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Chapter 12. Groovy integration

12.1. Groovy introduction
12.2. Writing Seam applications in Groovy
12.2.1. Writing Groovy components
12.2.2. seam-gen
12.3. Deployment
12.3.1. Deploying Groovy code
12.3.2. Native .groovy file deployment at development time
12.3.3. seam-gen

One aspect of JBoss Seam is its RAD (Rapid Application Development) capability. While not synonymous with RAD, one interesting tool in this space is dynamic languages. Until recently, choosing a dynamic language was required choosing a completely different development platform (a development platform with a set of APIs and a runtime so great that you would no longer want to use you old legacy Java [sic] APIs anymore, which would be lucky because you would be forced to use those proprietary APIs anyway). Dynamic languages built on top of the Java Virtual Machine, and Groovy in particular broke this approach in silos.

JBoss Seam now unites the dynamic language world with the Java EE world by seamlessly integrating both static and dynamic languages. JBoss Seam lets the application developer use the best tool for the task, without context switching. Writing dynamic Seam components is exactly like writing regular Seam components. You use the same annotations, the same APIs, the same everything.

Groovy is an agile dynamic language based on the Java language but with additional features inspired by Python, Ruby and Smalltalk. The strengths of Groovy are twofold:

There is not much to say about it. Since a Groovy object is a Java object, you can virtually write any Seam component, or any class for what it worth, in Groovy and deploy it. You can also mix Groovy classes and Java classes in the same application.

As you should have noticed by now, Seam uses annotations heavily. Be sure to use Groovy 1.1 or above for annotation support. Here are some example of groovy code used in a Seam application.

Deploying Groovy classes is very much like deploying Java classes (surprisingly, no need to write nor comply with a 3-letter composite specification to support a multi-language component framework).

Beyond standard deployments, JBoss Seam has the ability, at development time, to redeploy JavaBeans Seam component classes without having to restart the application, saving a lot of time in the development / test cycle. The same support is provided for GroovyBeans Seam components when the .groovy files are deployed.

A Groovy class is a Java class, with a bytecode representation just like a Java class. To deploy, a Groovy entity, a Groovy Session bean or a Groovy Seam component, a compilation step is necessary. A common approach is to use the gmaven-plugin maven plugin. Once compiles, a Groovy class is in no way different than a Java class and the application server will treat them equally. Note that this allow a seamless mix of Groovy and Java code.

JBoss Seam natively supports the deployment of .groovy files (ie without compilation) in incremental hotdeployment mode (development only). This enables a very fast edit/test cycle. To set up .groovy deployments, follow the configuration at Section 2.8, “Seam and incremental hot deployment” and deploy your Groovy code (.groovy files) into the WEB-INF/dev directory. The GroovyBean components will be picked up incrementally with no need to restart the application (and obviously not the application server either).

Be aware that the native .groovy file deployment suffers the same limitations as the regular Seam hotdeployment:

  • The components must be JavaBeans or GroovyBeans. They cannot be EJB3 bean

  • Entities cannot be hotdeployed

  • The hot-deployable components will not be visible to any classes deployed outside of WEB-INF/dev

  • Seam debug mode must be enabled