How do you create an asynchronous HTTP request in JAVA?

If you are in a JEE7 environment, you must have a decent implementation of JAXRS hanging around, which would allow you to easily make asynchronous HTTP request using its client API.

This would looks like this:

public class Main {    public static Future<Response> getAsyncHttp(final String url) {        return ClientBuilder.newClient().target(url).request().async().get();    }    public static void main(String ...args) throws InterruptedException, ExecutionException {        Future<Response> response = getAsyncHttp("http://www.nofrag.com");        while (!response.isDone()) {            System.out.println("Still waiting...");            Thread.sleep(10);        }        System.out.println(response.get().readEntity(String.class));    }}

Of course, this is just using futures. If you are OK with using some more libraries, you could take a look at RxJava, the code would then look like:

public static void main(String... args) {    final String url = "http://www.nofrag.com";    rx.Observable.from(ClientBuilder.newClient().target(url).request().async().get(String.class), Schedulers            .newThread())            .subscribe(                    next -> System.out.println(next),                    error -> System.err.println(error),                    () -> System.out.println("Stream ended.")            );    System.out.println("Async proof");}

And last but not least, if you want to reuse your async call, you might want to take a look at Hystrix, which - in addition to a bazillion super cool other stuff - would allow you to write something like this:

For example:

public class AsyncGetCommand extends HystrixCommand<String> {    private final String url;    public AsyncGetCommand(final String url) {        super(Setter.withGroupKey(HystrixCommandGroupKey.Factory.asKey("HTTP"))                .andCommandPropertiesDefaults(HystrixCommandProperties.Setter()                        .withExecutionIsolationThreadTimeoutInMilliseconds(5000)));        this.url = url;    }    @Override    protected String run() throws Exception {        return ClientBuilder.newClient().target(url).request().get(String.class);    } }

Calling this command would look like:

public static void main(String ...args) {    new AsyncGetCommand("http://www.nofrag.com").observe().subscribe(            next -> System.out.println(next),            error -> System.err.println(error),            () -> System.out.println("Stream ended.")    );    System.out.println("Async proof");}

PS: I know the thread is old, but it felt wrong that no ones mentions the Rx/Hystrix way in the up-voted answers.

You may also want to look at Async Http Client.

Note that java11 now offers a new HTTP api HttpClient, which supports fully asynchronous operation, using java's CompletableFuture.

It also supports a synchronous version, with calls like send, which is synchronous, and sendAsync, which is asynchronous.

Example of an async request (taken from the apidoc):

   HttpRequest request = HttpRequest.newBuilder()        .uri(URI.create("https://example.com/"))        .timeout(Duration.ofMinutes(2))        .header("Content-Type", "application/json")        .POST(BodyPublishers.ofFile(Paths.get("file.json")))        .build();   client.sendAsync(request, BodyHandlers.ofString())        .thenApply(HttpResponse::body)        .thenAccept(System.out::println);