环境准备

1、安装JDK

2、安装IDEA

3、安装数据库（如MySQL）

创建数据库和表

1、打开MySQL，创建数据库和表

CREATE DATABASE test;
USE test;
CREATE TABLE user (
    id INT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(50) NOT NULL,
    age INT NOT NULL
);

添加数据

1、向表中插入数据

INSERT INTO user (name, age) VALUES ('张三', 25);
INSERT INTO user (name, age) VALUES ('李四', 30);
INSERT INTO user (name, age) VALUES ('王五', 35);

Java代码实现

1、导入相关依赖

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysqlconnectorjava</artifactId>
    <version>8.0.26</version>
</dependency>

2、编写Java代码连接数据库并查询数据

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
public class Main {
    public static void main(String[] args) {
        try {
            // 加载驱动
            Class.forName("com.mysql.cj.jdbc.Driver");
            // 获取连接
            Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/test?useSSL=false&allowPublicKeyRetrieval=true&serverTimezone=UTC", "root", "123456");
            // 创建Statement对象
            Statement statement = connection.createStatement();
            // 执行查询
            ResultSet resultSet = statement.executeQuery("SELECT * FROM user");
            // 处理结果集
            while (resultSet.next()) {
                int id = resultSet.getInt("id");
                String name = resultSet.getString("name");
                int age = resultSet.getInt("age");
                System.out.println("ID: " + id + ", Name: " + name + ", Age: " + age);
            }
            // 关闭资源
            resultSet.close();
            statement.close();
            connection.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

运行结果

ID: 1, Name: 张三， Age: 25
ID: 2, Name: 李四， Age: 30
ID: 3, Name: 王五， Age: 35