<dependency>
  <groupId>org.apache.logging.log4j</groupId>
  <artifactId>log4j</artifactId>
  <version>2.1</version>
  <type>pom</type>
</dependency>

'org.apache.logging.log4j:log4j:pom:2.1'

<dependency org="org.apache.logging.log4j" name="log4j" rev="2.1">
  <artifact name="log4j" type="pom" />
</dependency>

@Grapes(
@Grab(group='org.apache.logging.log4j', module='log4j', version='2.1')
)

compile 'org.apache.logging.log4j:log4j:2.1'

[org.apache.logging.log4j/log4j "2.1"]

libraryDependencies += "org.apache.logging.log4j" %% "log4j" % "2.1"