GWT and Wicket
Why would you want to include GWT widgets as components in your Wicket pages?
Client-side State Can be Nice
Server round-trips can be heavy for implementing some types of client-side behavior. For example, what if you're tracking the coordinates of a mouse-over on an image? Doing a round-trip to check the mouse cursor location against some state on the server would be prohibitive. What if you could simply ship the Java code for those checks and the associated state to the client?
Starting Point for Integration
Here is a partial design for wrapping GWT widgets with Wicket components.
This class diagram captures the design of a potential integration between Wicket and GWT.
Create a central abstract class to represent your GWT widget as a Wicket component: GwtWicketComponent. This class implements a Wicket listener for RPC calls from the widget running on the client, and subtypes of GwtWidgetComponent like FooComponent provide and implementation of RemoteServiceServlet for fielding the calls.
GwtWidgetComponent extends Panel, and should have some associated markup that includes the container for your GWT widget. GwtWidgetComponent will automatically add an appropriate callback URI to an attribute of this container, which the client-side code must use to invoke RPC calls.
A special GwtRpcTarget implementation of IRequestTarget transports the RPC response payload back to the client via Wicket's standard RequestCycle.
FooComponent and FooService implement an example GWT-widget-as-wicket-component.
I concluded that the work of massaging GWT into some kind of cohesive development environment with Wicket outweighed the benefit to my project at the time I write this. Getting the GWT development shell to render pages out of their servlet which were also passed through the Wicket servlet filter was trivial, but that's where I stopped. Rectifying the URI schemes for the two frameworks to get them to cooperatively render a page was the next step. A specialized Wicket URICodingStrategy might help here.
Other improvements may come in the form of an incremental Eclipse builder for GWT, or other niftyness spawning from the Googleplex.