory
28     ClientHttpRequest request = getRequestFactory().createRequest(url, method);
29     initialize(request);
30     if (logger.isDebugEnabled()) {
31         logger.debug("HTTP " + method.name() + " " + url);
32     }
33     return request;
34 }
35
36 public ClientHttpRequestFactory getRequestFactory() {
37     List<ClientHttpRequestInterceptor> interceptors = getInterceptors();
38     if (!CollectionUtils.isEmpty(interceptors)) {
39         ClientHttpRequestFactory factory = this.interceptingRequestFactory;
40         if (factory == null) {
41             // 有拦截器的情况，super.getRequestFactory() 默认返回的是 SimpleClientHttpRequestFactory
42             factory = new InterceptingClientHttpRequestFactory(super.getRequestFactory(), interceptors);
43             this.interceptingRequestFactory = factory;
44         }
45         return factory;
46     }
47     else {
48         // 无拦截器的情况
49         return super.getRequestFactory();
50     }
51 }

InterceptingClientHttpRequestFactory 这个工厂类创建的 ClientHttpRequest 类型是 InterceptingClientHttpRequest。最终 RestTemplate 的 doExecute 方法中调用 ClientHttpRequest 的 execute 方法时，就调用到了 InterceptingClientHttpRequest 中的内部类 InterceptingRequestExecution 中。

在 InterceptingRequestExecution 的 execute 方法中，首先是遍历所有拦截器对 RestTemplate 定制化，最后则通过 requestFactory 创建 ClientHttpRequest 来发起最终的 HTTP 调用。从这里可以看出，无论有没有拦截器，其实最终都会使用 requestFactory 来创建 ClientHttpRequest。

 1 private class InterceptingRequestExecution implements ClientHttpRequestExecution {
 2     private final Iterator<ClientHttpRequestInterceptor> iterator;
 3
 4     @Override
 5     public ClientHttpResponse execute(HttpRequest request, byte[] body) throws IOException {
 6         if (this.iterator.hasNext()) {
 7             // 拦截器定制化 RestTemplate
 8             ClientHttpRequestInterceptor nextInterceptor = this.iterator.next();
 9             return nextInterceptor.intercept(request, body, this);
10         }
11         else {
12             HttpMethod method = request.getMethod();
13             // delegate => SimpleBufferingClientHttpRequest
14             ClientHttpRequest delegate = requestFactory.createRequest(request.getURI(), method);
15             //...
16             return delegate.execute();
17         }
18     }
19 }

这里的 requestFactory 就是前面传进来的 SimpleClientHttpRequestFactory，从它的 createRequest 方法可以看出，默认情况下，就是用的 JDK 标准 HTTP 库组件 HttpURLConnection 来进行服务间的请求通信。

 1 public ClientHttpRequest createRequest(URI uri, HttpMethod httpMethod) throws IOException {
 2     // JDK 标准HTTP库 HttpURLConnection
 3     HttpURLConnection connection = openConnection(uri.toURL(), this.proxy);
 4     prepareConnection(connection, httpMethod.name());
 5
 6     if (this.bufferRequestBody) {
 7         return new SimpleBufferingClientHttpRequest(connection, this.outputStreaming);
 8     }
 9     else {
10         return new SimpleStreamingClientHttpRequest(connection, this.chunkSize, this.outputStreaming);
11     }
12 }

总结：

从前面的源码分析可以看出，Ribbon 默认的 HTTP 客户端是 HttpURLConnection。

在前面默认的超时配置下，可以验证出超时配置并未生效，一直阻塞3秒后才返回了结果，说明 Ribbon 默认情况下就不支持超时重试。

而且 HttpURLConnection 每次都是新创建的，请求返回来之后就关闭连接，没有连接池管理机制，网络连接的建立和关闭本身就会损耗一定的性能，所以正式环境下，最好不要使用默认的配置。

② HttpClient 配置类

另外，我们从 RibbonClientConfiguration 配置类的定义可以看到，其导入了 HttpClientConfiguration、OkHttpRibbonConfiguration、RestClientRibbonConfiguration、HttpClientRibbonConfiguration 四个 HttpClient 的配置类，通过注释也可以了解到，最后一个是默认配置类，前面三个在某些配置启用的情况下才会生效。

1 @Configuration(proxyBeanMethods = false)
2 @EnableConfigurationProperties
3 // Order is important here, last should be the default, first should be optional
4 @Import({ HttpClientConfiguration.class, OkHttpRibbonConfiguration.class,
5         RestClientRibbonConfiguration.class, HttpClientRibbonConfiguration.class })
6 public class RibbonClientConfiguration {
7
8 }

进入 HttpClientRibbonConfiguration，这个配置类在 ribbon.httpclient.enabled=true 时才生效，而且默认为 true。在从 SpringClientFactory 中获取 ILoadBalancer 时，会通过这个配置类初始化 HttpClient，按先后顺序会初始化 HttpClientConnectionManager、CloseableHttpClient、RibbonLoadBalancingHttpClient。CloseableHttpClient 是 Apache HttpComponents HttpClient 中的组件，也就是说默认情况下应该是使用 apache HttpComponents 作为 HTTP 组件库。

但经过前面源码的分析，以及测试发现，最终其实走的的 HttpURLConnection，并没有用到 CloseableHttpClient。把 ribbon.httpclient.enabled 设置为 false，也没有什么影响，还是默认走 HttpURLConnection。我们后面再来分析这个问题。

 1 @Configuration(proxyBeanMethods = false)
 2 @ConditionalOnClass(name = "org.apache.http.client.HttpClient")
 3 // ribbon.httpclient.enabled more文为 true
 4 @ConditionalOnProperty(name = "ribbon.httpclient.enabled", matchIfMissing = true)
 5 public class HttpClientRibbonConfiguration {
 6
 7     @RibbonClientName
 8     private String name = "client";
 9
10     // RibbonLoadBalancingHttpClient
11     @Bean
12     @ConditionalOnMissingBean(AbstractLoadBalancerAwareClient.class)
13     @ConditionalOnMissingClass("org.springframework.retry.support.RetryTemplate")
14     public RibbonLoadBalancingHttpClient ribbonLoadBalancingHttpClient(
15             IClientConfig config, ServerIntrospector serverIntrospector,
16             ILoadBalancer loadBalancer, RetryHandler retryHandler,
17             CloseableHttpClient httpClient) {
18         RibbonLoadBalancingHttpClient client = new RibbonLoadBalancingHttpClient(
19                 httpClient, config, serverIntrospector);
20         client.setLoadBalancer(loadBalancer);
21         client.setRetryHandler(retryHandler);
22         Monitors.registerObject("Client_" + this.name, client);
23         return client;
24     }
25
26     // 在引入了 spring-retry 时，即可以重试的 RetryTemplate 时，就创建 RetryableRibbonLoadBalancingHttpClient
27     @Bean
28     @ConditionalOnMissingBean(AbstractLoadBalancerAwareClient.class)
29     @ConditionalOnClass(name = "org.springframework.retry.support.RetryTemplate")
30     public RetryableRibbonLoadBalancingHttpClient retryableRibbonLoadBalancingHttpClient(
31             IClientConfig config, ServerIntrospector serverIntrospector,
32             ILoadBalancer loadBalancer, RetryHandler retryHandler,
33             LoadBalancedRetryFactory loadBalancedRetryFactory,
34             CloseableHttpClient httpClient,
35             RibbonLoadBalancerContext ribbonLoadBalancerContext) {
36         RetryableRibbonLoadBalancingHttpClient client = new RetryableRibbonLoadBalancingHttpClient(
37                 httpClient, config, serverIntrospector, loadBalancedRetryFactory);
38         client.setLoadBalancer(loadBalancer);
39         client.setRetryHandler(retryHandler);
40         client.setRibbonLoadBalancerContext(ribbonLoadBalancerContext);
41         Monitors.registerObject("Client_" + this.name, client);
42         return client;
43     }
44
45     @Configuration(proxyBeanMethods = false)
46     protected static class ApacheHttpClientConfiguration {
47
48         private final Timer connectionManagerTimer = new Timer(
49                 "RibbonApacheHttpClientConfiguration.connectionManagerTimer", true);
50
51         private CloseableHttpClient httpClient;
52
53         @Autowired(required = false)
54         private RegistryBuilder registryBuilder;
55
56         // HttpClient 连接池管理器
57         @Bean
58         @ConditionalOnMissingBean(HttpClientConnectionManager.class)
59         public HttpClientConnectionManager httpClientConnectionManager(
60                 IClientConfig config,
61                 ApacheHttpClientConnectionManagerFactory connectionManagerFactory) {
62             RibbonProperties ribbon = RibbonProperties.from(config);
63             int maxTotalConnections = ribbon.maxTotalConnections();
64             int maxConnectionsPerHost = ribbon.maxConnectionsPerHost();
65             int timerRepeat = ribbon.connectionCleanerRepeatInterval();
66             long timeToLive = ribbon.poolKeepAliveTime();
67             TimeUnit ttlUnit = ribbon.getPoolKeepAliveTimeUnits();
68             final HttpClientConnectionManager connectionManager = connectionManagerFactory
69                     .newConnectionManager(false, maxTotalConnections,
70                             maxConnectionsPerHost, timeToLive, ttlUnit, registryBuilder);
71             this.connectionManagerTimer.schedule(new TimerTask() {
72                 @Override
73                 public void run() {
74                     connectionManager.closeExpiredConnections();
75                 }
76             }, 30000, timerRepeat);
77             return connectionManager;
78         }
79
80         // HttpClient => CloseableHttpClient
81         @Bean
82         @ConditionalOnMissingBean(CloseableHttpClient.class)
83         public CloseableHttpClient httpClient(ApacheHttpClientFactory httpClientFactory,
84                 HttpClientConnectionManager connectionManager, IClientConfig config) {
85             RibbonProperties ribbon = RibbonProperties.from(config);
86             Boolean followRedirects = ribbon.isFollowRedirects();
87             Integer connectTimeout = ribbon.connectTimeout();
88             RequestConfig defaultRequestConfig = RequestConfig.custom()
89                     .setConnectTimeout(connectTimeout)
90                     .setRedirectsEnabled(followRedirects).build();
91             this.httpClient = httpClientFactory.createBuilder()
92                     .setDefaultRequestConfig(defaultRequestConfig)
93                     .setConnectionManager(connectionManager).build();
94             return httpClient;
95         }
96     }
97 }

