动态网页技术--JSP（5）

一.过滤器

过滤器简介:
过滤器能够对Servlet容器的请求和响应对象进行检查和修改。
过滤器的作用:
过滤器在Servlet被调用之前检查Request对象，修改Request Header和Request内容
过滤器在Servlet被调用之后检查Response对象，修改Response Header和Response内容。
过滤的内容:
Servlet、JSP、HTML等文件

创建过滤器:
所有的过滤器类都必须实现javax.servlet.Filter接口
Filter接口还有3个必须实现的方法：
1.初始化方法

public void init (FilterConfig config)
2.过滤方法

public void doFilter(ServletRequest req,ServletResponse resp,FilterChain chain)

3.销毁过滤器方法

public void destroy( )

过滤器的配置，统一设置编码：

开发过滤器(Filter)的步骤:

1.创建类实现Filter接口

2.重写doFilter方法

3.在配置文件（web.xml）中过滤器进行注册

        <filter>
          <filter-name>formFilter</filter-name>
          <filter-class>com.neusoft.action.FormFilter</filter-class>
          <init-param>
           <param-name>encoding</param-name>       //对应过滤器中encoding
              <param-value>UTF-8</param-value>     //传递到过滤器
          </init-param>
      </filter>
      <filter-mapping>
          <filter-name>formFilter</filter-name>
          <url-pattern>/*</url-pattern>            
      </filter-mapping>

•需求: 使用过滤器修改字符集

form表单登录页面

 1 form.jsp登录页面
 2 
 3 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
 4 <%
 5     String path = request.getContextPath();
 6     String basePath = request.getScheme() + "://"
 7             + request.getServerName() + ":" + request.getServerPort()
 8             + path + "/";
 9 %>
10 
11 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
12 <html>
13     <head>
14         <base href="<%=basePath%>">
15 
16         <title>My JSP 'form.jsp' starting page</title>
17 
18         <meta http-equiv="pragma" content="no-cache">
19         <meta http-equiv="cache-control" content="no-cache">
20         <meta http-equiv="expires" content="0">
21         <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
22         <meta http-equiv="description" content="This is my page">
23         <!--
24     <link rel="stylesheet" type="text/css" href="styles.css">
25     -->
26 
27     </head>
28 
29     <body>
30         <form action="index.jsp" method="post">
31             提交数据
32             <input type="text" name="username" />
33             <input type="submit" value="提交" />
34         </form>
35     </body>
36 </html>

跳转到的页面

 1 跳转到index.jsp页面
 2 
 3 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
 4 <%@taglib   prefix="c"  uri="http://java.sun.com/jsp/jstl/core"%>
 5 <%
 6 String path = request.getContextPath();
 7 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
 8 %>
 9 
10 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
11 <html>
12   <head>
13     <base href="<%=basePath%>">
14     
15     <title>My JSP 'index.jsp' starting page</title>
16     <meta http-equiv="pragma" content="no-cache">
17     <meta http-equiv="cache-control" content="no-cache">
18     <meta http-equiv="expires" content="0">    
19     <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
20     <meta http-equiv="description" content="This is my page">
21     <!--
22     <link rel="stylesheet" type="text/css" href="styles.css">
23     -->
24   </head>
25   
26   <body>
27     您提交的数据是:<c:out value="${param.username}"></c:out>
28   </body>
29 </html>

创建过滤器，实现Filter接口

 1 FormFilter过滤器
 2 
 3 package com.neusoft.action;
 4 
 5 import java.io.IOException;
 6 
 7 import javax.servlet.Filter;
 8 import javax.servlet.FilterChain;
 9 import javax.servlet.FilterConfig;
10 import javax.servlet.ServletException;
11 import javax.servlet.ServletRequest;
12 import javax.servlet.ServletResponse;
13 
14 //过滤器类
15 public class FormFilter implements Filter {
16 
17     private String encoding = "iso-8859-1";
18     private FilterConfig config;
19     public void destroy() {
20         System.out.println("销毁FormFilter.destroy()");
21             config=null;
22     }
23 
24     // 过滤器的处理功能
25     public void doFilter(ServletRequest request, ServletResponse response,
26             FilterChain chain) throws IOException, ServletException {
27         System.out.println("过滤FormFilter.doFilter()");
28         // 将过滤链上的请求和响应向下一个过滤连传递
29         request.setCharacterEncoding(encoding);
30         chain.doFilter(request, response);
31     }
32 
33     public void init(FilterConfig config) throws ServletException {
34         System.out.println("初始化FormFilter.init()");
35         this.config=config;
36         // 去读web.xml中的初始化参数
37         String s = config.getInitParameter("encoding");
38         if (s != null) {
39             encoding = s;
40         }
41 
42     }
43 
44 }

web.xml中配置

 1 web.xml
 2 
 3 <?xml version="1.0" encoding="UTF-8"?>
 4 <web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
 5     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 6     xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
 7     http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
 8     <welcome-file-list>
 9         <welcome-file>index.jsp</welcome-file>
10     </welcome-file-list>
11 
12     <!-- 对过滤器注册 -->
13     <filter>
14         <filter-name>formFilter</filter-name>
15         <filter-class>com.neusoft.action.FormFilter</filter-class>
16         <init-param>
17             <param-name>encoding</param-name>
18             <param-value>UTF-8</param-value>
19         </init-param>
20     </filter>
21     <filter-mapping>
22         <filter-name>formFilter</filter-name>
23         <url-pattern>/*</url-pattern>
24     </filter-mapping>
25 
26 </web-app>

运行结果

form.jsp表单登录页面

使用过滤器修改字符集运行结果

•需求："张三"禁止登录，跳转404页面

创建my404.jsp

web.xml中添加

<filter>
<filter-name>StringFilter</filter-name>
<filter-class>com.neusoft.action.StringFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>StringFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>

 1 StringFilter处理“张三”禁止登录的过滤器
 2 
 3 package com.neusoft.action;
 4 
 5 import java.io.IOException;
 6 
 7 import javax.servlet.Filter;
 8 import javax.servlet.FilterChain;
 9 import javax.servlet.FilterConfig;
10 import javax.servlet.ServletException;
11 import javax.servlet.ServletRequest;
12 import javax.servlet.ServletResponse;
13 
14 import com.sun.net.httpserver.Filter.Chain;
15 
16 public class StringFilter implements Filter {
17 
18     public void destroy() {
19         // TODO Auto-generated method stub
20 
21     }
22 
23     public void doFilter(ServletRequest request, ServletResponse response,
24             FilterChain chain) throws IOException, ServletException {
25         String username = request.getParameter("username");
26         if ("张三".equals(username)) {
27             //response.getWriter().print("您输入了非法字符");
28    request.getRequestDispatcher("my404.jsp").forward(request, response);  //直接跳转index.jsp主页客户端，看不到跳my404.jsp

29 } else { 

30  chain.doFilter(request, response); 
31    } 
32  } 
33 
34 public void init(FilterConfig config) throws ServletException { 
35 // TODO Auto-generated method stub 
36
37  } 
38 
39 }

运行结果

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原文地址：https://www.cnblogs.com/Pioneer-HengYu/p/6649446.html