Java的1.3开始,对servlet2.3规范中加入了过滤器的支持。过滤器能够让我们对目标资源的请求和响应进行截取。
一些filter的特性:
1. Filter是Servlet规范的规定,需要Servlet容器的支持。
2. Filter不能使用Spring框架中的资源对象。
3. Filter只在Servlet前后起作用。
我们需要实现接口Filter中定义的方法:
/* * The contents of this file are subject to the terms * of the Common Development and Distribution License * (the "License"). You may not use this file except * in compliance with the License. * * You can obtain a copy of the license at * glassfish/bootstrap/legal/CDDLv1.0.txt or * https://glassfish.dev.java.net/public/CDDLv1.0.html. * See the License for the specific language governing * permissions and limitations under the License. * * When distributing Covered Code, include this CDDL * HEADER in each file and include the License file at * glassfish/bootstrap/legal/CDDLv1.0.txt. If applicable, * add the following below this CDDL HEADER, with the * fields enclosed by brackets "[]" replaced with your * own identifying information: Portions Copyright [yyyy] * [name of copyright owner] * * Copyright 2005 Sun Microsystems, Inc. All rights reserved. * * Portions Copyright Apache Software Foundation. */ package javax.servlet; import java.io.IOException; public interface Filter { public void init(FilterConfig filterConfig) throws ServletException; public void doFilter ( ServletRequest request, ServletResponse response, FilterChain chain ) throws IOException, ServletException; public void destroy(); }
/** * 自定义一个Filter * @author zhuli * @date 2014-7-20 */ public class TestFilter implements Filter { @Override public void init(FilterConfig filterConfig) throws ServletException { System.out.println("TestFiltern init"); //初始化容器的时候,这边会运行 } @Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { // TODO Auto-generated method stub HttpServletRequest request2 = (HttpServletRequest)request; String ip = IPUtil.getClientIp(request2); System.out.println("TestFiltern doFilter 请求前面就处理了 + ip: " + ip); chain.doFilter(request, response); //传递filter链 System.out.println("业务处理完了之后,会继续调用这个filter,然后调用这边"); } @Override public void destroy() { // TODO Auto-generated method stub System.out.println("TestFiltern destroy"); //销毁容器的时候,这边会运行 } }
结果:
TestFiltern doFilter 请求前面就处理了 + ip: 127.0.0.1
业务逻辑=========
业务处理完了之后,会继续调用这个filter,然后调用这边
在web.xml中,配置servlet前面配置Filter即可:
url-pattern可以配置符合哪些请求的需要走这个filter
<!-- TEST filter --> <filter> <filter-name>testFilter</filter-name> <filter-class>com.xxx.test.TestFilter</filter-class> </filter> <filter-mapping> <filter-name>testFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping>
可以先看一张图:
假设我们有两个过滤器,TestFilter和TestFilter1。
当web请求进来
->
我们执行TestFilter过滤器中chain.doFilter之前的代码(例如我们的例子中System.out.println("TestFiltern doFilter 请求前面就处理了");)
->
然后执行TestFilter2过滤器中chain.doFilter之前的代码
->
然后Servlet中的service方法
->
然后处理TestFilter2过滤器中chain.doFilter之后的代码
->
然后处理TestFilter过滤器中chain.doFilter之后的代码(例如我们的例子中System.out.println("业务处理完了之后,会继续调用这个filter,然后调用这边");)
1. init初始化。在web容器启动的时候,对Filter进行初始化。初始化会调用init()方法
2. 过滤。具体过滤是doFilter()方法
3. destroy销毁。在容器关闭的时候会对Filter进行销毁。
原文地址:http://blog.csdn.net/initphp/article/details/37988431