③ 默认配置下的 RestTemplate 的调用过程大致可以用下图来表示。

3、启用 RestClient

① 启用 RestClient

可以添加如下配置启用 RestClient：

 1 ribbon:
 2   # 关闭 httpclient
 3   httpclient:
 4     enabled: false
 5   # 启用 RestClient
 6   restclient:
 7     enabled: true
 8   # 启用 RestClient
 9   http:
10     client:
11       enabled: true

进入 RestClientRibbonConfiguration  可以看到，只要 ribbon.http.client.enabled、ribbon.restclient.enabled 其中一个配置了启用，就可以启用 RestClient。

 1 @SuppressWarnings("deprecation")
 2 @Configuration(proxyBeanMethods = false)
 3 // 启用条件 ConditionalOnRibbonRestClient
 4 @RibbonAutoConfiguration.ConditionalOnRibbonRestClient
 5 class RestClientRibbonConfiguration {
 6     @RibbonClientName
 7     private String name = "client";
 8
 9     // RestClient 已过期
10     @Bean
11     @Lazy
12     @ConditionalOnMissingBean(AbstractLoadBalancerAwareClient.class)
13     public RestClient ribbonRestClient(IClientConfig config, ILoadBalancer loadBalancer,
14             ServerIntrospector serverIntrospector, RetryHandler retryHandler) {
15         RestClient client = new RibbonClientConfiguration.OverrideRestClient(config, serverIntrospector);
16         client.setLoadBalancer(loadBalancer);
17         client.setRetryHandler(retryHandler);
18         return client;
19     }
20
21 }
22
23 @Target({ ElementType.TYPE, ElementType.METHOD })
24 @Retention(RetentionPolicy.RUNTIME)
25 @Documented
26 @Conditional(OnRibbonRestClientCondition.class)
27 @interface ConditionalOnRibbonRestClient {
28 }
29
30 private static class OnRibbonRestClientCondition extends AnyNestedCondition {
31     @Deprecated // remove in Edgware"
32     @ConditionalOnProperty("ribbon.http.client.enabled")
33     static class ZuulProperty {
34     }
35
36     @ConditionalOnProperty("ribbon.restclient.enabled")
37     static class RibbonProperty {
38     }
39 }

RestClient 继承自 AbstractLoadBalancerAwareClient。需要注意的是，RestClient 已经过期，所以生产环境中我们就不要启用 RestTemplate 了。

1 @Deprecated
2 public class RestClient extends AbstractLoadBalancerAwareClient<HttpRequest, HttpResponse> {
3
4 }

② LoadBalancerContext 类体系结构

负载均衡上下文 LoadBalancerContext 体系的类结构如下。可以看出，Ribbon 是支持 Feign、OkHttp、HttpClient、RestClient 的。默认配置下使用的实现类是 RibbonLoadBalancerContext。

③ RestTemplate 的 ClientHttpRequest 工厂类配置

接着看 RibbonAutoConfiguration 中有如下的配置，跟前面 RestClientRibbonConfiguration 也是一样，满足 @ConditionalOnRibbonRestClient 的条件。

可以看到，它会创建 RibbonClientHttpRequestFactory 并设置到 RestTemplate 中，也就是说，这时 RestTemplate 中的 requestFactory 就不是默认的 SimpleClientHttpRequestFactory 了，而是 RibbonClientHttpRequestFactory。

 1 @Configuration(proxyBeanMethods = false)
 2 @ConditionalOnClass(HttpRequest.class)
 3 @ConditionalOnRibbonRestClient
 4 protected static class RibbonClientHttpRequestFactoryConfiguration {
 5     @Autowired
 6     private SpringClientFactory springClientFactory;
 7
 8     @Bean
 9     public RestTemplateCustomizer restTemplateCustomizer(
10             final RibbonClientHttpRequestFactory ribbonClientHttpRequestFactory) {
11         // RestTemplate 设置 requestFactory 为 RibbonClientHttpRequestFactory
12         return restTemplate -> restTemplate
13                 .setRequestFactory(ribbonClientHttpRequestFactory);
14     }
15
16     // ClientHttpRequest 工厂类 => RibbonClientHttpRequestFactory
17     @Bean
18     public RibbonClientHttpRequestFactory ribbonClientHttpRequestFactory() {
19         return new RibbonClientHttpRequestFactory(this.springClientFactory);
20     }
21 }

而且，由于这里配置了 RestTemplateCustomizer，原本默认配置下，在 LoadBalancerAutoConfiguration 中创建 RestTemplateCustomizer 的方法就不会生效了。

LoadBalancerAutoConfiguration 中的 RestTemplateCustomizer 是向 RestTemplate 中添加 LoadBalancerInterceptor 拦截器，所以在启用了 RestClient 的情况下，原本的 LoadBalancerInterceptor 就不会生效了。

 1 @Configuration(proxyBeanMethods = false)
 2 @ConditionalOnMissingClass("org.springframework.retry.support.RetryTemplate")
 3 static class LoadBalancerInterceptorConfig {
 4
 5     @Bean
 6     public LoadBalancerInterceptor ribbonInterceptor(
 7             LoadBalancerClient loadBalancerClient,
 8             LoadBalancerRequestFactory requestFactory) {
 9         return new LoadBalancerInterceptor(loadBalancerClient, requestFactory);
10     }
11
12     @Bean
13     @ConditionalOnMissingBean
14     public RestTemplateCustomizer restTemplateCustomizer(
15             final LoadBalancerInterceptor loadBalancerInterceptor) {
16         return restTemplate -> {
17             List<ClientHttpRequestInterceptor> list = new ArrayList<>(
18                     restTemplate.getInterceptors());
19             list.add(loadBalancerInterceptor);
20             restTemplate.setInterceptors(list);
21         };
22     }
23 }

那么 RestTemplate 的 doExecute 方法中，在调用 createRequest 方法创建 ClientHttpRequest 时，就会用 RibbonClientHttpRequestFactory 来创建，进去可以看到 ClientHttpRequest 的实际类型就是 RibbonHttpRequest。

 1 public ClientHttpRequest createRequest(URI originalUri, HttpMethod httpMethod) throws IOException {
 2     String serviceId = originalUri.getHost();
 3     if (serviceId == null) {
 4         throw new IOException("Invalid hostname in the URI [" + originalUri.toASCIIString() + "]");
 5     }
 6     IClientConfig clientConfig = this.clientFactory.getClientConfig(serviceId);
 7     RestClient client = this.clientFactory.getClient(serviceId, RestClient.class);
 8     HttpRequest.Verb verb = HttpRequest.Verb.valueOf(httpMethod.name());
 9
10     return new RibbonHttpRequest(originalUri, verb, client, clientConfig);
11 }

调用 RibbonHttpRequest 的 execute 方法，实际组中是调用了它的 executeInternal 方法，然后最后是使用 RestClient 来发起负载均衡的调用。

 1 protected ClientHttpResponse executeInternal(HttpHeaders headers) throws IOException {
 2     try {
 3         // ...
 4         HttpRequest request = builder.build();
 5         // client => RestClient
 6         HttpResponse response = client.executeWithLoadBalancer(request, config);
 7         return new RibbonHttpResponse(response);
 8     }
 9     catch (Exception e) {
10         throw new IOException(e);
11     }
12 }

④ RestClient HTTP 调用

RestClient 的 executeWithLoadBalancer 实际是进入到父类 AbstractLoadBalancerAwareClient 的 executeWithLoadBalancer  方法中。

从这个方法可以知道，主要的负载均衡请求是在 LoadBalancerCommand 中的，LoadBalancerCommand 必定会通过负载均衡器 ILoadBalancer 得到一个 Server，然后通过 submit 的这个 ServerOperation 对原始URI进行重构，重构之后调用 RestClient 的 execute 发起HTTP请求。

 1 public T executeWithLoadBalancer(final S request, final IClientConfig requestConfig) throws ClientException {
 2     // 负载均衡命令
 3     LoadBalancerCommand<T> command = buildLoadBalancerCommand(request, requestConfig);
 4
 5     try {
 6         // 发起负载均衡请求
 7         return command.submit(
 8             new ServerOperation<T>() {
 9                 @Override
10                 public Observable<T> call(Server server) {
11                     // 重构 URI，将服务名用 Server 的 IP 和端口替换
12                     URI finalUri = reconstructURIWithServer(server, request.getUri());
13                     S requestForServer = (S) request.replaceUri(finalUri);
14                     try {
15                         // execute 发起调用，实际调用的是 RestClient 中的 execute
16                         return Observable.just(AbstractLoadBalancerAwareClient.this.execute(requestForServer, requestConfig));
17                     }
18                     catch (Exception e) {
19                         return Observable.error(e);
20                     }
21                 }
22             })
23             .toBlocking()
24             .single();
25     } catch (Exception e) {
26         //....
27     }
28 }

再看 RestClient 的 execute 方法，最终可以发现，RestClient 其实是使用基于 jersey 的 WebResource 来发起 HTTP 请求的。

