Ndtyjky

I'm looking for java client that can connect to a HTTP/2 based server.. The server is already supporting HTTP/2 API. I don't see the most popular Apache Http client https://hc.apache.org/ still supporting HTTP/2.

Does Apache have some implementation for Java client already that supports Http/2?

If not, Is there some java client that supports connecting to HTTP/2 preferably on Java 7?

Jetty's provides two HTTP/2 Java client APIs. Both require Java 8 and the mandatory use of the ALPN, as explained here.

Low level APIs

These APIs are based on HTTP2Client, it's based on the HTTP/2 concepts of session and streams and uses listeners to be notified of the HTTP/2 frames that arrive from the server.

    // Setup and start the HTTP2Client.

    HTTP2Client client = new HTTP2Client();

    SslContextFactory sslContextFactory = new SslContextFactory();

    client.addBean(sslContextFactory);

    client.start();



    // Connect to the remote host to obtains a Session.

    FuturePromise<Session> sessionPromise = new FuturePromise<>();

    client.connect(sslContextFactory, new InetSocketAddress(host, port), new ServerSessionListener.Adapter(), sessionPromise);

    Session session = sessionPromise.get(5, TimeUnit.SECONDS);



    // Use the session to make requests.

    HttpFields requestFields = new HttpFields();

    requestFields.put("User-Agent", client.getClass().getName() + "/" + Jetty.VERSION);

    MetaData.Request metaData = new MetaData.Request("GET", new HttpURI("https://webtide.com/"), HttpVersion.HTTP_2, requestFields);

    HeadersFrame headersFrame = new HeadersFrame(metaData, null, true);

    session.newStream(headersFrame, new Promise.Adapter<>(), new Stream.Listener.Adapter()

    {

        @Override

        public void onHeaders(Stream stream, HeadersFrame frame)

        {

            // Response headers.

            System.err.println(frame);

        }



        @Override

        public void onData(Stream stream, DataFrame frame, Callback callback)

        {

            // Response content.

            System.err.println(frame);

            callback.succeeded();

        }

    });

High Level APIs

Jetty's HttpClient provides a way to use different transports, one of which is the HTTP/2 transport. Applications will use the higher level HTTP APIs, but underneath Jetty will use HTTP/2 to transport the HTTP semantic.

In this way, applications can use the high level APIs provided by HttpClient transparently, and factor out what transport to use in configuration or startup code.

    // Setup and start HttpClient with HTTP/2 transport.

    HTTP2Client http2Client = new HTTP2Client();

    SslContextFactory sslContextFactory = new SslContextFactory();

    HttpClient httpClient = new HttpClient(new HttpClientTransportOverHTTP2(http2Client), sslContextFactory);

    httpClient.start();



    // Make a request.

    ContentResponse response = httpClient.GET("https://webtide.com/");

There is OkHttp: An HTTP & HTTP/2 client for Android and Java applications.

Jetty has support for HTTP2 starting from version 9.3. This includes the server and the client.

Apache httpclient-5 beta supports http/2 from jdk9 or above

example :

public static void main(final String args) throws Exception {

    final SSLContext sslContext = SSLContexts.custom().loadTrustMaterial(new TrustAllStrategy()).build();

    final PoolingAsyncClientConnectionManager connectionManager = PoolingAsyncClientConnectionManagerBuilder.create().setTlsStrategy(new H2TlsStrategy(sslContext, NoopHostnameVerifier.INSTANCE)).build();

    final IOReactorConfig ioReactorConfig = IOReactorConfig.custom().setSoTimeout(Timeout.ofSeconds(5)).build();

    final MinimalHttpAsyncClient client = HttpAsyncClients.createMinimal(HttpVersionPolicy.FORCE_HTTP_2, H2Config.DEFAULT, null, ioReactorConfig, connectionManager);



    client.start();

    final HttpHost target = new HttpHost("localhost", 8082, "https");

    final Future<AsyncClientEndpoint> leaseFuture = client.lease(target, null);

    final AsyncClientEndpoint endpoint = leaseFuture.get(10, TimeUnit.SECONDS);

    try {

        String requestUris = new String {"/"};

        CountDownLatch latch = new CountDownLatch(requestUris.length);

        for (final String requestUri: requestUris) {

            SimpleHttpRequest request = SimpleHttpRequest.get(target, requestUri);

            endpoint.execute(SimpleRequestProducer.create(request), SimpleResponseConsumer.create(), new FutureCallback<SimpleHttpResponse>() {

                    @Override

                    public void completed(final SimpleHttpResponse response) {

                        latch.countDown();

                        System.out.println(requestUri + "->" + response.getCode());

                        System.out.println(response.getBody());

                    }



                    @Override

                    public void failed(final Exception ex) {

                        latch.countDown();

                        System.out.println(requestUri + "->" + ex);

                        ex.printStackTrace();

                    }



                    @Override

                    public void cancelled() {

                        latch.countDown();

                        System.out.println(requestUri + " cancelled");

                    }



                });

        }

        latch.await();

    } catch (Exception e) {

        e.printStackTrace();

    }finally {

        endpoint.releaseAndReuse();

    }



    client.shutdown(ShutdownType.GRACEFUL);

}

refer : https://hc.apache.org/httpcomponents-client-5.0.x/examples-async.html