SpringMVC源码解读 - HandlerMapping - RequestMappingHandlerMapping初始化

RequestMappingHandlerMapping ,用于注解@Controller,@RequestMapping来定义controller.

 @Controller
 @RequestMapping(value = "books")
 public class BookController {

     @RequestMapping(value = "/{id}")
     @ResponseBody
     public String getBook(@PathVariable("id") String id) {
         // ...
         return id;
     }
 }

初始化时,3个类的大致分工如下:

　　AbstractHandlerMethodMapping定义整个算法流程;

　　RequestMappingInfoHandlerMapping提供匹配条件RequestMappingInfo的解析处理;

　　RequestMappingHandlerMapping根据@RequestMapping注解生成 RequestMappingInfo,同时提供isHandler实现

整个初始化工作由AbstractHandlerMethodMapping的initHandlerMethods主导.

　　1. 使用BeanFactoryUtils扫描应用下的Object或者直接从容器中获取Object

　　2. 迭代类,分别判断isHandler判断目标类是否Handler

　　　　2.1 RequestMappingHandlerMapping.isHandler根据@Controller或@RequestMapping注解判断(有任意一个)

　　3. 对handler解析出所有需要分发的方法detectHandlerMethods

　　　　3.1 获取原始的Class<?>

　　　　3.2 使用HandlerMethodSelector.selectMethods过滤具体handler method,预留getMappingForMethod模板方法给子类

　　　　　　RequestMappingHandlerMapping.getMappingForMethod根据类,方法上的RequestMapping注解生成匹配条件RequestMappingInfo

　　　　3.3 对过滤到的每个method进行注册registerHandlerMethod

　　　　　　a, 使用createHandlerMethod封装处理器为HandlerMethod

　　　　　　b, 判断之前是否已经匹配条件对应的处理器是否冲突(相同的匹配条件只能有一个对应的处理器)

　　　　　　c, 设置匹配条件到handler method的映射关系

　　　　　　d, 从匹配条件中解析出url,并注册到urlMap(url到匹配条件的映射),这边由RequestMappingInfoHandlerMapping.getMappingPathPatterns实现

　　4. 对HandlerMethod进行初始化handlerMethodsInitialized,其实现在什么都没做

在讲初始化之前,我们先来聊聊使用到的一些概念

　　1. 映射关系,url到匹配条件RequestMappingInfo,匹配条件到HandlerMethod

　　2. 特殊的MultiValueMap,特别在value是个List

　　3. 使用到注解@Controller,@RequestMapping

　　4. 封装处理器信息的HandlerMethod

　　5. 封装各类匹配条件的RequestMappingInfo(诸如pattern,http method,request parameter等)

　　6. RequestCondition记录匹配条件

1. 进行request分发前,需要在初始化时准备好映射关系,这边AbstractHandlerMethodMapping中有两个属性保存了映射关系

// AbstractHandlerMethodMapping

     // 匹配条件到HandlerMethod的映射
     private final Map<T, HandlerMethod> handlerMethods = new LinkedHashMap<T, HandlerMethod>();
     // url到匹配条件的映射
     private final MultiValueMap<String, T> urlMap = new LinkedMultiValueMap<String, T>();

2. 这边的MultiValueMap其实挺简单,就是map的值是个list

 public interface MultiValueMap<K, V> extends Map<K, List<V>> {
   // ...
 }

3. 我们再来看看这边使用到的两个注解:

// @Controller

     // org.springframework.stereotype.Controller
 @Target({ElementType.TYPE})
 @Retention(RetentionPolicy.RUNTIME)
 @Documented
 @Component
 public @interface Controller {

     /**
      * The value may indicate a suggestion for a logical component name,
      * to be turned into a Spring bean in case of an autodetected component.
      * @return the suggested component name, if any
      */
     String value() default "";

 }

// @RequestMapping

     // org.springframework.web.bind.annotation.RequestMapping
     @Target({ElementType.METHOD, ElementType.TYPE})
     @Retention(RetentionPolicy.RUNTIME)
     @Documented
     @Mapping
     public @interface RequestMapping {

         /**
          * url路径,如/myPath/*.do
          */
         String[] value() default {};

         /**
          * HTTP request methods 如:GET, POST, HEAD, OPTIONS, PUT, PATCH, DELETE, TRACE.
          */
         RequestMethod[] method() default {};

         /**
          * requeset parameter 有3种匹配方式,是否包含某个参数,参数值相等,参数值不等于某个值,如myParam!=myValue
          */
         String[] params() default {};

         /**
          * request的header
          */
         String[] headers() default {};

