HandlerMapping(1) handler 查找

文章环境说明：

       spring mvc 版本3.2.4.RELEASE，项目中注解方式注册Controller。

 

      众所周知Spring Mvc 中的DispatcherServlet中会使用HandlerMapping 将请求Url解析成为handler处理器。

关于HandlerMapping 实际只有两个突出的功能注册和查找。由于注册是在spring容器加载时就已将Controller的每一个方法注册成handler，学起来门槛较高。因此此文将先说查找反推出注册。

注：由于Spring Mvc 的版本不同所以相应代码存在出入，以下代码全部出于spring Mvc 3.2.4.RELEASE。

 

查找：

    在DispatcherServlet中doDispatch方法中可以看到根据request使用HandlerMapping获取HandlerExecutionChain对象。代码如下所示：

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
	HttpServletRequest processedRequest = request;
	HandlerExecutionChain mappedHandler = null;
	boolean multipartRequestParsed = false;
	WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
	try {
		ModelAndView mv = null;
		Exception dispatchException = null;
		try {
                        //在spring-servlet中是否配有MultipartResolver用于解析特殊
                       
 
			//的request 比如附件上传：CommonsMultipartResolver
                        processedRequest = checkMultipart(request);
			multipartRequestParsed = processedRequest != request;
			// Determine handler for the current request.
                        //根据request 在HandlerMapping 查找handler信息
			mappedHandler = getHandler(processedRequest, false);
                        .....
                }catch (Exception ex) {
			dispatchException = ex;
		}
		processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
	}catch (Exception ex) {
		triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
	}catch (Error err) {
		triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err);
	}finally {
		if (asyncManager.isConcurrentHandlingStarted()) {
			// Instead of postHandle and afterCompletion
			mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
			return;
		}
		// Clean up any resources used by a multipart request.
		if (multipartRequestParsed) {
			cleanupMultipart(processedRequest);
		}
	}
}

   DispatcherServlet中的getHandler代码如下所示：

 

@Deprecated
protected HandlerExecutionChain getHandler(HttpServletRequest request, boolean cache) throws Exception {
	return getHandler(request);
}
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
 
       //handlerMappings 在容器启动时就已经将handlerMapping进行了赋值
       for (HandlerMapping hm : this.handlerMappings) {
		if (logger.isTraceEnabled()) {
			logger.trace(
					"Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'");
		}
		HandlerExecutionChain handler = hm.getHandler(request);
		if (handler != null) {
			return handler;
		}
	}
	return null;
}

    关于handlerMappings 的赋值代码同样在DispatcherServlet代码中，代码如下所示

  

protected void initStrategies(ApplicationContext context) {
	initMultipartResolver(context);
	initLocaleResolver(context);
	initThemeResolver(context);
	//初始化handlerMapping
	initHandlerMappings(context);
	initHandlerAdapters(context);
	initHandlerExceptionResolvers(context);
	initRequestToViewNameTranslator(context);
	initViewResolvers(context);
	initFlashMapManager(context);
}
private void initHandlerMappings(ApplicationContext context) {
		this.handlerMappings = null;
		//可在Web.xml进行显示指定，默认是true 是否默认加载所有HandlerMapping下的values
		if (this.detectAllHandlerMappings) {
			// Find all HandlerMappings in the ApplicationContext, including ancestor contexts.
			//获取context中的所有HandlerMappings的子类，并将其下的values 初始化到handlerMappings中
			//其中的子类有
			//RequestMappingHandlerMapping(所有使用注解定义的Controller)
			//BeanNameUrlHandlerMapping(配置文件中定义的Interceptor)
			//SimpleUrlHandlerMapping(配置文件中的mvc:resources显示定义的)
			Map<String, HandlerMapping> matchingBeans =
					BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
			if (!matchingBeans.isEmpty()) {
				this.handlerMappings = new ArrayList<HandlerMapping>(matchingBeans.values());
				// We keep HandlerMappings in sorted order.
				OrderComparator.sort(this.handlerMappings);
			}
		}else {
			try {
				HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class);
				this.handlerMappings = Collections.singletonList(hm);
			}
			catch (NoSuchBeanDefinitionException ex) {
				// Ignore, we'll add a default HandlerMapping later.
			}
		}
		// Ensure we have at least one HandlerMapping, by registering
		// a default HandlerMapping if no other mappings are found.
		if (this.handlerMappings == null) {
			this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
			if (logger.isDebugEnabled()) {
				logger.debug("No HandlerMappings found in servlet '" + getServletName() + "': using default");
			}
		}
}

 至于在DispatcherServlet的getHandler调用的hm.getHandler()方法就比较简单，在RequestMappingHandlerMapping、BeanNameUrlHandlerMapping、SimpleUrlHandlerMapping类中并没有对其父类AbstractHandlerMapping的getHandler方法进行重写。其AbstractHandlerMapping的getHandler方法如下所示(spring MVC升级中对并未对此方法进行修改)：

public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
    //此段代码只会在controller是注解方式定义的时候使用到
	Object handler = getHandlerInternal(request);
	//如果在注解中没有查到相应Handler 取默认defaultHandler 
	if (handler == null) {
		handler = getDefaultHandler();
	}
	if (handler == null) {
		return null;
	}
	// Bean name or resolved handler?
	//当handler是String类型时直接从Contest容器中查找
	if (handler instanceof String) {
		String handlerName = (String) handler;
		handler = getApplicationContext().getBean(handlerName);
	}
	return getHandlerExecutionChain(handler, request);
}
protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
    //将handler转换为HandlerExecutionChain对象
	HandlerExecutionChain chain =
		(handler instanceof HandlerExecutionChain) ?
			(HandlerExecutionChain) handler : new HandlerExecutionChain(handler);
    //将拦截器放到HandlerExecutionChain 处理器中此处的拦截器继承自HandlerInterceptor
	chain.addInterceptors(getAdaptedInterceptors());
    //将拦截器放到HandlerExecutionChain 处理器中此处的拦截器继承自MappedInterceptor
	String lookupPath = urlPathHelper.getLookupPathForRequest(request);
	for (MappedInterceptor mappedInterceptor : mappedInterceptors) {
		if (mappedInterceptor.matches(lookupPath, pathMatcher)) {
			chain.addInterceptor(mappedInterceptor.getInterceptor());
		}
	}
	return chain;
}

 关于getHandlerInternal()方法，只在其子类AbstractHandlerMethodMapping<T>对其进行了实现。由于AbstractHandlerMethodMapping 此类较复杂，将于后续文章对其补充说明！