Spring Mvc 源码理解。

学习一个框架，首要的是要先领会它的设计思想。从抽象、从全局上来审视这个框架。其中最具有参考价值的，就是这个框架所定义的核心接口。核心接口定义了框架的骨架，也在最抽象的意义上表达了框架的设计思想。

前因：发现springMvc可以使用spring中的bean，way?

由于SpringMvc就是Servlet,必须先了解servlet原理：http://blog.youkuaiyun.com/czlpf/article/details/47781473

一。SpringMvc的入口分为 init() 和 service() 两个入口。

1.init()仅在DispatherServlet创建的时候执行一次，为容器和组件做初始化。

2.service()方法在每次http请求的时候都执行。

Servlet的所以请求都会通过执行HttpServlet中service(ServletRequest ,ServletResponse)方法，该方法执行了service(HttpServletRequest,HttpServletResponse)

而该方法在FrameworkServlet中被重写，所以执行FrameworkServlet中的service(HttpServletRequest,HttpServletResponse)方法。

-----》》FrameworkServlet.processRequest()

-----》》DispatcherServlet.doService()

-----》》DispatcherServlet.doDispatch()

这个doDispatch()就是每次http请求到springMvc的重点。

首先选择一个handler获得HandlerExecutionChain

        protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
		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;
	}

其中this.handlerMappings在init()方法已经初始化。详情查看init()流程。

下面研究这个HandlerExecutionChain：

HandlerExecutionChain类的代码不长，它定义在org.springframework.web.servlet包中，为了更直观的理解，先上代码。

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package org.springframework.web.servlet;   import java.util.ArrayList; import java.util.Arrays; import java.util.List;   import org.springframework.util.CollectionUtils;   public class HandlerExecutionChain {        private final Object handler;        private HandlerInterceptor[] interceptors;        private List<HandlerInterceptor> interceptorList;        public HandlerExecutionChain(Object handler) {          this (handler, null );      }        public HandlerExecutionChain(Object handler, HandlerInterceptor[] interceptors) {          if (handler instanceof HandlerExecutionChain) {              HandlerExecutionChain originalChain = (HandlerExecutionChain) handler;              this .handler = originalChain.getHandler();              this .interceptorList = new ArrayList<HandlerInterceptor>();              CollectionUtils.mergeArrayIntoCollection(originalChain.getInterceptors(), this .interceptorList);              CollectionUtils.mergeArrayIntoCollection(interceptors, this .interceptorList);          }          else {              this .handler = handler;              this .interceptors = interceptors;          }      }        public Object getHandler() {          return this .handler;      }        public void addInterceptor(HandlerInterceptor interceptor) {          initInterceptorList();          this .interceptorList.add(interceptor);      }        public void addInterceptors(HandlerInterceptor[] interceptors) {          if (interceptors != null ) {              initInterceptorList();              this .interceptorList.addAll(Arrays.asList(interceptors));          }      }        private void initInterceptorList() {          if ( this .interceptorList == null ) {              this .interceptorList = new ArrayList<HandlerInterceptor>();          }          if ( this .interceptors != null ) {              this .interceptorList.addAll(Arrays.asList( this .interceptors));              this .interceptors = null ;          }      }        public HandlerInterceptor[] getInterceptors() {          if ( this .interceptors == null && this .interceptorList != null ) {              this .interceptors = this .interceptorList.toArray( new HandlerInterceptor[ this .interceptorList.size()]);          }          return this .interceptors;      }        @Override      public String toString() {          if ( this .handler == null ) {              return "HandlerExecutionChain with no handler" ;          }          StringBuilder sb = new StringBuilder();          sb.append( "HandlerExecutionChain with handler [" ).append( this .handler).append( "]" );          if (!CollectionUtils.isEmpty( this .interceptorList)) {              sb.append( " and " ).append( this .interceptorList.size()).append( " interceptor" );              if ( this .interceptorList.size() > 1 ) {                  sb.append( "s" );              }          }          return sb.toString();      }   }

乱七八糟一大堆，相信你也没全看完，也没必要全看。其实只需要看两行足矣。

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private final Object handler;   private HandlerInterceptor[] interceptors;

不出我们所料，一个实质执行对象，还有一堆拦截器。这不就是Struts2中的实现么，SpringMVC没有避嫌，还是采用了这种封装。得到HandlerExecutionChain这个执行链（execution chain）之后，下一步的处理将围绕其展开。

在Dispatcher中，执行拦截器

在执行handler之前:

if (!mappedHandler.applyPreHandle(processedRequest, response)) {
					return;
				}

执行handler:

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

执行handler之后：

mappedHandler.applyPostHandle(processedRequest, response, mv);

异常拦截：

		catch (Exception ex) {
			triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
		}
		catch (Error err) {
			triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err);
		}

最终执行拦截：

		finally {
			if (asyncManager.isConcurrentHandlingStarted()) {
				// Instead of postHandle and afterCompletion
				if (mappedHandler != null) {
					mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
				}
			}
			else {
				// Clean up any resources used by a multipart request.
				if (multipartRequestParsed) {
					cleanupMultipart(processedRequest);
				}
			}
		}

配置拦截器：

 

java代码：

查看 复制到剪贴板 打印

1. <bean name="/test" class="cn.javass.chapter5.web.controller.TestController"/>  
2. <bean id="handlerInterceptor1"   
3. class="cn.javass.chapter5.web.interceptor.HandlerInterceptor1"/>  
4. <bean id="handlerInterceptor2"   
5. class="cn.javass.chapter5.web.interceptor.HandlerInterceptor2"/>  
6.    

 

java代码：

查看 复制到剪贴板 打印

1. <bean class="org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping">  
2.     <property name="interceptors">  
3.         <list>  
4.            <ref bean="handlerInterceptor1"/>  
5.           <ref bean="handlerInterceptor2"/>  
6.         </list>  
7.     </property>  
8. </bean>  

 

参考：

http://my.oschina.net/lichhao/blog/99039

http://downpour.iteye.com/blog/1341459

http://blog.youkuaiyun.com/soundfly/article/details/17380111

http://sishuok.com/forum/blogCategory/showByCategory.html?categories_id=106&user_id=2