Maven 3 - How to add annotation processor dependency?

Question

I need to run an annotation processor on my project's sources. The annotation processor should not become a transitive dependency of the project since it's only needed for annotation processing and nothing else.

Here is the complete (non-working) test pom I use for this:

<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>   <groupId>test</groupId>   <artifactId>test</artifactId>   <packaging>jar</packaging>   <version>1.0-SNAPSHOT</version>   <name>Test annotations</name>   <properties>     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>     <hibernate-jpamodelgen.version>1.2.0.Final</hibernate-jpamodelgen.version>   </properties>   <dependencies>     <dependency>       <groupId>javax</groupId>       <artifactId>javaee-api</artifactId>       <version>6.0</version>       <scope>provided</scope>     </dependency>   </dependencies>   <build>     <plugins>       <plugin>         <groupId>org.apache.maven.plugins</groupId>         <artifactId>maven-compiler-plugin</artifactId>         <version>3.0</version>         <configuration>           <annotationProcessors>             <annotationProcessor>               org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor</annotationProcessor>           </annotationProcessors>           <debug>true</debug>           <optimize>true</optimize>           <source>1.6</source>           <target>1.6</target>           <compilerArguments>             <AaddGeneratedAnnotation>true</AaddGeneratedAnnotation>             <Adebug>true</Adebug>           </compilerArguments>         </configuration>         <dependencies>           <dependency>             <groupId>org.hibernate</groupId>             <artifactId>hibernate-jpamodelgen</artifactId>             <version>${hibernate-jpamodelgen.version}</version>           </dependency>         </dependencies>       </plugin>     </plugins>   </build> </project> 

I explicitly defined org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor as an annotation processor in the plugin configuration for tests and I know it shouldn't be required.

The problem I'm encountering is that the hibernate-jpamodelgen dependency is not added to the compiler classpath so the annotation processor is not found and the build fails.

As per this answer, I tried adding the dependency as a build extension (not sure I understand what those are supposed to be!) like so:

<extensions>   <extension>     <groupId>org.hibernate</groupId>     <artifactId>hibernate-jpamodelgen</artifactId>     <version>${hibernate-jpamodelgen.version}</version>   </extension> </extensions> 

This also doesn't add hibernate-jpamodelgen to the compiler classpath.

The only thing I found which works so far is adding the dependency to the project in the <dependencies> section. This has the unfortunate side-effect of adding hibernate-jpamodelgen as a transitive dependency afterwards which I want to avoid.

My previous working setup uses the maven-processor-plugin plugin to achieve what I want. However, this plugin is not supported by eclipse m2e and the latest version of the maven-compiler-plugin now handles multiple compiler arguments properly so I'd rather use the latter.

Answer 1

The annotationProcessorPaths option can be used in recent versions of the Maven compiler plug-in:

<pluginManagement>     <plugins>         <plugin>             <groupId>org.apache.maven.plugins</groupId>             <artifactId>maven-compiler-plugin</artifactId>             <version>3.6.1</version>             <configuration>                 <annotationProcessorPaths>                     <annotationProcessorPath>                         <groupId>org.hibernate</groupId>                         <artifactId>hibernate-jpamodelgen</artifactId>                         <version>5.2.6.Final</version>                     </annotationProcessorPath>                 </annotationProcessorPaths>             </configuration>         </plugin>     </plugins> </pluginManagement> 

That way the processor is separated from the actual project dependencies. This option is also picked up by the Eclipse M2E plug-in if annotation processing is enabled for the project.

Answer 2

Add the dependency as an optional dependency (<optional>true</optional>). This will add the dependency under compilation, but will prevent it for being a transitive dependency:

<dependency>   <groupId>org.hibernate</groupId>   <artifactId>hibernate-jpamodelgen</artifactId>   <version>${hibernate-jpamodelgen.version}</version>   <optional>true</optional> </dependency> 

If you're creating an artifact in this module with all your dependencies in it (like a .war), you may use the <scope>provided</scope> instead. This both prevents the dependency to be transitive and to be included in the artifact the module produces.