With few exceptions (Web Start and Beans Persistence) there have been very few desktop related JSRs. Well, we're going to change that. Beans Binding, or JSR 295, has just passed inception ballot and the expert group is now forming. Wahoo!

Beans Binding

A big part of what we, desktop developers, have to write every day is component wiring code, or glue code. Glue code is the code that connects components to your application model. For example, connecting a slider's value propety to a property of the selected object in a table requires glue code. Here's an example.

  slider.addValueListener(new ChangeListener() {
    public void stateChanged(ChangeEvent e) {
      selectedObject.setFoo(slider.getValue());
    }
  });

  selectedObject.addPropertyChangeListener(new PropertyChangeListener() {
    public void propertyChanged(PropertyChangeEvent e) {
      if (e.getPropertyName() == null || "foo".equals(e.getPropertyName())) {
        slider.setValue(selectedObject.getFoo());
      }
    }
  });

Anyone that's written this code, and we all have, knows it's painful, tedious and error prone. YUCK!

Beans Binding aims to make it easy to bind two properties of two objects together. Taking the slider example, you might be able to bind the two together with the following code.

  bind(slider, "value", selectedObject, "foo");

This would bind the slider's value property to the selectedObject's foo property, such that changes to the slider are reflected in the selectedObject, and vice versa. Take this as just an example, the JSR was just filed, so no API has been decided upon.

Of course this is a simplified view of things, beans binding will likely accomodate converters, and possibly validators. To be successful it will also need to accomodate renderers. At this years JavaOne conference Hans and myself did a presentation on beans binding with a handful of demos. You can view the presentation here. The source for the first demo can be found here. Notice the source contains two variants, one implemented in terms of binding (BindingCaricatureController), the other with typical listeners (NoBindingCaricatureController). You can run the demo by clicking on the launch button below.

We also demoed how beans binding addresses more traditional database apps at JavaOne, but being a database app, it requires a bit more setup so I'm holding off on publishing it now. I'll return to it later on.

Data Binding

How does this relate to data binding, and specifically JSR 227: A Standard Data Binding & Data Access Facility for J2EE?

WARNING: I am not on the expert group for 227, and do not speak for Mike De Groot, the spec lead for 227. Mike was gracious enough to meet with me on various occasions to help me understand where he believes 227 is going. The following is based on those conversations, but as 227 is not finalized, it may change.

JSR 227 aims to make it easy to bind to any data, be it a ResultSet an XML service, you name it. 227 will not care about the type of your data, there will be an intermediary class used to access the data that knows the specific of your data. In this manner, assuming you have the intermediary layer, 227 will work with any data. Beans Binding is much narrower than that, it assumes you have your data in a well known type, a bean and possibly a Map. A big part of 227 includes declaratively describing the bindings and data, Beans Binding will not include a delcarative XML file describing the bindings and data.

So, why care about beans binding? If you're a good OO citizen you've already created some mapping layer from your database (or other backend) to real objects. Hibernate, Mustang's DataSet, and EJB 3 all do this; they provide a way for you to get real object graphs. Once you've done that, it'll just work with beans binding and the world will be a happier place. Ok, perhaps that's a bit grand, but at the least beans binding will simplify wiring your application objects to components.

What can you do?

As I mentioned, beans binding will be done as a JSR. If you are interested in helping shape the API, and have time to be on an expert group, head over to the home page for beans binding and click on the I would like to join this JSR link. For those that are interested, but can't commit the time, watch the home page for 295 for updates. Within the next month or so we'll settle on a java.net project for the prototype including public forums and what not.

    -Scott