Having used Grails for a project recently I want to share our experiences compared to standard J2EE application development.
Does it really confer rapid development benefits?
Definitely, it does. Even if the scaffolding path is left early and conventions are overriden to the own needs, the start-up period is very short, as we don't have to care for many different technologies. That kind of lightweightness makes us work not only faster, but also more precise and clean.
Writing tags was never easier - while with JSF we first deliberate about whether it's worth the effort, with Grails we just do it. To work testdriven and to achieve a high coverage rate is also made quite easy, although the different test cases and mocking strategies are sometimes inconsistent and buggy.
Switching from Java to Groovy is a great pleasure, we loved to have list and map literals, closures, builders, to throw away our boiler plate "map" implementation in Java and to write compact, meaningful and focused code.
What slows down the development speed is the not so perfect IDE-support, which also holds true for the IntelliJ plugin, that we use. The bad, often old and even wrong documentation scattered over different places (foiling the promise "the search is over") gets also in the way of rapid development. So we often had to fall back to source code reading - subsequently being scared by the underlying Spring class hierarchies.
