New to Java looking for a strategic approach..for a prototype

[andydowthwaite]

I have been tasked with implementing a Java prototype solution for the following problem.

1) Create a web application that creates updates and edits data in an open source database on a remote hosted server.
2) The same functionality needs to be built on a java application that can run on a desktop machine that has intermittent or limited internet connectivity.
3) When connectivity is available the data should be synced between the two databases.

So what web application framework, database should be used for a Java solution, could that same code be reused on a offline local data store how would it be sync. Would I need to build a Java desktop solution and a totally separate web solution ..seems alot of duplication
Software upgrades would need to be performed remotely when internet connection was Established.

I am looking for a RAD development tool too that I can produce a prototype of a single screen and prove a sync can be done.

any help would be most useful as I am new to Java an all its implementation

[Tolls]

Think layers.
The front end of each will be different, one being a servlet/JSP/whatever framework, the other being Swing.
The middle layer will be the same, consisting of whatever business logic there is, interacting with the front end and backend.
The backend (database layer) will have the same interface, but will be slightly different, with the web app interacting with the hosted server directly, and the desktop app interacting with both that and the local db depending. Including the synching code. You'll probably want to expose an 'offline' flag so the desktop app can display that info to the user, but that depends on your requirements.