package cn.techtiger.struts;
import java.io.IOException;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class OnlineFilter
extends HttpServlet
implements javax.servlet.Filter {
private static final long serialVersionUID = 1L;
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
throws ServletException, IOException { HttpServletRequest req = (HttpServletRequest) request; HttpServletResponse res = (HttpServletResponse) response; HttpSession session = req.getSession();
if (session.getAttribute(
"user") ==
null) { System.out.println(
"user has logged in."); res.sendRedirect(
"error.jsp");
return; }
else { chain.doFilter(request, response); } }
public void init(FilterConfig filterConfig) { System.out.println(
"OnlineFilter initialized."); }
public void destroy() { System.out.println(
"OnlineFilter destroied"); } } <hr/> 这是web.xml的配置 <filter> <filter-name>onlineFilter</filter-name> <filter-
class>cn.techtiger.struts.OnlineFilter</filter-
class> </filter> <filter-mapping> <filter-name>onlineFilter</filter-name> <url-pattern>u_*.jsp</url-pattern> </filter-mapping> 注意：url-pattern是匹配哪些url要通过这个filter过滤，目前配置就是验证以u_开头的.jsp文件。 <hr/> 这是几个测试的jsp文件 testFilter.jsp <%@ page pageEncoding=
"UTF-8" %> <html> <body> <% session.setAttribute(
"user",
"techtiger"); %> <form action=
"u_login.jsp" method=
"post" > <input type=submit value=
"测试用户登录"> </form> </body> </html> u_login.jsp <%@ page pageEncoding=
"UTF-8" %> <html> <body> 用户已经登录，所以可以看到此页面 <br> 用户退出后，再访问此页面就访问不到了，而是直接转向了error.jsp 在OnlineFilter.java中指定的。 <form action=
"exit.jsp" method=
"post" > <input type=submit value=
"用户退出"> </form> </body> </html> exit.jsp <% session.removeAttribute(
"user"); response.sendRedirect(
"u_login.jsp"); %> error.jsp <%@ page pageEncoding=
"UTF-8" %> <% out.println(
"错误"); %> <hr/> 测试的jsp文件，起始业testFilter.jsp，此页已经创建了session，所以当访问u_login.jsp时，通过了filter的过滤，点击退出，exit.jsp 删除掉了session attribute “user”(注意：exit.jsp不经过filter过滤)，然后返回u_login.jsp，此时已经没有session attribute “user"，所以filter把它跳转至error.jsp
