Hi Michael:
Thank you for your reply. But the problem is my design is view -> model -> dbclient, I have used Observer
pattern on view-model, the model class extends Observable, so that I can not use it on
db client and model. And the db client is not a thread, when client need send data to server it will be called and work for it. So if client wait for the reply continuelly, user can do nothing at that time.
Thanks.
Paul