第四章 SpringMVC之HandlerAdapter解析

          HandlerAdapter字面上的意思就是处理适配器，它的作用用一句话概括就是调用具体的方法对用户发来的请求来进行处理。当handlerMapping获取到执行请求的controller时，DispatcherServlte会根据controller对应的controller类型来调用相应的HandlerAdapter来进行处理。

        在贴源码之前先说一下HandlerAdapter处理的大体流程，这样就有一个大体的掌握。大体流程有三步：

        1.DispatcherServlte会根据配置文件信息注册HandlerAdapter，如果在配置文件中没有配置，那么DispatcherServlte会获取HandlerAdapter的默认配置，如果是读取默认配置的话，DispatcherServlte会读取DispatcherServlte.properties文件,该文件中配置了三种HandlerAdapter：HttpRequestHandlerAdapter，SimpleControllerHandlerAdapter和AnnotationMethodHandlerAdapter。DispatcherServlte会将这三个HandlerAdapter对象存储到它的handlerAdapters这个集合属性中，这样就完成了HandlerAdapter的注册。

        2.DispatcherServlte会根据handlerMapping传过来的controller与已经注册好了的HandlerAdapter一一匹配，看哪一种HandlerAdapter是支持该controller类型的，如果找到了其中一种HandlerAdapter是支持传过来的controller类型，那么该HandlerAdapter会调用自己的handle方法，handle方法运用java的反射机制执行controller的具体方法来获得ModelAndView,例如SimpleControllerHandlerAdapter是支持实现了controller接口的控制器，如果自己写的控制器实现了controller接口，那么SimpleControllerHandlerAdapter就会去执行自己写控制器中的具体方法来完成请求。

        下面是我自己写的代码。

        1.自己写的controller，就是我们自己写的控制器

          

package com.wangbiao.springMVC;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.multiaction.MultiActionController;

public class HelloWorld extends  MultiActionController{

	public ModelAndView sayHelloWorld(HttpServletRequest request, HttpServletResponse response) {
		String param = request.getParameter("param");
		System.out.println("springMVC测试：helloWorld;"+param);
		ModelAndView mv = new ModelAndView();
		mv.addObject("content", "springMVC HelloWorld:"+param);
		mv.setViewName("springMVC/helloWorld");
		ServletContext ctx = this.getServletContext();	
		return mv;
	}

}

 2.SpringMVC配置文件

       

 
        
        
	   
	             
	                          
	                                 /HelloWorld
	                          
	             
	
		
	
	             
	                           
	             
	
	
		
	            m   
		        execute
	
	
	    
          
              
              
              
              
                        
	

下面是源码

1.DispatcherServlet注册HandlerAdapter。DispatcherServlet的initHandlerAdapters方法,红色标记的部分是关键。由于在配置文件中没有对HandlerAdapter的相关配置，所以DispatcherServlet获取到的HandlerAdapter是三个默认的HandlerAdapter对象，分别是HttpRequestHandlerAdapter，SimpleControllerHandlerAdapter和AnnotationMethodHandlerAdapter，并将这三个对象存入handlerAdapter属性中去。

private void initHandlerAdapters(ApplicationContext context) {
		this.handlerAdapters = null;

		if (this.detectAllHandlerAdapters) {
			// Find all HandlerAdapters in the ApplicationContext, including ancestor contexts.
			Map matchingBeans =
					BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerAdapter.class, true, false);
			if (!matchingBeans.isEmpty()) {
				this.handlerAdapters = new ArrayList(matchingBeans.values());
				// We keep HandlerAdapters in sorted order.
				OrderComparator.sort(this.handlerAdapters);
			}
		}
		else {
			try {
				HandlerAdapter ha = context.getBean(HANDLER_ADAPTER_BEAN_NAME, HandlerAdapter.class);
				this.handlerAdapters = Collections.singletonList(ha);
			}
			catch (NoSuchBeanDefinitionException ex) {
				// Ignore, we'll add a default HandlerAdapter later.
			}
		}

		// Ensure we have at least some HandlerAdapters, by registering
		// default HandlerAdapters if no other adapters are found.
		if (this.handlerAdapters == null) {
			this.handlerAdapters = getDefaultStrategies(context, HandlerAdapter.class);
			if (logger.isDebugEnabled()) {
				logger.debug("No HandlerAdapters found in servlet '" + getServletName() + "': using default");
			}
		}
	}

2.根据handlerMapping传过来的Handler对象与DispatcherServlet集合属性handlerAdapter中的HandlerAdapter一一匹配，如果有支持Handler对象的HandlerAdapter，那么HandlerAdapter就会调用自己的handle方法处理请求。

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
		HttpServletRequest processedRequest = request;
		HandlerExecutionChain mappedHandler = null;
		int interceptorIndex = -1;

		try {
			ModelAndView mv;
			boolean errorView = false;

			try {
				processedRequest = checkMultipart(request);

				// Determine handler for the current request.
				mappedHandler = getHandler(processedRequest, false);
				if (mappedHandler == null || mappedHandler.getHandler() == null) {
					noHandlerFound(processedRequest, response);
					return;
				}

