If you want to do this with Java code, you can use the Guvnor REST api. Example URL (GET request):
http://localhost:8080/drools-guvnor/rest/packages/<packageName>/assets/<assetName>/source/
(substitute <packageName> and <assetName> with your concrete values. This will return you the bpmn2 (source) of your process in Guvnor. If you are using jaas auth in guvnor, you would need to use for example BASE64Encoder to encode usr/pwd and set the Authorization request property.
You can also use the Drools Eclipse plugin and use the Guvnor perspective to connect to your repository and view the sources, or you could write your own WebDav client also.
Hope this helps.