springmvc自定义拦截器

  自定义拦截器，我们在开发中基本上都会用到，做一些权限控制，日志等等

    下面用代码来解析下自定义拦截器

    首先定义一个自定义拦截器 

package com.asiainfo.springmvc.intercepter;

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

import org.apache.log4j.Logger;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

import com.asiainfo.springmvc.controller.BaseController;

public class DefineIntercepter implements HandlerInterceptor{
	
	private static final Logger logger = Logger.getLogger(BaseController.class);


	public boolean preHandle(HttpServletRequest request,
			HttpServletResponse response, Object handler) throws Exception {
		logger.debug("测试拦截器preHandle");
		
		return true;
	}

	public void postHandle(HttpServletRequest request,
			HttpServletResponse response, Object handler,
			ModelAndView modelAndView) throws Exception {
		logger.debug("测试拦截器postHandle");

		
	}

	public void afterCompletion(HttpServletRequest request,
			HttpServletResponse response, Object handler, Exception ex)
			throws Exception {
		logger.debug("测试拦截器afterCompletion");		
	}


}

在spring的xml文件中配置拦截管理器

<!-- 配置拦截器 -->
    <mvc:interceptors>
       <bean class="com.asiainfo.springmvc.intercepter.DefineIntercepter"></bean>
       <!--  
                可以定义拦截器拦截某个指定的controller 
                   比如我现在是配置url路径 是拦截local/*下面的所有请求，如果我变成format/testFormat，那么就不会被拦截
            -->
       <mvc:interceptor>
         <mvc:mapping path="/locale/*"/>
         <bean class="com.asiainfo.springmvc.intercepter.SecondIntercepter"></bean>
       </mvc:interceptor>
       <bean class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor"></bean>
    </mvc:interceptors>

结果：  

DEBUG [http-bio-8888-exec-8] - 测试拦截器preHandle
DEBUG [http-bio-8888-exec-8] - 测试locale===========
DEBUG [http-bio-8888-exec-8] - 测试拦截器postHandle
DEBUG [http-bio-8888-exec-8] - Rendering view [org.springframework.web.servlet.view.JstlView: name 'success'; URL [/WEB-INF/jsp/success.jsp]] in DispatcherServlet with name 'springmvc'
DEBUG [http-bio-8888-exec-8] - Forwarding to resource [/WEB-INF/jsp/success.jsp] in InternalResourceView 'success'
DEBUG [http-bio-8888-exec-8] - 测试拦截器afterCompletion

从测试结果中，可以看出，拦截器的执行顺序

   下面我们可以用源码来解读下，拦截器方法是在什么地方执行的

    DispatcherServlet

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 {
				processedRequest = checkMultipart(request);
				multipartRequestParsed = (processedRequest != request);

				// Determine handler for the current request.
				mappedHandler = getHandler(processedRequest);
				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()) {
						logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
					}
					if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
						return;
					}
				}

				if (!mappedHandler.applyPreHandle(processedRequest, response)) { //从这里进入到mappedHandler ,看到拦截器的preHandle
					return;
				}

				try {
					// Actually invoke the handler.
					mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
				}
				finally {
					if (asyncManager.isConcurrentHandlingStarted()) {
						return;
					}
				}

				applyDefaultViewName(request, mv);
				mappedHandler.applyPostHandle(processedRequest, response, mv);//从这里进去看postHandle
		
	}

}catch (Exception ex) {dispatchException = ex;}
    processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);//视图渲染和数据处理
}catch (Exception ex) {
    triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}catch (Error err) {triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err);
}finally {
    if (asyncManager.isConcurrentHandlingStarted()) 
        {// Instead of postHandle and afterCompletionmappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
            return;
}// Clean up any resources used by a multipart request.if (multipartRequestParsed) {cleanupMultipart(processedRequest);}}}

boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
		if (getInterceptors() != null) {
			for (int i = 0; i < getInterceptors().length; i++) {
				HandlerInterceptor interceptor = getInterceptors()[i];
				if (!interceptor.preHandle(request, response, this.handler)) {
					triggerAfterCompletion(request, response, null);
					return false;
				}
				this.interceptorIndex = i;
			}
		}
		return true;
	}

从这个方法可以看出，在执行目标方法之前，就执行了这个前置拦截器方法，如果前置拦截器方法返回false,那么就不会执行目标方法，然后执行AfterCompletion拦截器方法，然后结束。

    然后我们看第二个方法：   

void applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv) throws Exception {
		if (getInterceptors() == null) {
			return;
		}
		for (int i = getInterceptors().length - 1; i >= 0; i--) {
			HandlerInterceptor interceptor = getInterceptors()[i];
			interceptor.postHandle(request, response, this.handler, mv);
		}
	}

这个方法是目标方法的后面，但是在视图渲染的前面

  第三个方法：   

private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
			HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception {

		boolean errorView = false;

		if (exception != null) {
			if (exception instanceof ModelAndViewDefiningException) {
				logger.debug("ModelAndViewDefiningException encountered", exception);
				mv = ((ModelAndViewDefiningException) exception).getModelAndView();
			}
			else {
				Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
				mv = processHandlerException(request, response, handler, exception);
				errorView = (mv != null);
			}
		}

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

		if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
			// Concurrent handling started during a forward
			return;
		}

		if (mappedHandler != null) {
			mappedHandler.triggerAfterCompletion(request, response, null);//第三个方法
		}

这样就很简单明了，知道拦截器方法的执行顺序和过程