十三、过滤器，监听器的常见应用

十三、过滤器，监听器的常见应用

  1. 用户登录之后，向Session中放入用户的数据

  2. 进入主页面的时候要判断用户是否已经登录；要求：在过滤器中实现

    @Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
    HttpServletRequest request = (HttpServletRequest) servletRequest;
    HttpServletResponse response = (HttpServletResponse) servletResponse;
    if (request.getSession().getAttribute(Constant.USER_SESSION) == null) {
        response.sendRedirect("/error.jsp");
​
    }
    filterChain.doFilter(request,response);
}

小项目代码实现：

  1. 编写工具类

    package com.lyh.util;
​
public class Constant {
    public final static String USER_SESSION = "USER_SESSION";
}

  2. 写登录页面

    <%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1>登录页面</h1>
<form action="/servlet/login" method="post">
    <input type="text" name="username">
    <input type="submit">
</form>
​
</body>
</html>

  3. 写登录页面的servlet（LoginServlet）

    package com.lyh.servlet;
​
import com.lyh.util.Constant;
​
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 {
        //获取前端请求参数
        String username = req.getParameter("username");
        //如果你输入admin就会登录成功
        if (username.equals("admin")){
            req.getSession().setAttribute(Constant.USER_SESSION,req.getSession().getId());
            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);
    }
}

  4. 在web.xml 中注册servlet镜像

    <!--    当/servlet/*路径下的所以运行的服务器都会被过滤-->
<filter>
    <filter-name>CharacterEncodingFilter</filter-name>
    <filter-class>com.lyh.filter.CharacterEncodingFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>CharacterEncodingFilter</filter-name>
    <url-pattern>/servlet/*</url-pattern>
</filter-mapping>
​
<servlet>
    <servlet-name>LoginServlet</servlet-name>
    <servlet-class>com.lyh.servlet.LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>LoginServlet</servlet-name>
    <url-pattern>/servlet/login</url-pattern>
</servlet-mapping>

  5. 登录成功，登录失败，跳转页面

    <%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1>登录成功</h1>
<a href="/servlet/logout">注销</a>
​
</body>
</html>
    <%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1>错误</h1>
<a href="/Login.jsp">返回登录页面</a>
</body>
</html>

  6. 注销会有一个按钮（对应一个Servlet，编写注销的Servlet为LogoutServlet）

    package com.lyh.servlet;
​
import com.lyh.util.Constant;
​
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 {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //这时我们还有会话记录
        if (req.getSession().getAttribute(Constant.USER_SESSION)!=null){
            //把会话记录销毁
            req.getSession().removeAttribute(Constant.USER_SESSION);
            //重定向到注册页面
            resp.sendRedirect("/Login.jsp");
        }else {
            //重定向到注册页面
            resp.sendRedirect("/Login.jsp");
        }
    }
​
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}
​

  7. 注销的servle（LogoutServlet）t，也在web.xml 中注册一下

    <servlet>
    <servlet-name>LogoutServlet</servlet-name>
    <servlet-class>com.lyh.servlet.LogoutServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>LogoutServlet</servlet-name>
    <url-pattern>/servlet/logout</url-pattern>
</servlet-mapping>

  8. 成功页面中注销点击就跳转到Login.jsp

    <%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1>登录成功</h1>
<a href="/servlet/logout">注销</a>
​
</body>
</html>

  9. 写过滤器Filter

    package com.lyh.filter;
​
import com.lyh.util.Constant;
​
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 request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;
        if (request.getSession().getAttribute(Constant.USER_SESSION) == null) {
            response.sendRedirect("/error.jsp");
​
        }
        filterChain.doFilter(request,response);
    }
​
    @Override
    public void destroy() {
​
    }
}

  10. 在web,xml中注册过滤器

    <filter>
    <filter-name>SysFilter</filter-name>
    <filter-class>com.lyh.filter.SysFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>SysFilter</filter-name>
    <url-pattern>/sys/*</url-pattern>
</filter-mapping>

  11. 补充一点：我们这个过滤器是过滤页面的，sys这个包下面的页面都会被我们的过滤器过滤一遍

  12.  
posted @ 2022-12-04 19:27  菜鸡前来  阅读(9)  评论(0)  编辑  收藏  举报