Filter类的常用方法

更新时间：2022-02-07 11:39:42 来源：极悦浏览678次

Filter类其实也是servlet，它的作用是客户端请求到达时未达到servlet处理前拦截请求，可以对HttpServletRequest进行预处理，然后再把请求转交给后续的servlet处理;它也可会HttpServletResponse返回客户端前进行后处理。

Filter的通常用法：

1.用户授权判断，当用户请求达到时，验证用户是否已通过登录授权。

2.日志记录处理，记录用户特殊用户请求。

3.解码处理，负责对请求的内容统一进行解码。

Filter类需要实现javax.servlet.Filter接口，该接口有3个方法:init()、doFilter()、destroy()。

Filter的配置:

1.可以使用注释方式，在filter类前使用@WebFilter注释，filterName属性指定filter名称，urlPatterns属性指定过滤路径。

2.在web.xml中配置方式

以使用Filter实际用户授权控制实例：

目录结构如下

security目录下的资源需要授权后再能方式

login_proc.jsp为登录的处理页面(本应该使用servlet或者MVC框架来处理，为了省事而直接使用jsp页面，jsp其本质也是servlet)，当用户名和密码均为admin时表示登录成功。

error.jsp为未授权访问security的提示页面。

firstfilter.java为Filter类，实现security访问授权控制。

security/index.jsp文件内容:

<%@ 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>授权访问首页</title>
 </head>
 <body>
 <% out.println("你好，" + session.getAttribute("userName") + "!"); %>
 </body>
 </html>

 <%@ 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>用户登录</title>
 </head>
 <body>
     <form action="login_proc.jsp" method="post">
         用户名:<input type="text" name="userName" value=""></input><br/>
         密码:<input type="password" name="passWord" value=""></input><br/><br/>
         <input type="submit" value="提交"/>         
     </form>
 </body>
 </html>

 <%@ 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>Filter实例</title>
 </head>
 <body>
 <% 
     String userName = request.getParameter("userName");
     String passWord = request.getParameter("passWord");
     out.println(userName);
     out.println(passWord);
     if(userName.equals("admin") && passWord.equals("admin"))
     {
         session.setAttribute("userName", userName);
         response.sendRedirect("security/index.jsp");
     }
     else
     {
         response.sendRedirect("login.jsp");
     }
 %>
 </body>
 </html>

 <%@ 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>不好意思，出错了！</title>
 </head>
 <body>
 你还没有登录，请先<a href="login.jsp" name=login >登录</a>！ 
 </body>
 </html>

 package com.info.filter; 
 import java.io.IOException; 
 import javax.servlet.Filter;
 import javax.servlet.FilterChain;
 import javax.servlet.FilterConfig;
 import javax.servlet.ServletContext;
 import javax.servlet.ServletException;
 import javax.servlet.ServletRequest;
 import javax.servlet.ServletResponse;
 import javax.servlet.annotation.WebFilter;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 import javax.servlet.http.HttpSession;
 import javax.websocket.Session; 
 @WebFilter(filterName="firstfilter"
             ,urlPatterns={"/security/*"})
 public class firstfilter implements Filter {     
     private FilterConfig config; 
     @Override
     public void destroy() {
         // TODO Auto-generated method stub
         this.config = null;         
     } 
     @Override
     public void doFilter(ServletRequest request1, ServletResponse response1, FilterChain chain)
             throws IOException, ServletException {
         // TODO Auto-generated method stub         
         HttpServletRequest request = (HttpServletRequest) request1;
         HttpServletResponse response = (HttpServletResponse) response1;         
         ServletContext context = this.config.getServletContext();         
         HttpSession hsesson = request.getSession();
         if(hsesson.getAttribute("userName")==null || hsesson.getAttribute("userName").equals(""))
         {
             response.sendRedirect("/filterdemo/error.jsp");
         }
         else
         {
             //将请求继续传递直至达到最终访问资源
             chain.doFilter(request1, response1);
         }                  
         //--------------------Filter后处理开始-------------------------//
         //TODO
     } 
     @Override
     public void init(FilterConfig config) throws ServletException {
         // TODO Auto-generated method stub         
         this.config=config;         
     } 
 }

 <?xml version="1.0" encoding="UTF-8"?>
 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
   <display-name>filterdemo</display-name>
   <welcome-file-list>
     <welcome-file>index.html</welcome-file>
     <welcome-file>index.htm</welcome-file>
     <welcome-file>index.jsp</welcome-file>
     <welcome-file>default.html</welcome-file>
     <welcome-file>default.htm</welcome-file>
     <welcome-file>default.jsp</welcome-file>
   </welcome-file-list>
   <filter>
       <filter-name>firstfilter</filter-name>
       <filter-class>com.info.filter.firstfilter</filter-class>
   </filter>
   <filter-mapping>
       <filter-name>firstfilter</filter-name>
       <url-pattern>/security/*</url-pattern>
   </filter-mapping>
 </web-app>

注：web.xml中配置了filter类，则filter类中的注释则无效。