com.mysql.jdbc.exceptions.jdbc4.CommunicationsExce

我的连接到MySQL数据库的程序运行正常。然后，在不更改用于建立连接的任何代码的情况下，我得到了以下异常：

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

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server. 发生了什么？

用于获取连接的代码：

private static Connection getDBConnection() throws SQLException, InstantiationException, IllegalAccessException, ClassNotFoundException { String username = "user"; String password = "pass"; String url = "jdbc:mysql://www.domain.com:3306/dbName?connectTimeout=3000";

Class.forName("com.mysql.jdbc.Driver");
Connection conn = DriverManager.getConnection(url, username, password);
return conn;

}