Metawidget and Seam: saying goodbye to boilerplate code

This blog is to celebrate the inclusion of the Metawidget examples in the upcoming release of Seam. What is Metawidget? It's a 'smart User Interface widget' that populates itself, at runtime, with UI components to match the properties of your business objects.

If you think of a typical Seam stack, you may have JPA at the bottom, then EJB, then Seam itself, then JSF, then maybe RichFaces to add a bit of polish. But there is still a gap at the very top - a gap that leads to a lot of 'boilerplate code'. This is where Metawidget comes in.

Let me try and convey it visually using the image below. On the left are the complete contents of the book.xhtml file from the Seam Groovy Booking example. On the right are the complete contents from the new Seam Metawidget Groovy Booking example. The red boxes and lines highlight the chunks of boilerplate that have been replaced:

The original file is 177 lines long. The Metawidget equivalent is 52 lines. That represents a 70% reduction in code, on top of the considerable reductions Seam already affords when developing enterprise applications. This ability to retrofit existing UIs, integrating with existing front-end and back-end technologies, is unique to Metawidget.

Now I want to be completely fair here - I'm a developer, not a marketing guy! You also have to add a few extra annotations to your business classes, add the Metawidget JAR to your project and create a little metawidget.xml file. If we compare all the source files that change:


By comparing file sizes, we see the overall code reduction is around 20%. We could allow that in such a small example the size of metawidget.xml is more significant than it should be: for apps with hundreds of screens, the impact of 2,789 bytes of metawidget.xml will be negligible. So if we compare file sizes without including metawidget.xml, we see the overall code reduction is around 40%. If you repeat this exercise with the Seam Metawidget DVD Store example (also included in the Seam distribution) the overall reduction is around 30%.

Of course, on top of all that, lines of code is never a wondeful metric for comparing implementations. But anyway, hopefully you get the idea. Still, if you want a soundbite: Metawidget can save you up to 40% of your UI code.

My deepest thanks to the Seam guys, especially Dan Allen, for all their help integrating Metawidget into the Seam 2.1.2.GA build.