import java.sql.*;
import java.sql.DriverManager;
public final class MySqlConnect {

    public Connection conn;
    private Statement statement;
    public static MySqlConnect db;
    private MySqlConnect() {
        String url= "jdbc:mysql://localhost:3306/";
        String dbName = "test_db?serverTimezone=Europe/Moscow";
        String driver = "com.mysql.cj.jdbc.Driver";
        String userName = "test_user";
        String password = "test_password";
        try {
            Class.forName(driver);
            this.conn =DriverManager.getConnection(url+dbName,userName,password);
        }
        catch (Exception sqle) {
            sqle.printStackTrace();
        }
    }
    public static synchronized MySqlConnect getDbCon() {
        if ( db == null ) {
            db = new MySqlConnect();
        }
        return db;
    }
    public ResultSet query(String query) throws SQLException{
        statement = db.conn.createStatement();
        ResultSet res = statement.executeQuery(query);
        return res;
    }

    public int insert(String insertQuery) throws SQLException {
        statement = db.conn.createStatement();
        int result = statement.executeUpdate(insertQuery);
        return result;
    }
}

System.out.print("Возможность выборки из базы: " + !(MySqlConnect.getDbCon().query("SELECT 1").isClosed()));