I was thinking about some POE support for Resteasy.  On the client side add a poe() set of methods on ClientRequest and a @POE annotation for the Proxy framework.  I.e.

ClienRequest request = ...;
request.body("<stuff/>", "appliation/xml");
ClientResponse response = request.poe();

public interface MyService {
   public void poeIt(Data data);

The way they’d both work is a HEAD to the base URL would be sent to get the POE-Link, then a POST to the POE-Link would be done using the message body.  A Retry-like exception would be thrown if the POST fails.  For the serverside it could look something like this:

public void poeIt(@PathParam("sub") String subpath, @PathParam("id") @PoeGenerated int id) {...}

@PathParam combined with @PoeGenerated is an automatically uniquely generated id.  So, the user would invoke on /foo/{sub} and get back a POE link of /foo/{sub}/{id}.  i.e.

HEAD /foo/stuff

HTTP/1.1 200 OK
POE: 1
POE-Link: /foo/stuff/3333