Modified to skip registering the message classes if they are

already registered.  This avoids one of the issues of a client
running in the same JVM as a server that already registered these
classes.  This was the easy fix.

jme3-networking/src/main/java/com/jme3/network/service/serializer/ClientSerializerRegistrationsService.java

@@ -39,6 +39,8 @@ import com.jme3.network.message.SerializerRegistrationsMessage;
 import com.jme3.network.serializing.Serializer;
 import com.jme3.network.service.AbstractClientService;
 import com.jme3.network.service.ClientServiceManager;
+import java.util.logging.Level;
+import java.util.logging.Logger;
 
 
 /**
@@ -48,14 +50,21 @@ import com.jme3.network.service.ClientServiceManager;
  */
 public class ClientSerializerRegistrationsService extends AbstractClientService 
                                                   implements MessageListener<Client> {
+                                                  
+    static final Logger log = Logger.getLogger(SerializerRegistrationsMessage.class.getName());
 
     @Override
     protected void onInitialize( ClientServiceManager serviceManager ) {
-        // Make sure our message type is registered
-        // This is the minimum we'd need just to be able to register
-        // the rest... otherwise we can't even receive this message.
-        Serializer.registerClass(SerializerRegistrationsMessage.class);
-        Serializer.registerClass(SerializerRegistrationsMessage.Registration.class);
+    
+        // Make sure our message type is registered if it isn't already
+        if( Serializer.getSerializer(SerializerRegistrationsMessage.class, false) == null ) {
+            // This is the minimum we'd need just to be able to register
+            // the rest... otherwise we can't even receive this message.
+            Serializer.registerClass(SerializerRegistrationsMessage.class);
+            Serializer.registerClass(SerializerRegistrationsMessage.Registration.class);
+        } else {
+            log.log(Level.INFO, "Skipping registration of SerializerRegistrationsMessage.");
+        }
         
         // Add our listener for that message type
         serviceManager.getClient().addMessageListener(this, SerializerRegistrationsMessage.class);