如何实现一个异步的HTTP客户端输入流，而不是字节数组输入流？

Question

我正在使用异步Http客户端从互联网下载大量（可能很大）的文件。在我的情况下，我需要将这些下载URL的字节InputStream发送到另一个服务进行解析。一个天真的做法是这样的：

AsyncHttpClient asyncHttpClient = Dsl.asyncHttpClient(Dsl.config()
    .setMaxConnectionsPerHost(-1)
    .setMaxConnections(-1)
    .setPooledConnectionIdleTimeout(60 * 10 * 1000)
    .setConnectionTtl(6 * 60 * 1000)
    .setConnectTimeout(5 * 1000)
    .setRequestTimeout(5 * 60 * 1000)
    .setFollowRedirect(true)
    .setRealm(new Realm.Builder(username, password)
        .setNtlmDomain(domain)
        .setScheme(Realm.AuthScheme.NTLM)
        .build())
Response httpGetResponse = asyncHttpClient.prepareGet(url).execute().get();
return httpGetResponse.getResponseBodyAsStream();

但是在异步Http请求的教程中，我们了解到与HTTP Components Http客户端不同的是，异步Http客户端将整个文件下载到内存中。这在我的情况下很快会导致OOM（内存溢出）问题。因此，另一种选择是：

Response httpGetResponse = asyncHttpClient.prepareGet(url).execute(new AsyncHandler<Response>() {
    private final Response.ResponseBuilder builder = new Response.ResponseBuilder();

    @Override
    public State onBodyPartReceived(HttpResponseBodyPart bodyPart) throws Exception {
      bodyPart.getBodyByteBuffer(); // Each chunk of bytes will be fed into this method.
                                    // I need to write these bytes to the resuting input stream
                                    // without streaming them all into memory.
      return State.CONTINUE;
    }

    @Override
    public State onHeadersReceived(HttpHeaders headers) throws Exception {
      builder.accumulate(headers);
      return State.CONTINUE;
    }

    @Override
    public State onStatusReceived(HttpResponseStatus responseStatus) throws Exception {
      builder.accumulate(responseStatus);
      return State.CONTINUE;
    }

    @Override
    public Response onCompleted() throws Exception {
      return builder.build();
    }

    @Override
    public void onThrowable(Throwable t) {

    }
  }).get();

什么是获取输入流中字节的最简单、最干净的方法？

我有两个想法：

1）将输入写入文件，然后流式传输文件 或者 2）立即返回一个管道输入流，字节将在接收到它们时被写入管道输入流。

是否有人可以分享一个可用的示例？

- Nicholas DiPiazza

Answer 1

我正确地假设有人已经完成了这个任务。实际上，在我搜索“异步http客户端”和“管道输入流”后，我在项目本身中找到了这个：

https://github.com/AsyncHttpClient/async-http-client/blob/master/client/src/main/java/org/asynchttpclient/handler/BodyDeferringAsyncHandler.java

用法：

  PipedInputStream pipedInputStream = new PipedInputStream();
  PipedOutputStream pipedOutputStream = new PipedOutputStream(pipedInputStream);
  BodyDeferringAsyncHandler bodyDeferringAsyncHandler = new BodyDeferringAsyncHandler(pipedOutputStream);
  Future<Response> futureResponse = asyncHttpClient.prepareGet(url).execute(bodyDeferringAsyncHandler);
  Response response = bodyDeferringAsyncHandler.getResponse();
  if (response.getStatusCode() == 200) {
    return new BodyDeferringAsyncHandler.BodyDeferringInputStream(futureResponse,
        bodyDeferringAsyncHandler,
        pipedInputStream);
  } else {
    return null;
  }

- Nicholas DiPiazza