 1 private HttpResponse execute(HttpRequest.Verb verb, URI uri,
 2         Map<String, Collection<String>> headers, Map<String, Collection<String>> params,
 3         IClientConfig overriddenClientConfig, Object requestEntity) throws Exception {
 4     // ...
 5     // WebResource 是基于 jersey 封装的 HTTP 客户端组件
 6     WebResource xResource = restClient.resource(uri.toString());
 7     ClientResponse jerseyResponse;
 8     Builder b = xResource.getRequestBuilder();
 9     Object entity = requestEntity;
10
11     switch (verb) {
12     case GET:
13         jerseyResponse = b.get(ClientResponse.class);
14         break;
15     case POST:
16         jerseyResponse = b.post(ClientResponse.class, entity);
17         break;
18     case PUT:
19         jerseyResponse = b.put(ClientResponse.class, entity);
20         break;
21     case DELETE:
22         jerseyResponse = b.delete(ClientResponse.class);
23         break;
24     case HEAD:
25         jerseyResponse = b.head();
26         break;
27     case OPTIONS:
28         jerseyResponse = b.options(ClientResponse.class);
29         break;
30     default:
31         throw new ClientException(
32                 ClientException.ErrorType.GENERAL,
33                 "You have to one of the REST verbs such as GET, POST etc.");
34     }
35
36     thisResponse = new HttpClientResponse(jerseyResponse, uri, overriddenClientConfig);
37     if (thisResponse.getStatus() == 503){
38         thisResponse.close();
39         throw new ClientException(ClientException.ErrorType.SERVER_THROTTLED);
40     }
41     return thisResponse;
42 }

⑤ 最后，RestTemplate 基于 RestClient 的请求流程可以用下图来做个总结。

4、Apache HttpClient 或 OkHttp 对 RestTemplate 不生效（BUG？）

① Apache HttpClient

默认情况下，ribbon.httpclient.enabled=true，在 HttpClientRibbonConfiguration 中会初始化 apache httpcomponents 相关的组件，前已经分析过了，但是在 RestTemplate 中并未使用相关的组件。

也就是说，默认情况下启用了 apache httpcomponents，但是 RestTemplate 最后是使用 HttpURLConnection 来发起 HTTP 请求的，而不是配置的 CloseableHttpClient。

② OkHttp

首先需要加入 OkHttp 的依赖：

1 <dependency>
2     <groupId>com.squareup.okhttp3</groupId>
3     <artifactId>okhttp</artifactId>
4 </dependency>

然后添加如下配置就可以启用 OkHttp：

1 ribbon:
2   httpclient:
3     enabled: false
4   # 启用 okhttp
5   okhttp:
6     enabled: true

配置 ribbon.okhttp.enabled=true 后，在 OkHttpRibbonConfiguration 中会初始化 OkHttp 相关的组件。

但是调试之后会发现，其实它还是走的默认的流程，就是最终用 HttpURLConnection 发起 HTTP 请求，跟 httpcomponents 是一样的效果。

 1 @Configuration(proxyBeanMethods = false)
 2 @ConditionalOnProperty("ribbon.okhttp.enabled")
 3 @ConditionalOnClass(name = "okhttp3.OkHttpClient")
 4 public class OkHttpRibbonConfiguration {
 5
 6     @RibbonClientName
 7     private String name = "client";
 8
 9     @Bean
10     @ConditionalOnMissingBean(AbstractLoadBalancerAwareClient.class)
11     @ConditionalOnClass(name = "org.springframework.retry.support.RetryTemplate")
12     public RetryableOkHttpLoadBalancingClient retryableOkHttpLoadBalancingClient(
13             IClientConfig config, ServerIntrospector serverIntrospector,
14             ILoadBalancer loadBalancer, RetryHandler retryHandler,
15             LoadBalancedRetryFactory loadBalancedRetryFactory, OkHttpClient delegate,
16             RibbonLoadBalancerContext ribbonLoadBalancerContext) {
17         RetryableOkHttpLoadBalancingClient client = new RetryableOkHttpLoadBalancingClient(
18                 delegate, config, serverIntrospector, loadBalancedRetryFactory);
19         client.setLoadBalancer(loadBalancer);
20         client.setRetryHandler(retryHandler);
21         client.setRibbonLoadBalancerContext(ribbonLoadBalancerContext);
22         Monitors.registerObject("Client_" + this.name, client);
23         return client;
24     }
25
26     @Bean
27     @ConditionalOnMissingBean(AbstractLoadBalancerAwareClient.class)
28     @ConditionalOnMissingClass("org.springframework.retry.support.RetryTemplate")
29     public OkHttpLoadBalancingClient okHttpLoadBalancingClient(IClientConfig config,
30             ServerIntrospector serverIntrospector, ILoadBalancer loadBalancer,
31             RetryHandler retryHandler, OkHttpClient delegate) {
32         OkHttpLoadBalancingClient client = new OkHttpLoadBalancingClient(delegate, config,
33                 serverIntrospector);
34         client.setLoadBalancer(loadBalancer);
35         client.setRetryHandler(retryHandler);
36         Monitors.registerObject("Client_" + this.name, client);
37         return client;
38     }
39
40     @Configuration(proxyBeanMethods = false)
41     protected static class OkHttpClientConfiguration {
42
43         private OkHttpClient httpClient;
44
45         @Bean
46         @ConditionalOnMissingBean(ConnectionPool.class)
47         public ConnectionPool httpClientConnectionPool(IClientConfig config,
48                 OkHttpClientConnectionPoolFactory connectionPoolFactory) {
49             RibbonProperties ribbon = RibbonProperties.from(config);
50             int maxTotalConnections = ribbon.maxTotalConnections();
51             long timeToLive = ribbon.poolKeepAliveTime();
52             TimeUnit ttlUnit = ribbon.getPoolKeepAliveTimeUnits();
53             return connectionPoolFactory.create(maxTotalConnections, timeToLive, ttlUnit);
54         }
55
56         @Bean
57         @ConditionalOnMissingBean(OkHttpClient.class)
58         public OkHttpClient client(OkHttpClientFactory httpClientFactory,
59                 ConnectionPool connectionPool, IClientConfig config) {
60             RibbonProperties ribbon = RibbonProperties.from(config);
61             this.httpClient = httpClientFactory.createBuilder(false)
62                     .connectTimeout(ribbon.connectTimeout(), TimeUnit.MILLISECONDS)
63                     .readTimeout(ribbon.readTimeout(), TimeUnit.MILLISECONDS)
64                     .followRedirects(ribbon.isFollowRedirects())
65                     .connectionPool(connectionPool).build();
66             return this.httpClient;
67         }
68
69         @PreDestroy
70         public void destroy() {
71             if (httpClient != null) {
72                 httpClient.dispatcher().executorService().shutdown();
73                 httpClient.connectionPool().evictAll();
74             }
75         }
76
77     }
78
79 }

View Cod

③ 启用 HttpClient 或 OkHttp 不生效的原因

经过前面的分析，可以知道启用 apache httpcomponents 或者 OkHttp，对 RestTemplate 都没有起作用，最终还是用 HttpURLConnection 发起 HTTP 请求。那为什么为出现这种情况呢？我们可以看下 RestTemplate  的 setRequestFactory 方法。

通过 RestTemplate 的 setRequestFactory 方法的注释也可以了解到，默认的 requestFactory 是 SimpleClientHttpRequestFactory，它是基于 JDK 标准 HTTP 库的 HttpURLConnection。

默认的 HttpURLConnection 不支持 PATCH，如果想支持，需设置为 Apache HttpComponents 或 OkHttp 的 request factory。

 1 /**
 2  * Set the request factory that this accessor uses for obtaining client request handles.
 3  * <p>The default is a {@link SimpleClientHttpRequestFactory} based on the JDK's own
 4  * HTTP libraries ({@link java.net.HttpURLConnection}).
 5  * <p><b>Note that the standard JDK HTTP library does not support the HTTP PATCH method.
 6  * Configure the Apache HttpComponents or OkHttp request factory to enable PATCH.</b>
 7  * @see #createRequest(URI, HttpMethod)
 8  * @see SimpleClientHttpRequestFactory
 9  * @see org.springframework.http.client.HttpComponentsAsyncClientHttpRequestFactory
10  * @see org.springframework.http.client.OkHttp3ClientHttpRequestFactory
11  */
12 public void setRequestFactory(ClientHttpRequestFactory requestFactory) {
13     Assert.notNull(requestFactory, "ClientHttpRequestFactory must not be null");
14     this.requestFactory = requestFactory;
15 }

ClientHttpRequestFactory 体系类结构如下：

那 RestClient 又是如何生效的呢？通过上一节的分析可以知道，在 RibbonAutoConfiguration 中有如下的配置，这个 RibbonClientHttpRequestFactoryConfiguration 通过自定义 RestTemplateCustomizer 向 RestTemplate 设置了 requestFactory 为 RibbonClientHttpRequestFactory。

 1 @Configuration(proxyBeanMethods = false)
 2 @ConditionalOnClass(HttpRequest.class)
 3 @ConditionalOnRibbonRestClient
 4 protected static class RibbonClientHttpRequestFactoryConfiguration {
 5     @Autowired
 6     private SpringClientFactory springClientFactory;
 7
 8     @Bean
 9     public RestTemplateCustomizer restTemplateCustomizer(final RibbonClientHttpRequestFactory ribbonClientHttpRequestFactory) {
10         return restTemplate -> restTemplate.setRequestFactory(ribbonClientHttpRequestFactory);
11     }
12
13     @Bean
14     public RibbonClientHttpRequestFactory ribbonClientHttpRequestFactory() {
15         return new RibbonClientHttpRequestFactory(this.springClientFactory);
16     }
17 }

RibbonClientHttpRequestFactory 是对应 RestClient 的，也就是说要启用 OkHttp 或 HttpClient，还需自己创建对应的 ClientHttpRequestFactory，并设置给 RestTemplate。从上面的类结构可以看出，是提供了 HttpComponentsClientHttpRequestFactory 和 OkHttp3ClientHttpRequestFactory 工厂类了的。

