关于javaWeb的Filter过滤器

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关于javaWeb的Filter过滤器

Filter是如何实现拦截的？

　　Filter接口中有一个doFilter方法，当我们编写好Filter，并配置对哪个web资源进行拦截后，WEB服务器每次在调用web资源的service方法之前，都会先调用一下filter的doFilter方法，因此，在该方法内编写代码可达到如下目的：

调用目标资源之前，让一段代码执行。
是否调用目标资源（即是否让用户访问web资源）。
调用目标资源之后，让一段代码执行。

　　web服务器在调用doFilter方法时，会传递一个filterChain对象进来，filterChain对象是filter接口中最重要的一个对象，它也提供了一个doFilter方法，开发人员可以根据需求决定是否调用此方法，调用该方法，则web服务器就会调用web资源的service方法，即web资源就会被访问，否则web资源不会被访问。

其实Filter和Servlet很类似，读者可以根据servlet来比较着学习Filter

下面通过一个完整的项目来介绍Filter的作用。

先要继承Filter接口：

对账号的验证：

<span style="font-size:18px;"><span style="font-size:18px;"><span style="font-size:18px;">package com.cn.zhu;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;public class Unamefilter implements Filter {public void destroy() {// TODO Auto-generated method stub}public void doFilter(ServletRequest request, ServletResponse response,FilterChain chain) throws IOException, ServletException {            System.out.println("开始执行，doFilter");       String  inuname=fliterconfig.getInitParameter("uname1");       String uname=request.getParameter("uname");       if(!inuname.equals(uname)){       request.setAttribute("message", "用户名不正确");       request.getRequestDispatcher("/login.jsp").forward(request, response);       return;       }chain.doFilter(request, response);//放行           }   private FilterConfig  fliterconfig;public void init(FilterConfig filter) throws ServletException {   this.fliterconfig=filter;         System.out.println("开始执行，init");}}</span></span></span>

对密码的验证

<span style="font-size:18px;"><span style="font-size:18px;">package com.cn.zhu;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;public class Unamefilter implements Filter {public void destroy() {// TODO Auto-generated method stub}public void doFilter(ServletRequest request, ServletResponse response,FilterChain chain) throws IOException, ServletException {            System.out.println("开始执行，doFilter");       String  inuname=fliterconfig.getInitParameter("uname1");       String uname=request.getParameter("uname");       if(!inuname.equals(uname)){       request.setAttribute("message", "用户名不正确");       request.getRequestDispatcher("/login.jsp").forward(request, response);       return;       }chain.doFilter(request, response);//放行           }   private FilterConfig  fliterconfig;public void init(FilterConfig filter) throws ServletException {   this.fliterconfig=filter;         System.out.println("开始执行，init");}}</span></span>

一个登陆的请求：login.jsp页面

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>    <base href="<%=basePath%>">        <title>My JSP 'login.jsp' starting page</title>    <meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0">    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"><meta http-equiv="description" content="This is my page"><!--<link rel="stylesheet" type="text/css" href="styles.css">--> <style type="text/css"><!--body {background-color:#6F00D2;background-image: url(image/12885844_113021655000_2[1].jpg);}.ww1 {height: 30px;width: 180px;}</style>    <script  language="javascript">//javascript check函数，用于检查表单中输入的用户昵称和登录密码是否为空function check(){           return true;}</script>       </head>    <body>  <h1 align="center">管理员登录</h1>  <form action="hello.jsp" method="post">  <table align="center">               <tr>                                     <td height="45">      账号  <input type="text" name="uname" value="${param.uname}" height="45"/><br> </td>                    <td><font color="red">${message }</font>  </td>               </tr>                                <tr>                                     <td  height="45">          密码     <input type="password" name="upassword"  height="45"/><br> </td>                    <td>  <font color="red">${passmessage }</font>  </td>               </tr>          <tr>                  <td>                  <button onclick="return check();" style="background: rgb(0, 142, 173);           padding: 7px 10px; border-radius: 4px; border: 1px solid rgb(26, 117, 152);           border-image: none; color: rgb(255, 255, 255); font-weight: bold;" >登录</button>           </td>           </tr>               </form>       </table>  </body></html>

web.xml配置信息如下账号默认为Tom,密码为123456，

这个账号密码，可以换成数据库的信息。

<?xml version="1.0" encoding="UTF-8"?><web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">  <servlet>    <description>This is the description of my J2EE component</description>    <display-name>This is the display name of my J2EE component</display-name>    <servlet-name>Liststudentss</servlet-name>    <servlet-class>com.mvc.Liststudentss</servlet-class>  </servlet>  <servlet>    <description>This is the description of my J2EE component</description>    <display-name>This is the display name of my J2EE component</display-name>    <servlet-name>Deletestudent</servlet-name>    <servlet-class>com.mvc.Deletestudent</servlet-class>  </servlet>  <servlet>    <description>This is the description of my J2EE component</description>    <display-name>This is the display name of my J2EE component</display-name>    <servlet-name>InsertStudent</servlet-name>    <servlet-class>com.mvc.InsertStudent</servlet-class>  </servlet>  <servlet-mapping>    <servlet-name>Liststudentss</servlet-name>    <url-pattern>/liststudents</url-pattern>  </servlet-mapping>  <servlet-mapping>    <servlet-name>Deletestudent</servlet-name>    <url-pattern>/deletestudent</url-pattern>  </servlet-mapping>  <servlet-mapping>    <servlet-name>InsertStudent</servlet-name>    <url-pattern>/InsertStudent</url-pattern>  </servlet-mapping>  <welcome-file-list>        <welcome-file>login.jsp</welcome-file>  </welcome-file-list>                    <!--过滤器配置--!>  <context-param>      <param-name>upassword</param-name>     <param-value>123456</param-value> </context-param> <filter>      <display-name>Unamefilter</display-name>      <filter-name>Unamefilter</filter-name>     <filter-class>com.cn.zhu.Unamefilter</filter-class>   <init-param>       <param-name>uname1</param-name>       <param-value>Tom</param-value>   </init-param>  </filter> <filter-mapping>       <filter-name>Unamefilter</filter-name>      <url-pattern>/hello.jsp</url-pattern>   </filter-mapping>  <filter>      <display-name>PasswordFilter</display-name>      <filter-name>PasswordFilter</filter-name>      <filter-class>com.cn.zhu.PasswordFilter</filter-class> </filter>  <filter-mapping>     <filter-name>PasswordFilter</filter-name>     <url-pattern>/hello.jsp</url-pattern>  </filter-mapping> </web-app>

界面如下

测试界面：如果账号或密码输入不正确，Filter会直接拦截。

JSP+servlet+Filter完整的项目在这里，如有需要请点击下载

地址： http://pan.baidu.com/s/1ckc5hO 密码 dhp8

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