在MySQL数据库中创建一个test_users数据表，添加3个字段：id，user，password。并录入几条记录。
定义一个login.html,里边定义两个请求字段：user，password。发送请求到loginServlet
在创建一个LoginServlet(需要继承自HttpServlet，并重写其doPost方法)，
在其中获取请求的user，password
利用JDBC从test_users中查询有没有和页面输入的user，password对应的记录
若有，响应Hello：xxx，若没有，响应Sorry：xxx xxx为user。
数据库：
JSP：
<%--
Created by IntelliJ IDEA.
User: dell
Date: 2019/5/26
Time: 17:08
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>
<form action="LoginServlet1" method="POST">
姓名：<input type="text" name="username">
密码：<input type="password" name="password">
<input type="submit" value="submit">
</form>
</body>
</html>
HttpServlet：
package com.demo.javaweb;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.*;
public class LoginServlet1 extends HttpServlet {
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String username = req.getParameter("username");
String password = req.getParameter("password");
String sql = "select count(id) from test_users where user=? and password=?";
Connection conn = null;
PreparedStatement preparedStatement = null;
ResultSet resultSet = null;
try {
Class.forName("com.mysql.cj.jdbc.Driver");
String url = "jdbc:mysql://localhost:3306/yang?serverTimezone=UTC";
String user = "root";
String password1 = "password";
conn = DriverManager.getConnection(url,user,password1);
preparedStatement = conn.prepareStatement(sql);
preparedStatement.setString(1,username);
preparedStatement.setString(2,password);
resultSet = preparedStatement.executeQuery();
PrintWriter printWriter = resp.getWriter();
if (resultSet.next()){
int count = resultSet.getInt(1);
if (count>0){
printWriter.print("Hello! "+ username);
}else{
printWriter.print("Sorry " + username);
}
}
} catch (Exception e) {
e.printStackTrace();
}finally {
if (resultSet!=null){
try {
resultSet.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (preparedStatement!=null){
try {
preparedStatement.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (conn!=null){
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
}
Web.xml
<servlet>
<servlet-name>LoginServlet1</servlet-name>
<servlet-class>com.demo.javaweb.LoginServlet1</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>LoginServlet1</servlet-name>
<url-pattern>/LoginServlet1</url-pattern>
</servlet-mapping>
运行：
