I’ve decided to use Apache Maven for building the code for my new project. So far I have had a love-hate relationship with Maven. If you don’t know what maven is, the folks over at Apache say Maven is …

“… a software project management and comprehension tool. Based on the concept of a project object model (POM), Maven can manage a project’s build, reporting and documentation from a central piece of information.”

Unfortunately that definition is about as vague as you can get so I will explain what Maven gives me and my project. This also happens to be the list of what I love about Maven:

• Maven enforces a standardized project structure to all modules in a project.
• Maven handles dependencies between libraries.
• Maven builds all of my code and creates a distribution package.

Essentially by using Maven, I can get all of these things without having to write and maintain ant scripts to do most of the work for me. Maven is not without its problems though.

• Often times the number of lines of XML you need to write ends up to be just as complicated and long as an ant script to do the same thing.
• I’ve found a lot of bugs particularly with the assembly module. It seems to include dependencies of modules that are set with the “compile” or “test” scope only.
• The Groovy building plugin for maven does not yet work for Groovy 1.5.x.

I still think using maven was a good choice for my project. It may have some qwerks but I think that I am further ahead than if I had to build everything from scratch.

Using Maven to Generate a Build Number

Earlier I metioned that I use the subversion revision number as a build number. This is actually quite easy to do from Maven. The following plugin descriptor provides you access to the subversion revision number using the ${scm.revision} property. <build> <plugins> <plugin> <artifactId>maven-scm-plugin</artifactId> <executions> <execution> <id>getting-scm.revision</id> <phase>validate</phase> <goals> <goal>update</goal> </goals> </execution> </executions> </plugin> </plugins> </build>  Once you have access to the revision number, you can construct a build number using the product version and the revision number. I have added this build number to the Implementation-Version property of the jar manifest. The following plugin definition does this for me: <plugin> <artifactId>maven-jar-plugin</artifactId> <version>2.1</version> <configuration> <archive> <manifestEntries> <Implementation-Version>${this.version}.\${scm.revision}</Implementation-Version>
</manifestEntries>
</archive>
</configuration>
</plugin>



The resulting manifest in the jar looks something like this:

Manifest-Version: 1.0
Archiver-Version: Plexus Archiver
Created-By: Apache Maven
Built-By: cdail
Build-Jdk: 1.6.0_03
Implementation-Version: 1.0-SNAPSHOT.93



From Java code, this build number can be easily retrieved. The following code retrieves the Implementation-Version from the manifest:

Package p = getClass().getPackage();
String version = p.getImplementationVersion();



The result is quite elegant but it takes a bit of work to get things into place. Like with many other things to do with Maven, it takes a while to figure out how to do what you want and you need to write a bunch of XML. Once that was done, everything fell into place. It is hard to say at this point if this is better or worse than the chunk of ant script I used to use to perform the same function.