The categories ReST end point returns HTTP 500 when querying it with a browser.

Almost any GET request against the OpenNMS ReST API can be performed through a normal browser, and you should see the XML generated.

Now, this is not the case of several GET requests implemented in CategoryRestService. The reason for this is because the methods associated with those GET requests don't have the Provides annotation, which confuses the browser.

Just by adding that annotation fixes the problem.