javaweb学习23：Filter实现权限拦截

javaweb学习23：Filter实现权限拦截

• 监听器：GUI编程中经常使用；

• 过滤器：重点理解过滤器；

 

• 需求：

  • 用户登录后才能进入主页！

  • 用户注销后就不能进入主页了！

  • 核心：Session的用法；

 

• 思路：

  • 1，用户登录之后，向Session中放入用户的数据；

  • 2，进入主页的时候，要判断用户是否已经登录；要求：过滤器实现；

 

 

• 代码案例：login.jsp

  <%@ page contentType="text/html;charset=UTF-8" language="java" %>
  <html>
  <head>
      <title>Title</title>
  </head>
  <body>
  ​
  <form action="/servlet/login" method="post">
      用户名：<input type="text" name="username">
      <br>
      <input type="submit">
  </form>
  ​
  </body>
  </html>

• 代码案例：success.jsp

  <%@ page contentType="text/html;charset=UTF-8" language="java" %>
  <html>
  <head>
      <title>成功页面</title>
  </head>
  <body>
  <%--
  <%
      Object user_session = request.getSession().getAttribute("USER_SESSION");
      if(user_session==null){
          response.sendRedirect("/login.jsp");
      }
  %>--%>
  ​
  ​
  <h1>主页</h1>
  ​
  <p>
      <a href="/servlet/logout">注销</a>
  </p>
  ​
  </body>
  </html>

• 代码案例：error.sjp

  <%@ page contentType="text/html;charset=UTF-8" language="java" %>
  <html>
  <head>
      <title>错误</title>
  </head>
  <body>
  ​
  <h1>错误</h1>
  ​
  <p>
      <a href="/login.jsp">返回首页</a>
  </p>
  ​
  </body>
  </html>
  ​

• 代码案例：登录Servlet

  public class LoginServlet extends HttpServlet {
  ​
      @Override
      protected 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")){//登录成功
              req.getSession().setAttribute("USER_SESSION",req.getSession().getId());
              //登录成功之后，重定向到成功页面
              resp.sendRedirect("/sys/success.jsp");
          }else{//登录失败
  ​
              resp.sendRedirect("/error.jsp");
  ​
          }
  ​
  ​
      }
  ​
      @Override
      protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
          doGet(req, resp);
      }
  }
  ​
  ​

• 代码案例：退出Servlet

  ​
  public class LogoutServlet  extends HttpServlet {
  ​
      @Override
      protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  ​
          //移除登录的那个session即可实现推出操作：
          Object user_session = req.getSession().getAttribute("USER_SESSION");
          if(user_session !=null ){
              req.getSession().removeAttribute("USER_SESSION");
              resp.sendRedirect("/login.jsp");
          }else{
              resp.sendRedirect("/login.jsp");
          }
  ​
      }
  ​
      @Override
      protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
          doGet(req, resp);
      }
  }

• 代码案例：过滤器

  ​
  /**
   * 过滤器
   */
  public class SysFilter implements Filter {
  ​
  ​
      public void init(FilterConfig filterConfig) throws ServletException {
  ​
      }
  ​
      public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
          System.out.println("开始处理...");
          HttpServletRequest req=(HttpServletRequest)request;
          HttpServletResponse resp=(HttpServletResponse)response;
          Object username = req.getSession().getAttribute("USER_SESSION");
  ​
          if(username == null){
              resp.sendRedirect("/error.jsp");
          }
  ​
          chain.doFilter(request,response);//放行
          System.out.println("结束处理...");
      }
  ​
      public void destroy() {
  ​
      }
  }
  ​

• 代码案例：web.xml

  <?xml version="1.0" encoding="UTF-8"?>
  <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
           version="4.0">
      
  ​
      <!--注册一个Servlet-->
      <servlet>
          <servlet-name>loginServlet</servlet-name>
          <servlet-class>com.servlet.LoginServlet</servlet-class>
      </servlet>
  ​
      <servlet-mapping>
          <servlet-name>loginServlet</servlet-name>
          <url-pattern>/servlet/login</url-pattern>
      </servlet-mapping>
  ​
  ​
      <!--注册一个Servlet-->
      <servlet>
          <servlet-name>logoutServlet</servlet-name>
          <servlet-class>com.servlet.LogoutServlet</servlet-class>
      </servlet>
  ​
      <servlet-mapping>
          <servlet-name>logoutServlet</servlet-name>
          <url-pattern>/servlet/logout</url-pattern>
      </servlet-mapping>
  ​
  ​
      <!--配置Filter过滤器-->
      <filter>
          <filter-name>SysFilter</filter-name>
          <filter-class>com.lesson.demo01.SysFilter</filter-class>
      </filter>
  ​
      <filter-mapping>
          <filter-name>SysFilter</filter-name>
          <!--只要是/servlet/的任何请求，都会经过这个过滤器 -->
          <url-pattern>/sys/*</url-pattern>
      </filter-mapping>
  ​
  ​
  </web-app>
  ​