Java基础95 过滤器 Filter

1、filter 过滤器的概述

filter过滤器：是面向切面编程的一种实现策略，在不影响原来的程序流程的前提下，将一些业务逻辑切入流程中，在请求达到目标之前进行处理，一般用于编码过滤、权限过滤、....

2、filter 过滤器的创建步骤

1、创建一个普通的java类实现filter接口
  2、实现接口中的三个方法(init,doFilter,destory)
  3、配置过滤器(web.xml)

3、实例_编码过滤器

 package com.shore.a_filter;

 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 CharsetEncoding implements Filter{
     private String encoding;
     public void init(FilterConfig config) throws ServletException {//过滤器初始化
          encoding = config.getInitParameter("encoding");//获取web.xml配置文件中的参数
     }

     public void doFilter(ServletRequest request, ServletResponse response,
             FilterChain chain) throws IOException, ServletException {
         request.setCharacterEncoding(encoding);
         response.setCharacterEncoding(encoding);
         chain.doFilter(request, response);//放行
     }

     public void destroy() {//过滤器被销毁（服务器停止，才会被销毁）

     }
 }

web.xml 配置文件

 <?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">

   <!-- 编码过滤 -->
   <filter>
       <!-- 类名 -->
       <filter-name>CharsetEncoding</filter-name>
       <!-- 类路径 -->
       <filter-class>com.shore.a_filter.CharsetEncoding</filter-class>
       <init-param>
           <!-- 参数名 -->
           <param-name>encoding</param-name>
           <!-- 编码 -->
           <param-value>UTF-8</param-value>
       </init-param>
   </filter>

   <filter-mapping>
       <!-- 类名 -->
       <filter-name>CharsetEncoding</filter-name>
       <!--  /* 表示过滤(拦截)所有页面(请求)     *.xxx 表示拦截该指定后缀结尾的页面(请求) -->
       <url-pattern>/*</url-pattern>
   </filter-mapping>

   <welcome-file-list>
     <welcome-file>index.jsp</welcome-file>
   </welcome-file-list>
 </web-app>

附录

 过滤器

 package com.shore.b_filter;

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

 public class LoginFilter implements Filter{
         private String[] passlist;
     public void init(FilterConfig Config) throws ServletException {
         passlist=Config.getInitParameter("passList").split(",");
         System.out.println("第一步");
     }

     public void doFilter(ServletRequest req, ServletResponse resp,
             FilterChain chain) throws IOException, ServletException {
         //会重复执行一次
         System.out.println("第二步");
         //获取request对象
         HttpServletRequest request=(HttpServletRequest)req;
         HttpServletResponse response=(HttpServletResponse)resp;
         //获取客户端的资源路径
         String uri = request.getRequestURI();
         //获取请求资源路径
         int index = uri.lastIndexOf("/");//获取路径中的最后一个斜杠的下标
         String source = uri.substring(index+1);//截取斜杠后面的所有字符串
         System.out.println(source);
         boolean flag = false;//定义标记
         for(String s:passlist){//遍历
             if(s.trim().equals(source)){
                 flag = true;
             }
         }
         if(flag){//如果flag=true则放行
             chain.doFilter(request, response);
         }else{
             //获取session的内容
             Object obj = request.getSession().getAttribute("user");
             if(obj == null){
                 //未登录
                 request.setAttribute("msg","请先登录");
                 request.getRequestDispatcher("index.jsp").forward(request, response);
             }else{
                 System.out.println("第五步");
                 chain.doFilter(request, response);//放行
             }
         }
     }

     public void destroy() {

     }
 }

web.xml 配置文件

 <?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">

  <!-- 配置过滤器-->
  <filter>
     <!-- 类名 -->
      <filter-name>LoginFilter</filter-name>
     <!-- 类路径 -->
      <filter-class>com.shore.b_filter.LoginFilter</filter-class>
      <init-param>
         <!-- 参数名 -->
          <param-name>passList</param-name>
         <!-- passList参数的值（放行index和reg页面，即：不用登陆也可直接访问这两个页面） -->
          <param-value>index.jsp,reg.jsp</param-value>
      </init-param>
  </filter>
  <filter-mapping>
     <!-- 类名 -->
      <filter-name>LoginFilter</filter-name>
     <!-- 拦截所有jsp页面 -->
      <url-pattern>*.jsp</url-pattern>
  </filter-mapping>