         /**
          * request的content type
          */
         String[] consumes() default {};

         /**
          * 返回内容的content type
          */
         String[] produces() default {};

     }
 }

4. HandlerMethod封装了处理器相关的全部信息,如类Object,方法Method,BeanFactory,参数MethodParameter[],原始方法Method

// HandlerMethod

     // org.springframework.web.method.HandlerMethod
     private final Object bean;// 因为final不可修改,所以下面每次需要修改信息时,都需要new一个

     private final Method method;

     private final BeanFactory beanFactory;

     private final MethodParameter[] parameters;

     private final Method bridgedMethod;

5. 这边匹配条件的范型只有一个实现,RequestMappingInfo.匹配条件里记录的是RequestCondition子类,用于诸如pattern,http method,request parameter等

// RequestMappingInfo

     // javax.servlet.http.HttpServletRequest.RequestMappingInfo
 public final class RequestMappingInfo implements RequestCondition<RequestMappingInfo> {

     private final PatternsRequestCondition patternsCondition;

     private final RequestMethodsRequestCondition methodsCondition;

     private final ParamsRequestCondition paramsCondition;

     private final HeadersRequestCondition headersCondition;

     private final ConsumesRequestCondition consumesCondition;

     private final ProducesRequestCondition producesCondition;

     private final RequestConditionHolder customConditionHolder;
     // ...

 }

6. 最后再简单看看RequestCondition ,这边定义了3个方法

 package org.springframework.web.servlet.mvc.condition;
     public interface RequestCondition<T> {
         /**
          * 拼接条件
          */
         T combine(T other);

         /**
          * 查找匹配的条件,并返回
          */
         T getMatchingCondition(HttpServletRequest request);

         /**
          * 用于排序
          */
         int compareTo(T other, HttpServletRequest request);
     }

看看继承体系吧,老套路,定义接口,然后模板方法实现主要逻辑,具体算法留给子类实现,还有正事要做,还是后期再细化吧.

正文

整个初始化工作由AbstractHandlerMethodMapping的initHandlerMethods主导.copy一段,省得回去比对看

　　1. 使用BeanFactoryUtils扫描应用下的Object或者直接从容器中获取Object

　　2. 迭代类,分别判断isHandler判断目标类是否Handler

　　　　2.1 RequestMappingHandlerMapping.isHandler根据@Controller或@RequestMapping注解判断(有任意一个)

　　3. 对handler解析出所有需要分发的方法detectHandlerMethods

　　　　3.1 获取原始的Class<?>

　　　　3.2 使用HandlerMethodSelector.selectMethods过滤具体handler method,预留getMappingForMethod模板方法给子类

　　　　　　RequestMappingHandlerMapping.getMappingForMethod根据类,方法上的RequestMapping注解生成匹配条件RequestMappingInfo

　　　　3.3 对过滤到的每个method进行注册registerHandlerMethod

　　　　　　a, 使用createHandlerMethod封装处理器为HandlerMethod

　　　　　　b, 判断之前是否已经匹配条件对应的处理器是否冲突(相同的匹配条件只能有一个对应的处理器)

　　　　　　c, 设置匹配条件到handler method的映射关系

　　　　　　d, 从匹配条件中解析出url,并注册到urlMap(url到匹配条件的映射),这边由RequestMappingInfoHandlerMapping.getMappingPathPatterns实现

　　4. 对HandlerMethod进行初始化handlerMethodsInitialized,其实现在什么都没做

// AbstractHandlerMethodMapping

 /** 这个方法哪来的,具体看备注的InitializingBean
      * Detects handler methods at initialization.
      */
     public void afterPropertiesSet() {
         initHandlerMethods();
     }

     /**扫描ApplicationContext中的bean,然后筛选handler method 并注册
      * Scan beans in the ApplicationContext, detect and register handler methods.
      * @see #isHandler(Class)
      * @see #getMappingForMethod(Method, Class)
      * @see #handlerMethodsInitialized(Map)
      */
     protected void initHandlerMethods() {
         if (logger.isDebugEnabled()) {
             logger.debug("Looking for request mappings in application context: " + getApplicationContext());
         }

         String[] beanNames = (this.detectHandlerMethodsInAncestorContexts ?
                 BeanFactoryUtils.beanNamesForTypeIncludingAncestors(getApplicationContext(), Object.class) :
                 getApplicationContext().getBeanNamesForType(Object.class));

         for (String beanName : beanNames) {
             if (isHandler(getApplicationContext().getType(beanName))){
                 detectHandlerMethods(beanName);
             }
         }
         handlerMethodsInitialized(getHandlerMethods());
     }

预留给子类实现的判断handler,实际是由RequestMappingHandlerMapping实现　　

// AbstractHandlerMethodMapping

     /**
      * Whether the given type is a handler with handler methods.
      * @param beanType the type of the bean being checked
      * @return "true" if this a handler type, "false" otherwise.
      */
     protected abstract boolean isHandler(Class<?> beanType);

// RequestMappingHandlerMapping

这边判断的逻辑很简单,类上使用Controller或RequestMapping其中至少一个注解就可以.

