Apache HttpComponents – HttpAsyncClient Quick Start

HttpAsyncClient Quick Start

1. Download 'Binary' package of the latest HttpAsyncClient 4.1 release or configure dependency on HttpAsyncClient module using a dependency manager of your choice as described here.
2. HttpAsyncClient 4.1 requires Java 1.6 or newer.
3. The code fragment below illustrates the most fundamental aspects of asynchronous request execution with HttpAsyncClient.

   CloseableHttpAsyncClient httpclient = HttpAsyncClients.createDefault();
   try {
       // Start the client
       httpclient.start();
   
       // Execute request
       final HttpGet request1 = new HttpGet("http://www.apache.org/");
       Future<HttpResponse> future = httpclient.execute(request1, null);
       // and wait until a response is received
       HttpResponse response1 = future.get();
       System.out.println(request1.getRequestLine() + "->" + response1.getStatusLine());
   
       // One most likely would want to use a callback for operation result
       final CountDownLatch latch1 = new CountDownLatch(1);
       final HttpGet request2 = new HttpGet("http://www.apache.org/");
       httpclient.execute(request2, new FutureCallback<HttpResponse>() {
   
           public void completed(final HttpResponse response2) {
               latch1.countDown();
               System.out.println(request2.getRequestLine() + "->" + response2.getStatusLine());
           }
   
           public void failed(final Exception ex) {
               latch1.countDown();
               System.out.println(request2.getRequestLine() + "->" + ex);
           }
   
           public void cancelled() {
               latch1.countDown();
               System.out.println(request2.getRequestLine() + " cancelled");
           }
   
       });
       latch1.await();
   
       // In real world one most likely would also want to stream
       // request and response body content
       final CountDownLatch latch2 = new CountDownLatch(1);
       final HttpGet request3 = new HttpGet("http://www.apache.org/");
       HttpAsyncRequestProducer producer3 = HttpAsyncMethods.create(request3);
       AsyncCharConsumer<HttpResponse> consumer3 = new AsyncCharConsumer<HttpResponse>() {
   
           HttpResponse response;
   
           @Override
           protected void onResponseReceived(final HttpResponse response) {
               this.response = response;
           }
   
           @Override
           protected void onCharReceived(final CharBuffer buf, final IOControl ioctrl) throws IOException {
               // Do something useful
           }
   
           @Override
           protected void releaseResources() {
           }
   
           @Override
           protected HttpResponse buildResult(final HttpContext context) {
               return this.response;
           }
   
       };
       httpclient.execute(producer3, consumer3, new FutureCallback<HttpResponse>() {
   
           public void completed(final HttpResponse response3) {
               latch2.countDown();
               System.out.println(request3.getRequestLine() + "->" + response3.getStatusLine());
           }
   
           public void failed(final Exception ex) {
               latch2.countDown();
               System.out.println(request3.getRequestLine() + "->" + ex);
           }
   
           public void cancelled() {
               latch2.countDown();
               System.out.println(request3.getRequestLine() + " cancelled");
           }
   
       });
       latch2.await();
   
   } finally {
       httpclient.close();
   }

4. Take a look at the HttpCore tutorial for introduction to fundamentals of asynchronous HTTP communication with HttpComponents.
5. Another good way of getting started with HttpAsyncClient is by seeing it in action. Take a look at the samples shipped with the release package or available online.