Zookeeper使用--开源客户端
一、ZkClient
ZkClient是在Zookeeper原生API接口之上进行了包装,是一个更易用的Zookeeper客户端,其内部还实现了诸如Session超时重连、Watcher反复注册等功能。
1.1 添加依赖
在pom.xml文件中添加如下内容即可。
<dependency>
<groupId>com.101tec</groupId>
<artifactId>zkclient</artifactId>
<version>0.2</version>
</dependency>
1.2 创建会话
使用ZkClient可以轻松的创建会话,连接到服务端。
package com.hust.grid.leesf.zkclient.examples; import java.io.IOException;
import org.I0Itec.zkclient.ZkClient; public class Create_Session_Sample {
public static void main(String[] args) throws IOException, InterruptedException {
ZkClient zkClient = new ZkClient("127.0.0.1:2181", 5000);
System.out.println("ZooKeeper session established.");
}
}
运行结果:
ZooKeeper session established.
结果表明已经成功创建会话。
1.3 创建节点
ZkClient提供了递归创建节点的接口,即其帮助开发者完成父节点的创建,再创建子节点。
package com.hust.grid.leesf.zkclient.examples;
import org.I0Itec.zkclient.ZkClient; public class Create_Node_Sample {
public static void main(String[] args) throws Exception {
ZkClient zkClient = new ZkClient("127.0.0.1:2181", 5000);
String path = "/zk-book/c1";
zkClient.createPersistent(path, true);
System.out.println("success create znode.");
}
}
运行结果:
success create znode.
结果表明已经成功创建了节点,值得注意的是,在原生态接口中是无法创建成功的(父节点不存在),但是通过ZkClient可以递归的先创建父节点,再创建子节点。
可以看到确实成功创建了/zk-book和/zk-book/c1两个节点。
1.4 删除节点
ZkClient提供了递归删除节点的接口,即其帮助开发者先删除所有子节点(存在),再删除父节点。
package com.hust.grid.leesf.zkclient.examples; import org.I0Itec.zkclient.ZkClient; public class Del_Data_Sample {
public static void main(String[] args) throws Exception {
String path = "/zk-book";
ZkClient zkClient = new ZkClient("127.0.0.1:2181", 5000);
zkClient.createPersistent(path, "");
zkClient.createPersistent(path+"/c1", "");
zkClient.deleteRecursive(path);
System.out.println("success delete znode.");
}
}
运行结果:
success delete znode.
结果表明ZkClient可直接删除带子节点的父节点,因为其底层先删除其所有子节点,然后再删除父节点。
1.5 获取子节点
package com.hust.grid.leesf.zkclient.examples; import java.util.List; import org.I0Itec.zkclient.IZkChildListener;
import org.I0Itec.zkclient.ZkClient; public class Get_Children_Sample { public static void main(String[] args) throws Exception {
String path = "/zk-book";
ZkClient zkClient = new ZkClient("127.0.0.1:2181", 5000);
zkClient.subscribeChildChanges(path, new IZkChildListener() {
public void handleChildChange(String parentPath, List<String> currentChilds) throws Exception {
System.out.println(parentPath + " 's child changed, currentChilds:" + currentChilds);
}
}); zkClient.createPersistent(path);
Thread.sleep(1000);
zkClient.createPersistent(path + "/c1");
Thread.sleep(1000);
zkClient.delete(path + "/c1");
Thread.sleep(1000);
zkClient.delete(path);
Thread.sleep(Integer.MAX_VALUE);
}
}
运行结果:
/zk-book 's child changed, currentChilds:[]
/zk-book 's child changed, currentChilds:[c1]
/zk-book 's child changed, currentChilds:[]
/zk-book 's child changed, currentChilds:null
结果表明:
客户端可以对一个不存在的节点进行子节点变更的监听。
一旦客户端对一个节点注册了子节点列表变更监听之后,那么当该节点的子节点列表发生变更时,服务端都会通知客户端,并将最新的子节点列表发送给客户端
该节点本身的创建或删除也会通知到客户端。
1.6 获取数据
package com.hust.grid.leesf.zkclient.examples; import org.I0Itec.zkclient.IZkDataListener;
import org.I0Itec.zkclient.ZkClient; public class Get_Data_Sample {
public static void main(String[] args) throws Exception {
String path = "/zk-book";
ZkClient zkClient = new ZkClient("127.0.0.1:2181", 5000);
zkClient.createEphemeral(path, "123"); zkClient.subscribeDataChanges(path, new IZkDataListener() {
public void handleDataDeleted(String dataPath) throws Exception {
System.out.println("Node " + dataPath + " deleted.");
} public void handleDataChange(String dataPath, Object data) throws Exception {
System.out.println("Node " + dataPath + " changed, new data: " + data);
}
}); System.out.println(zkClient.readData(path));
zkClient.writeData(path, "456");
Thread.sleep(1000);
zkClient.delete(path);
Thread.sleep(Integer.MAX_VALUE);
}
}
运行结果:
123
Node /zk-book changed, new data: 456
Node /zk-book deleted.
