Servlet 3.0 asynchronous

Question

What's the diffrence between servlet 3.0 asynchronous feature against:

Оld servlet implementation:

doGet(request,response) {
Thread t = new Thread(new Runnable()
     void run(){
        // heavy processing
        response.write(result)
     }
}
t.start();

In servlet 3.0 if I waste a thread to do heavy processing - I earn one more thread in the container, but I waste it in heavy processing... :(

Could somebody help?

Answer 1

This won't work. Once your doGet method ends, the response is complete and sent back to the client. Your thread may or may not still be running, but it can't change the response any longer.

What the new async feature in Servlet 3.0 does, is that it allows you to free the request thread for processing another request. What happens is the following:

RequestThread:  |-- doGet() { startAsync() }  // Thread free to do something else
WorkerThread:                 |-- do heavy processing --|
OtherThread:                                            |-- send response --|

The important thing is that once RequestThread has started asynchronous processing via a call to startAsync(...), it is free to do something else. It can accept new requests, for example. This improves throughput.