错误：com.mysql.jdbc.exceptions.jdbc4.CommunicationsException：通信链接失败

Question

ERROR MESSAGE in SERVER

    [2019-01-07 09:44:02] ERROR 
    :com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications 
    link failure
    [2019-01-07 09:44:02]
    [2019-01-07 09:44:02] The last packet sent successfully to the server was 0 
    milliseconds ago. The driver has not received any packets from the server.

But testing in local.. No problem.. No Error message..

1. Commit libraries..

    mysql-connector-java-5.1.47-bin.jar mysql-connector-java-5.1.47.jar 

2. JDBC URL ALTER

    jdbc:mysql://IP:3306/ID -> jdbc:mysql://IP:3306/ID?autoReconnect=true 

   Changed Error Message..

    [2019-01-07 11:04:32] Error : com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server. Attempted reconnect 3 times. Giving up. 

ControlDAO.java

private final static String DRIVER = "com.mysql.jdbc.Driver";
private final static String URL = 
"jdbc:mysql://IP:3306/ID?autoReconnect=true;

public static void CsNumberCheck(String s) { 
    try {           
        Class.forName(DRIVER);

        conn = DriverManager.getConnection(URL, "ID", "PW");
        System.out.println(conn);

        stat = conn.createStatement();

        int result = 0;

        sql = Query;

        rs = stat.executeQuery(sql);

        while ( rs.next() ) {
            result = rs.getInt(1);
        }

        rs.close();
        stat.close();

        System.out.println(result);

        CsNumberResult(result, OrangeEmail);
    }
    catch (ClassNotFoundException e) {
        System.out.println("Driver Loading Failed..");
    }
    catch (SQLException e) {
        System.out.println("Error : " + e);
    }
}

Socket.java

     ControlDAO.CsNumberCheck(s);

• But nothing result about "Sysout", Only Error Message....

Answer 1

Check your windows services to see if your MySQL server is running. That might be a probable cause. If it's not, start it and try to reconnect.