Learned today: Reverse Ajax

Issue 1.09 of Javamagazin has an interesting article about DWR.

Particularly nice is the explanation and overview of Reverse Ajax.

There are three techniques how to realize Reverse Ajax:

Polling - bases on continuous requests by the client, if the server has data he can put it in a response.

Comet - based on long requests, there is always a request available on which the server can send a response. Comet itself can be realized in two ways:

Long Polling: Server sends a complete HTTP Response. Request is closed. Client immediately sends a new request.

Streaming: The server returns only a Partial HTTP Response, the initial request is not closed.

Piggyback - fully passive, client events are needed. Server sends additional data on top of a normal response.