java写入mysql中文乱码问题

String url = "jdbc:mysql://localhost:3306/mydatabase?useUnicode=true&characterEncoding=UTF-8";
String user = "username";
String password = "password";

try (Connection conn = DriverManager.getConnection(url, user, password)) {
    // 数据库操作
} catch (SQLException e) {
    e.printStackTrace();
}

CREATE DATABASE mydatabase CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
CREATE TABLE mytable (
    id INT PRIMARY KEY,
    name VARCHAR(255)
) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;

java -Dfile.encoding=UTF-8 -jar myapp.jar

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;

public class MySQLExample {
    public static void main(String[] args) {
        String url = "jdbc:mysql://localhost:3306/mydatabase?useUnicode=true&characterEncoding=UTF-8";
        String user = "username";
        String password = "password";

        try (Connection conn = DriverManager.getConnection(url, user, password)) {
            String sql = "INSERT INTO mytable (id, name) VALUES (?, ?)";
            try (PreparedStatement pstmt = conn.prepareStatement(sql)) {
                pstmt.setInt(1, 1);
                pstmt.setString(2, "中文");
                pstmt.executeUpdate();
                System.out.println("数据插入成功！");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}