登录页面JDBC案例

package com.study;
public class User {
    private String username;
    private String password;
    public User(String username, String password) {
        this.username = username;
        this.password = password;
    }
    public User() {
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
}

driverClassName=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://localhost:3306/db?serverTimezone=GMT%2B8&useOldAliasMetadataBehavior=true
username=root
password=12345
# ???????
initialSize=5
# ?????
maxActive=10
# ??????
maxWait=3000

package com.study;
import com.alibaba.druid.pool.DruidDataSourceFactory;
import javax.sql.DataSource;
import java.io.FileInputStream;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;
import java.util.Scanner;
public class Login {
    // 查询所有用户
    public static ArrayList<User> SelectAll(Connection conn) throws Exception {
        //2. 定义SQL
        String sql = "select * from users;";
        //3. 获取pstmt对象
        PreparedStatement pstmt = conn.prepareStatement(sql);
        //4. 设置参数
        //5. 执行SQL
        ResultSet rs = pstmt.executeQuery();
        //6. 处理结果 List<User> 封装User对象，装载List集合
        User user = null;
        ArrayList<User> users = new ArrayList<>();
        while (rs.next()){
            // 获取数据
            String username = rs.getString("username");
            String userpwd = rs.getString("userpwd");
//            System.out.println(username + " " + userpwd);
            users.add(new User(username, userpwd)); // 每次都需要创建一个新对象
            // 不然就是浅拷贝了 会导致每次的数据一样的
        }
//         System.out.println(users);
//        System.out.println(users.size());
        //7. 释放资源
        rs.close();
        pstmt.close();
        return users;
    }
    public static void Add(Connection conn, User user) throws Exception {
        // 接收页面提交的参数
        String username = user.getUsername();
        String password = user.getPassword();
        //2. 定义SQL
        String sql = "insert into users(username, userpwd) values(?,?);";
        //3. 获取pstmt对象
        PreparedStatement pstmt = conn.prepareStatement(sql);
        //4. 设置参数
        pstmt.setString(1,username);
        pstmt.setString(2,password);
        //5. 执行SQL
        int count = pstmt.executeUpdate(); // 影响的行数
        //6. 处理结果
        System.out.println(count > 0);
        //7. 释放资源
        pstmt.close();
    }
    public static void main(String[] args) throws Exception{
        Properties prop = new Properties();
        prop.load(new FileInputStream("src/druid.properties"));
        //4. 获取连接池对象
        DataSource dataSource = DruidDataSourceFactory.createDataSource(prop);
        //5. 获取数据库连接 Connection
        Connection conn = dataSource.getConnection();
        ArrayList<User> users = SelectAll(conn);
        boolean flag = false; // 判断是否登录成功
        System.out.println("首先演示登录");
        Scanner in = new Scanner(System.in);
        System.out.print("请输入你的账号：");
        String username = in.nextLine();
//        System.out.println(username);
        System.out.print("请输入你的密码：");
        String password = in.nextLine();
//        System.out.println(password);
        for (int i = 0; i < users.size(); i++) {
            User user = users.get(i);
//            System.out.println(user.getUsername() + " " + user.getPassword());
            if (username.equals(user.getUsername()) && password.equals(user.getPassword())){
                System.out.println("登录成功");
                flag = true;
                break;
            }
        }
        if (flag == false){
            System.out.println("登录失败");
        }
        System.out.println("现在演示注册");
        System.out.print("请输入你的新账号：");
        username = in.nextLine();
        System.out.print("请输入你的新密码：");
        password = in.nextLine();
        User user = new User(username, password);
        Add(conn, user);
    }
}