Maven build helper POMs

A typical misconception in Maven is that if you want to build a project in a special way, or parameterize it somehow, profiles are the thing for you. My opinion is that..

Profiles are POM smell.
While I know they have their uses, I have abused profiles heavily in the past, and seen others do this too. What might start off as a simple little trick to get some desired build eventually leads to:

• One profile for each testing category (unit, database, web-tests, etc)
• (Hint: Use a test framework that supports grouping)
• One profile for each environment/stage configuration (testing, live, etc)
• (Hint: Use a tool that supports stage-aware configuration)
• One profile for each artifact assembly (exclude module X when deploying in certain environments)

The POM ends up awfully complicated, you get confusion around what kind of artifact is deployed where, and people start hating Maven because they forget -P parameters when they build, and end up rebuilding the whole project to change some single configuration.

The point of a POM is that the output of the build, the artifact, should always be the same thing.

If you want to build *a different thing*, you probably should build another project. Andrew Spencer recently wrote a nice article about best practices in Maven profiles. If you want more advice you should have a look.

An example from the other day:  I wanted to build a sub-set of the modules in a rather large multi-module project. In order to speed up the build, I wanted to exclude the modules with static contents (texts and resources):

	<?xml version="1.0" encoding="UTF-8"?>
	<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
	<groupId>com.tfnico.examples</groupId>
	<artifactId>foo</artifactId>
	<version>1.0-SNAPSHOT</version>
	<relativePath>./pom.xml</relativePath>
	</parent>
	<name>Fast build</name>
	<groupId>com.tfnico.examples</groupId>
	<artifactId>foo-fastbuild</artifactId>
	<version>1.0-SNAPSHOT</version>
	<packaging>pom</packaging>
	<modules>
	<module>foo-core</module>
	<module>foo-web</module>
	<!-- Here there are just two projects,
	the parent/normal foo project has more,
	but we don't need to build them in the
	fast build -->
	</modules>
	</project>

view raw fastbuild-pom.xml hosted with ❤ by GitHub

Instead of making a quickbuild-profile, I made an adjacent fastbuild-pom.xml that extends the original, but excludes the static modules:

	<?xml version="1.0" encoding="UTF-8"?>
	<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
	<groupId>com.tfnico.examples</groupId>
	<artifactId>foo</artifactId>
	<version>1.0-SNAPSHOT</version>
	<relativePath>./pom.xml</relativePath>
	</parent>
	<name>Fast build</name>
	<groupId>com.tfnico.examples</groupId>
	<artifactId>foo-fastbuild</artifactId>
	<version>1.0-SNAPSHOT</version>
	<packaging>pom</packaging>
	<modules>
	<module>foo-core</module>
	<module>foo-web</module>
	<!-- Here there are just two projects,
	the parent/normal foo project has more,
	but we don't need to build them in the
	fast build -->
	</modules>
	</project>

view raw fastbuild-pom.xml hosted with ❤ by GitHub

This build I can invoke in the CI-server:

mvn clean install -f fastbuild-pom.xml


So, not too much duplication of the original pom, and very unobtrusive.

Remember that in 95% of the cases you want to create profiles, there is probably a better tool for what you are trying to do. I think the best cases for profiles are read in their activation docs: Making it possible to build the project on different JDK's, or different OS. Then again, the whole point of Java is to be platform-independent, so this seldom an issue.