AsyncHttpClient

Async Http Client

Asynchronous Http and WebSocket Client library for Java
Under Other
By AsyncHttpClient

java netty async asynchttpclient ahc

Async Http Client

Follow @AsyncHttpClient on Twitter.


The AsyncHttpClient (AHC) library allows Java applications to easily execute HTTP requests and asynchronously process HTTP responses.
The library also supports the WebSocket Protocol.


It's built on top of Netty. It's currently compiled on Java 8 but runs on Java 9 too.


New Roadmap RFCs!

Well, not really RFCs, but as I am ramping up to release a new version, I would appreciate the comments from the community. Please add an issue and label it RFC and I'll take a look!


Installation

Binaries are deployed on Maven Central.


Import the AsyncHttpClient Bill of Materials (BOM) to add dependency management for AsyncHttpClient artifacts to your project:


xml
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.asynchttpclient</groupId>
<artifactId>async-http-client-bom</artifactId>
<version>LATEST_VERSION</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>


Add a dependency on the main AsyncHttpClient artifact:


xml
<dependencies>
<dependency>
<groupId>org.asynchttpclient</groupId>
<artifactId>async-http-client</artifactId>
</dependency>
</dependencies>


The async-http-client-extras-* and other modules can also be added without having to specify the version for each dependency, because they are all managed via the BOM.


Version

AHC doesn't use SEMVER, and won't.



Check CHANGES.md for migration path between versions.


Basics

Feel free to check the Javadoc or the code for more information.


Dsl

Import the Dsl helpers to use convenient methods to bootstrap components:


java
import static org.asynchttpclient.Dsl.*;


Client

```java
import static org.asynchttpclient.Dsl.*;


AsyncHttpClient asyncHttpClient = asyncHttpClient();
```


AsyncHttpClient instances must be closed (call the close method) once you're done with them, typically when shutting down your application.
If you don't, you'll experience threads hanging and resource leaks.


AsyncHttpClient instances are intended to be global resources that share the same lifecycle as the application.
Typically, AHC will usually underperform if you create a new client for each request, as it will create new threads and connection pools for each.
It's possible to create shared resources (EventLoop and Timer) beforehand and pass them to multiple client instances in the config. You'll then be responsible for closing those shared resources.


Configuration

Finally, you can also configure the AsyncHttpClient instance via its AsyncHttpClientConfig object:


```java
import static org.asynchttpclient.Dsl.*;


AsyncHttpClient c = asyncHttpClient(config().setProxyServer(proxyServer("127.0.0.1", 38080)));
```


HTTP
Sending Requests
Basics

AHC provides 2 APIs for defining requests: bound and unbound.
AsyncHttpClient and Dsl` provide methods for standard HTTP methods (POST, PUT, etc) but you can also pass a custom one.


```java
import org.asynchttpclient.*;


// bound
Future whenResponse = asyncHttpClient.prepareGet("http://www.example.com/").execute();


// unbound
Request request = get("http://www.example.com/").build();
Future whenResponse = asyncHttpClient.executeRequest(request);
```


Setting Request Body

Use the setBody method to add a body to the request.


This body can be of type:
* java.io.File
* byte[]
* List<byte[]>
* String
* java.nio.ByteBuffer
* java.io.InputStream
* Publisher<io.netty.bufferByteBuf>
* org.asynchttpclient.request.body.generator.BodyGenerator


BodyGenerator is a generic abstraction that let you create request bodies on the fly.
Have a look at FeedableBodyGenerator if you're looking for a way to pass requests chunks on the fly.


Multipart

Use the addBodyPart method to add a multipart part to the request.


This part can be of type:
* ByteArrayPart
* FilePart
* InputStreamPart
* StringPart


Dealing with Responses
Blocking on the Future

execute methods return a java.util.concurrent.Future. You can simply block the calling thread to get the response.


java
Future<Response> whenResponse = asyncHttpClient.prepareGet("http://www.example.com/").execute();
Response response = whenResponse.get();


This is useful for debugging but you'll most likely hurt performance or create bugs when running such code on production.
The point of using a non blocking client is to NOT BLOCK the calling thread!


