Java gateway server only support RMI protocol, but WebLogic doesn't support RMI. It's necessary to use IIOP protocol.
http://docs.oracle.com/cd/E13222_01/wls/docs90/jmx/accessWLS.html

Also, there is a difference in environment parameter of JMXConnectorFactory.connect method for WebLogic JMX

Current java gateway code:

env = new HashMap<String, String[]>();
env.put(JMXConnector.CREDENTIALS, new String[]

);

Sample code from WebLogic documentation:

Hashtable h = new Hashtable();
h.put(Context.SECURITY_PRINCIPAL, username);
h.put(Context.SECURITY_CREDENTIALS, password);
h.put(JMXConnectorFactory.PROTOCOL_PROVIDER_PACKAGES, "weblogic.management.remote");