The atlassian-rest-module-6.0.1.jar repackages JAX-RS 1.0.
For plugins that don't need to be rest servers, the jaxrs-ri-2.25.1.jar implementation of JAX-RS 2.0 is more convenient to use.
However in repackaging JAX-RS-1.0, the atlassian-rest-module also appears to import the javax.ws.rs.ext package.
At runtime, it ends up using the javax.ws.rs.ext.RuntimeDelegate from the jaxrs-ri-2.25.1.jar bundle, and registers a 1.0 implementation of RuntimeDelegate via the RuntimeDelegate.setInstance() method.
This causes plugins that use the jaxrs-ri-2.25.1.jar bundle to fail, with exceptions like:
At present, the workaround is to either:
use JAX-RS 1.0
embed JAX-RS 2.0 dependencies in plugins