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46.6. Asynchronous Processing on the Client

Overview
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JAX-RS 2.0 supports asynchronous processing of invocations on the client side. Two different styles of asynchronous processing are supported: either using a java.util.concurrent.Future<V> return value; or by registering an invocation callback.

Asynchronous invocation with Future return value
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Using the Future<V> approach to asynchronous processing, you can invoke a client request asynchronously, as follows: 
// Java
import javax.ws.rs.client.ClientBuilder;
import javax.ws.rs.client.Client;
import java.util.concurrent.Future;
import javax.ws.rs.core.Response;
...
Client client = ClientBuilder.newClient();
Future<Response> futureResp = client.target("http://example.org/bookstore/books/123")
                     .request("application/xml")
                     .async()
                     .get();
...
// At a later time, check (and wait) for the response:
Response resp = futureResp.get();
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You can use a similar approach for typed responses. For example, to get a response of type, BookInfo: 
Client client = ClientBuilder.newClient();
Future<BookInfo> futureResp = client.target("http://example.org/bookstore/books/123")
                     .request("application/xml")
                     .async()
                     .get(BookInfo.class);
...
// At a later time, check (and wait) for the response:
BookInfo resp = futureResp.get();
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Asynchronous invocation with invocation callback
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Instead of accessing the return value using a Future<V> object, you can define an invocation callback (using javax.ws.rs.client.InvocationCallback<RESPONSE>), as follows: 
// Java
import javax.ws.rs.client.ClientBuilder;
import javax.ws.rs.client.Client;
import java.util.concurrent.Future;
import javax.ws.rs.core.Response;
import javax.ws.rs.client.InvocationCallback;
...
Client client = ClientBuilder.newClient();
Future<Response> futureResp = client.target("http://example.org/bookstore/books/123")
                     .request("application/xml")
                     .async()
                     .get(
    new InvocationCallback<Response>() {
        @Override
        public void completed(final Response resp) {
            // Do something when invocation is complete
            ...
        }

        @Override
        public void failed(final Throwable throwable) {
            throwable.printStackTrace();
        }
    });
...
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You can use a similar approach for typed responses: 
// Java
import javax.ws.rs.client.ClientBuilder;
import javax.ws.rs.client.Client;
import java.util.concurrent.Future;
import javax.ws.rs.core.Response;
import javax.ws.rs.client.InvocationCallback;
...
Client client = ClientBuilder.newClient();
Future<BookInfo> futureResp = client.target("http://example.org/bookstore/books/123")
                     .request("application/xml")
                     .async()
                     .get(
    new InvocationCallback<BookInfo>() {
        @Override
        public void completed(final BookInfo resp) {
            // Do something when invocation is complete
            ...
        }

        @Override
        public void failed(final Throwable throwable) {
            throwable.printStackTrace();
        }
    });
...
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