Maven Theory: Archetypes

Maven is a complex system to swallow in its entirety. Most persons first encounter it because they want to wield the dependency magic it offers. These persons are not savvy to the notion of repositories and with them the administrative work required to build and manage them. They are not likely to understand that Maven can build complex websites, containing useful reports on project health, with little configuration and user effort. These are things that Maven accomplishes in a very elegant manor (in my opinion). You see Maven 2 was built almost from scratch, using the knowledge gained in the creation of the original Maven. Hence a sound architecture was built in Maven 2 that has proven adaptable to many tasks.

In this post I want to talk more about one of the extension points of Maven 2. Archetypes. These are a lot like templates. When invoked an archetype will either create a new project, or add to an existing one. Archetypes can be created by an end user and deployed into a repository. This allows others to access the archetype and reuse it. A little while back I was doing a fair bit of SOAP service programming. I was using XFire in the creation of these projects, along with other Java technologies. After the first couple projects I decided creating an archetype for XFire projects would be handy. So I created an archetype project that could generate a bare bones Maven 2 project. This project would contain a pom with all the needed dependencies, and a simple "Hello World" SOAP service and an integration test. Now whenever I wanted to create a new XFire project I would just invoke this archetype; giving me a good head start! Now I would like to point out that, if you are like me, you would normally just find the 'similar' project then copy and paste. Then you trim down the copy or whatever. That is a viable alternative, although I feel one is better off with a nearly clean canvas when striking out on a project.

So now that I have talked your ear off, let me give an example of using a real archetype to generate a full project. The base Maven has an archetype for creating Maven projects. Seems reasonable eh? So to create your next computational masterpiece start with the command:

mvn archetype:create -DgroupId=com.someguy -DartifactId=masterpiece

And tadah you now have a folder called 'masterpiece' which contains a very basic Maven 2 project. There are other archetypes you can run with out any special setup, including an archetype to create archtypes! Now I'm not advocating creating an archetype as a precursor to any new project. Create one whenever you start to notice a pattern between projects. A good candidate for me was Spring, Hibernate and other dependencies I used very often in web projects. I created a simple archetype to create a bare bones web MVC application using these dependencies. With this I could start creating the controllers and .jsp pages in my application right away, rather than mucking around copying some old ant project :)

I will write up some better examples on archetypes down the road. I would like to give an example of creating a simple archetype. Keep tuned in for more, and do not hesitate to leave a comment or contact with ideas.