过滤器常见应用——实现登陆注销

用户登陆之后才能进入主页！用户注销后就不能进入主页了

用户登陆之后，向Session中放入用户的数据进入主页的时候要判断用户是否已经登陆；要求：在过滤器中实现

这个小项目，用到的JSP页面有：登陆界面，首页，异常界面，登陆成功

登陆成功界面我是放在web下面的sys文件夹中

用到的Servlet有：LoginServlet、LogoutServlet

LoginServlet.java

package com.godairo.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 {@Overrideprotected void doGet(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")){ //登陆成功req.getSession().setAttribute("USER_SESSION",req.getSession().getId());resp.sendRedirect("/sys/success.jsp");}else {//登陆失败resp.sendRedirect("/error.jsp");}}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);}}

LogoutServlet.java

package com.godairo.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 LogoutServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {Object user_session = request.getSession().getAttribute("USER_SESSION");if (user_session!=null){request.getSession().removeAttribute("USER_SESSION");response.sendRedirect("/Login.jsp");}else{response.sendRedirect("/Login.jsp");}}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);}}

Login.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %> 登陆

index.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %> 当前有<%=this.getServletConfig().getServletContext().getAttribute("OnlineCount")%>人在线

error.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %> 错误页面！ 没有权限，用户名错误

返回登陆页面

success.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %> 主页

注销

web.xml 

LoginServlet com.godairo.servlet.LoginServlet LoginServlet /servlet/login LogoutServlet com.godairo.servlet.LogoutServlet LogoutServlet /servlet/logout

首次运行测试

 

 

到这里，进行的很成功，但是存在一个问题，我们注销后，返回到登陆界面，我们把登陆成功的路径复制到地址栏去运行，还是会进入登陆成功界面，这就说明，还没进行登陆就可以直接进入到登陆成功界面，这下我们需要进行拦截。 

SysFilter.java

package com.godairo.filter;import com.godairo.util.Constant;import javax.servlet.*;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;public class SysFilter implements Filter {public void init(FilterConfig filterConfig) throws ServletException {}public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {HttpServletRequest request1 = (HttpServletRequest) request;HttpServletResponse response1 = (HttpServletResponse) response;if (request1.getSession().getAttribute(Constant.USER_SESSION)==null){response1.sendRedirect("/error.jsp");}chain.doFilter(request,response);}public void destroy() {}}

这里有个点我们需要注意一下，在getSession的时候，也就是拿到用户信息的时候，其实可以

request1.getSession().getAttribute("USER_SESSION")

但是规范化的话，一搬这么多Session，都会存储在类里，也就是常量里，如果公司需要名字的话，这里就不用一个个去改了，而是在常量类里去改一下就好了