				// Determine handler adapter for the current request.
				HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

                // Process last-modified header, if supported by the handler.
				String method = request.getMethod();
				boolean isGet = "GET".equals(method);
				if (isGet || "HEAD".equals(method)) {
					long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
					if (logger.isDebugEnabled()) {
						String requestUri = urlPathHelper.getRequestUri(request);
						logger.debug("Last-Modified value for [" + requestUri + "] is: " + lastModified);
					}
					if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
						return;
					}
				}

				// Apply preHandle methods of registered interceptors.
				HandlerInterceptor[] interceptors = mappedHandler.getInterceptors();
				if (interceptors != null) {
					for (int i = 0; i < interceptors.length; i++) {
						HandlerInterceptor interceptor = interceptors[i];
						if (!interceptor.preHandle(processedRequest, response, mappedHandler.getHandler())) {
							triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null);
							return;
						}
						interceptorIndex = i;
					}
				}

				// Actually invoke the handler.
				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

				// Do we need view name translation?
				if (mv != null && !mv.hasView()) {
					mv.setViewName(getDefaultViewName(request));
				}

				// Apply postHandle methods of registered interceptors.
				if (interceptors != null) {
					for (int i = interceptors.length - 1; i >= 0; i--) {
						HandlerInterceptor interceptor = interceptors[i];
						interceptor.postHandle(processedRequest, response, mappedHandler.getHandler(), mv);
					}
				}
			}
			catch (ModelAndViewDefiningException ex) {
				logger.debug("ModelAndViewDefiningException encountered", ex);
				mv = ex.getModelAndView();
			}
			catch (Exception ex) {
				Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
				mv = processHandlerException(processedRequest, response, handler, ex);
				errorView = (mv != null);
			}

			// Did the handler return a view to render?
			if (mv != null && !mv.wasCleared()) {
				render(mv, processedRequest, response);
				if (errorView) {
					WebUtils.clearErrorRequestAttributes(request);
				}
			}
			else {
				if (logger.isDebugEnabled()) {
					logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() +
							"': assuming HandlerAdapter completed request handling");
				}
			}

			// Trigger after-completion for successful outcome.
			triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null);
		}

		catch (Exception ex) {
			// Trigger after-completion for thrown exception.
			triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, ex);
			throw ex;
		}
		catch (Error err) {
			ServletException ex = new NestedServletException("Handler processing failed", err);
			// Trigger after-completion for thrown exception.
			triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, ex);
			throw ex;
		}

		finally {
			// Clean up any resources used by a multipart request.
			if (processedRequest != request) {
				cleanupMultipart(processedRequest);
			}
		}
	}

getHandlerAdapter方法

protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
		for (HandlerAdapter ha : this.handlerAdapters) {
			if (logger.isTraceEnabled()) {
				logger.trace("Testing handler adapter [" + ha + "]");
			}
			if (ha.supports(handler)) {
				return ha;
			}
		}
		throw new ServletException("No adapter for handler [" + handler +
				"]: Does your handler implement a supported interface like Controller?");
	}

HandlerAdapter接口

/*
 * Copyright 2002-2008 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * MVC framework SPI interface, allowing parameterization of core MVC workflow.
 *
 * 
Interface that must be implemented for each handler type to handle a request.
 * This interface is used to allow the {@link DispatcherServlet} to be indefinitely
 * extensible. The DispatcherServlet accesses all installed handlers through this
 * interface, meaning that it does not contain code specific to any handler type.
 *
 * 
Note that a handler can be of type Object. This is to enable
 * handlers from other frameworks to be integrated with this framework without
 * custom coding, as well as to allow for annotation handler objects that do
 * not obey any specific Java interface.
 *
 * 
This interface is not intended for application developers. It is available
 * to handlers who want to develop their own web workflow.
 *
 * 
Note: HandlerAdaptger implementators may implement the
 * {@link org.springframework.core.Ordered} interface to be able to specify a
 * sorting order (and thus a priority) for getting applied by DispatcherServlet.
 * Non-Ordered instances get treated as lowest priority.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @see org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter
 * @see org.springframework.web.servlet.handler.SimpleServletHandlerAdapter
 */
public interface HandlerAdapter {
	
	/**
	 * Given a handler instance, return whether or not this HandlerAdapter can
	 * support it. Typical HandlerAdapters will base the decision on the handler
	 * type. HandlerAdapters will usually only support one handler type each.
	 * 
A typical implementation:
	 * 

	 * return (handler instanceof MyHandler);
	 * 
	 * @param handler handler object to check
	 * @return whether or not this object can use the given handler
	 */
	boolean supports(Object handler); 
	
	/**
	 * Use the given handler to handle this request.
	 * The workflow that is required may vary widely.
	 * @param request current HTTP request
	 * @param response current HTTP response
	 * @param handler handler to use. This object must have previously been passed
	 * to the supports method of this interface, which must have
	 * returned true.
	 * @throws Exception in case of errors
	 * @return ModelAndView object with the name of the view and the required
	 * model data, or null if the request has been handled directly
	 */
	ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception;

