How do I get rosjava development environment setup?

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I am running through the rosjava Getting Started, but I am having trouble with the environment setup. When I try a gradle build.gradle on the example file, I get:

FAILURE: Build failed with an exception.

• Where: Build file '/home/pjmartin/my_workspace/ycpjava/build.gradle' line: 16

• What went wrong: A problem occurred evaluating root project 'ycpjava'. Cause: Could not find method maven() for arguments [build_7srnsdir7dj4a7drkst1r6jo3l$_run_closure1_closure3@4f980c26] on root project 'ycpjava'.

Why would there be a Maven error? I am new to both the Gradle process and rosjava. Any guidance would be helpful!