这里其实也比较奇怪，既然启用了 apache httpcomponents 或者 OkHttp，却没有创建默认的 ClientHttpRequestFactory 实现类设置给 RestTemplate，感觉这是 spring-cloud-netflix-ribbon 的一个 BUG。

5、定制 RestTemplate 使用 Apache httpcomponents

如果想让 RestTemplate 使用 httpcomponents  的组件，就需要自己创建一个 ClientHttpRequestFactory，并设置给 RestTemplate。下面我们一步步来看看如何修复这个问题。

① 设置 HttpComponentsClientHttpRequestFactory

httpcomponents  中提供的 ClientHttpRequestFactory 实现类是 HttpComponentsClientHttpRequestFactory，但是并不能直接使用这个工厂类，因为它创建的 HttpComponentsClientHttpRequest 不具备重试的能力，它直接使用 CloseableHttpClient 执行请求，虽然有超时的功能，但不能重试。而且，它本质上也没有负载均衡的能力，需要借助 LoadBalancerInterceptor 拦截器来重构 URI。

 1 final class HttpComponentsClientHttpRequest extends AbstractBufferingClientHttpRequest {
 2     private final HttpClient httpClient;
 3     private final HttpUriRequest httpRequest;
 4     private final HttpContext httpContext;
 5
 6     @Override
 7     protected ClientHttpResponse executeInternal(HttpHeaders headers, byte[] bufferedOutput) throws IOException {
 8         // ...
 9         // httpClient => CloseableHttpClient
10         HttpResponse httpResponse = this.httpClient.execute(this.httpRequest, this.httpContext);
11         return new HttpComponentsClientHttpResponse(httpResponse);
12     }
13 }

所以，如果不需要重试的功能，可以直接创建一个 HttpComponentsClientHttpRequest，并设置给 RestTemplate 即可。这样就会使用 LoadBalancerInterceptor 来做负载均衡，重构 URI，然后用 HttpComponentsClientHttpRequest 来执行请求。

1 @Bean
2 @LoadBalanced
3 public RestTemplate restTemplate() {
4     HttpComponentsClientHttpRequestFactory requestFactory = new HttpComponentsClientHttpRequestFactory();
5     RestTemplate restTemplate = new RestTemplate();
6     restTemplate.setRequestFactory(requestFactory);
7     return restTemplate;
8 }

② 定制 apache ClientHttpRequestFactory

如果想让 RestTemplate 即有负载均衡的能力，又能使用 apache HttpComponents 组件，且具备重试的功能，我们就需要自己定制 ClientHttpRequestFactory 了。关于重试后面再单独来讲。

对比 RestClient 可以发现，RibbonClientHttpRequestFactory 创建的 RibbonHttpRequest 其实是使用 RestClient 执行请求，而 RestClient  内部使用 LoadBalancerCommand 来进行重试。

类似的，我们至少要用上已经配置好的 RibbonLoadBalancingHttpClient 来执行请求，所以需要自定义一个类似的 RibbonHttpRequest 。

1）定制 apache ClientHttpRequest

创建 ApacheClientHttpRequest 继承自 RibbonHttpRequest，核心的点在于要注入 RibbonLoadBalancingHttpClient，如果要支持重试，需注入 RetryableRibbonLoadBalancingHttpClient。RetryableRibbonLoadBalancingHttpClient 在引入 spring-retry 后才会创建，这个后面分析重试时再看。

然后在 executeInternal 根据 retryable 判断，如果要重试，就调用 execute 方法，看 RetryableRibbonLoadBalancingHttpClient 的源码可以发现，它本身是支持负载均衡的，会自动选择 Server。

如果不需要重试，就需要调用 executeWithLoadBalancer，它是利用 LoadBalancerCommand 来提交请求，就跟 RestClient 是一样的了。但是不一样的地方是 RibbonLoadBalancingHttpClient 的 executeWithLoadBalancer 是不会进行重试的，这个也放到后面分析。

 1 package com.lyyzoo.sunny.register.ribbon.apache;
 2
 3 import java.io.IOException;
 4 import java.net.URI;
 5 import java.util.ArrayList;
 6
 7 import com.netflix.client.config.IClientConfig;
 8 import com.netflix.client.http.HttpResponse;
 9 import org.springframework.cloud.netflix.ribbon.RibbonHttpRequest;
10 import org.springframework.cloud.netflix.ribbon.RibbonHttpResponse;
11 import org.springframework.cloud.netflix.ribbon.apache.RetryableRibbonLoadBalancingHttpClient;
12 import org.springframework.cloud.netflix.ribbon.apache.RibbonApacheHttpRequest;
13 import org.springframework.cloud.netflix.ribbon.apache.RibbonLoadBalancingHttpClient;
14 import org.springframework.cloud.netflix.ribbon.support.RibbonCommandContext;
15 import org.springframework.http.HttpHeaders;
16 import org.springframework.http.HttpMethod;
17 import org.springframework.http.client.ClientHttpResponse;
18 import org.springframework.util.LinkedMultiValueMap;
19
20 /**
21  * Apache ClientHttpRequest
22  *
23  * @author bojiangzhou
24  */
25 public class ApacheClientHttpRequest extends RibbonHttpRequest {
26
27     private final URI uri;
28
29     private final HttpMethod httpMethod;
30
31     private final String serviceId;
32
33     private final RibbonLoadBalancingHttpClient client;
34
35     private final IClientConfig config;
36     /**
37      * 是否重试
38      */
39     private final boolean retryable;
40
41     public ApacheClientHttpRequest(URI uri,
42                                    HttpMethod httpMethod,
43                                    String serviceId,
44                                    RibbonLoadBalancingHttpClient client,
45                                    IClientConfig config,
46                                    boolean retryable) {
47         super(uri, null, null, config);
48         this.uri = uri;
49         this.httpMethod = httpMethod;
50         this.serviceId = serviceId;
51         this.client = client;
52         this.config = config;
53         this.retryable = retryable;
54         if (retryable && !(client instanceof RetryableRibbonLoadBalancingHttpClient)) {
55             throw new IllegalArgumentException("Retryable client must be RetryableRibbonLoadBalancingHttpClient");
56         }
57     }
58
59     @Override
60     protected ClientHttpResponse executeInternal(HttpHeaders headers) throws IOException {
61         try {
62             RibbonCommandContext ribbonCommandContext = new RibbonCommandContext(serviceId, httpMethod.name(),
63                     uri.toString(), retryable, headers, new LinkedMultiValueMap<>(), null, new ArrayList<>());
64
65             RibbonApacheHttpRequest request = new RibbonApacheHttpRequest(ribbonCommandContext);
66
67             HttpResponse response;
68             if (retryable) {
69                 // RetryableRibbonLoadBalancingHttpClient 本身具备负载均衡的能力
70                 response = client.execute(request, config);
71             } else {
72                 // RibbonLoadBalancingHttpClient 需调用 executeWithLoadBalancer 才具备负载均衡的能力
73                 response = client.executeWithLoadBalancer(request, config);
74             }
75
76             return new RibbonHttpResponse(response);
77         } catch (Exception e) {
78             throw new IOException(e);
79         }
80     }
81 }

2）定制 apache ClientHttpRequestFactory

创建 ApacheClientHttpRequestFactory 继承自 HttpComponentsClientHttpRequestFactory，主要是在 createRequest 方法中创建自定义的 ApacheClientHttpRequest。RibbonLoadBalancingHttpClient 可以从 SpringClientFactory 中获取。

 1 package com.lyyzoo.sunny.register.ribbon.apache;
 2
 3 import java.io.IOException;
 4 import java.net.URI;
 5
 6 import com.netflix.client.config.IClientConfig;
 7 import org.springframework.cloud.netflix.ribbon.SpringClientFactory;
 8 import org.springframework.cloud.netflix.ribbon.apache.RibbonLoadBalancingHttpClient;
 9 import org.springframework.http.HttpMethod;
10 import org.springframework.http.client.ClientHttpRequest;
11 import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
12 import org.springframework.lang.NonNull;
13
14 /**
15  * Apache HttpComponents ClientHttpRequest factory
16  *
17  * @author bojiangzhou
18  */
19 public class ApacheClientHttpRequestFactory extends HttpComponentsClientHttpRequestFactory {
20
21     private final SpringClientFactory clientFactory;
22     private final boolean retryable;
23
24     public ApacheClientHttpRequestFactory(SpringClientFactory clientFactory, boolean retryable) {
25         this.clientFactory = clientFactory;
26         this.retryable = retryable;
27     }
28
29     @Override
30     @NonNull
31     public ClientHttpRequest createRequest(URI originalUri, HttpMethod httpMethod) throws IOException {
32         String serviceId = originalUri.getHost();
33         if (serviceId == null) {
34             throw new IOException(
35                     "Invalid hostname in the URI [" + originalUri.toASCIIString() + "]");
36         }
37         IClientConfig clientConfig = this.clientFactory.getClientConfig(serviceId);
38         RibbonLoadBalancingHttpClient httpClient = this.clientFactory.getClient(serviceId, RibbonLoadBalancingHttpClient.class);
39
40         return new ApacheClientHttpRequest(originalUri, httpMethod, serviceId, httpClient, clientConfig, retryable);
41     }
42 }

3）定制 apache ClientHttpRequestFactory 配置类

跟 RestClient 的配置类类似，定制 ApacheClientHttpRequestFactory 的配置类，同样的，默认启用 httpclient。在存在 RetryTemplate 时，就设置 ApacheClientHttpRequestFactory 的 retryable 参数为 true，否则为 false。

然后自定义 RestTemplateCustomizer，将 ApacheClientHttpRequestFactory 设置到 RestTemplate 中，注意这时 LoadBalancerInterceptor 就不会添加到 RestTemplate 中了。

