Flickr has a robust set of web services for accessing their hosted photos, and more. There's already a wide variety of API kits to adapt the various response formats (XML-RPC, REST, SOAP) to different languages ... including .NET, PHP, Ruby, Python, Perl, and others. However, the Java contingent is a little weak. To support the Flickr Portlet I am developing for the Portlet Repository project, I started the Quickr Flickr project. This is essentially a Java wrapper around the Flickr REST services.
I think I've done a fair job of making it simple to use the Flickr web services from Java. If you're interested in writing Java applications or web applications that build on Flickr, take a look at Quickr Flickr! It's not completely built-out yet (it doesn't map to all of the Flickr service methods), but it's getting there.