Setting callbacks on the ListenableFuture

execute methods actually return a org.asynchttpclient.ListenableFuture similar to Guava's.
You can configure listeners to be notified of the Future's completion.


java
ListenableFuture<Response> whenResponse = ???;
Runnable callback = () -> {
try {
Response response = whenResponse.get();
System.out.println(response);
} catch (InterruptedException | ExecutionException e) {
e.printStackTrace();
}
};
java.util.concurrent.Executor executor = ???;
whenResponse.addListener(() -> ???, executor);


If the executor parameter is null, callback will be executed in the IO thread.
You MUST NEVER PERFORM BLOCKING operations in there, typically sending another request and block on a future.


Using custom AsyncHandlers

execute methods can take an org.asynchttpclient.AsyncHandler to be notified on the different events, such as receiving the status, the headers and body chunks.
When you don't specify one, AHC will use a org.asynchttpclient.AsyncCompletionHandler;


AsyncHandler methods can let you abort processing early (return AsyncHandler.State.ABORT) and can let you return a computation result from onCompleted that will be used as the Future's result.
See AsyncCompletionHandler implementation as an example.


The below sample just capture the response status and skips processing the response body chunks.


Note that returning ABORT closes the underlying connection.


```java
import static org.asynchttpclient.Dsl.;
import org.asynchttpclient.
;
import io.netty.handler.codec.http.HttpHeaders;


Future whenStatusCode = asyncHttpClient.prepareGet("http://www.example.com/")
.execute(new AsyncHandler() {
private Integer status;
@Override
public State onStatusReceived(HttpResponseStatus responseStatus) throws Exception {
status = responseStatus.getStatusCode();
return State.ABORT;
}
@Override
public State onHeadersReceived(HttpHeaders headers) throws Exception {
return State.ABORT;
}
@Override
public State onBodyPartReceived(HttpResponseBodyPart bodyPart) throws Exception {
return State.ABORT;
}
@Override
public Integer onCompleted() throws Exception {
return status;
}
@Override
public void onThrowable(Throwable t) {
}
});


Integer statusCode = whenStatusCode.get();
```


Using Continuations

ListenableFuture has a toCompletableFuture method that returns a CompletableFuture.
Beware that canceling this CompletableFuture won't properly cancel the ongoing request.
There's a very good chance we'll return a CompletionStage instead in the next release.


java
CompletableFuture<Response> whenResponse = asyncHttpClient
.prepareGet("http://www.example.com/")
.execute()
.toCompletableFuture()
.exceptionally(t -> { /* Something wrong happened... */ } )
.thenApply(response -> { /* Do something with the Response */ return resp; });
whenResponse.join(); // wait for completion


You may get the complete maven project for this simple demo from org.asynchttpclient.example


WebSocket

Async Http Client also supports WebSocket.
You need to pass a WebSocketUpgradeHandler where you would register a WebSocketListener.


```java
WebSocket websocket = c.prepareGet("ws://demos.kaazing.com/echo")
.execute(new WebSocketUpgradeHandler.Builder().addWebSocketListener(
new WebSocketListener() {


      @Override
public void onOpen(WebSocket websocket) {
websocket.sendTextFrame("...").sendTextFrame("...");
}

@Override
public void onClose(WebSocket websocket) {
}

@Override
public void onTextFrame(String payload, boolean finalFragment, int rsv) {
System.out.println(payload);
}

@Override
public void onError(Throwable t) {
}
}).build()).get();


```


Reactive Streams

AsyncHttpClient has built-in support for reactive streams.


You can pass a request body as a Publisher<ByteBuf> or a ReactiveStreamsBodyGenerator.


You can also pass a StreamedAsyncHandler<T> whose onStream method will be notified with a Publisher<HttpResponseBodyPart>.


See tests in package org.asynchttpclient.reactivestreams for examples.


WebDAV

AsyncHttpClient has build in support for the WebDAV protocol.
The API can be used the same way normal HTTP request are made:


java
Request mkcolRequest = new RequestBuilder("MKCOL").setUrl("http://host:port/folder1").build();
Response response = c.executeRequest(mkcolRequest).get();

or


java
Request propFindRequest = new RequestBuilder("PROPFIND").setUrl("http://host:port").build();
Response response = c.executeRequest(propFindRequest, new AsyncHandler() {
// ...
}).get();


More

You can find more information on Jean-Fran├žois Arcand's blog. Jean-Fran├žois is the original author of this library.
Code is sometimes not up-to-date but gives a pretty good idea of advanced features.



User Group

Keep up to date on the library development by joining the Asynchronous HTTP Client discussion group


Google Group


Contributing

Of course, Pull Requests are welcome.


Here are the few rules we'd like you to respect if you do so: