How to measure Code Coverage of a RestFul API

I have a maven based multi-module Jersey project which exposes few RestFul API. Project Structure is like -

Project

• Module1

  ----------src

  --------- unit test

• Module2

  ----------src

  --------- unit test

• Module3

  ----------src

  --------- unit test

• ModuleN - this module contains Integration Tests which will hit endpoints exposed by project and test the whole service like a black box

  ----------src

  --------- unit test

I have gone though a lot of blogs and articles but everywhere we have half information. can someone point me or guide me how can I do it.

Thanks -Shahid