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