This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
As stated, you're limited by the language. GWT client side code only currently supports jdk 1.4 and even that is very limited in the JRE emulation. Check out this link that shows you the javadocs for the classes that are supported (http://code.google.com/webtoolkit/documentation/jre.html). Very limited indeed.
But with that said, I haven't had any problems writing a fairly decent size GWT application for our project. Pretty much if I can't do anything on the client side because of the limited emulation, I wrap the call in an RPC invocation and do it on the server side, which is full jdk 1.5 (or even 1.6) supported.
I’ve looked at a lot of different solutions, and in my humble opinion Aspose is the way to go. Here’s the link: http://aspose.com