Single Sourcing RAP/RCP apps

Scenario

You read about RAP [1] to be able to do pretty much that is possible with RCP, and thus, decided to provide a web version of your eclipse plugin.
So, you install and setup the RAP tooling [2]. You change your target platform to compile against the RAP runtime. Several compile errors arise. After some research you read about RAP not being fully compatible with its RCP counterpart and that you will have to apply single sourcing techniques to get your plugin work on RAP.
A bit more of your research reveals the following approaches used for single sourcing:

• use reflection to determine whether a specific functionality is available
• swap non-working code into a bundle fragment
• use osgi services for each functionality to be single sourced
• use byte code weaving to patch non-working code at runtime
• etc. (Are there any more to be listed here?)

This approach

This approach is based on a central single sourcing service (think OSGi). It provides an interface for registering and executing wrapped code by a user defined id:


Let us explain this by a simple example: In your RCP you are adding a mouse move listener to a control:

Composite comp = new Composite( parent, SWT.None );
comp.addMouseMoveListener( new MouseMoveListener() {
 public void mouseMove( MouseEvent e ) {
  System.out.println( "mouse location: "
   + e.x + ", " + e.y );
 }
} );

As you might know, RAP does not support mouse move events, and thus, this has to be single sourced.
We, first, have to register the wrapped code, i.e. the part that is not runnable on RAP:

ISingleSourcingService service = ISingleSourcingService.INSTANCE.get();
service.registerExec( "my.execs.addMouseMoveListenerToComposite",
 new IExec() {
  public Object run( Object... params ) {
   Composite comp = (Composite) params[ 0 ];
   comp.addMouseMoveListener( new MouseMoveListener() {
    public void mouseMove( MouseEvent e ) {
     System.out.println( "mouse location: "
      + e.x + ", " + e.y );
    }
   } );
   return null;
  }
 } );
 }

Then, we can call the single sourcing service to execute the wrapped code:

Composite comp = new Composite( parent, SWT.None );
service.execute( "my.execs.addMouseMoveListenerToComposite", null, comp );

This code can be used on both of the platforms, since it does not cause any errors anymore.

Missing clues

Where to register wrapped code?
The preferred way is a separate plugin to host the code. When running on RCP, you will have to make sure that this plugin has been started. On RAP, you would just exclude that plugin from deployment. The other way around is valid as well.

Where to find the sources?
You can checkout the sources from http://erdalkaraca.googlecode.com/svn/trunk/org.eclipse.labs.singlesrc.

[1] http://eclipse.org/rap/introduction.php
[2] http://eclipse.org/rap/gettingstarted.php