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Async Http Client library purpose is to allow Java applications to easily execute HTTP requests and
asynchronously process the HTTP responses.
/*
* Copyright (c) 2010-2012 Sonatype, Inc. All rights reserved.
*
* This program is licensed to you under the Apache License Version 2.0,
* and you may not use this file except in compliance with the Apache License Version 2.0.
* You may obtain a copy of the Apache License Version 2.0 at http://www.apache.org/licenses/LICENSE-2.0.
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the Apache License Version 2.0 is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the Apache License Version 2.0 for the specific language governing permissions and limitations there under.
*/
package com.ning.http.client;
import com.ning.http.client.Response.ResponseBuilder;
import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.Semaphore;
/**
* An AsyncHandler that returns Response (without body, so status code and
* headers only) as fast as possible for inspection, but leaves you the option
* to defer body consumption.
*
* This class introduces new call: getResponse(), that blocks caller thread as
* long as headers are received, and return Response as soon as possible, but
* still pouring response body into supplied output stream. This handler is
* meant for situations when the "recommended" way (using
* client.prepareGet("http://foo.com/aResource").execute().get()
* would not work for you, since a potentially large response body is about to
* be GETted, but you need headers first, or you don't know yet (depending on
* some logic, maybe coming from headers) where to save the body, or you just
* want to leave body stream to some other component to consume it.
*
* All these above means that this AsyncHandler needs a bit of different
* handling than "recommended" way. Some examples:
*
*
* FileOutputStream fos = ...
* BodyDeferringAsyncHandler bdah = new BodyDeferringAsyncHandler(fos);
* // client executes async
* Future<Response> fr = client.prepareGet("http://foo.com/aresource").execute(
* bdah);
* // main thread will block here until headers are available
* Response response = bdah.getResponse();
* // you can continue examine headers while actual body download happens
* // in separate thread
* // ...
* // finally "join" the download
* fr.get();
*
*
*
* PipedOutputStream pout = new PipedOutputStream();
* BodyDeferringAsyncHandler bdah = new BodyDeferringAsyncHandler(pout);
* // client executes async
* Future<Response> fr = client.prepareGet("http://foo.com/aresource").execute(bdah);
* // main thread will block here until headers are available
* Response response = bdah.getResponse();
* if (response.getStatusCode() == 200) {
* InputStream pin = new BodyDeferringInputStream(fr,new PipedInputStream(pout));
* // consume InputStream
* ...
* } else {
* // handle unexpected response status code
* ...
* }
*
*/
public class BodyDeferringAsyncHandler implements AsyncHandler {
private final ResponseBuilder responseBuilder = new ResponseBuilder();
private final CountDownLatch headersArrived = new CountDownLatch(1);
private final OutputStream output;
private boolean responseSet;
private volatile Response response;
private volatile Throwable throwable;
private final Semaphore semaphore = new Semaphore(1);
public BodyDeferringAsyncHandler(final OutputStream os) {
this.output = os;
this.responseSet = false;
}
public void onThrowable(Throwable t) {
this.throwable = t;
// Counting down to handle error cases too.
// In "premature exceptions" cases, the onBodyPartReceived() and
// onCompleted()
// methods will never be invoked, leaving caller of getResponse() method
// blocked forever.
try {
semaphore.acquire();
} catch (InterruptedException e) {
// Ignore
} finally {
headersArrived.countDown();
semaphore.release();
}
try {
closeOut();
} catch (IOException e) {
// ignore
}
}
public STATE onStatusReceived(HttpResponseStatus responseStatus)
throws Exception {
responseBuilder.reset();
responseBuilder.accumulate(responseStatus);
return STATE.CONTINUE;
}
public STATE onHeadersReceived(HttpResponseHeaders headers)
throws Exception {
responseBuilder.accumulate(headers);
return STATE.CONTINUE;
}
public STATE onBodyPartReceived(HttpResponseBodyPart bodyPart)
throws Exception {
// body arrived, flush headers
if (!responseSet) {
response = responseBuilder.build();
responseSet = true;
headersArrived.countDown();
}
bodyPart.writeTo(output);
return STATE.CONTINUE;
}
protected void closeOut() throws IOException {
try {
output.flush();
} finally {
output.close();
}
}
public Response onCompleted() throws IOException {
if (!responseSet) {
response = responseBuilder.build();
responseSet = true;
}
// Counting down to handle error cases too.
// In "normal" cases, latch is already at 0 here
// But in other cases, for example when because of some error
// onBodyPartReceived() is never called, the caller
// of getResponse() would remain blocked infinitely.
// By contract, onCompleted() is always invoked, even in case of errors
headersArrived.countDown();
closeOut();
try {
semaphore.acquire();
if (throwable != null) {
IOException ioe = new IOException(throwable.getMessage());
ioe.initCause(throwable);
throw ioe;
} else {
// sending out current response
return responseBuilder.build();
}
} catch (InterruptedException e) {
return null;
} finally {
semaphore.release();
}
}
/**
* This method -- unlike Future.get() -- will block only as long,
* as headers arrive. This is useful for large transfers, to examine headers
* ASAP, and defer body streaming to it's fine destination and prevent
* unneeded bandwidth consumption. The response here will contain the very
* 1st response from server, so status code and headers, but it might be
* incomplete in case of broken servers sending trailing headers. In that
* case, the "usual" Future.get() method will return complete
* headers, but multiple invocations of getResponse() will always return the
* 1st cached, probably incomplete one. Note: the response returned by this
* method will contain everything except the response body itself,
* so invoking any method like Response.getResponseBodyXXX() will result in
* error! Also, please not that this method might return null
* in case of some errors.
*
* @return a {@link Response}
* @throws InterruptedException
*/
public Response getResponse() throws InterruptedException, IOException {
// block here as long as headers arrive
headersArrived.await();
try {
semaphore.acquire();
if (throwable != null) {
IOException ioe = new IOException(throwable.getMessage());
ioe.initCause(throwable);
throw ioe;
} else {
return response;
}
} finally {
semaphore.release();
}
}
// ==
/**
* A simple helper class that is used to perform automatic "join" for async
* download and the error checking of the Future of the request.
*/
public static class BodyDeferringInputStream extends FilterInputStream {
private final Future future;
private final BodyDeferringAsyncHandler bdah;
public BodyDeferringInputStream(final Future future,
final BodyDeferringAsyncHandler bdah, final InputStream in) {
super(in);
this.future = future;
this.bdah = bdah;
}
/**
* Closes the input stream, and "joins" (wait for complete execution
* together with potential exception thrown) of the async request.
*/
public void close() throws IOException {
// close
super.close();
// "join" async request
try {
getLastResponse();
} catch (Exception e) {
IOException ioe = new IOException(e.getMessage());
ioe.initCause(e);
throw ioe;
}
}
/**
* Delegates to {@link BodyDeferringAsyncHandler#getResponse()}. Will
* blocks as long as headers arrives only. Might return
* null. See
* {@link BodyDeferringAsyncHandler#getResponse()} method for details.
*
* @return a {@link Response}
* @throws InterruptedException
*/
public Response getAsapResponse() throws InterruptedException,
IOException {
return bdah.getResponse();
}
/**
* Delegates to Future#get() method. Will block
* as long as complete response arrives.
*
* @return a {@link Response}
* @throws InterruptedException
* @throws ExecutionException
*/
public Response getLastResponse() throws InterruptedException,
ExecutionException {
return future.get();
}
}
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