Apache 或其他一些 CLIENT JAVA 实现是否支持 HTTP/2？

Question

我正在寻找可以连接到基于 HTTP/2 的服务器的 Java 客户端。该服务器已经支持 HTTP/2 API。我看不到最流行的 Apache Http 客户端 https://hc.apache.org/ 仍然支持 HTTP/2。

Apache 是否已经有一些支持 Http/2 的 Java 客户端实现？

如果没有，是否有一些 Java 客户端支持连接到 HTTP/2，最好是在 Java 7 上？

Answer 1

Jetty 提供了两个 HTTP/2 Java 客户端 API。两者都需要 Java 8（或更高版本）和强制使用 ALPN，如 here 所述。

低级 API

这些 API 基于 HTTP2Client，它基于 session 和 streams 的 HTTP/2 概念，并使用侦听器来通知 HTTP/2 从服务器到达的帧。

    // 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();
        }
    });

高级 API

Jetty 的HttpClient 提供了一种使用different transports 的方法，其中之一就是HTTP/2 transport。应用程序将使用更高级别的 HTTP API，但在 Jetty 下将使用 HTTP/2 来传输 HTTP 语义。

通过这种方式，应用程序可以透明地使用 HttpClient 提供的高级 API，并确定在配置或启动代码中使用什么传输。

    // 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/");

Answer 2

有OkHttp: An HTTP & HTTP/2 client for Android and Java applications。

Answer 3

Jetty 从 9.3 版开始支持 HTTP2。这包括服务器和the client。

Answer 4

Apache httpclient-5 beta 支持 jdk9 或更高版本的 http/2

例子：

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);
}

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