结果表明可以成功监听节点数据变化或删除事件。
1.7 检测节点是否存在
package com.hust.grid.leesf.zkclient.examples; import org.I0Itec.zkclient.ZkClient; public class Exist_Node_Sample {
public static void main(String[] args) throws Exception {
String path = "/zk-book";
ZkClient zkClient = new ZkClient("127.0.0.1:2181", 2000);
System.out.println("Node " + path + " exists " + zkClient.exists(path));
}
}
运行结果:
Node /zk-book exists false
结果表明,可以通过ZkClient轻易检测节点是否存在,其相比于原生态的接口更易于理解。
二、Curator客户端
Curator解决了很多Zookeeper客户端非常底层的细节开发工作,包括连接重连,反复注册Watcher和NodeExistsException异常等,现已成为Apache的顶级项目。
2.1 添加依赖
在pom.xml文件中添加如下内容即可。
<dependency>
<groupId>org.apache.curator</groupId>
<artifactId>curator-framework</artifactId>
<version>2.4.2</version>
</dependency>
2.2 创建会话
Curator除了使用一般方法创建会话外,还可以使用fluent风格进行创建。
package com.hust.grid.leesf.curator.examples; import org.apache.curator.RetryPolicy;
import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.retry.ExponentialBackoffRetry; public class Create_Session_Sample {
public static void main(String[] args) throws Exception {
RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);
CuratorFramework client = CuratorFrameworkFactory.newClient("127.0.0.1:2181", 5000, 3000, retryPolicy);
client.start();
System.out.println("Zookeeper session1 established. ");
CuratorFramework client1 = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181")
.sessionTimeoutMs(5000).retryPolicy(retryPolicy).namespace("base").build();
client1.start();
System.out.println("Zookeeper session2 established. ");
}
}
运行结果:
Zookeeper session1 established.
Zookeeper session2 established.
