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spring-mvc拦截器

   概述:

    spring-mvc拦截器主要是通过实现 HandlerInterceptor接口，在spring-mvc的核心DispatcherServlet执行主要处理请求方法doDispatch时，由处理器映射器HandlerMapping根据请求对象requset的请求路径，找到对应的Handler以及包装HandlerInterceptor实现类组装成HandlerInterceptorChain，然后由HandlerInterceptorChain根据Handler执行的前后等顺序，调用具体每个拦截器的方法。

   HandlerInterceptor 拦截器主要会在前置处理方法可处理并拦截请求，后置处理方法后执行处理，如果某个拦截器的前置处理执行了，那么最终处理方法不管是前置处理中断请求还是报错，最终处理方法必然执行。

   下面看看DispatcherServlet经过简化的主要执行代码doDispatch()

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {		HttpServletRequest processedRequest = request;		HandlerExecutionChain mappedHandler = null;		try {			ModelAndView mv = null;			Exception dispatchException = null;			try {                // 由HandlerMapping 找到handle并包装拦截器组装成HandlerExecutionChain				mappedHandler = getHandler(processedRequest);				// 因为handler可以是任意类型，因此需要由一个HandlerAdapter来包装调用				HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());				                // 前置处理链				if (!mappedHandler.applyPreHandle(processedRequest, response)) {					return;				}                                // 实际调用方法        		mv = ha.handle(processedRequest, response, mappedHandler.getHandler());                // 后置处理链				mappedHandler.applyPostHandle(processedRequest, response, mv);			}			catch (Exception ex) {				dispatchException = ex;			}            // 处理视图结果---内部包含拦截器的最终处理（即不异常也要执行最终处理）			processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);		}		catch (Exception ex) {            // 最终处理链			triggerAfterCompletion(processedRequest, response, mappedHandler, ex);		}		finally {		    // ....		}

   下面我们自己实现一个spring-mvc的拦截器链以及其他相关类的简易模拟。

一、模拟的主要类介绍

HandlerInterceptor 拦截器

    此接口有三个方法，分别表示在处理器Handler请求执行前，执行后，执行完成的处理。

         请求前置处理：preHandle(Request request, Response response, Handler handler)     请求后置处理：postHandle(Request request,Response response, Handler handler)     请求最终处理：afterCompletion(Request request, Response response, Handler handler, Exception exc)          HandlerExecutionChain  拦截器链：       功能概述：     拦截器链实例内部有List<HandlerInterceptor> 的变量，初始化的时候用来添加拦截器, 并且用了一个int  类型interceptorIndex变量，它表示多少个拦截器执行了前置操作preHandle()方法，如果前置方法出错，那么已经完成前置操作的拦截器，需要做对应的afterCompletion最终处理的操作, afterCompletion操作是执行完成或执行出错会进行执行的方法。      其他类：     Handler 处理器，本来是用处理器适配器进行执行请求，简化就设置成一个固定处理请求的Handler类     Request 请求类, 简化成一个msg的pojo类     Response 响应类，简化成一个msg的pojo类

二、范例代码

public class MvcFilterDemo {		/**模拟request*/	static class Request {		public Request(String msg) {			super();			this.msg = msg;		}		private String msg;		public String getMsg() {			return msg;		}		public void setMsg(String msg) {			this.msg = msg;		}	}		/**模拟response*/	static class Response{		private String msg;		public String getMsg() {			return msg;		}		public void setMsg(String msg) {			this.msg = msg;		}	}		/**处理接口*/	static interface Handler {		public Object invoke (Request request, Response response) ;	}		/** 拦截器接口*/	static interface HandlerInterceptor {		boolean preHandle(Request request, Response response, Handler handler);		void postHandle(Request request, Response response, Handler handler);		void afterCompletion(Request request, Response response, Exception exc);	}		/**	 * 拦截器链	 */	static class HandlerExecutionChain {		private Handler handler;		private HandlerInterceptor[] interceptors; // 拦截链调用辅助用途		private List
   
