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

 1 package com.shore.a_filter;
 2 
 3 import java.io.IOException;
 4 
 5 import javax.servlet.Filter;
 6 import javax.servlet.FilterChain;
 7 import javax.servlet.FilterConfig;
 8 import javax.servlet.ServletException;
 9 import javax.servlet.ServletRequest;
10 import javax.servlet.ServletResponse;
11 
12 public class CharsetEncoding implements Filter{
13     private String encoding;
14     public void init(FilterConfig config) throws ServletException {//过滤器初始化
15          encoding = config.getInitParameter("encoding");//获取web.xml配置文件中的参数
16     }
17 
18     public void doFilter(ServletRequest request, ServletResponse response,
19             FilterChain chain) throws IOException, ServletException {
20         request.setCharacterEncoding(encoding);
21         response.setCharacterEncoding(encoding);
22         chain.doFilter(request, response);//放行
23     }
24     
25     public void destroy() {//过滤器被销毁（服务器停止，才会被销毁）
26         
27     }
28 }

web.xml 配置文件

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <web-app version="2.5" 
 3     xmlns="http://java.sun.com/xml/ns/javaee" 
 4     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
 5     xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
 6     http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
 7 
 8   <!-- 编码过滤 -->
 9   <filter>
10       <!-- 类名 -->
11       <filter-name>CharsetEncoding</filter-name>
12       <!-- 类路径 -->
13       <filter-class>com.shore.a_filter.CharsetEncoding</filter-class>
14       <init-param>
15           <!-- 参数名 -->
16           <param-name>encoding</param-name>
17           <!-- 编码 -->
18           <param-value>UTF-8</param-value>
19       </init-param>
20   </filter>
21   
22   <filter-mapping>
23       <!-- 类名 -->
24       <filter-name>CharsetEncoding</filter-name>
25       <!--  /* 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) -->
26       <url-pattern>/*</url-pattern>
27   </filter-mapping>
28 
29 
30   <welcome-file-list>
31     <welcome-file>index.jsp</welcome-file>
32   </welcome-file-list>
33 </web-app>

附录

过滤器

 1 package com.shore.b_filter;
 2 
 3 import java.io.IOException;
 4 
 5 import javax.servlet.Filter;
 6 import javax.servlet.FilterChain;
 7 import javax.servlet.FilterConfig;
 8 import javax.servlet.ServletException;
 9 import javax.servlet.ServletRequest;
10 import javax.servlet.ServletResponse;
11 import javax.servlet.http.HttpServletRequest;
12 import javax.servlet.http.HttpServletResponse;
13 
14 public class LoginFilter implements Filter{
15         private String[] passlist;
16     public void init(FilterConfig Config) throws ServletException {
17         passlist=Config.getInitParameter("passList").split(",");
18         System.out.println("第一步");
19     }
20 
21     public void doFilter(ServletRequest req, ServletResponse resp,
22             FilterChain chain) throws IOException, ServletException {
23         //会重复执行一次
24         System.out.println("第二步");
25         //获取request对象
26         HttpServletRequest request=(HttpServletRequest)req;
27         HttpServletResponse response=(HttpServletResponse)resp;
28         //获取客户端的资源路径
29         String uri = request.getRequestURI();
30         //获取请求资源路径
31         int index = uri.lastIndexOf("/");//获取路径中的最后一个斜杠的下标
32         String source = uri.substring(index+1);//截取斜杠后面的所有字符串
33         System.out.println(source);
34         boolean flag = false;//定义标记
35         for(String s:passlist){//遍历
36             if(s.trim().equals(source)){
37                 flag = true;
38             }
39         }
40         if(flag){//如果flag=true则放行
41             chain.doFilter(request, response);
42         }else{
43             //获取session的内容
44             Object obj = request.getSession().getAttribute("user");
45             if(obj == null){
46                 //未登录
47                 request.setAttribute("msg","请先登录");
48                 request.getRequestDispatcher("index.jsp").forward(request, response);
49             }else{
50                 System.out.println("第五步");
51                 chain.doFilter(request, response);//放行
52             }
53         }
54     }
55 
56     public void destroy() {
57         
58     }
59 }

web.xml 配置文件

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <web-app version="2.5" 
 3     xmlns="http://java.sun.com/xml/ns/javaee" 
 4     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
 5     xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
 6     http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
 7 
 8  <!-- 配置过滤器-->
 9  <filter>
10     <!-- 类名 -->
11      <filter-name>LoginFilter</filter-name>
12     <!-- 类路径 -->
13      <filter-class>com.shore.b_filter.LoginFilter</filter-class>    
14      <init-param>
15         <!-- 参数名 -->
16          <param-name>passList</param-name>
17         <!-- 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） -->
18          <param-value>index.jsp,reg.jsp</param-value>
19      </init-param>
20  </filter>
21  <filter-mapping>
22     <!-- 类名 -->
23      <filter-name>LoginFilter</filter-name>
24     <!-- 拦截所有jsp页面 -->
25      <url-pattern>*.jsp</url-pattern>
26  </filter-mapping>
27  
28   <!-- 编码过滤 -->
29   <filter>
30       <filter-name>CharsetEncoding</filter-name>
31       <filter-class>com.shore.a_filter.CharsetEncoding</filter-class>
32       <init-param>
33           <param-name>encoding</param-name>
34           <param-value>UTF-8</param-value>
35       </init-param>
36   </filter>
37   <filter-mapping>
38       <filter-name>CharsetEncoding</filter-name>
39     <!--  /* 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) -->
40       <url-pattern>/*</url-pattern>
41   </filter-mapping>
42 
43 
44   <servlet>
45     <description>This is the description of my J2EE component</description>
46     <display-name>This is the display name of my J2EE component</display-name>
47     <servlet-name>LoginServlet</servlet-name>
48     <servlet-class>com.shore.b_servlets.LoginServlet</servlet-class>
49   </servlet>
50   <servlet>
51     <description>This is the description of my J2EE component</description>
52     <display-name>This is the display name of my J2EE component</display-name>
53     <servlet-name>RegisterServlet</servlet-name>
54     <servlet-class>com.shore.b_servlets.RegisterServlet</servlet-class>
55   </servlet>
56   
57   <servlet-mapping>
58     <servlet-name>LoginServlet</servlet-name>
59     <url-pattern>/LoginServlet</url-pattern>
60   </servlet-mapping>
61   <servlet-mapping>
62     <servlet-name>RegisterServlet</servlet-name>
63     <url-pattern>/RegisterServlet</url-pattern>
64   </servlet-mapping>
65   
66   
67   <welcome-file-list>
68     <welcome-file>index.jsp</welcome-file>
69   </welcome-file-list>
70 </web-app>

