用filter实现验证登录

package com.mr.filter; import javax.servlet.*; import javax.servlet.http.*; import java.io.*; import java.util.*; @SuppressWarnings("unused") public class FilterLogin extends HttpServlet implements Filter { /** * */ private static final long serialVersionUID = 3149440487310586051L; private FilterConfig filterConfig; public void init(FilterConfig filterConfig) throws ServletException { this.filterConfig = filterConfig; } public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws ServletException, IOException { HttpSession session=((HttpServletRequest)request).getSession(); response.setCharacterEncoding("gb2312"); //响应客户端类型 if(session.getAttribute("user")==null){ //判断session中是否有user这个对象 PrintWriter out=response.getWriter(); //创建一个输出流 //如果为空则通过javaScript脚本出输出提示并跳转到index.jsp页面 out.print("<script language=javascript>alert('您还没有登录！！！');window.location.href='../index.jsp';</script>"); }else{ filterChain.doFilter(request, response);//否则继续执行 } } public void destroy() { } }