Jsp通过Filter实现UrlRewriter原理

web.xml文件：

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
 3  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">
 4  <welcome-file-list>
 5   <welcome-file>index.jsp</welcome-file>
 6  </welcome-file-list>
 7     <filter>
 8         <filter-name>UrlRewriterHelper</filter-name>
 9         <filter-class>helper.UrlRewriterHelper</filter-class>
10     </filter>
11     <filter-mapping>
12         <filter-name>UrlRewriterHelper</filter-name>
13         <url-pattern>/*</url-pattern>
14     </filter-mapping>
15 </web-app>

web.xml

UrlRewriterHelper文件：

 1 package helper;
 2 
 3 import java.io.IOException;
 4 import java.net.HttpRetryException;
 5 
 6 import javax.servlet.Filter;
 7 import javax.servlet.FilterChain;
 8 import javax.servlet.FilterConfig;
 9 import javax.servlet.RequestDispatcher;
10 import javax.servlet.ServletException;
11 import javax.servlet.ServletRequest;
12 import javax.servlet.ServletResponse;
13 import javax.servlet.http.HttpServletRequest;
14 
15 public class UrlRewriterHelper implements Filter {
16 
17     @Override
18     public void destroy() {
19         // TODO Auto-generated method stub
20 
21     }
22 
23     @Override
24     public void doFilter(ServletRequest arg0, ServletResponse response,
25             FilterChain arg2) throws IOException, ServletException {
26         // TODO Auto-generated method stub
27         if (arg0 instanceof HttpServletRequest) {
28             HttpServletRequest request = (HttpServletRequest) arg0;
29             String url = request.getRequestURI();
30             int beginIndex = url.lastIndexOf(".htm");
31             if (beginIndex == url.length() - 4) {
32                 String newUrl = url.substring(0, beginIndex) + ".jsp";
33                 String contextRoot = request.getContextPath();
34                 beginIndex = newUrl.indexOf(contextRoot);
35                 if (beginIndex == 0) {
36                     newUrl = newUrl.substring(contextRoot.length());
37                     RequestDispatcher dispatcher = request.getRequestDispatcher(newUrl);
38                     dispatcher.forward(request, response);
39                     return;
40                 }
41             }
42         }
43         arg2.doFilter(arg0, response);
44     }
45 
46     @Override
47     public void init(FilterConfig arg0) throws ServletException {
48         // TODO Auto-generated method stub
49         
50     }
51 
52 }

UrlRewriterHelper