Instead of trying to reinvent the wheel and creating your own java library for jira. I would recommend you look at some java libraries already built to communicate with JIRA.
Based on your error message it is indicating your not making the call correctly (HTTP Version Not Supported).
https://bitbucket.org/atlassian/jira-rest-java-client[
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I've done the same thing in .net using a .net library for JIRA and it works just fine so i know what you are wanting to do is possible...for the most part at least.