Asynchronous task from Java servlet

Question

I need to perform an asynchronous task when a RESTful web service endpoint is called. Effectively, the endpoint is asked to perform a body of work with a POST operation. It should immediately return a 200 OK to the caller, spawn a thread and perform it's resource intensive task. On completion, the thread would then POST to a corresponding endpoint on the caller (another REST server) indicating success (passing a token that represents the initial transaction request).

What are the best practice approaches for performing asynchronous actions inside a servlet that I should be aware of?

Answer 1

Servlet 3.0 has support for asynchronous operations. Tomcat 7.0 is already stable, so you can get it and try the new features.

If you don't need to output data continously, but to simply start a background process, then you can use any asynchronous mechanism available:

• Executors framework
• new Thread(new Runnable())
• @Async (spring/ejb)

Answer 2

Aside from the complexities of async coding in Java, another "best practice" in RESTful web services is to use HTTP status codes to describe your server's response as accurately as possible. Unless you have a compelling reason to stick with 200 (ie a client which you can't change expects this), you should return HTTP 202:

202 Accepted

The request has been accepted for processing, but the processing has not been completed.