JPAMetaModelEntityProcessor and generated source folder

pom.xml

<plugins>
    <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <configuration>
            <source>1.6</source>
            <target>1.6</target>
            <compilerArguments>
                <processor>org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor</processor>
            </compilerArguments>
        </configuration>
    </plugin>
    <plugin>
        <groupId>org.codehaus.mojo</groupId>
        <artifactId>build-helper-maven-plugin</artifactId>
        <version>1.7</version>
        <executions>
            <execution>
                <id>add-source</id>
                <phase>generate-sources</phase>
                <goals>
                    <goal>add-source</goal>
                </goals>
                <configuration>
                    <sources>
                        <source>${project.build.directory}/generated-sources/annotations</source>
                    </sources>
                </configuration>
            </execution>
        </executions>
    </plugin>
</plugins>

see more:
http://mojo.codehaus.org/build-helper-maven-plugin/usage.html
http://blog.tfd.co.uk/2009/07/29/howto-add-more-than-one-source-directory-into-a-maven-build/