Creating a global RPC system for GWTP

AbstractAsyncCallback.java

public interface AbstractAsyncCallback<T> extends AsyncCallback<T>
{
  	// this method is not implemented in AsyncCallbackImpl, but in each presenter separately
	void onReturn(T result);
}

AsyncCallbackImpl.java

import com.google.gwt.event.shared.GwtEvent;
import com.google.gwt.event.shared.HasHandlers;
import com.google.web.bindery.event.shared.EventBus;

/**
 * Global RPC System
 */
public abstract class AsyncCallbackImpl<T> implements AbstractAsyncCallback<T>, HasHandlers
{
 	@Inject
	private static EventBus eventBus; 
	// Don't forget "requestStaticInjection(AsyncCallbackImpl.class)" in your Clientmodule or GIN won't inject this!
	
	public AsyncCallbackImpl()
	{
		// perform any pre-dispatch logic here
		fireEvent(new ActionSentEvent()); // adds loading bar
	}
	
	// perform any post-dispatch logic here
	@Override
	public void onSuccess(T result)
	{
   		 // do the success action (implemented in each presenter)
		onReturn(result);
		
		fireEvent(new ActionReturnedEvent()); // removes loading bar
	}
	
	@Override
	public void onFailure(Throwable caught)
	{
		fireEvent(new ActionReturnedEvent()); // removes loading bar
		
		Window.alert("Communication to the server has failed.");
		MyUtilities.processThrowable(caught); // utility class deals with exception
	}
	
	@Override
	public void fireEvent(GwtEvent<?> event)
	{
		eventBus.fireEvent(event);
	}
	
}

YourPresenter.java

private void addAccountDetails()
	{
		GetAccounts action = new GetAccounts();
		
		dispatchAsync.execute(action, new AsyncCallbackImpl<GetAccountsResult>()
		{
			@Override
			public void onReturn(GetAccountsResult result)
			{
				accounts = result.getAccounts();
				processAccountDetails(accounts);
			}
		});
    		// method above is chained from onSuccess (which also executes global code to stop showing loading bar)
	}