   <!-- 编码过滤 -->
   <filter>
       <filter-name>CharsetEncoding</filter-name>
       <filter-class>com.shore.a_filter.CharsetEncoding</filter-class>
       <init-param>
           <param-name>encoding</param-name>
           <param-value>UTF-8</param-value>
       </init-param>
   </filter>
   <filter-mapping>
       <filter-name>CharsetEncoding</filter-name>
     <!--  /* 表示过滤(拦截)所有页面(请求)     *.xxx 表示拦截该指定后缀结尾的页面(请求) -->
       <url-pattern>/*</url-pattern>
   </filter-mapping>

   <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>LoginServlet</servlet-name>
     <servlet-class>com.shore.b_servlets.LoginServlet</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>RegisterServlet</servlet-name>
     <servlet-class>com.shore.b_servlets.RegisterServlet</servlet-class>
   </servlet>

   <servlet-mapping>
     <servlet-name>LoginServlet</servlet-name>
     <url-pattern>/LoginServlet</url-pattern>
   </servlet-mapping>
   <servlet-mapping>
     <servlet-name>RegisterServlet</servlet-name>
     <url-pattern>/RegisterServlet</url-pattern>
   </servlet-mapping>

   <welcome-file-list>
     <welcome-file>index.jsp</welcome-file>
   </welcome-file-list>
 </web-app>

servlet

 package com.shore.b_servlets;

 import java.io.IOException;
 import java.io.PrintWriter;

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

 public class LoginServlet extends HttpServlet {

     public void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         doPost(request, response);
     }

     public void doPost(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         String name=request.getParameter("uname");
         String pass=request.getParameter("upass");
         System.out.println("第四步");
         if(!"".equals(name.trim())){
             //将当前登录的用户存储到session中
             request.getSession().setAttribute("user",name);
             //跳转到主页
             response.sendRedirect("main.jsp");

         }else{
             request.setAttribute("msg","请输入账号和密码");
             request.getRequestDispatcher("index.jsp").forward(request, response);
         }
     }
 }

登录页面

 <%@ 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 'index.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">
     -->
   </head>
   <body>
           <%
               System.out.println("第三步");
           %>
           <form action="LoginServlet1" method="post">
               <input type="text" name="uname"/>
              <input type="password" name="upass"/>
              <input type="submit" value="登录"/>
              <span>没有账号?<a href="reg.jsp">立即注册</a></span>
           </form>
           <hr>
           <span style="color: red;">${requestScope.msg}</span>
   </body>
 </html>

注册页面

 <%@ 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 'reg.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">
     -->

   </head>

   <body>
     <form action="RegisterServlet">
         <input type="text" name="uname" placeholder="请输入账号"/>
         <input type="password" name="upass" placeholder="请输入密码"/>
         <input type="password" name="upass" placeholder="请输入重复密码"/>
         <input type="submit" value="注册"/>
     </form>
   </body>
 </html>

主页面

 <%@ 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 'main.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">
     -->

   </head>

   <body>
     欢迎来到主页
   </body>
 </html>

Struts2下的拦截器（interceptor）和 过滤器（Filter）

原创作者：DSHORE

作者主页：http://www.cnblogs.com/dshore123/

原文出自：https://www.cnblogs.com/dshore123/p/10703859.html

欢迎转载，转载务必说明出处。（如果本文对您有帮助，可以点击一下右下角的 推荐，或评论，谢谢！）