Получил, чтобы работать по-своему - это был вопрос версий.
@ khmarbaise * В версии 1002 * есть несколько хороших идей, например, гибкость версии.
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<groovy.version>2.0.0-beta-2</groovy.version>
</properties>
<dependencies>
<!-- ... something ... -->
<dependency>
<groupId>org.codehaus.groovy</groupId>
<artifactId>groovy</artifactId>
<version>${groovy.version}</version>
</dependency>
<dependency>
<groupId>org.codehaus.gmaven.runtime</groupId>
<artifactId>gmaven-runtime-1.7</artifactId>
<version>1.3</version>
<exclusions>
<exclusion>
<groupId>org.codehaus.groovy</groupId>
<artifactId>groovy-all</artifactId>
</exclusion>
</exclusions>
</dependency>
</dependencies>
<!-- ... something ... -->
<build>
<!-- make Java compile from groovy folders as well... -->
<sourceDirectory>src/main/groovy</sourceDirectory>
<testSourceDirectory>src/test/groovy</testSourceDirectory>
<plugins>
<plugin>
<groupId>org.codehaus.gmaven</groupId>
<artifactId>gmaven-plugin</artifactId>
<version>1.3</version>
<dependencies>
<dependency>
<groupId>org.codehaus.groovy</groupId>
<artifactId>groovy</artifactId>
<version>${groovy.version}</version>
</dependency>
<dependency>
<groupId>org.codehaus.gmaven.runtime</groupId>
<artifactId>gmaven-runtime-1.7</artifactId>
<version>1.3</version>
<exclusions>
<exclusion>
<groupId>org.codehaus.groovy</groupId>
<artifactId>groovy</artifactId>
</exclusion>
</exclusions>
</dependency>
</dependencies>
<executions>
<execution>
<configuration>
<providerSelection>1.7</providerSelection>
</configuration>
<goals>
<goal>generateStubs</goal>
<goal>compile</goal>
<goal>generateTestStubs</goal>
<goal>testCompile</goal>
</goals>
</execution>
</executions>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>2.3.2</version>
<configuration>
<source>1.5</source>
<target>1.5</target>
</configuration>
</plugin>
</plugins>