	/**
	 * Same contract as for HttpServlet's getLastModified method.
	 * Can simply return -1 if there's no support in the handler class.
	 * @param request current HTTP request
	 * @param handler handler to use
	 * @return the lastModified value for the given handler
	 * @see javax.servlet.http.HttpServlet#getLastModified
	 * @see org.springframework.web.servlet.mvc.LastModified#getLastModified
	 */
	long getLastModified(HttpServletRequest request, Object handler);

}

再来看一下自己写的控制器HelloWorld继承了MultiActionController。MultiActionController又继承了AbstractController，AbstractController实现了Controller。这样就看DispatcherServlet属性中的HandlerApater谁支持Controller类型的处理器了。在运行的过程中发现SimpleControllerHandlerAdapter是支持Controller类型的控制器的。
来看一下SimpleControllerHandlerAdapter的代码

public class SimpleControllerHandlerAdapter implements HandlerAdapter {

	public boolean supports(Object handler) {
		return (handler instanceof Controller);
	}

	public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
			throws Exception {

		return ((Controller) handler).handleRequest(request, response);
	}

	public long getLastModified(HttpServletRequest request, Object handler) {
		if (handler instanceof LastModified) {
			return ((LastModified) handler).getLastModified(request);
		}
		return -1L;
	}

}

再看一下Controller源码,Controller接口只有一个handleRequest方法

public interface Controller {

	/**
	 * Process the request and return a ModelAndView object which the DispatcherServlet
	 * will render. A null return value is not an error: It indicates that
	 * this object completed request processing itself, thus there is no ModelAndView
	 * to render.
	 * @param request current HTTP request
	 * @param response current HTTP response
	 * @return a ModelAndView to render, or null if handled directly
	 * @throws Exception in case of errors
	 */
	ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception;

}

再看看实现了Controller接口的AbstractController类

public abstract class AbstractController extends WebContentGenerator implements Controller {

	private boolean synchronizeOnSession = false;


	/**
	 * Set if controller execution should be synchronized on the session,
	 * to serialize parallel invocations from the same client.
	 * 
More specifically, the execution of the handleRequestInternal
	 * method will get synchronized if this flag is "true". The best available
	 * session mutex will be used for the synchronization; ideally, this will
	 * be a mutex exposed by HttpSessionMutexListener.
	 * 
The session mutex is guaranteed to be the same object during
	 * the entire lifetime of the session, available under the key defined
	 * by the SESSION_MUTEX_ATTRIBUTE constant. It serves as a
	 * safe reference to synchronize on for locking on the current session.
	 * 
In many cases, the HttpSession reference itself is a safe mutex
	 * as well, since it will always be the same object reference for the
	 * same active logical session. However, this is not guaranteed across
	 * different servlet containers; the only 100% safe way is a session mutex.
	 * @see org.springframework.web.servlet.mvc.AbstractController#handleRequestInternal
	 * @see org.springframework.web.util.HttpSessionMutexListener
	 * @see org.springframework.web.util.WebUtils#getSessionMutex(javax.servlet.http.HttpSession)
	 */
	public final void setSynchronizeOnSession(boolean synchronizeOnSession) {
		this.synchronizeOnSession = synchronizeOnSession;
	}

	/**
	 * Return whether controller execution should be synchronized on the session.
	 */
	public final boolean isSynchronizeOnSession() {
		return this.synchronizeOnSession;
	}


	public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response)
			throws Exception {

		// Delegate to WebContentGenerator for checking and preparing.
		checkAndPrepare(request, response, this instanceof LastModified);

		// Execute handleRequestInternal in synchronized block if required.
		if (this.synchronizeOnSession) {
			HttpSession session = request.getSession(false);
			if (session != null) {
				Object mutex = WebUtils.getSessionMutex(session);
				synchronized (mutex) {
					return handleRequestInternal(request, response);
				}
			}
		}
		
		return handleRequestInternal(request, response);
	}

	/**
	 * Template method. Subclasses must implement this.
	 * The contract is the same as for handleRequest.
	 * @see #handleRequest
	 */
	protected abstract ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response)
	    throws Exception;

}

再看一下继承了AbstractController的MultiActionController，MultiActionController中有对AbstractController的handleRequestInternal的实现

protected ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response)
			throws Exception {
		try {
			String methodName = this.methodNameResolver.getHandlerMethodName(request);
			return invokeNamedMethod(methodName, request, response);
		}
		catch (NoSuchRequestHandlingMethodException ex) {
			return handleNoSuchRequestHandlingMethod(ex, request, response);
		}
	}

可以看出在MultiActionController的handleRequestInternal方法中分为两步，第一步是找寻执行该请求的方法名，第二步是调用invokeNamedMethod方法。
invokeNamedMethod方法源码

protected final ModelAndView invokeNamedMethod(
			String methodName, HttpServletRequest request, HttpServletResponse response) throws Exception {

		Method method = this.handlerMethodMap.get(methodName);
		if (method == null) {
			throw new NoSuchRequestHandlingMethodException(methodName, getClass());
		}

		try {
			Class[] paramTypes = method.getParameterTypes();
			List