<dependency>
  <groupId>org.apache.logging.log4j</groupId>
  <artifactId>log4j-api-java9</artifactId>
  <version>2.13.1</version>
  <type>pom</type>
</dependency>

'org.apache.logging.log4j:log4j-api-java9:pom:2.13.1'

<dependency org="org.apache.logging.log4j" name="log4j-api-java9" rev="2.13.1">
  <artifact name="log4j-api-java9" type="pom" />
</dependency>

@Grapes(
@Grab(group='org.apache.logging.log4j', module='log4j-api-java9', version='2.13.1')
)

compile 'org.apache.logging.log4j:log4j-api-java9:2.13.1'

libraryDependencies += "org.apache.logging.log4j" % "log4j-api-java9" % "2.13.1"

[org.apache.logging.log4j/log4j-api-java9 "2.13.1"]