JAVA高级面试进阶训练营视频教程

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首先写一个过滤器的类，如下：

 1 package com.util;
 2 
 3 import java.io.IOException;
 4 import java.io.UnsupportedEncodingException;
 5 
 6 import javax.servlet.Filter;
 7 import javax.servlet.FilterChain;
 8 import javax.servlet.FilterConfig;
 9 import javax.servlet.ServletException;
10 import javax.servlet.ServletRequest;
11 import javax.servlet.ServletResponse;
12 import javax.servlet.http.HttpServletRequest;
13 import javax.servlet.http.HttpServletRequestWrapper;
14 import javax.servlet.http.HttpServletResponse;
15 import javax.servlet.http.HttpSession;
16 
17 
18 //过滤器处理表单传到servlet的乱码问题
19 public class MyFilter implements Filter{
20     //自写一个request换掉原来的request,重写里面的getParemeter方法，可以设置编码
21     class MyRequest extends HttpServletRequestWrapper{
22         
23         @Override
24         public String getParameter(String param) {
25             String value = null;
26             try {
27                 //post
28                 super.setCharacterEncoding(encoding);//把编码转换为encoding
29                 value = super.getParameter(param);
30                 if(super.getMethod().equalsIgnoreCase("GET")){
31                     if(value!=null){
32                         value = new String(value.getBytes("iso8859-1"),encoding);
33                     }
34                 }
35             } catch (UnsupportedEncodingException e) {
36                 // TODO Auto-generated catch block
37                 e.printStackTrace();
38             }
39             return value;
40         }
41 
42         public MyRequest(HttpServletRequest request) {
43             super(request);
44         }
45         
46     }
47     protected String encoding=null; 
48     public void destroy() { //销毁
49         // TODO Auto-generated method stub
50         this.encoding=null;
51     }
52    //对编码问题进行转换
53     public void doFilter(ServletRequest request, ServletResponse response,
54             FilterChain chain) throws IOException, ServletException {
55         // TODO Auto-generated method stub
56         response.setContentType("text/html;charset="+encoding);
57         //过滤未登录用户
58         HttpServletRequest req = (HttpServletRequest) request;
59         HttpServletResponse resp = (HttpServletResponse) response;
60         String path=req.getServletPath();
61         String param=req.getQueryString();
62         if(path!=null){
63             path=path+"?"+param;//全请求路径
64         }
65         if(path.endsWith("myAddress")||path.endsWith("myJingDong")||path.indexOf("myShouCang")!=-1||path.endsWith("updateUser")||path.indexOf("showOrder")!=-1||path.indexOf("showValidOrder")!=-1||path.indexOf("showCancelOrder")!=-1||path.indexOf("fillOrder")!=-1){
66             HttpSession session = req.getSession();
67             String userName = (String) session.getAttribute("username");
68             if(userName == null){
69                 session.setAttribute("url", path.replaceFirst("/", ""));
70                 System.out.println(session.getAttribute("url"));
71                 resp.sendRedirect("user.do?op=loginAction");
72                 return;
73             }
74         }
75         //把过滤器给下一个过滤器或资源处理器
76         chain.doFilter(new MyRequest((HttpServletRequest) request), response); 
77     }
78 
79     public void init(FilterConfig filterConfig) throws ServletException {
80         // TODO Auto-generated method stub
81         this.encoding=filterConfig.getInitParameter("encoding");//encoding在web.xml中指定
82     }
83 
84 }

然后在web.xml对该过滤器进行注册和映射：

<filter>
    <filter-name>EncodingFilter</filter-name>
    <filter-class>com.util.MyFilter</filter-class>
    <init-param>
       <param-name>encoding</param-name>
       <param-value>utf-8</param-value>
    </init-param>
  </filter>
 <filter-mapping>
     <filter-name>EncodingFilter</filter-name>
     <url-pattern>/*</url-pattern>
 </filter-mapping>

上面写的过滤器MyFilter类，本来只能处理post提交的数据(post是先处理后接收，get是先接收后处理)。

但是MyFilter里面在对任何页面过滤的时候，来了一个偷梁换柱：把原来客户端请求的request给换掉了，换成自己定义的一个request了，即内部类MyRequest，不过该类要继承一个类HttpServletRequestWrapper。

在自定义的一个内部类MyRequest里面，实现了一个好强大的功能，就是重写了request的getParameter()方法。该方法里面即处理了post提交，又能处理get提交，返回的值就是处理后的值，所以该过滤器就能实现处理post和get提交的乱码问题！