Two days ago I did some internal research in order to understand how do resolved properties propagate from Maven to Ant via maven-antrun-plugin. On my way I had to recall several rarely remembered facts and learn some new ones. The implications of their combination leads to pretty interesting results that are worth writing them down. At least, now I’ll know where to look for this information next time.

Fact #1
There are multiple sources for properties resolution in Maven – implicit project properties (like project.version), environment variables, user-defined properties (ones you use in properties tag or your pom.xml), Java system properties… The full list with detailed explanations is available in The Complete Reference online book.
Pay attention – when you “override” some user-defined property via command line parameter (-D), in fact you are setting a new Java system property. This works because system properties have higher precedence during properties resolution process.

Fact #2
All properties that are explicitly used in pom.xml are resolved before Maven lifecycle actually starts, even before the initialize phase. It happens when so-called “effective pom” (full project definition, including all implicit data and configuration settings propagated from parent project) is generated. BTW, you can see this in action by call mvn help:effective-pom on your project.

Implication #1
Modifications of project properties that happen during project lifecycle have no effect on the effective pom – it is just too late. Examples of such modifications include groovy scripts (via gmaven-plugin) and properties loaded from external files via maven-properties-plugin. So, why do we need them at all? Since they can be used by other plugins in runtime, when they are read directly from properties collection during plugin invocation.

Continue reading “Properties resolution in Maven and its implications on Antrun plugin” →

As you probably know, maven-antrun-plugin provides a custom AttachArtifact task that is able to attach artifacts generated by Ant to the current Maven project. The usage is really straightforward with inline Ant targets, but an attempt to use this task with external build.xml results in an error:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-antrun-plugin:1.7:run (...) on project ...: 
  An Ant BuildException has occured: The following error occurred while executing this line:
[ERROR] C:\...\build.xml:158: Maven project reference not found: maven.project

[ The solution described here does not really work. See update at the bottom. ]

The solution is simple – external Ant invocation should inherit references from the inline target:

<plugin>
	<artifactId>maven-antrun-plugin</artifactId>
	<executions>
		<execution>
			<id>...</id>
			<phase>compile</phase>
			<goals>
				<goal>run</goal>
			</goals>
			<configuration>
				<target>
					<ant antfile="build.xml" target="..." inheritRefs="true" />
				</target>
			</configuration>
		</execution>
	</executions>
</plugin>

Update: It appears that this change eliminates the error, but the artifact is not actually attached. I’ve opened a bug report to the Maven Antrun Plugin team about that.