jelastic 数据库连接问题

如何使用 jdbc 连接到 jelastic 数据库

private static final String USER = "user";
    private static final String PASS = "pass";
    private static final String URL =  "jdbc:mysql://node30220-learning.j.dnr.kz/user";

    public static void main(String[] args) {
        Connection conn = null;
        Statement stmt = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            System.out.println("Connecting to database...");
            conn = DriverManager.getConnection(URL, USER, PASS);
            stmt = conn.createStatement();
            String sql;
            sql = "SELECT * FROM DUAL";
            ResultSet rs = stmt.executeQuery(sql);
            while (rs.next()) {

            }
            rs.close();
            stmt.close();
            conn.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        System.out.println("Goodbye!");
    }

一切似乎都是正确的，但我得到一个例外

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure