GContracts provides annotations to implement interface contracts aka design by contract in Groovy classes.
'org.gcontracts:gcontracts-core:1.2.3'
<dependency>
<groupId>org.gcontracts</groupId>
<artifactId>gcontracts-core</artifactId>
<version>1.2.3</version>
</dependency>
<dependency org="org.gcontracts" name="gcontracts-core" rev="1.2.3"/>
"org.gcontracts", "gcontracts-core", "1.2.3"