package com.cscy.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 {

	@Override

	public void destroy() {

		// TODO Auto-generated method stub

	}

	@Override

	public void doFilter(ServletRequest request, ServletResponse response,

			FilterChain chain) throws IOException, ServletException {

		// 获得在下面代码中要用的request,response,session对象

		HttpServletRequest servletRequest = (HttpServletRequest) request;

		HttpServletResponse servletResponse = (HttpServletResponse) response;

		HttpSession session = servletRequest.getSession();

		// 获得用户请求的URI

		String path = servletRequest.getRequestURI();

		//System.out.println(path);

		// 从session里取信息

		String name = (String) session.getAttribute("name");

		// 登陆页面无需过滤

		if(path.indexOf("/login.jsp") > -1) {

			chain.doFilter(servletRequest, servletResponse);

			return;   }

		// 判断如果没有取到信息,就跳转到登陆页面

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

			// 跳转到登陆页面

			servletResponse.sendRedirect("/dome/login.jsp");

			} else {

				// 已经登陆,继续此次请求

				chain.doFilter(request, response);

		}

	}

	@Override

	public void init(FilterConfig filterConfig) throws ServletException {

		// TODO Auto-generated method stub

	}

}

<!-- 配置 登陆 过滤器 -->

    <filter>

        <filter-name>login</filter-name>

        <filter-class>com.cscy.Filter.LoginFilter</filter-class>

    </filter>

    <filter-mapping>

        <filter-name>login</filter-name>

        <url-pattern>*.jsp</url-pattern>

<!--此处写/*代表浏览器地址栏中的所有请求都会被拦截 包括css文件和js文件 .jsp这是仅拦截以.jsp结尾的请求 -->

    </filter-mapping>