     /**
      * {@inheritDoc}
      * Expects a handler to have a type-level @{@link Controller} annotation.
      */
     @Override
     protected boolean isHandler(Class<?> beanType) {
         return ((AnnotationUtils.findAnnotation(beanType, Controller.class) != null) ||
                 (AnnotationUtils.findAnnotation(beanType, RequestMapping.class) != null));
     }

// AbstractHandlerMethodMapping

     /**
      * Look for handler methods in a handler.
      * @param handler the bean name of a handler or a handler instance
      */
     protected void detectHandlerMethods(final Object handler) {
         Class<?> handlerType = (handler instanceof String) ?
                 getApplicationContext().getType((String) handler) : handler.getClass();

         final Class<?> userType = ClassUtils.getUserClass(handlerType);

         Set<Method> methods = HandlerMethodSelector.selectMethods(userType, new MethodFilter() {
             public boolean matches(Method method) {
                 return getMappingForMethod(method, userType) != null;
             }
         });

         for (Method method : methods) {
             T mapping = getMappingForMethod(method, userType);
             registerHandlerMethod(handler, method, mapping);
         }
     }

// AbstractHandlerMethodMapping

这边具体的实现是由RequestMappingHandlerMapping实现,根据注解生产匹配关系,这边实现类是RequestMappingInfo,就是代码有点多,慢慢看

     /**
      * Provide the mapping for a handler method. A method for which no
      * mapping can be provided is not a handler method.
      * @param method the method to provide a mapping for
      * @param handlerType the handler type, possibly a sub-type of the method's
      * declaring class
      * @return the mapping, or {@code null} if the method is not mapped
      */
     protected abstract T getMappingForMethod(Method method, Class<?> handlerType);

// RequestMappingHandlerMapping

     /**
      * Uses method and type-level @{@link RequestMapping} annotations to create
      * the RequestMappingInfo.
      *
      * @return the created RequestMappingInfo, or {@code null} if the method
      * does not have a {@code @RequestMapping} annotation.
      *
      * @see #getCustomMethodCondition(Method)
      * @see #getCustomTypeCondition(Class)
      */
     @Override
     protected RequestMappingInfo getMappingForMethod(Method method, Class<?> handlerType) {
         RequestMappingInfo info = null;
         // 读取方法上的RequestMapping注解信息
         RequestMapping methodAnnotation = AnnotationUtils.findAnnotation(method, RequestMapping.class);
         if (methodAnnotation != null) {
             // 读取自定义的条件,这边没有使用
             RequestCondition<?> methodCondition = getCustomMethodCondition(method);
             // 根据方法上的RequsetMapping注解和自定义条件,生成匹配条件.这边的匹配条件包括http method,request parameter,request header等
             info = createRequestMappingInfo(methodAnnotation, methodCondition);
             // 读取类上的RequestMapping注解信息
             RequestMapping typeAnnotation = AnnotationUtils.findAnnotation(handlerType, RequestMapping.class);
             if (typeAnnotation != null) {
                 RequestCondition<?> typeCondition = getCustomTypeCondition(handlerType);
                 // 生成类上的匹配条件,并合并方法上的
                 info = createRequestMappingInfo(typeAnnotation, typeCondition).combine(info);
             }
         }
         return info;
     }

// RequestMappingHandlerMapping

     /**
      * Created a RequestMappingInfo from a RequestMapping annotation.
      */
     private RequestMappingInfo createRequestMappingInfo(RequestMapping annotation, RequestCondition<?> customCondition) {
         String[] patterns = resolveEmbeddedValuesInPatterns(annotation.value());
         return new RequestMappingInfo(
                 new PatternsRequestCondition(patterns, getUrlPathHelper(), getPathMatcher(),
                         this.useSuffixPatternMatch, this.useTrailingSlashMatch, this.fileExtensions),
                 new RequestMethodsRequestCondition(annotation.method()),
                 new ParamsRequestCondition(annotation.params()),
                 new HeadersRequestCondition(annotation.headers()),
                 new ConsumesRequestCondition(annotation.consumes(), annotation.headers()),
                 new ProducesRequestCondition(annotation.produces(), annotation.headers(), getContentNegotiationManager()),
                 customCondition);
     }

