I'll first ask my simple networking question and then explain how I got there...
Q. Using JME 3.1, when a network client connects to a server and does client.start(), how does it know that everything has settled down from creating the connection and setting up the serializer classes so that it can safely send its first message?
Explanation of how I got here, purely for those that may be interested:
My 'game' started just as a bit of tinkering about 6 months ago with JME 3.0 and Java, neither of which I'd used before, but many years ago I was involved with a few 3D games. Without going into the gory details, it morphed into a distributed system with multiple servers and multiple clients each of which may or may not be on the same PC. After a bit of trouble with the way it handled serialization I got it all working, but I wanted to use Java 8. This meant JME 3.1 was required. That broke my setup in major ways.
Firstly, the clients no longer register classes for serialization.... easy fix, just don't do it on the client.
Secondly, it doesn't like more than one server on a JVM, which was a big problem for me, but I've overcome this with a hastily written message broker; every message now has to make 2 hops but it turns out this has other advantages including that I can now monitor all the messages using the broker.
Finally, under 3.0 both server and client had to register serialization classes so the serialization was guaranteed already set up before the first message was sent, but on 3.1 you only code it on the server and the server informs the client of what can be serialized and sent when the connection is made. However, this takes some time and I was left scratching my head for a while as to why my client failed to send when run normally but was happy when running in the debugger. Once I twigged that the serialization hadn't been initialised fully, my simple solution was to put in a 1 second delay. However, I seek the proper way of doing it.
I may also have got the wrong end of stick about the networking so any corrections/clarifications are also welcome.