I have put this code here for two reasons:

• 1. to help others get started on the very useful feature of Tasks and Workers connected by Queues
• 2. slightly suprised at the lack of complete code java examples for appengine queues.

The whole concept is similar to a producer + consumer pattern, connected by a queue. Only the Task = producer, the Worker = Consumer.

This is a nice way of doing threads without the boiler plate thread code. Rather it's kept to http.

To run on the command line:

ensure you are running java 7 !!!

>mvn appengine:devserver

http://localhost:8080/custom/queueTask?message=hello

You will observe the logs come out in a non sequential (different) order ! And there you have a more responsive design. So the worker could be used for sending emails, or sending an sms via a third party.

Firstly, look at the web.xml, and take note of the servlet mappings for QueueMailTaskServlet and SendConfirmationLLServlet.

Now, take a look at QueueMailTaskServlet

This is the route in, so that when you call it via a HTTP GET, it will create a Task to be POSTed to /mail/low-level as well as a parameter named message, to be placed on the default queue.

Note, there is no knowledge of the receiving servlet, just the queue and the url (/mail/low-level). This is the glue that connects the call to the worker. They are both nicely decoupled from each other.

Now, look at the SendConfirmationLLServlet, it will act when POSTed to, and will write out a message.

If this was synchronous, then the last thing being written out to the console would be "doing something else now". But it is not.