public class Main extends JavaPlugin implements Listener {

    private Connection connection;
    private String host, database, username, password;
    private int port;

@Override
    public void onEnable() {
        host = "localhost";
        port = 3306;
        database = "";
        username = "root";
        password = "";
        try {
            openConnection();
            Statement statement = connection.createStatement();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
}
    public void openConnection() throws SQLException, ClassNotFoundException {
        if (connection != null && !connection.isClosed()) {
            return;
        }

        synchronized (this) {
            if (connection != null && !connection.isClosed()) {
                return;
            }
            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection("jdbc:mysql://" + this.host+ ":" + this.port + "/" + this.database, this.username, this.password);
        }
    }
}