servlet

 1 package com.shore.b_servlets;
 2 
 3 import java.io.IOException;
 4 import java.io.PrintWriter;
 5 
 6 import javax.servlet.ServletException;
 7 import javax.servlet.http.HttpServlet;
 8 import javax.servlet.http.HttpServletRequest;
 9 import javax.servlet.http.HttpServletResponse;
10 
11 public class LoginServlet extends HttpServlet {
12 
13     public void doGet(HttpServletRequest request, HttpServletResponse response)
14             throws ServletException, IOException {
15         doPost(request, response);
16     }
17 
18     public void doPost(HttpServletRequest request, HttpServletResponse response)
19             throws ServletException, IOException {
20         String name=request.getParameter("uname");
21         String pass=request.getParameter("upass");
22         System.out.println("第四步");
23         if(!"".equals(name.trim())){
24             //将当前登录的用户存储到session中
25             request.getSession().setAttribute("user",name);
26             //跳转到主页
27             response.sendRedirect("main.jsp");
28             
29         }else{
30             request.setAttribute("msg","请输入账号和密码");
31             request.getRequestDispatcher("index.jsp").forward(request, response);
32         }
33     }
34 }

登录页面

 1 <%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
 2 <%
 3 String path = request.getContextPath();
 4 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
 5 %>
 6 
 7 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
 8 <html>
 9   <head>
10     <base href="<%=basePath%>">
11     
12     <title>My JSP 'index.jsp' starting page</title>
13     <meta http-equiv="pragma" content="no-cache">
14     <meta http-equiv="cache-control" content="no-cache">
15     <meta http-equiv="expires" content="0">    
16     <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
17     <meta http-equiv="description" content="This is my page">
18     <!--
19     <link rel="stylesheet" type="text/css" href="styles.css">
20     -->
21   </head>
22   <body>
23           <% 
24               System.out.println("第三步");
25           %>
26           <form action="LoginServlet1" method="post">
27               <input type="text" name="uname"/>
28              <input type="password" name="upass"/>
29              <input type="submit" value="登录"/>
30              <span>没有账号?<a href="reg.jsp">立即注册</a></span>
31           </form>
32           <hr>
33           <span style="color: red;">${requestScope.msg}</span>
34   </body>
35 </html>

注册页面

 1 <%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
 2 <%
 3 String path = request.getContextPath();
 4 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
 5 %>
 6 
 7 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
 8 <html>
 9   <head>
10     <base href="<%=basePath%>">
11     
12     <title>My JSP 'reg.jsp' starting page</title>
13     
14     <meta http-equiv="pragma" content="no-cache">
15     <meta http-equiv="cache-control" content="no-cache">
16     <meta http-equiv="expires" content="0">    
17     <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
18     <meta http-equiv="description" content="This is my page">
19     <!--
20     <link rel="stylesheet" type="text/css" href="styles.css">
21     -->
22 
23   </head>
24   
25   <body>
26     <form action="RegisterServlet">
27         <input type="text" name="uname" placeholder="请输入账号"/>
28         <input type="password" name="upass" placeholder="请输入密码"/>
29         <input type="password" name="upass" placeholder="请输入重复密码"/>
30         <input type="submit" value="注册"/>
31     </form>
32   </body>
33 </html>

主页面

 1 <%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
 2 <%
 3 String path = request.getContextPath();
 4 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
 5 %>
 6 
 7 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
 8 <html>
 9   <head>
10     <base href="<%=basePath%>">
11     
12     <title>My JSP 'main.jsp' starting page</title>
13     
14     <meta http-equiv="pragma" content="no-cache">
15     <meta http-equiv="cache-control" content="no-cache">
16     <meta http-equiv="expires" content="0">    
17     <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
18     <meta http-equiv="description" content="This is my page">
19     <!--
20     <link rel="stylesheet" type="text/css" href="styles.css">
21     -->
22 
23   </head>
24   
25   <body>
26     欢迎来到主页
27   </body>
28 </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

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Java基础95 过滤器 Filter

1、filter 过滤器的概述

2、filter 过滤器的创建步骤

3、实例_编码过滤器

附录

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

Struts2下的拦截器（interceptor）和过滤器（Filter）