How can something like BOSH be implemented using Java Servlets

Question

BOSH (Bidirectional-streams Over Synchronous HTTP) is a sneaky way of implementing 2-way client-server communication in situations where true server-push is not allowed, most obviously to let a server push data to a browser client without having to use client polling.

It works by the client sending a request to the server, and the server doesn't respond immediately... rather it remembers the request but only responds when it has some data to send. When this happens the client immediately sends another request so there is virtually always a 'stored request' sitting on the server ready to push data to the client.

At least, that's how I think it works!

Update: My question is how you can do this using a Java EE stack i.e standard servlets. Is this possible using say Servlet 2.x (I'm a bit rusty so I don't know if you can decline to send a response or something) or only using extensions through a wrapper like Atmosphere?

Answer 1

Not an equivalent but Servlet 3.0 introduces an Asynchronous API. With or without Servlet 3.0, there is also Atmosphere.

See also

• Servlet 3.0 Asynchronous API or Atmosphere? Easy decision!
• Asynchronous HTTP and Comet architectures
• Jean François Arcand blog (the author of Atmosphere)

Answer 2

Maybe you are looking for something like comet, a kind of reverse AJAX in which the client initiates the connection, allowing the server to push data when it wants.

EDIT: I realize you are looking for solutions in Java and when we think of AJAX we immediately think of JavaScript, but the term has been tainted lately and it represents a concept more than a JavaScript solution. Comet is very much a concept like AJAX and can also be implemented in the programming language of your choice.