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过滤器Filter(拦截jsp页面的跳转)案例：
创建一个 Filter , class类: 其继承于 接口 Filte（接口导包：import javax.servlet.Filter;）
在 web.xml 文件中配置并映射该 Filter. 其中 url-pattern 指定该 Filter 可以拦截哪些资源, 即可以通过哪些 url 访问到该 Filter，并进行拦截；
案例：username=Tom,password=1234,设计Filter类，及jsp页面实现，输入username和password是否等于Tom和1234，不等拦截index.jsp页面跳转到hello.jsp页面，等的或，在在hello，显示；
1.建立UserNameFilter类：继承于接口Filter（接口导包：import javax.servlet.Filter;）
package com.lanqiao.javatest;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;import org.apache.catalina.connector.Request;public class UserNameFilter implements Filter{ //构造方法 public UserNameFilter(){ } public void destroy() { } @Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { String initUser=filterConfig.getInitParameter("username"); String username=request.getParameter("username"); if(!initUser.equals(username)){ request.setAttribute("message", "用户名不正确！！！"); request.getRequestDispatcher("/login.jsp").forward(request, response); return ; } chain.doFilter(request, response); } private FilterConfig filterConfig; @Override public void init(FilterConfig filterConfig) throws ServletException { this.filterConfig=filterConfig; }}
2.建立PasswordFilter类：继承于接口Filter（接口导包：import javax.servlet.Filter;）
package com.lanqiao.javatest;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 PasswordFilter implements Filter { public PasswordFilter() { // TODO Auto-generated constructor stub } @Override public void destroy() { } @Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { String initPassword=filterConfig.getServletContext().getInitParameter("password"); String password=request.getParameter("password"); if(!initPassword.equals(password)){ request.setAttribute("message", "密码不正确！！！"); request.getRequestDispatcher("/login.jsp").forward(request, response); return ; } chain.doFilter(request, response); } private FilterConfig filterConfig; @Override public void init(FilterConfig filterConfig) throws ServletException { this.filterConfig=filterConfig; } }
3.在WEB-FIN下的web.xml文件下的配置和映射：
<?xml version="1.0" encoding="UTF-8"?><web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5"> <display-name>day-12</display-name> <filter> <filter-name>UserNameFilter</filter-name> <filter-class>com.lanqiao.javatest.UserNameFilter</filter-class> <init-param> <param-name>username</param-name> <param-value>Tom</param-value> </init-param> </filter> <filter-mapping> <filter-name>UserNameFilter</filter-name> <url-pattern>/hello.jsp</url-pattern> </filter-mapping> <filter> <filter-name>password</filter-name> <filter-class>com.lanqiao.javatest.PasswordFilter</filter-class> </filter> <filter-mapping> <filter-name>password</filter-name> <url-pattern>/hello.jsp</url-pattern> </filter-mapping> <context-param> <param-name>password</param-name> <param-value>1234</param-value> </context-param> </web-app>
4.index.jsp页面：输入username和password;
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Insert title here</title></head><body> <font color="red">${message }</font> <br><br> <form action="hello.jsp" method="post"> username:<input type="text" name="username" /><br> password:<input type="password" name="password"/><br> <input type="submit" value="http://www.mamicode.com/Submit"/> </form> </body></html>
5.hello.jsp页面：
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Insert title here</title></head><body> Hello:${param.username }</body></html>
过滤器Filter(拦截jsp页面的跳转)案例：
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