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