Java JDBC communications link failure after publishing

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Java

SQL

JDBC

google-app-engine

I have created my first API using java httpServlet on netbeans. After days working I could finally connect it to this mySQL googleCloud database and get results locally. But once this API is published on google cloud using appengine, below error was thrown:

 Error sqlException: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.

But the mySQL database is allowing access for all IPs, so what could be the problem? Below is my code:

public class HelloServlet extends HttpServlet {

    @Override
    public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {

        PrintWriter out = resp.getWriter();
        //out.println("Dear vistor, you are accessing my first project deployed on cloud. Thank you");

        try {
            if (SystemProperty.environment.value() == SystemProperty.Environment.Value.Production) {
    Class.forName("com.mysql.jdbc.GoogleDriver");
     
        url = "jdbc:google:mysql://test-123:myInstance/myDatabase?user=root&useUnicode=true&characterEncoding=UTF-8";
    } else {
        Class.forName("com.mysql.jdbc.Driver");
        url = "jdbc:mysql://1.2.3.4:3306/myDatabase?user=root&password=test";
    }
    Connection connection = DriverManager.getConnection(url);
    try (Statement statement = connection.createStatement()) {
                ResultSet resultSet = statement.executeQuery("select test from tableTest;");
                while (resultSet.next()) {
                    out.println(resultSet.getString(1));
                }
            }        
        }catch(Exception ex){
            out.println("Exception:" + ex.toString());
        }
    }   
}

Could it be because of my projectD (because it has special character) ? Please help me

What I have tried:

I have seen this multiple times and I did the exact solution like here and here