Java EE (Java Enterprise Edition) General Discussion

I want to do that i tried to convert datetime between the local
timezone of the SERVER machine (not the CLIENT machine) and the UTC datetime.

What I want to do in my WEB application is let the user at the client side
enter a datetime (using calendar) Then, when the page postback to the server
side, the appplication have to know from which timezone the CLIENT is (note
that: this is a WEB app. There are a thousand of clients from the internet)
and then convert the entered datetime into UTC datetime before saving it
into database. Later when showing the UTC datetime retrieved from our
database, I want first it is converted to the local CLIENT timezone before
show it on the web UI.