 1 package com.lyyzoo.sunny.register.ribbon.apache;
 2
 3 import org.apache.http.client.HttpClient;
 4 import org.springframework.beans.factory.annotation.Autowired;
 5 import org.springframework.boot.autoconfigure.AutoConfigureAfter;
 6 import org.springframework.boot.autoconfigure.AutoConfigureBefore;
 7 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 8 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
 9 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingClass;
10 import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
11 import org.springframework.cloud.client.loadbalancer.AsyncLoadBalancerAutoConfiguration;
12 import org.springframework.cloud.client.loadbalancer.LoadBalancerAutoConfiguration;
13 import org.springframework.cloud.client.loadbalancer.RestTemplateCustomizer;
14 import org.springframework.cloud.netflix.ribbon.SpringClientFactory;
15 import org.springframework.context.annotation.Bean;
16 import org.springframework.context.annotation.Configuration;
17 import org.springframework.web.client.RestTemplate;
18
19 /**
20  *
21  * @author bojiangzhou
22  */
23 @Configuration
24 @ConditionalOnClass(RestTemplate.class)
25 @AutoConfigureAfter(name = "org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration")
26 @AutoConfigureBefore({LoadBalancerAutoConfiguration.class, AsyncLoadBalancerAutoConfiguration.class})
27 @ConditionalOnProperty(name = "ribbon.httpclient.restTemplate.enabled", matchIfMissing = true)
28 public class ApacheClientHttpRequestFactoryConfiguration {
29
30     @Configuration(proxyBeanMethods = false)
31     @ConditionalOnClass(HttpClient.class)
32     @ConditionalOnProperty(name = "ribbon.httpclient.enabled", matchIfMissing = true)
33     static class HttpComponentsClientHttpRequestFactoryConfiguration {
34
35         @Autowired
36         private SpringClientFactory springClientFactory;
37
38         @Bean
39         @ConditionalOnMissingBean
40         public RestTemplateCustomizer restTemplateCustomizer(
41                 final ApacheClientHttpRequestFactory apacheClientHttpRequestFactory) {
42             return restTemplate -> restTemplate
43                     .setRequestFactory(apacheClientHttpRequestFactory);
44         }
45
46         @Bean
47         @ConditionalOnMissingClass("org.springframework.retry.support.RetryTemplate")
48         public ApacheClientHttpRequestFactory apacheClientHttpRequestFactory() {
49             return new ApacheClientHttpRequestFactory(springClientFactory, false);
50         }
51
52         @Bean
53         @ConditionalOnClass(name = "org.springframework.retry.support.RetryTemplate")
54         public ApacheClientHttpRequestFactory retryableApacheClientHttpRequestFactory() {
55             return new ApacheClientHttpRequestFactory(springClientFactory, true);
56         }
57     }
58 }

4）简单调试下

配置好之后，把 demo-consumer 服务启动起来，简单测试下。

a) 首先请求会进入到 RestTemplate 的 doExecute 中，然后通过 createRequest，调用 ApacheClientHttpRequestFactory 创建 ApacheClientHttpRequest。

b) 接着调用 ApacheClientHttpRequest 的 execute 方法，在 ApacheClientHttpRequest  的 executeInternal 中，就会调用 RibbonLoadBalancingHttpClient 的 executeWithLoadBalancer 方法。

c) 最后，进入 RibbonLoadBalancingHttpClient 的 execute 方法中，它又将请求转给了代理对象 delegate 来执行，delegate 就是在 HttpClientRibbonConfiguration 中配置的 CloseableHttpClient 对象，实际类型是 InternalHttpClient。

经过验证，通过自定义的配置，最终使得 RestTemplate 可以使用 apache httpcomponents 组件来执行 HTTP 请求。重试那块后面再来研究。

③ 还是用一张图来总结下 RestTemplate 基于 apache HttpClient 后的执行流程

6、定制 RestTemplate 使用 OkHttp

① 设置 OkHttp3ClientHttpRequestFactory

类似的，可以给 RestTemplate 直接设置 OkHttp3ClientHttpRequestFactory，但它同样也不具备重试的能力。

1 @Bean
2 @LoadBalanced
3 public RestTemplate restTemplate() {
4     OkHttp3ClientHttpRequestFactory requestFactory = new OkHttp3ClientHttpRequestFactory();
5     RestTemplate restTemplate = new RestTemplate();
6     restTemplate.setRequestFactory(requestFactory);
7     return restTemplate;
8 }

② 定制 OkHttp ClientHttpRequestFactory

与定制 apache httpcomponents  类似，我这里就直接把三个类的代码放出来了。

a) OkHttpClientHttpRequest：

 1 package com.lyyzoo.sunny.register.ribbon.okhttp;
 2
 3 import java.io.IOException;
 4 import java.net.URI;
 5 import java.util.ArrayList;
 6
 7 import com.netflix.client.config.IClientConfig;
 8 import com.netflix.client.http.HttpResponse;
 9 import org.springframework.cloud.netflix.ribbon.RibbonHttpRequest;
10 import org.springframework.cloud.netflix.ribbon.RibbonHttpResponse;
11 import org.springframework.cloud.netflix.ribbon.okhttp.OkHttpLoadBalancingClient;
12 import org.springframework.cloud.netflix.ribbon.okhttp.OkHttpRibbonRequest;
13 import org.springframework.cloud.netflix.ribbon.okhttp.RetryableOkHttpLoadBalancingClient;
14 import org.springframework.cloud.netflix.ribbon.support.RibbonCommandContext;
15 import org.springframework.http.HttpHeaders;
16 import org.springframework.http.HttpMethod;
17 import org.springframework.http.client.ClientHttpResponse;
18 import org.springframework.util.LinkedMultiValueMap;
19
20 /**
21  * OkHttp ClientHttpRequest
22  *
23  * @author bojiangzhou
24  */
25 public class OkHttpClientHttpRequest extends RibbonHttpRequest {
26
27     private final URI uri;
28
29     private final HttpMethod httpMethod;
30
31     private final String serviceId;
32
33     private final OkHttpLoadBalancingClient client;
34
35     private final IClientConfig config;
36     /**
37      * 是否重试
38      */
39     private final boolean retryable;
40
41     public OkHttpClientHttpRequest(URI uri,
42                                    HttpMethod httpMethod,
43                                    String serviceId,
44                                    OkHttpLoadBalancingClient client,
45                                    IClientConfig config,
46                                    boolean retryable) {
47         super(uri, null, null, config);
48         this.uri = uri;
49         this.httpMethod = httpMethod;
50         this.serviceId = serviceId;
51         this.client = client;
52         this.config = config;
53         this.retryable = retryable;
54         if (retryable && !(client instanceof RetryableOkHttpLoadBalancingClient)) {
55             throw new IllegalArgumentException("Retryable client must be RetryableOkHttpLoadBalancingClient");
56         }
57     }
58
59     @Override
60     protected ClientHttpResponse executeInternal(HttpHeaders headers) throws IOException {
61         try {
62             RibbonCommandContext ribbonCommandContext = new RibbonCommandContext(serviceId, httpMethod.name(),
63                     uri.toString(), retryable, headers, new LinkedMultiValueMap<>(), null, new ArrayList<>());
64
65             OkHttpRibbonRequest request = new OkHttpRibbonRequest(ribbonCommandContext);
66
67             HttpResponse response;
68             if (retryable) {
69                 // RetryableRibbonLoadBalancingHttpClient 本身具备负载均衡的能力
70                 response = client.execute(request, config);
71             } else {
72                 // RibbonLoadBalancingHttpClient 需调用 executeWithLoadBalancer 才具备负载均衡的能力
73                 response = client.executeWithLoadBalancer(request, config);
74             }
75
76             return new RibbonHttpResponse(response);
77         } catch (Exception e) {
78             throw new IOException(e);
79         }
80     }
81 }

b) OkHttpClientHttpRequestFactory

 1 package com.lyyzoo.sunny.register.ribbon.okhttp;
 2
 3 import java.io.IOException;
 4 import java.net.URI;
 5
 6 import com.netflix.client.config.IClientConfig;
 7 import org.springframework.cloud.netflix.ribbon.SpringClientFactory;
 8 import org.springframework.cloud.netflix.ribbon.okhttp.OkHttpLoadBalancingClient;
 9 import org.springframework.http.HttpMethod;
10 import org.springframework.http.client.ClientHttpRequest;
11 import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
12 import org.springframework.lang.NonNull;
13
14 /**
15  * OkHttp ClientHttpRequest factory
16  *
17  * @author bojiangzhou
18  */
19 public class OkHttpClientHttpRequestFactory extends HttpComponentsClientHttpRequestFactory {
20
21     private final SpringClientFactory clientFactory;
22     private final boolean retryable;
23
24     public OkHttpClientHttpRequestFactory(SpringClientFactory clientFactory, boolean retryable) {
25         this.clientFactory = clientFactory;
26         this.retryable = retryable;
27     }
28
29     @Override
30     @NonNull
31     public ClientHttpRequest createRequest(URI originalUri, HttpMethod httpMethod) throws IOException {
32         String serviceId = originalUri.getHost();
33         if (serviceId == null) {
34             throw new IOException(
35                     "Invalid hostname in the URI [" + originalUri.toASCIIString() + "]");
36         }
37         IClientConfig clientConfig = this.clientFactory.getClientConfig(serviceId);
38         OkHttpLoadBalancingClient httpClient = this.clientFactory.getClient(serviceId, OkHttpLoadBalancingClient.class);
39
40         return new OkHttpClientHttpRequest(originalUri, httpMethod, serviceId, httpClient, clientConfig, retryable);
41     }
42 }

