package com.gavin.filter;

import java.io.IOException;

import javax.servlet.Filter;

import javax.servlet.FilterChain;

import javax.servlet.FilterConfig;

import javax.servlet.ServletException;

import javax.servlet.ServletRequest;

import javax.servlet.ServletResponse;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import javax.servlet.http.HttpSession;

public class LoginFilter implements Filter {

    public void destroy() {

        // TODO Auto-generated method stub

    }

    public void doFilter(ServletRequest req, ServletResponse resp,

            FilterChain chain) throws IOException, ServletException {

        // TODO Auto-generated method stub

        HttpServletResponse response = (HttpServletResponse) resp;

        HttpServletRequest request = (HttpServletRequest) req;

        HttpSession session = request.getSession(true);

        String username = (String) session.getAttribute("username");//

        String url = request.getRequestURI();

        if (username == null || username.equals("")) {

            // 判断获取的路径不为空且不是访问登录页面或执行登录操作时跳转

            if (url != null && !url.equals("") && (url.indexOf("Login") < 0 && url.indexOf("login") < 0)) {

                response.sendRedirect("login.jsp");

                return;

            }

        }

        // 已通过验证，用户访问继续

        chain.doFilter(req, resp);

    }

    public void init(FilterConfig filterConfig) throws ServletException {

        // TODO Auto-generated method stub

    }

}

 <filter>

  <filter-name>loginFilter</filter-name>

  <filter-class>com.gavin.filter.LoginFilter</filter-class>

 </filter>

 <filter-mapping>

  <filter-name>loginFilter</filter-name>

  <url-pattern>/*</url-pattern>

 </filter-mapping>