Hi Trustin, I have made all the changes (about an half hour so quite quickly), and it is really perfect and more clear now. So I think your original idea from the first mail (splitting MessageHandler by adding addSentMessageHandler and addReceivedMessageHandler) and the given implementation were the good one (as always) !!! I really thank you and it gives me the opportunity to correct the logic of my program !
I feel like the idea to make final those functions (messageSent and messageReceived) in DemuxingIoHandler should be done in order to prevent some users (like me) to override them and so breaking the Mina's logic. Again, a very big thank you ! Frederic