c) OkHttpClientHttpRequestFactoryConfiguration

 1 package com.lyyzoo.sunny.register.ribbon.okhttp;
 2
 3 import org.springframework.beans.factory.annotation.Autowired;
 4 import org.springframework.boot.autoconfigure.AutoConfigureAfter;
 5 import org.springframework.boot.autoconfigure.AutoConfigureBefore;
 6 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 7 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
 8 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingClass;
 9 import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
10 import org.springframework.cloud.client.loadbalancer.AsyncLoadBalancerAutoConfiguration;
11 import org.springframework.cloud.client.loadbalancer.LoadBalancerAutoConfiguration;
12 import org.springframework.cloud.client.loadbalancer.RestTemplateCustomizer;
13 import org.springframework.cloud.netflix.ribbon.SpringClientFactory;
14 import org.springframework.context.annotation.Bean;
15 import org.springframework.context.annotation.Configuration;
16 import org.springframework.web.client.RestTemplate;
17
18 /**
19  *
20  * @author bojiangzhou
21  */
22 @Configuration
23 @ConditionalOnClass(RestTemplate.class)
24 @AutoConfigureAfter(name = "org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration")
25 @AutoConfigureBefore({LoadBalancerAutoConfiguration.class, AsyncLoadBalancerAutoConfiguration.class})
26 @ConditionalOnProperty(name = "ribbon.okhttp.restTemplate.enabled", matchIfMissing = true)
27 public class OkHttpClientHttpRequestFactoryConfiguration {
28
29     @Configuration(proxyBeanMethods = false)
30     @ConditionalOnProperty("ribbon.okhttp.enabled")
31     @ConditionalOnClass(name = "okhttp3.OkHttpClient")
32     static class ClientHttpRequestFactoryConfiguration {
33
34         @Autowired
35         private SpringClientFactory springClientFactory;
36
37         @Bean
38         @ConditionalOnMissingBean
39         public RestTemplateCustomizer restTemplateCustomizer(
40                 final OkHttpClientHttpRequestFactory okHttpClientHttpRequestFactory) {
41             return restTemplate -> restTemplate
42                     .setRequestFactory(okHttpClientHttpRequestFactory);
43         }
44
45         @Bean
46         @ConditionalOnMissingClass("org.springframework.retry.support.RetryTemplate")
47         public OkHttpClientHttpRequestFactory okHttpClientHttpRequestFactory() {
48             return new OkHttpClientHttpRequestFactory(springClientFactory, false);
49         }
50
51         @Bean
52         @ConditionalOnClass(name = "org.springframework.retry.support.RetryTemplate")
53         public OkHttpClientHttpRequestFactory retryableOkHttpClientHttpRequestFactory() {
54             return new OkHttpClientHttpRequestFactory(springClientFactory, true);
55         }
56     }
57 }

七、RestTemplate 超时重试

1、AbstractLoadBalancerAwareClient

① AbstractLoadBalancerAwareClient

通过上一节的分析，可以知道有重试功能的其实有两个组件，一个是 Ribbon 的 LoadBalancerCommand，一个是 spring-retry 的 RetryTemplate。RetryableRibbonLoadBalancingHttpClient 和 RetryableOkHttpLoadBalancingClient 都要依赖 RetryTemplate，所以必须先引入 spring-retry 依赖，它们最终都是使用 RetryTemplate 实现请求重试的能力的。除了 RetryTemplate，其它客户端想要获取重试的功能，就要用 ribbon 中的 AbstractLoadBalancerAwareClient 相关的组件，并调用 executeWithLoadBalancer 方法。

再看下 AbstractLoadBalancerAwareClient 的体系，通过源码可以了解到：

• RetryableFeignLoadBalancer、RetryableRibbonLoadBalancingHttpClient、RetryableOkHttpLoadBalancingClient 都是使用 RetryTemplate 实现重试功能的，也就是 spring-retry 的重试。
• RestClient、FeignLoadBalancer、RibbonLoadBalancingHttpClient、OkHttpLoadBalancingClient 是在 AbstractLoadBalancerAwareClient 中使用 LoadBalancerCommand 实现重试功能的，就是是 Ribbon 的重试。

② executeWithLoadBalancer

具体的 AbstractLoadBalancerAwareClient 客户端想要负载均衡调用以及能进行重试，需调用 AbstractLoadBalancerAwareClient 的 executeWithLoadBalancer 方法。

在这个方法里面，它先构建了 LoadBalancerCommand，然后用 command 提交了一个 ServerOperation，这个 ServerOperation 中对 URI 进行了 重构，转到具体的 LoadBalancerContext 去执行请求。

 1 public T executeWithLoadBalancer(final S request, final IClientConfig requestConfig) throws ClientException {
 2     // 负载均衡命令
 3     LoadBalancerCommand<T> command = buildLoadBalancerCommand(request, requestConfig);
 4
 5     try {
 6         return command.submit(
 7             new ServerOperation<T>() {
 8                 @Override
 9                 public Observable<T> call(Server server) {
10                     // 重构URI
11                     URI finalUri = reconstructURIWithServer(server, request.getUri());
12                     S requestForServer = (S) request.replaceUri(finalUri);
13                     try {
14                         // 使用具体的 AbstractLoadBalancerAwareClient 客户端执行请求
15                         return Observable.just(AbstractLoadBalancerAwareClient.this.execute(requestForServer, requestConfig));
16                     }
17                     catch (Exception e) {
18                         return Observable.error(e);
19                     }
20                 }
21             })
22             .toBlocking()
23             .single();
24     }
25 }

再看 buildLoadBalancerCommand 方法，它首先会通过 getRequestSpecificRetryHandler 方法获取请求重试处理器 RequestSpecificRetryHandler，而 getRequestSpecificRetryHandler 是一个抽象方法。这里就要重点注意了。

 1 // 抽象方法，获取请求重试处理器
 2 public abstract RequestSpecificRetryHandler getRequestSpecificRetryHandler(S request, IClientConfig requestConfig);
 3
 4 protected LoadBalancerCommand<T> buildLoadBalancerCommand(final S request, final IClientConfig config) {
 5     // 获取请求重试处理器
 6     RequestSpecificRetryHandler handler = getRequestSpecificRetryHandler(request, config);
 7     LoadBalancerCommand.Builder<T> builder = LoadBalancerCommand.<T>builder()
 8             .withLoadBalancerContext(this)
 9             .withRetryHandler(handler)
10             .withLoadBalancerURI(request.getUri());
11     customizeLoadBalancerCommandBuilder(request, config, builder);
12     return builder.build();
13 }

2、请求重试处理器 RequestSpecificRetryHandler

① 先了解下 RequestSpecificRetryHandler：

• 首先看它的构造方法，注意第一个参数和第二个参数，因为不同的 getRequestSpecificRetryHandler 方法实现，主要差异就在于这两个参数。
• 然后看 isRetriableException，这个方法就是 LoadBalancerCommand 用来判断异常后是否需要重试的方法，可以了解到 okToRetryOnAllErrors=true 时就可以重试，否则 okToRetryOnConnectErrors=true 才可能重试。需要注意的是就算这个方法返回 true 也不一定会重试，这跟重试次数也是有一定关系的。

 1 public RequestSpecificRetryHandler(boolean okToRetryOnConnectErrors, boolean okToRetryOnAllErrors, RetryHandler baseRetryHandler, @Nullable IClientConfig requestConfig) {
 2     Preconditions.checkNotNull(baseRetryHandler);
 3     this.okToRetryOnConnectErrors = okToRetryOnConnectErrors;
 4     this.okToRetryOnAllErrors = okToRetryOnAllErrors;
 5     this.fallback = baseRetryHandler;
 6     if (requestConfig != null) {
 7         // 在同一个Server上重试的次数
 8         if (requestConfig.containsProperty(CommonClientConfigKey.MaxAutoRetries)) {
 9             retrySameServer = requestConfig.get(CommonClientConfigKey.MaxAutoRetries);
10         }
11         // 重试下一个Server的次数
12         if (requestConfig.containsProperty(CommonClientConfigKey.MaxAutoRetriesNextServer)) {
13             retryNextServer = requestConfig.get(CommonClientConfigKey.MaxAutoRetriesNextServer);
14         }
15     }
16 }
17
18 @Override
19 public boolean isRetriableException(Throwable e, boolean sameServer) {
20     // 所有错误都重试
21     if (okToRetryOnAllErrors) {
22         return true;
23     }
24     // ClientException 才可能重试
25     else if (e instanceof ClientException) {
26         ClientException ce = (ClientException) e;
27         if (ce.getErrorType() == ClientException.ErrorType.SERVER_THROTTLED) {
28             return !sameServer;
29         } else {
30             return false;
31         }
32     }
33     else  {
34         // 连接错误才重试，就是抛出 SocketException 异常时才重试
35         return okToRetryOnConnectErrors && isConnectionException(e);
36     }
37 }

② 不同 LoadBalancerCommand 的 getRequestSpecificRetryHandler 实现

a）RestClient

默认配置下，RestClient 的 getRequestSpecificRetryHandler 会走到最后一步，okToRetryOnConnectErrors、okToRetryOnAllErrors 都为 true，也就是说 isRetriableException 始终返回 true，也就是说抛出异常都会重试。

 1 @Override
 2 public RequestSpecificRetryHandler getRequestSpecificRetryHandler(
 3         HttpRequest request, IClientConfig requestConfig) {
 4     if (!request.isRetriable()) {
 5         return new RequestSpecificRetryHandler(false, false, this.getRetryHandler(), requestConfig);
 6     }
 7     if (this.ncc.get(CommonClientConfigKey.OkToRetryOnAllOperations, false)) {
 8         return new RequestSpecificRetryHandler(true, true, this.getRetryHandler(), requestConfig);
 9     }
10     if (request.getVerb() != HttpRequest.Verb.GET) {
11         return new RequestSpecificRetryHandler(true, false, this.getRetryHandler(), requestConfig);
12     } else {
13         // okToRetryOnConnectErrors、okToRetryOnAllErrors 都为 true
14         return new RequestSpecificRetryHandler(true, true, this.getRetryHandler(), requestConfig);
15     }
16 }

b）AbstractLoadBalancingClient

AbstractLoadBalancingClient 中的 getRequestSpecificRetryHandler 相当于一个默认实现，默认情况下 okToRetryOnAllOperations 为 false，最后也会到最后一步，即 okToRetryOnConnectErrors、okToRetryOnAllErrors 都为 true，isRetriableException 始终返回 true。

