Code Splitting for Non-Presenters in GWTP

One of the interesting features in GWT is Code Splitting. It allows you to load part of your application only when it is needed. This reduces your app’s loading time and makes for a better user experience.

What is a split point?

Code splitting allows you to separate your code in multiple fragments (more specifically, in multiple JavaScript files). Each location where you choose to separate your code is called a split point. If you want an analogy, each split point is like a door for the content behind it. The main advantage (other than a faster initial loading time) is if a user never accesses some heavy part of your app that is less often used, the total download that the user requires to navigate your app is also reduced.


In GWTP, when you want to put one of your Presenters behind a split point, you can use the @ProxyCodeSplit annotation to do it.


Sometimes, you want to group some Presenters (“bundle” them) behind a split point. That way, they will be grouped in a unique JavaScript file, which is sometimes more time-efficient than multiple files.

The first thing that you have to do is create an interface with the names of your different bundles, and use the @ProxyCodeSplitBundle annotation. GWT Code Generation will kick off and generate all that you need to separate the Presenters as you wish.

For example, you can write your interface like as follows (taken from Arcbees’ website) :

You can then use the annotation on your Proxy and the name of the bundle you want your Presenter to be in :

Bundles for Non-Presenters

A question that we get quite often these days is how to use this annotation function for Java classes that are not Presenters. These annotations are tailored for Presenters, but not for other use cases.

Suppose we want to bundle two services (FirstService and SecondService) behind a split point. We will have to first create a concrete class for our bundle.

We now have access, via our getters, to each of our services.

Now, if we want to use these services, we can inject the MyBundle class with AsyncProvider (this is necessary for GWT to do its code splitting).

You can now retrieve your service (the best practice is in the onBind() function if you are in a Presenter) this way :

I hope this article helped you understand how split points work, in particular with the non-Presenter bundles. Don’t forget to subscribe to our newsletter if you want more articles like this.