通常情况下，java web项目都是通过过滤器来判断session是否失效。下面做了一个例子，实现过滤器验证用户的会话是否丢失。
web.xml中的配置：

1. <filter>  
   
2.         <filter-name>filter</filter-name>  
   
3.         <filter-class>com.zyujie
   
4. .common.LoginFilter</filter-class>  
   
5.     </filter>  
   
6.     <!-- servlet规范，不能以/*.jsp这样的结尾，写全，或者写成/app/*，这样的才行 -->  
   
7.     <filter-mapping>  
   
8.         <filter-name>filter</filter-name>  
   
9.         <url-pattern>/*</url-pattern>  
   
10.     </filter-mapping>  
    
11.       
    
12.     <session-config>   
    
13.         <session-timeout>1</session-timeout>  
    
14.     </session-config>  

复制代码

过滤器类：

1. package com.itheima.common;
   
2. 
   
3. import java.io.IOException;
   
4. import java.io.PrintWriter;
   
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.HttpServletResponse;
    
14. import javax.servlet.http.HttpSession;
    
15. 
    
16. public class LoginFilter implements Filter {
    
17. 
    
18. public void destroy() {
    
19. // TODO Auto-generated method stub
    
20. 
    
21. }
    
22. 
    
23. public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
    
24. // TODO Auto-generated method stub
    
25. HttpServletRequest request = (HttpServletRequest) req;
    
26. HttpServletResponse response = (HttpServletResponse) res;
    
27. HttpSession session = request.getSession();
    
28. // 如果session不为空，则可以浏览其他页面
    
29. String url = request.getServletPath();
    
30. System.out.println(url);
    
31. //这里判断目录，后缀名，当然也可以写在web.xml中，用url-pattern进行拦截映射
    
32. if ((!request.getServletPath().equals("/login.action"))
    
33. && (!request.getServletPath().equals("/login.jsp"))
    
34. && (!request.getServletPath().equals("/relogin.jsp"))
    
35. && (!request.getServletPath().equals("/jquery-1.8.0.min.js"))) {
    
36. System.out.println(request.getServletPath());
    
37. if (session.getAttribute("userInfo") == null) {
    
38. session.invalidate();
    
39. response.setContentType("text/html;charset=gb2312");
    
40. PrintWriter out = response.getWriter();
    
41. out.println("<script language='javascript' type='text/javascript'>");
    
42. out.println("alert('由于你长时间没有操作,导致Session失效!请你重新登录!');window.location.href='" + request.getContextPath() + "/relogin.jsp'");
    
43. out.println("</script>");
    
44. } else {
    
45. chain.doFilter(request, response);
    
46. }
    
47. } else {
    
48. chain.doFilter(request, response);
    
49. }
    
50. 
    
51. }
    
52. 
    
53. public void init(FilterConfig arg0) throws ServletException {
    
54. // TODO Auto-generated method stub
    
55. 
    
56. }
    
57. 
    
58. }

复制代码

【阳哥专栏】点点滴滴记录最真实的黑马
http://bbs.itheima.com/thread-117773-1-1.html
(出处: 黑马程序员IT技术论坛)

通常情况下，java web项目都是通过过滤器来判断session是否失效。下面做了一个例子，实现过滤器验证用户的会话是否丢失。
web.xml中的配置：

1. <filter>  
   
2.         <filter-name>filter</filter-name>  
   
3.         <filter-class>com.zyujie
   
4. .common.LoginFilter</filter-class>  
   
5.     </filter>  
   
6.     <!-- servlet规范，不能以/*.jsp这样的结尾，写全，或者写成/app/*，这样的才行 -->  
   
7.     <filter-mapping>  
   
8.         <filter-name>filter</filter-name>  
   
9.         <url-pattern>/*</url-pattern>  
   
10.     </filter-mapping>  
    
11.       
    
12.     <session-config>   
    
13.         <session-timeout>1</session-timeout>  
    
14.     </session-config>  

复制代码

过滤器类：

1. package com.itheima.common;
   
2. 
   
3. import java.io.IOException;
   
4. import java.io.PrintWriter;
   
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.HttpServletResponse;
    
14. import javax.servlet.http.HttpSession;
    
15. 
    
16. public class LoginFilter implements Filter {
    
17. 
    
18. public void destroy() {
    
19. // TODO Auto-generated method stub
    
20. 
    
21. }
    
22. 
    
23. public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
    
24. // TODO Auto-generated method stub
    
25. HttpServletRequest request = (HttpServletRequest) req;
    
26. HttpServletResponse response = (HttpServletResponse) res;
    
27. HttpSession session = request.getSession();
    
28. // 如果session不为空，则可以浏览其他页面
    
29. String url = request.getServletPath();
    
30. System.out.println(url);
    
31. //这里判断目录，后缀名，当然也可以写在web.xml中，用url-pattern进行拦截映射
    
32. if ((!request.getServletPath().equals("/login.action"))
    
33. && (!request.getServletPath().equals("/login.jsp"))
    
34. && (!request.getServletPath().equals("/relogin.jsp"))
    
35. && (!request.getServletPath().equals("/jquery-1.8.0.min.js"))) {
    
36. System.out.println(request.getServletPath());
    
37. if (session.getAttribute("userInfo") == null) {
    
38. session.invalidate();
    
39. response.setContentType("text/html;charset=gb2312");
    
40. PrintWriter out = response.getWriter();
    
41. out.println("<script language='javascript' type='text/javascript'>");
    
42. out.println("alert('由于你长时间没有操作,导致Session失效!请你重新登录!');window.location.href='" + request.getContextPath() + "/relogin.jsp'");
    
43. out.println("</script>");
    
44. } else {
    
45. chain.doFilter(request, response);
    
46. }
    
47. } else {
    
48. chain.doFilter(request, response);
    
49. }
    
50. 
    
51. }
    
52. 
    
53. public void init(FilterConfig arg0) throws ServletException {
    
54. // TODO Auto-generated method stub
    
55. 
    
56. }
    
57. 
    
58. }

复制代码

【阳哥专栏】点点滴滴记录最真实的黑马
http://bbs.itheima.com/thread-117773-1-1.html
(出处: 黑马程序员IT技术论坛)