     /**
      * Resolve placeholder values in the given array of patterns.
      * @return a new array with updated patterns
      */
     protected String[] resolveEmbeddedValuesInPatterns(String[] patterns) {
         if (this.embeddedValueResolver == null) {
             return patterns;
         }
         else {
             String[] resolvedPatterns = new String[patterns.length];
             for (int i=0; i < patterns.length; i++) {
                 resolvedPatterns[i] = this.embeddedValueResolver.resolveStringValue(patterns[i]);
             }
             return resolvedPatterns;
         }
     }

// AbstractHandlerMethodMapping

 /**
      * Register a handler method and its unique mapping.
      * @param handler the bean name of the handler or the handler instance
      * @param method the method to register
      * @param mapping the mapping conditions associated with the handler method
      * @throws IllegalStateException if another method was already registered
      * under the same mapping
      */
     protected void registerHandlerMethod(Object handler, Method method, T mapping) {
         HandlerMethod newHandlerMethod = createHandlerMethod(handler, method);
         HandlerMethod oldHandlerMethod = handlerMethods.get(mapping);
         if (oldHandlerMethod != null && !oldHandlerMethod.equals(newHandlerMethod)) {
             throw new IllegalStateException("Ambiguous mapping found. Cannot map '" + newHandlerMethod.getBean()
                     + "' bean method \n" + newHandlerMethod + "\nto " + mapping + ": There is already '"
                     + oldHandlerMethod.getBean() + "' bean method\n" + oldHandlerMethod + " mapped.");
         }

         this.handlerMethods.put(mapping, newHandlerMethod);// 匹配条件requestMappingInfo 到处理器HandlerMethod
         if (logger.isInfoEnabled()) {
             logger.info("Mapped \"" + mapping + "\" onto " + newHandlerMethod);
         }

         Set<String> patterns = getMappingPathPatterns(mapping);
         for (String pattern : patterns) {
             if (!getPathMatcher().isPattern(pattern)) {
                 this.urlMap.add(pattern, mapping);// url到匹配条件RequestMappingInfo
             }
         }
     }

// AbstractHandlerMethodMapping

     /**
      * Create the HandlerMethod instance.
      * @param handler either a bean name or an actual handler instance
      * @param method the target method
      * @return the created HandlerMethod
      */
     protected HandlerMethod createHandlerMethod(Object handler, Method method) {
         HandlerMethod handlerMethod;
         if (handler instanceof String) {
             String beanName = (String) handler;
             handlerMethod = new HandlerMethod(beanName, getApplicationContext(), method);
         }
         else {
             handlerMethod = new HandlerMethod(handler, method);
         }
         return handlerMethod;
     }

// AbstractHandlerMethodMapping

     /**
      * Extract and return the URL paths contained in a mapping.
      */
     protected abstract Set<String> getMappingPathPatterns(T mapping);

RequestMappingInfoHandlerMapping会实现这个模板方法

// RequestMappingInfoHandlerMapping

     /**
      * Get the URL path patterns associated with this {@link RequestMappingInfo}.
      */
     @Override
     protected Set<String> getMappingPathPatterns(RequestMappingInfo info) {
         return info.getPatternsCondition().getPatterns();
     }

备注:

1. 这边的afterPropertiesSet是因为实现了InitializingBean接口

// org.springframework.beans.factory.InitializingBean

 /**
  * Interface to be implemented by beans that need to react once all their
  * properties have been set by a BeanFactory: for example, to perform custom
  * initialization, or merely to check that all mandatory properties have been set.
  *
  * <p>An alternative to implementing InitializingBean is specifying a custom
  * init-method, for example in an XML bean definition.
  * For a list of all bean lifecycle methods, see the BeanFactory javadocs.
  *
  * @author Rod Johnson
  * @see BeanNameAware
  * @see BeanFactoryAware
  * @see BeanFactory
  * @see org.springframework.beans.factory.support.RootBeanDefinition#getInitMethodName
  * @see org.springframework.context.ApplicationContextAware
  */
 public interface InitializingBean {

     /**
      * Invoked by a BeanFactory after it has set all bean properties supplied
      * (and satisfied BeanFactoryAware and ApplicationContextAware).
      * <p>This method allows the bean instance to perform initialization only
      * possible when all bean properties have been set and to throw an
      * exception in the event of misconfiguration.
      * @throws Exception in the event of misconfiguration (such
      * as failure to set an essential property) or if initialization fails.
      */
     void afterPropertiesSet() throws Exception;

 }