值得注意的是session2会话含有隔离命名空间,即客户端对Zookeeper上数据节点的任何操作都是相对/base目录进行的,这有利于实现不同的Zookeeper的业务之间的隔离。
2.3 创建节点
注意:在ZooKeeper中规定了所有非叶子节点必须为持久节点。
通过使用Fluent风格的接口,开发人员可以进行自由组合来完成各种类型节点的创建。
package com.hust.grid.leesf.curator.examples; import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.retry.ExponentialBackoffRetry;
import org.apache.zookeeper.CreateMode; public class Create_Node_Sample {
public static void main(String[] args) throws Exception {
String path = "/zk-book/c1";
CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181")
.sessionTimeoutMs(5000).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build();
client.start();
client.create().creatingParentsIfNeeded().withMode(CreateMode.EPHEMERAL).forPath(path, "init".getBytes());
System.out.println("success create znode: " + path);
}
}
运行结果:
success create znode: /zk-book/c1
其中,也创建了/zk-book/c1的父节点/zk-book节点。
2.4 删除节点
package com.hust.grid.leesf.curator.examples; import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.retry.ExponentialBackoffRetry;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.data.Stat; public class Del_Data_Sample {
public static void main(String[] args) throws Exception {
String path = "/zk-book/c1";
CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181")
.sessionTimeoutMs(5000).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build();
client.start();
client.create().creatingParentsIfNeeded().withMode(CreateMode.EPHEMERAL).forPath(path, "init".getBytes());
Stat stat = new Stat();
System.out.println(new String(client.getData().storingStatIn(stat).forPath(path)));
client.delete().deletingChildrenIfNeeded().withVersion(stat.getVersion()).forPath(path);
System.out.println("success delete znode " + path);
Thread.sleep(Integer.MAX_VALUE);
}
}
运行结果:
init
success delete znode /zk-book/c1
结果表明成功删除/zk-book/c1节点。
2.5 获取数据
package com.hust.grid.leesf.curator.examples; import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.retry.ExponentialBackoffRetry;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.data.Stat; public class Get_Data_Sample {
public static void main(String[] args) throws Exception {
String path = "/zk-book";
CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181")
.sessionTimeoutMs(5000).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build();
client.start();
client.create().creatingParentsIfNeeded().withMode(CreateMode.EPHEMERAL).forPath(path, "init".getBytes());
Stat stat = new Stat();
System.out.println(new String(client.getData().storingStatIn(stat).forPath(path)));
}
}
运行结果:
init
结果表明成功获取了节点的数据。
2.6 更新数据
package com.hust.grid.leesf.curator.examples; import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.retry.ExponentialBackoffRetry;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.data.Stat; public class Set_Data_Sample {
public static void main(String[] args) throws Exception {
String path = "/zk-book";
CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181")
.sessionTimeoutMs(5000).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build();
client.start();
client.create().creatingParentsIfNeeded().withMode(CreateMode.EPHEMERAL).forPath(path, "init".getBytes());
Stat stat = new Stat();
client.getData().storingStatIn(stat).forPath(path);
System.out.println("Success set node for : " + path + ", new version: "
+ client.setData().withVersion(stat.getVersion()).forPath(path).getVersion());
try {
client.setData().withVersion(stat.getVersion()).forPath(path);
} catch (Exception e) {
System.out.println("Fail set node due to " + e.getMessage());
}
}
}
运行结果:
Success set node for : /zk-book, new version: 1
Fail set node due to KeeperErrorCode = BadVersion for /zk-book
结果表明当携带数据版本不一致时,无法完成更新操作。
2.7 异步接口
如同Zookeeper原生API提供了异步接口,Curator也提供了异步接口。在Zookeeper中,所有的异步通知事件处理都是由EventThread这个线程来处理的,EventThread线程用于串行处理所有的事件通知,其可以保证对事件处理的顺序性,但是一旦碰上复杂的处理单元,会消耗过长的处理时间,从而影响其他事件的处理,Curator允许用户传入Executor实例,这样可以将比较复杂的事件处理放到一个专门的线程池中去。