 1 @Override
 2 public RequestSpecificRetryHandler getRequestSpecificRetryHandler(final S request, final IClientConfig requestConfig) {
 3     // okToRetryOnAllOperations：是否所有操作都重试，默认 false
 4     if (this.okToRetryOnAllOperations) {
 5         return new RequestSpecificRetryHandler(true, true, this.getRetryHandler(), requestConfig);
 6     }
 7     if (!request.getContext().getMethod().equals("GET")) {
 8         return new RequestSpecificRetryHandler(true, false, this.getRetryHandler(), requestConfig);
 9     }
10     else {
11         return new RequestSpecificRetryHandler(true, true, this.getRetryHandler(), requestConfig);
12     }
13 }

c）RibbonLoadBalancingHttpClient

RibbonLoadBalancingHttpClient 也重载了 getRequestSpecificRetryHandler，但是它设置了 okToRetryOnConnectErrors、okToRetryOnAllErrors 都为 false，isRetriableException 始终返回 false。

至此我们应该就知道为什么调用 RibbonLoadBalancingHttpClient 的 executeWithLoadBalancer 不具备重试的功能的原因了。所以启用 apache httpclient 时，RibbonLoadBalancingHttpClient 调用是不支持重试的。

1 @Override
2 public RequestSpecificRetryHandler getRequestSpecificRetryHandler(RibbonApacheHttpRequest request, IClientConfig requestConfig) {
3     // okToRetryOnConnectErrors、okToRetryOnAllErrors 都为 false
4     return new RequestSpecificRetryHandler(false, false, RetryHandler.DEFAULT, requestConfig);
5 }

RetryableRibbonLoadBalancingHttpClient 中也重写了 getRequestSpecificRetryHandler，同样也是设置 okToRetryOnConnectErrors、okToRetryOnAllErrors 都为 false。但是在引入 spring-retry 后，它会使用 RetryTemplate 实现重试的功能。

1 @Override
2 public RequestSpecificRetryHandler getRequestSpecificRetryHandler(RibbonApacheHttpRequest request, IClientConfig requestConfig) {
3     // okToRetryOnConnectErrors、okToRetryOnAllErrors 都为 false
4     return new RequestSpecificRetryHandler(false, false, RetryHandler.DEFAULT, null);
5 }

d）OkHttpLoadBalancingClient

OkHttpLoadBalancingClient 并没有重写 getRequestSpecificRetryHandler，所以它是使用父类 AbstractLoadBalancingClient 中的方法，也就是 okToRetryOnConnectErrors、okToRetryOnAllErrors 都为 true。所以，启用 okhttp 时，OkHttpLoadBalancingClient 是支持重试的，这里需要注意。

而 RetryableOkHttpLoadBalancingClient 跟 RetryableRibbonLoadBalancingHttpClient 一样的重写方式，使用 RetryTemplate 实现重试。

1 @Override
2 public RequestSpecificRetryHandler getRequestSpecificRetryHandler(RibbonApacheHttpRequest request, IClientConfig requestConfig) {
3     // okToRetryOnConnectErrors、okToRetryOnAllErrors 都为 false
4     return new RequestSpecificRetryHandler(false, false, RetryHandler.DEFAULT, null);
5 }

3、LoadBalancerCommand

看 LoadBalancerCommand 的 submit 方法，这个方法是重试的核心代码。

• 首先获取了同一个Server重试次数 maxRetrysSame 和 重试下一个Server的次数 maxRetrysNext，其实就是前面配置的 ribbon.MaxAutoRetries 和 ribbon.MaxAutoRetriesNextServer，我设置的是 1。
• 然后创建了一个 Observable，它的第一层会先通过 loadBalancerContext 获取 Server。在重试下一个 Server 时，这里就会获取下一个 Server。
• 在第二层，又创建了一个 Observable，这个 Observable 就是调用 ServerOperation 的，就是重构 URI，调用具体的 AbstractLoadBalancerAwareClient 执行请求。
• 在第二层里，会根据 maxRetrysSame 重试同一个 Server，从 retryPolicy 中可以了解到，当重试次数大于 maxRetrysSame 后，同一个 Server 重试就结束了，否则就用 retryHandler.isRetriableException 判断是否重试，这个前面已经分析过了。
• 在外层，则根据 maxRetrysNext 重试不同的 Server，从 retryPolicy 中可以了解到，当不同Server重试次数大于 maxRetrysNext 后，就重试结束了，整个重试也就结束了，如果还是失败，就会进入 onErrorResumeNext 进行最后的失败处理。

最后来总结一下 LoadBalancerCommand 重试：

• 重试分为同一个 Server 重试和重试下一个Server，当重试次数大于设置的重试值时，就停止重试。否则通过 retryHandler.isRetriableException 判断是否重试。
• 那这里一共请求了多少次呢？可以总结出如下公式：请求次数 = （maxRetrysSame + 1） * （maxRetrysNext + 1），所以按 ribbon.MaxAutoRetries = 1、ribbon.MaxAutoRetriesNextServer = 1 的配置，如果每次请求都超时，就会发起 4 次请求。

 1 public Observable<T> submit(final ServerOperation<T> operation) {
 2     final ExecutionInfoContext context = new ExecutionInfoContext();
 3
 4     // 同一个Server重试次数
 5     final int maxRetrysSame = retryHandler.getMaxRetriesOnSameServer();
 6     // 重试下一个Server的次数
 7     final int maxRetrysNext = retryHandler.getMaxRetriesOnNextServer();
 8
 9     // 创建一个 Observable
10     Observable<T> o =
11             // 使用 loadBalancerContext 获取 Server
12             (server == null ? selectServer() : Observable.just(server))
13             .concatMap(new Func1<Server, Observable<T>>() {
14                 @Override
15                 public Observable<T> call(Server server) {
16                     // 设置Server
17                     context.setServer(server);
18                     final ServerStats stats = loadBalancerContext.getServerStats(server);
19
20                     // 创建 Observable
21                     Observable<T> o = Observable
22                             .just(server)
23                             .concatMap(new Func1<Server, Observable<T>>() {
24                                 @Override
25                                 public Observable<T> call(final Server server) {
26                                     // 增加尝试次数
27                                     context.incAttemptCount();
28                                     // ...
29                                     // 调用 ServerOperation
30                                     return operation.call(server).doOnEach(new Observer<T>() {
31                                         // 一些回调方法
32                                     });
33                                 }
34                             });
35                     // 重试同一个Server
36                     if (maxRetrysSame > 0)
37                         o = o.retry(retryPolicy(maxRetrysSame, true));
38                     return o;
39                 }
40             });
41
42     if (maxRetrysNext > 0 && server == null)
43         // 重试不同Server
44         o = o.retry(retryPolicy(maxRetrysNext, false));
45
46     return o.onErrorResumeNext(new Func1<Throwable, Observable<T>>() {
47         @Override
48         public Observable<T> call(Throwable e) {
49             // 异常处理
50             return Observable.error(e);
51         }
52     });
53 }
54
55 // retryPolicy 返回一个是否重试的断言
56 private Func2<Integer, Throwable, Boolean> retryPolicy(final int maxRetrys, final boolean same) {
57     return new Func2<Integer, Throwable, Boolean>() {
58         @Override
59         public Boolean call(Integer tryCount, Throwable e) {
60             // 请求拒绝异常就不允许重试
61             if (e instanceof AbortExecutionException) {
62                 return false;
63             }
64             // 尝试次数是否大于最大重试次数
65             if (tryCount > maxRetrys) {
66                 return false;
67             }
68             // 使用 RequestSpecificRetryHandler 判断是否重试
69             return retryHandler.isRetriableException(e, same);
70         }
71     };
72 }

4、RetryTemplate

① spring-retry

要启用 RetryTemplate 需先引入 spring-retry：

1 <dependency>
2     <groupId>org.springframework.retry</groupId>
3     <artifactId>spring-retry</artifactId>
4 </dependency>

以 RetryableRibbonLoadBalancingHttpClient 为例，先看看它的 execute 方法，它先创建了负载均衡重试策略类 LoadBalancedRetryPolicy，然后将请求调用的逻辑封装到 RetryCallback 中，最后其实就是用 RetryTemplate 执行这个 RetryCallback，也就是说请求重试的逻辑都在 RetryTemplate 中。

