How do you create an asynchronous HTTP request in JAVA

Question

I m fairly new to Java  so this may seem obvious to some  I ve worked a lot with ActionScript  which is very much event based and I love that  I recently tried to write a small bit of Java code that does a POST request  but I ve been faced with the problem that it s a synchronous request  so the code execution waits for the request to complete  time out or present an error   How can I create an asynchronous request  where the code continues the execution and a callback is invoked when the HTTP request is complete  I ve glanced at threads  but I m thinking it s overkill

User · Answer

It has to be made clear the HTTP protocol is synchronous and this has nothing to do with the programming language. Client sends a request and gets a synchronous response.

If you want to an asynchronous behavior over HTTP, this has to be built over HTTP (I don't know anything about ActionScript but I suppose that this is what the ActionScript does too). There are many libraries that could give you such functionality (e.g. Jersey SSE). Note that they do somehow define dependencies between the client and the server as they do have to agree on the exact non standard communication method above HTTP.

If you cannot control both the client and the server or if you don't want to have dependencies between them, the most common approach of implementing asynchronous (e.g. event based) communication over HTTP is using the webhooks approach (you can check this for an example implementation in java).

Hope I helped!

User · Answer

You may also want to look at Async Http Client

User · Answer

Apache HttpComponents also have an async http client now too            lt dependency gt         lt groupId gt org apache httpcomponents lt  groupId gt         lt artifactId gt httpasyncclient lt  artifactId gt         lt version gt 4 0-beta4 lt  version gt       lt  dependency gt       import java io IOException  import java nio CharBuffer  import java util concurrent Future   import org apache http HttpResponse  import org apache http impl nio client CloseableHttpAsyncClient  import org apache http impl nio client HttpAsyncClients  import org apache http nio IOControl  import org apache http nio client methods AsyncCharConsumer  import org apache http nio client methods HttpAsyncMethods  import org apache http protocol HttpContext   public class HttpTest      public static void main final String   args  throws Exception        final CloseableHttpAsyncClient httpclient   HttpAsyncClients          createDefault        httpclient start        try         final Future lt Boolean gt  future   httpclient execute            HttpAsyncMethods createGet  http   www google com               new MyResponseConsumer    null         final Boolean result   future get          if  result    null  amp  amp  result booleanValue              System out println  Request successfully executed            else           System out println  Request failed                  System out println  Shutting down          finally         httpclient close              System out println  Done           static class MyResponseConsumer extends AsyncCharConsumer lt Boolean gt          Override     protected void onResponseReceived final HttpResponse response                Override     protected void onCharReceived final CharBuffer buf  final IOControl ioctrl          throws IOException         while  buf hasRemaining              System out print buf get                         Override     protected void releaseResources                 Override     protected Boolean buildResult final HttpContext context          return Boolean TRUE

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Here is a solution using apache HttpClient and making the call in a separate thread  This solution is useful if you are only making one async call  If you are making multiple calls I suggest using apache HttpAsyncClient and placing the calls in a thread pool  import java lang Thread   import org apache hc client5 http classic methods HttpGet  import org apache hc client5 http impl classic CloseableHttpClient  import org apache hc client5 http impl classic HttpClients   public class ApacheHttpClientExample       public static void main final String   args  throws Exception           try  final CloseableHttpClient httpclient   HttpClients createDefault                  final HttpGet httpget   new HttpGet  quot http   httpbin org get quot                new Thread    - gt                     final String responseBody   httpclient execute httpget                  start

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Based on a link to Apache HTTP Components on this SO thread  I came across the Fluent facade API for HTTP Components   An example there shows how to set up a queue of asynchronous HTTP requests  and get notified of their completion failure cancellation    In my case  I didn t need a queue  just one async request at a time   Here s where I ended up  also using URIBuilder from HTTP Components  example here    import java net URI  import java net URISyntaxException  import java util concurrent ExecutorService  import java util concurrent Executors  import java util concurrent Future  import org apache http client fluent Async  import org apache http client fluent Content  import org apache http client fluent Request  import org apache http client utils URIBuilder  import org apache http concurrent FutureCallback          URIBuilder builder   new URIBuilder    builder setScheme  http   setHost  myhost com   setPath   folder        setParameter  query0    val0        setParameter  query1    val1            URI requestURL   null  try       requestURL   builder build      catch  URISyntaxException use      ExecutorService threadpool   Executors newFixedThreadPool 2   Async async   Async newInstance   use threadpool   final Request request   Request Get requestURL    Future lt Content gt  future   async execute request  new FutureCallback lt Content gt          public void failed  final Exception e            System out println e getMessage          request             public void completed  final Content content            System out println  Request completed     request           System out println  Response  n   content asString                public void cancelled

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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 lt Response gt  getAsyncHttp final String url            return ClientBuilder newClient   target url  request   async   get               public static void main String    args  throws InterruptedException  ExecutionException           Future lt Response gt  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 - gt  System out println next                       error - gt  System err println error                          - gt  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 lt String gt         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 - gt  System out println next               error - gt  System err println error                  - gt  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

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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

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You may want to take a look at this question  Asynchronous IO in Java   It looks like your best bet  if you don t want to wrangle the threads yourself is a framework  The previous post mentions Grizzly  https   grizzly dev java net   and Netty  http   www jboss org netty     From the netty docs   The Netty project is an effort to provide an asynchronous event-driven network application framework and tools for rapid development of maintainable high performance  amp  high scalability protocol servers  amp  clients

[java] How do you create an asynchronous HTTP request in JAVA?

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