package com.hust.grid.leesf.curator.examples; import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors; import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.framework.api.BackgroundCallback;
import org.apache.curator.framework.api.CuratorEvent;
import org.apache.curator.retry.ExponentialBackoffRetry;
import org.apache.zookeeper.CreateMode; public class Create_Node_Background_Sample {
static String path = "/zk-book";
static CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181")
.sessionTimeoutMs(5000).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build();
static CountDownLatch semaphore = new CountDownLatch(2);
static ExecutorService tp = Executors.newFixedThreadPool(2); public static void main(String[] args) throws Exception {
client.start();
System.out.println("Main thread: " + Thread.currentThread().getName()); client.create().creatingParentsIfNeeded().withMode(CreateMode.EPHEMERAL).inBackground(new BackgroundCallback() {
public void processResult(CuratorFramework client, CuratorEvent event) throws Exception {
System.out.println("event[code: " + event.getResultCode() + ", type: " + event.getType() + "]" + ", Thread of processResult: " + Thread.currentThread().getName());
System.out.println();
semaphore.countDown();
}
}, tp).forPath(path, "init".getBytes()); client.create().creatingParentsIfNeeded().withMode(CreateMode.EPHEMERAL).inBackground(new BackgroundCallback() {
public void processResult(CuratorFramework client, CuratorEvent event) throws Exception {
System.out.println("event[code: " + event.getResultCode() + ", type: " + event.getType() + "]" + ", Thread of processResult: " + Thread.currentThread().getName());
semaphore.countDown();
}
}).forPath(path, "init".getBytes()); semaphore.await();
tp.shutdown();
}
}
运行结果:
Main thread: main
event[code: -110, type: CREATE], Thread of processResult: main-EventThread
event[code: 0, type: CREATE], Thread of processResult: pool-3-thread-1
其中,创建节点的事件由线程池自己处理,而非默认线程处理。
Curator除了提供很便利的API,还提供了一些典型的应用场景,开发人员可以使用参考更好的理解如何使用Zookeeper客户端,所有的都在recipes包中,只需要在pom.xml中添加如下依赖即可
<dependency>
<groupId>org.apache.curator</groupId>
<artifactId>curator-recipes</artifactId>
<version>2.4.2</version>
</dependency>
2.8 节点监听
package com.hust.grid.leesf.curator.examples; import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.framework.recipes.cache.NodeCache;
import org.apache.curator.framework.recipes.cache.NodeCacheListener;
import org.apache.curator.retry.ExponentialBackoffRetry;
import org.apache.zookeeper.CreateMode; public class NodeCache_Sample {
static String path = "/zk-book/nodecache";
static CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181")
.sessionTimeoutMs(5000).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build(); public static void main(String[] args) throws Exception {
client.start();
client.create().creatingParentsIfNeeded().withMode(CreateMode.EPHEMERAL).forPath(path, "init".getBytes());
final NodeCache cache = new NodeCache(client, path, false);
cache.start(true);
cache.getListenable().addListener(new NodeCacheListener() {
public void nodeChanged() throws Exception {
System.out.println("Node data update, new data: " + new String(cache.getCurrentData().getData()));
}
});
client.setData().forPath(path, "u".getBytes());
Thread.sleep(1000);
client.delete().deletingChildrenIfNeeded().forPath(path);
Thread.sleep(Integer.MAX_VALUE);
}
}
运行结果:
Node data update, new data: u
当节点数据变更后收到了通知。NodeCache不仅可以监听数据节点的内容变更,也能监听指定节点是否存在。
2.9 子节点监听
package com.hust.grid.leesf.curator.examples; import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.framework.recipes.cache.PathChildrenCache;
import org.apache.curator.framework.recipes.cache.PathChildrenCache.StartMode;
import org.apache.curator.framework.recipes.cache.PathChildrenCacheEvent;