     interceptorList = new ArrayList
    
     (); // 装拦截器		private int interceptorIndex = -1; // 前置执行的角标		public HandlerExecutionChain(Handler handler) {			this.handler = handler;		}		public Handler getHandler() {			return this.handler;		}		public void addInterceptor(HandlerInterceptor interceptor) {			this.interceptorList.add(interceptor);		}		public HandlerInterceptor[] getInterceptors() {			if (this.interceptors == null && this.interceptorList != null) {				this.interceptors = this.interceptorList.toArray(new HandlerInterceptor[this.interceptorList.size()]);			}			return this.interceptors == null ? new HandlerInterceptor[0] : this.interceptors;		}				// 1、前置执行所有 ： 每次for循环，后记录已经执行的拦截器角标，并且如果拦截器返回false，此时的最后一个拦截器要执行下最终处理方法。		boolean applyPreHandle(Request request, Response response) throws Exception {			HandlerInterceptor[] interceptors = getInterceptors();				for (int i = 0; i < interceptors.length; i++) {					HandlerInterceptor interceptor = interceptors[i];					if (!interceptor.preHandle(request, response, this.handler)) {						triggerAfterCompletion(request, response, null);						return false;					}					this.interceptorIndex = i;				}			return true;		}				// 2、后置执行所有：按反方向全部拦截器都执行。		void applyPostHandle(Request request, Response response) throws Exception {			HandlerInterceptor[] interceptors = getInterceptors();			for (int i = interceptors.length - 1; i >= 0; i--) {				HandlerInterceptor interceptor = interceptors[i];				interceptor.postHandle(request, response, this.handler);			}		}				// 3、最终执行：前置操作过不管是否中断请求还是出错，这个都会进行执行。		void triggerAfterCompletion(Request request, Response response, Exception ex) throws Exception {			HandlerInterceptor[] interceptors = getInterceptors();			for (int i = this.interceptorIndex; i >= 0; i--) {				HandlerInterceptor interceptor = interceptors[i];				try {					interceptor.afterCompletion(request, response, ex);				} catch (Throwable ex2) {				}			}		}		}			/**	 * 请求调度总类	 */	static class DispatcherServlet{				private HandlerExecutionChain chain ;		public void setChain(HandlerExecutionChain chain) {			this.chain = chain;		}				public void doService(Request request, Response response) throws Exception {			Handler handler = chain.getHandler();			try {				// 前置拦截 --- 如果false，内部会				if (!chain.applyPreHandle(request, response)) {					return;				}				Exception dispatchException = null;				try {					handler.invoke(request, response);					// 后置执行					chain.applyPostHandle(request, response);				} catch (Exception e) {					dispatchException = e;				}				// 最终执行				chain.triggerAfterCompletion(request, response, dispatchException);			} catch (Exception e) {				chain.triggerAfterCompletion(request, response, e);			} finally {				 // ....			}		}	}		测试阶段//		public static class MyHandler implements Handler {		@Override		public Object invoke(Request request, Response response) {			System.out.println("handler处理方法进行实际处理");			String old = request.getMsg() ;			request.setMsg(old + "[real excute]");			return "hello wolrd";		}	}		static class HandlerInterceptorOne implements HandlerInterceptor {		@Override		public boolean preHandle(Request request, Response response, Handler handler) {			String old = request.getMsg() ;			request.setMsg(old + "[one excute]");			System.out.println("one 前置执行");			return true;		}		@Override		public void postHandle(Request request, Response response, Handler handler) {			System.out.println("one 后置执行");		}		@Override		public void afterCompletion(Request request, Response response, Exception exc) {			System.out.println("one 最终执行");		}	}		static class HandlerInterceptorTwo implements HandlerInterceptor {		@Override		public boolean preHandle(Request request, Response response, Handler handler) {			String old = request.getMsg() ;			request.setMsg(old + "[two excute]");			System.out.println("two 前置执行");			return true;		}		@Override		public void postHandle(Request request, Response response, Handler handler) {			System.out.println("two 后置执行");		}		@Override		public void afterCompletion(Request request, Response response, Exception exc) {			System.out.println("two 最终执行");		}	}			/**	 * 测试： 	 */	public static void main(String[] args) throws Exception {		DispatcherServlet dispatcherServlet = new DispatcherServlet();		MyHandler myHandler = new MyHandler();		HandlerInterceptorOne oneInterceptor = new HandlerInterceptorOne();		HandlerInterceptorTwo twoInterceptor = new HandlerInterceptorTwo();		HandlerExecutionChain chain = new HandlerExecutionChain(myHandler);		chain.addInterceptor(oneInterceptor);		chain.addInterceptor(twoInterceptor);				dispatcherServlet.setChain(chain);		Request request = new Request("base request");		Response response = new Response();		dispatcherServlet.doService(request, response);		System.out.println("最终结果" + request.getMsg());//		one 前置执行//		two 前置执行//		handler处理方法进行实际处理//		two 后置执行//		one 后置执行//		two 最终执行//		one 最终执行//		最终结果base request[one excute][two excute][real excute]	}	}
    
   

完毕！

 

 

 

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