Using External Libraries

I want to use GSON library in my project, I want to find out if it is allowed. If it is do I just add it in the pom.xml file.

You should be using gson-2.2.4. Please compare with the withings binding ( https://github.com/openhab/openhab/tree/master/bundles/binding/org.openhab.binding.withings ) on how to add the binary jar to your project and reference it from MANIFEST.MF