import org.apache.curator.framework.recipes.cache.PathChildrenCacheListener;
import org.apache.curator.retry.ExponentialBackoffRetry;
import org.apache.zookeeper.CreateMode; public class PathChildrenCache_Sample {
static String path = "/zk-book";
static CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181")
.retryPolicy(new ExponentialBackoffRetry(1000, 3)).sessionTimeoutMs(5000).build(); public static void main(String[] args) throws Exception {
client.start();
PathChildrenCache cache = new PathChildrenCache(client, path, true);
cache.start(StartMode.POST_INITIALIZED_EVENT);
cache.getListenable().addListener(new PathChildrenCacheListener() {
public void childEvent(CuratorFramework client, PathChildrenCacheEvent event) throws Exception {
switch (event.getType()) {
case CHILD_ADDED:
System.out.println("CHILD_ADDED," + event.getData().getPath());
break;
case CHILD_UPDATED:
System.out.println("CHILD_UPDATED," + event.getData().getPath());
break;
case CHILD_REMOVED:
System.out.println("CHILD_REMOVED," + event.getData().getPath());
break;
default:
break;
}
}
});
client.create().withMode(CreateMode.PERSISTENT).forPath(path);
Thread.sleep(1000);
client.create().withMode(CreateMode.PERSISTENT).forPath(path + "/c1");
Thread.sleep(1000);
client.delete().forPath(path + "/c1");
Thread.sleep(1000);
client.delete().forPath(path);
Thread.sleep(Integer.MAX_VALUE);
}
}
运行结果:
CHILD_ADDED,/zk-book/c1
CHILD_REMOVED,/zk-book/c1
监听节点的子节点,包括新增、数据变化、删除三类事件。
2.10 Master选举
借助Zookeeper,开发者可以很方便地实现Master选举功能,其大体思路如下:选择一个根节点,如/master_select,多台机器同时向该节点创建一个子节点/master_select/lock,利用Zookeeper特性,最终只有一台机器能够成功创建,成功的那台机器就是Master。
package com.hust.grid.leesf.curator.examples; import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.framework.recipes.leader.LeaderSelector;
import org.apache.curator.framework.recipes.leader.LeaderSelectorListenerAdapter;
import org.apache.curator.retry.ExponentialBackoffRetry; public class Recipes_MasterSelect {
static String master_path = "/curator_recipes_master_path";
static CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181")
.retryPolicy(new ExponentialBackoffRetry(1000, 3)).build(); public static void main(String[] args) throws Exception {
client.start();
LeaderSelector selector = new LeaderSelector(client, master_path, new LeaderSelectorListenerAdapter() {
public void takeLeadership(CuratorFramework client) throws Exception {
System.out.println("成为Master角色");
Thread.sleep(3000);
System.out.println("完成Master操作,释放Master权利");
}
});
selector.autoRequeue();
selector.start();
Thread.sleep(Integer.MAX_VALUE);
}
}
运行结果:
成为Master角色
完成Master操作,释放Master权利
成为Master角色
以上结果会反复循环,并且当一个应用程序完成Master逻辑后,另外一个应用程序的相应方法才会被调用,即当一个应用实例成为Master后,其他应用实例会进入等待,直到当前Master挂了或者推出后才会开始选举Master。
2.11 分布式锁
为了保证数据的一致性,经常在程序的某个运行点需要进行同步控制。以流水号生成场景为例,普通的后台应用通常采用时间戳方式来生成流水号,但是在用户量非常大的情况下,可能会出现并发问题。
package com.hust.grid.leesf.curator.examples; import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.concurrent.CountDownLatch; public class Recipes_NoLock {
public static void main(String[] args) throws Exception {
final CountDownLatch down = new CountDownLatch(1);
for (int i = 0; i < 10; i++) {
new Thread(new Runnable() {
public void run() {
try {
down.await();
} catch (Exception e) {
}
SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss|SSS");
String orderNo = sdf.format(new Date());
System.err.println("生成的订单号是 : " + orderNo);
}
}).start();
}
down.countDown();
}
}
运行结果:
生成的订单号是 : 16:29:10|590
生成的订单号是 : 16:29:10|590
生成的订单号是 : 16:29:10|591
生成的订单号是 : 16:29:10|591
生成的订单号是 : 16:29:10|590
生成的订单号是 : 16:29:10|590
生成的订单号是 : 16:29:10|591
生成的订单号是 : 16:29:10|590
生成的订单号是 : 16:29:10|592
生成的订单号是 : 16:29:10|591
结果表示订单号出现了重复,即普通的方法无法满足业务需要,因为其未进行正确的同步。可以使用Curator来实现分布式锁功能。
package com.hust.grid.leesf.curator.examples; import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.concurrent.CountDownLatch;
