Fail to create gem behind the corporate proxy

Start with rubyUtils.gradle at line 85 and the downloadAndInstallJRuby task that fails while accessing RubyGems through the corporate proxy. Check the project guide for the Java output plugin example and determine whether an offline build or an internal RubyGems mirror is supported. Done means the example plugin can build without reaching external repositories, with the configuration documented.

I'm trying to create a simple java output plugin following the guide in "logstash-ouput-java example"

While executing the gradle task 'downloadAndInstallJRuby' i got the following error message:

Net::HTTPServerException: 407 "Proxy Authentication Required"
                   error! at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/net/http/response.rb:122
                    value at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/net/http/response.rb:131
                  connect at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/net/http.rb:962
                 do_start at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/net/http.rb:924
                    start at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/net/http.rb:919
         setup_connection at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/request/http_pool.rb:43
         setup_connection at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/request/https_pool.rb:7
          make_connection at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/request/http_pool.rb:39
                 checkout at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/request/http_pool.rb:20
           connection_for at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/request.rb:132
          perform_request at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/request.rb:187
                    fetch at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/request.rb:156
                  request at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/remote_fetcher.rb:368
               fetch_http at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/remote_fetcher.rb:251
               fetch_path at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/remote_fetcher.rb:292
  dependency_resolver_set at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/source.rb:96
                pick_sets at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/resolver/best_set.rb:24
                     each at org/jruby/RubyArray.java:1814
              each_source at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/source_list.rb:98
                pick_sets at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/resolver/best_set.rb:23
                 find_all at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/resolver/best_set.rb:29
                 find_all at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/resolver/installer_set.rb:155
       add_always_install at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/resolver/installer_set.rb:56
     resolve_dependencies at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/dependency_installer.rb:480
              install_gem at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/commands/install_command.rb:201
             install_gems at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/commands/install_command.rb:262
                     each at org/jruby/RubyArray.java:1814
             install_gems at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/commands/install_command.rb:258
                  execute at uri:classloader:/META-INF/jruby.home/lib/ruby/stdlib/rubygems/commands/install_command.rb:165
                   <main> at <script>:6

> Task :foobar-logstash-output:downloadAndInstallJRuby FAILED
:foobar-logstash-output:downloadAndInstallJRuby (Thread[Execution worker for ':',5,main]) completed. Took 19.78 secs.

FAILURE: Build failed with an exception.

* Where:
Script '...<skipped>...\foobar-logstash-output\rubyUtils.gradle' line: 85

Because of corporate policies and security restrictions it is not allowed to dowload artifacts from internet.

Is there any possibility to build the custom plugin "offline" without connecting to the internet repositories?

Or how can i alternatively configure in my build a "rubygems"-mirror that is placed inside my company?

Thanks.