I recently needed to develop a pure-Java prototype application that supported multiple web protocols. The JDK comes with built-in support that meet the needs of many application developers who primarily want to interact with web protocols using URLs (effectively the same way that a end-user uses a browser).

If you have tried the standard JDK libraries and you need more, the table below contains a summary of my brief investigations and the libraries I chose to use. You'll notice I favoured Jakarta's libraries - that's because they're generally very functional, well supported and they have open-source licenses that permit use and contribution by both open and closed source developers.

If you want an abstract API that sits on top of other web protocols, take a look at the Filesystems API in the NetBeans Open APIs suite; the Explorer and Modules APIs also look useful. I hope to find some time to probe NetBeans in more depth one of these dark winter evenings.

Finally, if you're looking for an implementation for another protocol, freshmeat "java protocol -GPL" is certainly not the worst place to start, especially if you drill-down further using the advanced search option.