import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.framework.recipes.locks.InterProcessMutex;
import org.apache.curator.retry.ExponentialBackoffRetry; public class Recipes_Lock {
static String lock_path = "/curator_recipes_lock_path";
static CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181")
.retryPolicy(new ExponentialBackoffRetry(1000, 3)).build(); public static void main(String[] args) throws Exception {
client.start();
final InterProcessMutex lock = new InterProcessMutex(client, lock_path);
final CountDownLatch down = new CountDownLatch(1);
for (int i = 0; i < 30; i++) {
new Thread(new Runnable() {
public void run() {
try {
down.await();
lock.acquire();
} catch (Exception e) {
}
SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss|SSS");
String orderNo = sdf.format(new Date());
System.out.println("生成的订单号是 : " + orderNo);
try {
lock.release();
} catch (Exception e) {
}
}
}).start();
}
down.countDown();
}
}
运行结果:
生成的订单号是 : 16:31:50|293
生成的订单号是 : 16:31:50|319
生成的订单号是 : 16:31:51|278
生成的订单号是 : 16:31:51|326
生成的订单号是 : 16:31:51|402
生成的订单号是 : 16:31:51|420
生成的订单号是 : 16:31:51|546
生成的订单号是 : 16:31:51|602
生成的订单号是 : 16:31:51|626
生成的订单号是 : 16:31:51|656
生成的订单号是 : 16:31:51|675
生成的订单号是 : 16:31:51|701
生成的订单号是 : 16:31:51|708
生成的订单号是 : 16:31:51|732
生成的订单号是 : 16:31:51|763
生成的订单号是 : 16:31:51|785
生成的订单号是 : 16:31:51|805
生成的订单号是 : 16:31:51|823
生成的订单号是 : 16:31:51|839
生成的订单号是 : 16:31:51|853
生成的订单号是 : 16:31:51|868
生成的订单号是 : 16:31:51|884
生成的订单号是 : 16:31:51|897
生成的订单号是 : 16:31:51|910
生成的订单号是 : 16:31:51|926
生成的订单号是 : 16:31:51|939
生成的订单号是 : 16:31:51|951
生成的订单号是 : 16:31:51|965
生成的订单号是 : 16:31:51|972
生成的订单号是 : 16:31:51|983
结果表明此时已经不存在重复的流水号。
2.12 分布式计数器
分布式计数器的典型应用是统计系统的在线人数,借助Zookeeper也可以很方便实现分布式计数器功能:指定一个Zookeeper数据节点作为计数器,多个应用实例在分布式锁的控制下,通过更新节点的内容来实现计数功能。
package com.hust.grid.leesf.curator.examples; import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.framework.recipes.atomic.AtomicValue;
import org.apache.curator.framework.recipes.atomic.DistributedAtomicInteger;
import org.apache.curator.retry.ExponentialBackoffRetry;
import org.apache.curator.retry.RetryNTimes; public class Recipes_DistAtomicInt {
static String distatomicint_path = "/curator_recipes_distatomicint_path";
static CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181")
.retryPolicy(new ExponentialBackoffRetry(1000, 3)).build(); public static void main(String[] args) throws Exception {
client.start();
DistributedAtomicInteger atomicInteger = new DistributedAtomicInteger(client, distatomicint_path,
new RetryNTimes(3, 1000));
AtomicValue<Integer> rc = atomicInteger.add(8);
System.out.println("Result: " + rc.succeeded());
}
}
运行结果:
Result: true
结果表明已经将数据成功写入数据节点中。
2.13 分布式Barrier
如同JDK的CyclicBarrier,Curator提供了DistributedBarrier来实现分布式Barrier。
package com.hust.grid.leesf.curator.examples; import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.framework.recipes.barriers.DistributedBarrier;
import org.apache.curator.retry.ExponentialBackoffRetry; public class Recipes_Barrier {
static String barrier_path = "/curator_recipes_barrier_path";
static DistributedBarrier barrier; public static void main(String[] args) throws Exception {
for (int i = 0; i < 5; i++) {
new Thread(new Runnable() {
public void run() {
try {
CuratorFramework client = CuratorFrameworkFactory.builder()
.connectString("127.0.0.1:2181")
.retryPolicy(new ExponentialBackoffRetry(1000, 3)).build();
client.start();
barrier = new DistributedBarrier(client, barrier_path);
System.out.println(Thread.currentThread().getName() + "号barrier设置");
barrier.setBarrier();
barrier.waitOnBarrier();
System.err.println("启动...");
} catch (Exception e) {
}
}
}).start();
}
Thread.sleep(2000);
barrier.removeBarrier();
}
}
运行结果:
Thread-1号barrier设置
Thread-2号barrier设置
Thread-4号barrier设置
Thread-3号barrier设置
Thread-0号barrier设置
启动...
