How to understand this kind of use of AsyncHandler in an asynchronous web service client code, in Java?

Question

I ran into this piece of code when learning to write an asynchronous client of a web service. I am trying to understand how "new AsyncHandler<Inventory>() {...}" is used here. I am relatively new to Java, and there are a few things that I don't understand:

AsyncHandler is from javax.xml.ws.AsyncHandler, and how Inventory, an local or custom object can be part of it. What does AsyncHandler<Inventory> mean?
Is the use of "new AsyncHandler<Inventory>() {...}" an instantiation or implementation of the class AsyncHandler?
what is the relationship of handleResponse and AsyncHandler?

Here is the code:

public class StockWebServiceClientCallbackMainMyCopy {
    private static Logger log = Logger.getLogger(StockWebServiceClientCallbackMain.class.getName());

    @SuppressWarnings("unchecked")
    public static void main(String[] args) throws Exception {
        final Stock stockPort = new StockService().getStockPort();
        log.info("Got StockService port successfully");

        final int thresh = 2;
        // TODO: (53.01) Call async method passing in callback method
        //               In the callback method, print out all the items and exit
        //               Important: call System.exit() from callback
        stockPort.getStockItemsWithQuantityLessThanAsync(thresh, new AsyncHandler<Inventory>(){
            @Override
            public void handleResponse(Response<Inventory> response) {
                log.info("Callback invoked");
                try{
                    Inventory inventory = response.get();
                    for (Item item : inventory.getItems()){
                        System.out.println(item.getProductId() + " " + item.getQuantity());
                    }
                    System.exit(0);
                }
                catch(Exception e){
                    e.printStackTrace();
                }
            }           
        });

        // TODO: (53.02) Note simulation of other activity using Thread.sleep()
        while (true){
            try{
                Thread.sleep(1000);
            } catch (InterruptedException e){
                // ok
            }
        }
    }
}

score 0 · Answer 1 · answered Jul 24 '14 at 16:49

javax.xml.ws.AsyncHandler is an interface. What you are doing in your code is creating an instance of an "anonymous" class which implements this interface.

The interface (AsyncHandler) defines a single method called handleResponse. You override this method in the your code.

The interface uses a template , which can be any type. So when you implement the interface, you specify the type of the object you expect to get returned from your service call.

How to understand this kind of use of AsyncHandler in an asynchronous web service client code, in Java?

1 Answers1