I installed Groovy-Eclipse Feature 2.9.1.xx-201411241807-e44 which seems to contain groovy 2.3.7 but the Eclipse IDE does not show any Javadoc.

I assume that the Javadoc should be part of the Eclipse Groovy installation based on this old blog post from Andy http://andrewclement.blogspot.de/2009/12/groovy-eclipse-and-javadoc-hovers.html