I am writing a custom plugin where I need to iterate all dependencies for a war project including its transitive dependencies but only for a given groupId. Is there build-in functionality in gradle for this or do I need to write my own script for this?
Which version of Gradle do you need to target? Gradle 1.2 has better API for this.
I am using 1.2 and currently use more less the approach described here:
http://gradle.1045684.n5.nabble.com/transitive-dependency-list-td4793535.html
And how is that not working for you?
sorry it works 
But maybe there was a simpler way like: project.getDependencyTree() that would eg. return an iterator to the root.
Gradle 1.2 introduced a new (incubating) API that may be easier to work with depending on what you want: http://gradle.org/docs/current/release-notes#dependency-resolution-result-api
Its focus is slightly different.