 1 public RibbonApacheHttpResponse execute(final RibbonApacheHttpRequest request, final IClientConfig configOverride) throws Exception {
 2     //...
 3
 4     // 负载均衡重试策略 RibbonLoadBalancedRetryPolicy
 5     final LoadBalancedRetryPolicy retryPolicy = loadBalancedRetryFactory.createRetryPolicy(this.getClientName(), this);
 6
 7     RetryCallback<RibbonApacheHttpResponse, Exception> retryCallback = context -> {
 8         // ...
 9         // delegate => CloseableHttpClient
10         final HttpResponse httpResponse = RetryableRibbonLoadBalancingHttpClient.this.delegate.execute(httpUriRequest);
11         // ...
12         // 成功 返回结果
13         return new RibbonApacheHttpResponse(httpResponse, httpUriRequest.getURI());
14     };
15
16     LoadBalancedRecoveryCallback<RibbonApacheHttpResponse, HttpResponse> recoveryCallback = new LoadBalancedRecoveryCallback<RibbonApacheHttpResponse, HttpResponse>()//...
17
18     return this.executeWithRetry(request, retryPolicy, retryCallback, recoveryCallback);
19 }
20
21 private RibbonApacheHttpResponse executeWithRetry(RibbonApacheHttpRequest request,
22         LoadBalancedRetryPolicy retryPolicy,
23         RetryCallback<RibbonApacheHttpResponse, Exception> callback,
24         RecoveryCallback<RibbonApacheHttpResponse> recoveryCallback)
25         throws Exception {
26     RetryTemplate retryTemplate = new RetryTemplate();
27
28     // retryable => 取自 RibbonCommandContext 设置的 retryable 参数
29     boolean retryable = isRequestRetryable(request);
30     // 设置重试策略
31     retryTemplate.setRetryPolicy(retryPolicy == null || !retryable
32             ? new NeverRetryPolicy() : new RetryPolicy(request, retryPolicy, this, this.getClientName()));
33
34     BackOffPolicy backOffPolicy = loadBalancedRetryFactory.createBackOffPolicy(this.getClientName());
35     retryTemplate.setBackOffPolicy(backOffPolicy == null ? new NoBackOffPolicy() : backOffPolicy);
36
37     // 利用 retryTemplate 执行请求 callback
38     return retryTemplate.execute(callback, recoveryCallback);
39 }

需要注意的是，在 executeWithRetry 中，会判断是否要重试，判断的逻辑中 getRetryable 其实就是取的 ApacheClientHttpRequest 中 executeInternal 方法里创建的 RibbonCommandContext 设置的 retryable 参数，这就和前面定制化的逻辑衔接上了。

1 private boolean isRequestRetryable(ContextAwareRequest request) {
2     if (request.getContext() == null || request.getContext().getRetryable() == null) {
3         return true;
4     }
5     return request.getContext().getRetryable();
6 }

② RetryTemplate

进入 RetryTemplate 的 execute 方法，核心的逻辑我精简成如下代码，主要就是一个 while 循环判断是否可以重试，然后调用 retryCallback 执行请求。请求失败后，比如超时，抛出异常，就会 registerThrowable 来注册异常。

 1 protected <T, E extends Throwable> T doExecute(RetryCallback<T, E> retryCallback,
 2         RecoveryCallback<T> recoveryCallback, RetryState state) throws E, ExhaustedRetryException {
 3
 4     // retryPolicy => InterceptorRetryPolicy
 5     RetryPolicy retryPolicy = this.retryPolicy;
 6     BackOffPolicy backOffPolicy = this.backOffPolicy;
 7     //....
 8     try {
 9         // ...
10         // canRetry 判断是否重试
11         while (canRetry(retryPolicy, context) && !context.isExhaustedOnly()) {
12             try {
13                 // retryCallback 调用
14                 return retryCallback.doWithRetry(context);
15             }
16             catch (Throwable e) {
17                 // ...
18                 // 注册异常
19                 registerThrowable(retryPolicy, state, context, e);
20                 // ...
21             }
22         }
23         exhausted = true;
24         return handleRetryExhausted(recoveryCallback, context, state);
25     }
26     //...
27 }

看 canRetry 方法，它实际是调用了 InterceptorRetryPolicy 的 canRetry。第一次调用时，会去获取 Server；否则就用 RibbonLoadBalancedRetryPolicy 判断是否重试下一个 Server，注意它判断的逻辑是 GET 请求或者允许所有操作操作重试，且 Server 重试次数 nextServerCount  小于等于配置的 MaxAutoRetriesNextServer 。也就是说，while 循环判断的 canRetry 是重试下一个 Server 的。

 1 protected boolean canRetry(RetryPolicy retryPolicy, RetryContext context) {
 2     return retryPolicy.canRetry(context);
 3 }
 4
 5 //////////// InterceptorRetryPolicy
 6 public boolean canRetry(RetryContext context) {
 7     LoadBalancedRetryContext lbContext = (LoadBalancedRetryContext) context;
 8     if (lbContext.getRetryCount() == 0 && lbContext.getServiceInstance() == null) {
 9         // 获取 Server
10         lbContext.setServiceInstance(this.serviceInstanceChooser.choose(this.serviceName));
11         return true;
12     }
13     // RibbonLoadBalancedRetryPolicy => 重试下一个Server
14     return this.policy.canRetryNextServer(lbContext);
15 }
16
17 ///////// RibbonLoadBalancedRetryPolicy
18 public boolean canRetryNextServer(LoadBalancedRetryContext context) {
19     // 判断重试下一个Server
20     return nextServerCount <= lbContext.getRetryHandler().getMaxRetriesOnNextServer()
21             && canRetry(context);
22 }
23
24 public boolean canRetry(LoadBalancedRetryContext context) {
25     // GET 请求或者允许所有操作重试时，就允许重试
26     HttpMethod method = context.getRequest().getMethod();
27     return HttpMethod.GET == method || lbContext.isOkToRetryOnAllOperations();
28 }

接着看请求失败后的注册异常 registerThrowable，它最后会向 RibbonLoadBalancedRetryPolicy 注册异常。在 RibbonLoadBalancedRetryPolicy 的 registerThrowable 方法中，如果不重试同一个Server且可以重试下一个Server，就会轮询获取下一个Server。如果可以在同一个Server上重试，sameServerCount 计数器就+1，否则重置 sameServerCount，然后 nextServerCount +1。

 1 protected void registerThrowable(RetryPolicy retryPolicy, RetryState state,
 2         RetryContext context, Throwable e) {
 3     retryPolicy.registerThrowable(context, e);
 4     registerContext(context, state);
 5 }
 6
 7 ///////// InterceptorRetryPolicy /////////
 8 public void registerThrowable(RetryContext context, Throwable throwable) {
 9     LoadBalancedRetryContext lbContext = (LoadBalancedRetryContext) context;
10     lbContext.registerThrowable(throwable);
11     // RibbonLoadBalancedRetryPolicy
12     this.policy.registerThrowable(lbContext, throwable);
13 }
14
15 ///////// RibbonLoadBalancedRetryPolicy /////////
16 public void registerThrowable(LoadBalancedRetryContext context, Throwable throwable) {
17     //...
18     // 如果不在在同一个Server 上重试且可以重试下一个Server，则重新选择一个 Server
19     if (!canRetrySameServer(context) && canRetryNextServer(context)) {
20         context.setServiceInstance(loadBalanceChooser.choose(serviceId));
21     }
22
23     // 同一个Server重试超过设置的值后，就重置 sameServerCount
24     if (sameServerCount >= lbContext.getRetryHandler().getMaxRetriesOnSameServer()
25             && canRetry(context)) {
26         // 重置 nextServerCount
27         sameServerCount = 0;
28         // 下一个Server重试次数+1
29         nextServerCount++;
30         if (!canRetryNextServer(context)) {
31             // 不能重试下一个Server了
32             context.setExhaustedOnly();
33         }
34     }
35     else {
36         // 同一个Server重试次数+1
37         sameServerCount++;
38     }
39 }
40
41 // 判断是否重试同一个Server
42 public boolean canRetrySameServer(LoadBalancedRetryContext context) {
43     return sameServerCount < lbContext.getRetryHandler().getMaxRetriesOnSameServer()
44             && canRetry(context);
45 }
46
47 public boolean canRetry(LoadBalancedRetryContext context) {
48     // GET 请求或者允许所有操作重试时，就允许重试
49     HttpMethod method = context.getRequest().getMethod();
50     return HttpMethod.GET == method || lbContext.isOkToRetryOnAllOperations();
51 }

5、Ribbon 重试总结

① 首先，Ribbon 关于超时和重试的配置参数如下，这些参数也可以针对某个客户端配置：

 1 ribbon:
 2   # 客户端读取超时时间
 3   ReadTimeout: 1000
 4   # 客户端连接超时时间
 5   ConnectTimeout: 1000
 6   # 默认只重试 GET，设置为 true 时将重试所有类型，如 POST、PUT、DELETE
 7   OkToRetryOnAllOperations: false
 8   # 同一个Server重试次数
 9   MaxAutoRetries: 1
10   # 最多重试几个Server
11   MaxAutoRetriesNextServer: 1

② RetryTemplate 是 spring-retry 的重试组件，LoadBalancerCommand 是 Ribbon 的重试组件。它们重试的请求次数是一样的，重试逻辑也是类似，都是先重试当前 Server，再重试下一个Server，总的请求次数 = （MaxAutoRetries + 1） * （MaxAutoRetriesNextServer + 1）。

③ 但是有点差别的是，RetryTemplate 会判断请求方法为 GET 或者 OkToRetryOnAllOperations=true 时才允许重试，而 LoadBalancerCommand  是所有 http 方法都可以重试。这个其实是有问题的，一般只有GET才允许重试，因为GET是查询操作，接口是幂等的，而POST、PUT、DELETE一般是非幂等的。所以一般更建议使用 RetryTemplate，并且配置 OkToRetryOnAllOperations=false。

④ 为了提升服务间通信性能，一般可以启用 apache httpclient 或者 OkHttp，如果要启用重试功能，还需要引入 spring-retry 依赖。重试时，当前Server就不要重试了（MaxAutoRetries=0），直接重试下一个Server。

 1 ribbon:
 2   # 客户端读取超时时间
 3   ReadTimeout: 1000
 4   # 客户端连接超时时间
 5   ConnectTimeout: 1000
 6   # 默认只重试 GET，设置为 true 时将重试所有类型，如 POST、PUT、DELETE
 7   OkToRetryOnAllOperations: false
 8   # 同一个Server重试次数
 9   MaxAutoRetries: 0
10   # 最多重试几个Server
11   MaxAutoRetriesNextServer: 1
12   # 启用 httpclient
13   httpclient:
14     enabled: false
15   # 启用 RestClient
16   restclient:
17     enabled: false
18   # 启用 okhttp
19   okhttp:
20     enabled: true