JavaWeb【Filter】

11、Filter

Filter: filter, used to filter website data

• Dealing with Chinese garbled characters
• Login authentication

Filter development steps:

1. Guide package

2. Write a filter

package com.jiang.filter;

import javax.servlet.*;
import java.io.IOException;

public class CharacterEncodingFilter implements Filter {
    //初始化: web服务器启动，就已经初始化了，随时等待过滤对象出现
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("CharacterEncodingFilter初始化");
    }
    //Chain: 链
    /*
    * 1.过滤中的所有代码，在过滤特定请求的时候都会执行
    * 2.必须要让过滤器继续通行
    * filterChain.doFilter(servletRequest,servletResponse);
    * */

    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        servletRequest.setCharacterEncoding("utf-8");
        servletResponse.setCharacterEncoding("utf-8");
        servletResponse.setContentType("text/html;charset=UTF-8");
        System.out.println("CharacterEncodingFilter执行前");
        filterChain.doFilter(servletRequest,servletResponse);//让我们的请求继续走，如果不写，程序到这里就被拦截停止
        System.out.println("CharacterEncodingFilter执行后");
    }

    //销毁
    public void destroy() {
        System.out.println("CharacterEncodingFilter销毁");

    }
}

package com.jiang.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 ShowServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        /*resp.setCharacterEncoding("utf-8");*/
        resp.getWriter().write("你好，世界！");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        super.doPost(req, resp);
    }
}

<?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"
         metadata-complete="true">

    <servlet>
        <servlet-name>ShowServlet</servlet-name>
        <servlet-class>com.jiang.servlet.ShowServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>ShowServlet</servlet-name>
        <url-pattern>/servlet/show</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>ShowServlet</servlet-name>
        <url-pattern>/show</url-pattern>
    </servlet-mapping>
    
    <filter>
        <filter-name>CharacterEncodingFilter</filter-name>
        <filter-class>com.jiang.filter.CharacterEncodingFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>CharacterEncodingFilter</filter-name>
        <!--只要是/servlet的任何请求，都会经过这个过滤器-->
        <url-pattern>/servlet/*</url-pattern>
    </filter-mapping>

</web-app>

 The user can only enter the homepage after logging in, and cannot enter the homepage if the user logs out

1. After the user logs in, put the user's data into the Session

2. To enter the homepage, it is necessary to judge whether the user has logged in; requirement: implement in the filter

Filter: SysFilter.java

package com.jiang.filter;

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 servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

        //ServletRequest  HttpServletRequest
        //下转型对象，在过滤器中子类才能够调用session
        HttpServletRequest request= (HttpServletRequest) servletRequest;
        HttpServletResponse response= (HttpServletResponse) servletResponse;
        if(request.getSession().getAttribute("USER_SESSION")==null){
            response.sendRedirect("/error.jsp");
        }
        filterChain.doFilter(request,response);
    }

    public void destroy() {

    }
}

Log in:

package com.jiang.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 {

        //获取前端请求的参数
        String username = req.getParameter("username");
        if(username.equals("admin")){
            req.getSession().setAttribute("USER_SESSION",req.getSession().getId());
            resp.sendRedirect("/sys/success.jsp");
        }else{
            resp.sendRedirect("/error.jsp");
        }


    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        super.doPost(req, resp);
    }
}

<%--
  Created by IntelliJ IDEA.
  User: Administrator
  Date: 2022/4/1 0001
  Time: 12:20
  To change this template use File | Settings | File Templates.
--%>
<%@ 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="get">
    <input type="text" name="username">
    <input type="submit">
</form>
</body>
</html>

Logout after successful login:

package com.jiang.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 {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        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 {
        super.doPost(req, resp);
    }
}

 

<%--
  Created by IntelliJ IDEA.
  User: Administrator
  Date: 2022/4/1 0001
  Time: 11:46
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>

<h1>主页</h1>

<a href="/servlet/logout">注销</a>

</body>
</html>

login error

<%--
  Created by IntelliJ IDEA.
  User: Administrator
  Date: 2022/4/1 0001
  Time: 12:20
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1>错误</h1>
<h3>没有权限，用户名错误</h3>
<a href="/login.jsp">返回登录页面</a>
</body>
</html>

 constant util

package com.jiang.util;

public class Constant {
    public static String USER_SESSION="USER_SESSION";
}

Finally, don’t forget to configure 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"
         metadata-complete="true">
    <servlet>
    <servlet-name>LoginServlet</servlet-name>
    <servlet-class>com.jiang.servlet.LoginServlet</servlet-class>
</servlet>
    <servlet-mapping>
        <servlet-name>LoginServlet</servlet-name>
        <url-pattern>/servlet/login</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>LogoutServlet</servlet-name>
        <servlet-class>com.jiang.servlet.LogoutServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>LogoutServlet</servlet-name>
        <url-pattern>/servlet/logout</url-pattern>
    </servlet-mapping>
    
    <filter>
        <filter-name>SysFilter</filter-name>
        <filter-class>com.jiang.filter.SysFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>SysFilter</filter-name>
        <url-pattern>/sys/*</url-pattern>
    </filter-mapping>


</web-app>

 

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https://www.bilibili.com/video/BV12J411M7Sj?p=25&spm_id_from=pageDriver