According to http://docs.atlassian.com/jira/REST/5.0.5/#id78518 and http://docs.atlassian.com/jira/REST/latest/#id75724, to add a watcher, you need to send the String "username" to the server.

That String is not a valid JSON string and will fail in a strict parser like the Java JSON layer.

The workaround provided in https://answers.atlassian.com/questions/61770/please-help-got-error-400-when-trying-to-add-watcher-using-rest-api about using the curl command cannot easily be implemented in Java either.

Would it be possible to fix that issue and request a proper JSON syntax like:

{"name":"fred"}