24. 过滤器使用

登录: 用户登录之后才能进入主页!用户注销后就不能进入主页了!

1. 用户登录之后，向Sesison中放入用户的数据

   package com.karl.servlet;
   
   import javax.servlet.ServletException;
   import javax.servlet.http.HttpServlet;
   import javax.servlet.http.HttpServletRequest;
   import javax.servlet.http.HttpServletResponse;
   import java.io.IOException;
   
   public class LoginServlet extends HttpServlet {
       @Override
       protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
           doPost(req, resp);
       }
   
       @Override
       protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
           //获取前端请求的参数
           String username = req.getParameter("username");
           if (username.equals("admin")){//登录成功
               req.getSession().setAttribute("USER_SESSION",req.getSession().getId());
               resp.sendRedirect(req.getContextPath()+"/sys/success.jsp");
           }else {
               resp.sendRedirect(req.getContextPath()+"/error.jsp");
           }
       }
   }
   

2. i进入主页的时候要判断用户是否已经登录; 要求:在过滤器中实现!

   package com.karl.filter;
   
   import javax.servlet.*;
   import javax.servlet.http.HttpServletRequest;
   import javax.servlet.http.HttpServletResponse;
   import java.io.IOException;
   
   public class SysFilter implements Filter {
       @Override
       public void init(FilterConfig filterConfig) throws ServletException {
   
       }
   
       @Override
       public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
           HttpServletRequest servletReq = (HttpServletRequest)servletRequest;
           HttpServletResponse servletResp = (HttpServletResponse) servletResponse;
   
           if(null == servletReq.getSession().getAttribute("USER_SESSION")){
               servletResp.sendRedirect(servletReq.getContextPath()+"/error.jsp");
           }
   
           filterChain.doFilter(servletRequest, servletResponse);
       }
   
       @Override
       public void destroy() {
   
       }
   }
   

3. 注销

   package com.karl.servlet;
   
   import javax.servlet.ServletException;
   import javax.servlet.http.HttpServlet;
   import javax.servlet.http.HttpServletRequest;
   import javax.servlet.http.HttpServletResponse;
   import java.io.IOException;
   import java.util.HashMap;
   
   public class LogoutServlet extends HttpServlet {
       @Override
       protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
           Object user_session = req.getSession().getAttribute("USER_SESSION");
           if (null != user_session){
               req.getSession().removeAttribute("USER_SESSION");
               resp.sendRedirect(req.getContextPath()+"/index.jsp");
           }else {
               resp.sendRedirect(req.getContextPath()+"/index.jsp");
           }
   
       }
   
       @Override
       protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
           doGet(req, resp);
       }
   }