How to provide specific GWT implementations

Question

Suppose I am working on exposing some of my server-side classes to a GWT application, but certain parts could be done much better using GWT-specific components (like JSNI, for instance).

What are some techniques for doing so without being too hacky?

For instance, I am aware of using a subpackage and using the <super-source/> tag, but this requires the package names to be different, which causes eclipse to complain. The general solution in the community is to then tell eclipse to use that as a source folder, but then eclipse complains about there being two classes with the same name.

Ideally, there would just be a way to keep everything in a single source tree, and actually have different classes which apply the alternate implementations. This would feel like a more OO approach.

I would like to add a suffix to a class like _gwt which accomplishes this automatically, and I know I could write a script to do this kind of transformation, but that is a kludge for sure.

I've been considering using Google's GIN/GUICE libraries for my projects in general, and I think there might be some kind of a solution there, but I am not sure as I have not thoroughly investigated it.

What are some solutions you have tried in the past on GWT projects?

Answer 1

The easiest way to have split implementations is to use super-source code, but only enough to instantiate a uniquely-named instance or dispatch to a different method. Ideally, the super-source implementation is just a few lines long, and not so bad that you can't roll it by hand.

To work around the Eclipse / javac double-mapping and package name issues, the GWT source uses two top-level roots for user code: user/src and user/super. For example, the AutoBeans package has a split-implementation of JSON quoting and evaluation, one for the JVM and one for the browser.

There's really no non-kludgy way to implement super-source, as this is a feature way outside what you can specify in the language. There's nothing that lets you say "use this implementation in this environment" without the use of some external tool.