JavaWeb【Filter】

11、Filter

Filter：过滤器，用来过滤网站的数据

• 处理中文乱码
• 登录验证

Filter开发步骤：

1.导包

2.编写过滤器

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>

 用户登录之后才能够进入主页，如果用户注销则无法进入主页

1、用户登录之后，向Session中放入用户的数据

2、进入主页的适合要判断用户是否已经登录；要求：在过滤器中实现

过滤器：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() {

    }
}

登录：

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>

登陆成功后注销：

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>

登录错误

<%--
  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>

 常量util

package com.jiang.util;

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

最后别忘记配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