启动...
启动...
启动...
启动...
结果表明通过DistributedBarrier可以实现类似于CyclicBarrier的分布式Barrier功能。
三、Curator工具类
3.1 ZKPaths
其提供了简单的API来构建znode路径、递归创建、删除节点等。
package com.hust.grid.leesf.curator.examples; import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.retry.ExponentialBackoffRetry;
import org.apache.curator.utils.ZKPaths;
import org.apache.curator.utils.ZKPaths.PathAndNode;
import org.apache.zookeeper.ZooKeeper; public class ZKPaths_Sample {
static String path = "/curator_zkpath_sample";
static CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181")
.sessionTimeoutMs(5000).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build(); public static void main(String[] args) throws Exception {
client.start();
ZooKeeper zookeeper = client.getZookeeperClient().getZooKeeper(); System.out.println(ZKPaths.fixForNamespace(path, "sub"));
System.out.println(ZKPaths.makePath(path, "sub"));
System.out.println(ZKPaths.getNodeFromPath("/curator_zkpath_sample/sub1")); PathAndNode pn = ZKPaths.getPathAndNode("/curator_zkpath_sample/sub1");
System.out.println(pn.getPath());
System.out.println(pn.getNode()); String dir1 = path + "/child1";
String dir2 = path + "/child2";
ZKPaths.mkdirs(zookeeper, dir1);
ZKPaths.mkdirs(zookeeper, dir2);
System.out.println(ZKPaths.getSortedChildren(zookeeper, path)); ZKPaths.deleteChildren(client.getZookeeperClient().getZooKeeper(), path, true);
}
}
运行结果:
/curator_zkpath_sample/sub
/curator_zkpath_sample/sub
sub1
/curator_zkpath_sample
sub1
[child1, child2]
借助ZKPaths可快速方便的完成节点的创建等操作。
3.2 EnsurePath
其提供了一种能够确保数据节点存在的机制,当上层业务希望对一个数据节点进行操作时,操作前需要确保该节点存在。
package com.hust.grid.leesf.curator.examples; import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.retry.ExponentialBackoffRetry;
import org.apache.curator.utils.EnsurePath; public class EnsurePathDemo {
static String path = "/zk-book/c1";
static CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181")
.sessionTimeoutMs(5000).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build(); public static void main(String[] args) throws Exception {
client.start();
client.usingNamespace("zk-book"); EnsurePath ensurePath = new EnsurePath(path);
ensurePath.ensure(client.getZookeeperClient());
ensurePath.ensure(client.getZookeeperClient()); EnsurePath ensurePath2 = client.newNamespaceAwareEnsurePath("/c1");
ensurePath2.ensure(client.getZookeeperClient());
}
}
EnsurePath采取了如下节点创建方式,试图创建指定节点,如果节点已经存在,那么就不进行任何操作,也不对外抛出异常,否则正常创建数据节点。
参考资料
http://www.cnblogs.com/leesf456/p/6032716.html
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