okhttp、retrofit 2未提供上传、下载的进度回调，但是很多应用在UI显示方面需要加入进度显示。实现方式如下：

========

下载进度及拦截器：

public class DownloadProgressInterceptor implements Interceptor {
  private DownloadProgressListener progressListener;

  public DownloadProgressInterceptor(DownloadProgressListener progressListener) {
    this.progressListener = progressListener;
  }

  @Override public Response intercept(Chain chain) throws IOException {
    Response originalResponse = chain.proceed(chain.request());
    return originalResponse.newBuilder()
        .body(new DownloadProgressResponseBody(originalResponse.body(), progressListener))
        .build();
  }

  private static class DownloadProgressResponseBody extends ResponseBody {

    private final ResponseBody responseBody;
    private final DownloadProgressListener progressListener;
    private BufferedSource bufferedSource;

    public DownloadProgressResponseBody(ResponseBody responseBody,
        DownloadProgressListener progressListener) {
      this.responseBody = responseBody;
      this.progressListener = progressListener;
    }

    @Override public MediaType contentType() {
      return responseBody.contentType();
    }

    @Override public long contentLength() throws IOException {
      return responseBody.contentLength();
    }

    @Override public BufferedSource source() throws IOException {
      if (bufferedSource == null) {
        bufferedSource = Okio.buffer(source(responseBody.source()));
      }
      return bufferedSource;
    }

    private Source source(Source source) {
      return new ForwardingSource(source) {
        long totalBytesRead = 0L;

        @Override public long read(Buffer sink, long byteCount) throws IOException {
          long bytesRead = super.read(sink, byteCount);
          // read() returns the number of bytes read, or -1 if this source is exhausted.
          totalBytesRead += bytesRead != -1 ? bytesRead : 0;

          if (null != progressListener) {
            progressListener.update(totalBytesRead, responseBody.contentLength(), bytesRead == -1);
          }
          return bytesRead;
        }
      };
    }
  }

  public interface DownloadProgressListener {
    void update(long bytesRead, long contentLength, boolean done);
  }
}

上传进度

/**
 * Decorates an OkHttp request body to count the number of bytes written when writing it. Can
 * decorate any request body, but is most useful for tracking the upload progress of large
 * multipart requests.
 *
 * @author Leo Nikkilä
 */
public class CountingRequestBody extends RequestBody {

  protected RequestBody delegate;
  protected Listener listener;

  protected CountingSink countingSink;

  public CountingRequestBody(RequestBody delegate, Listener listener) {
    this.delegate = delegate;
    this.listener = listener;
  }

  @Override public MediaType contentType() {
    return delegate.contentType();
  }

  @Override public long contentLength() {
    try {
      return delegate.contentLength();
    } catch (IOException e) {
      e.printStackTrace();
    }
    return -1;
  }

  @Override public void writeTo(BufferedSink sink) throws IOException {
    BufferedSink bufferedSink;

    countingSink = new CountingSink(sink);
    bufferedSink = Okio.buffer(countingSink);

    delegate.writeTo(bufferedSink);

    bufferedSink.flush();
  }

  protected final class CountingSink extends ForwardingSink {

    private long bytesWritten = 0;

    public CountingSink(Sink delegate) {
      super(delegate);
    }

    @Override public void write(Buffer source, long byteCount) throws IOException {
      super.write(source, byteCount);

      bytesWritten += byteCount;
      listener.onRequestProgress(bytesWritten, contentLength());
    }
  }

  public static interface Listener {

    public void onRequestProgress(long bytesWritten, long contentLength);
  }
}

上传进度拦截器

public class UpLoadProgressInterceptor implements Interceptor {
  private CountingRequestBody.Listener progressListener;

  public UpLoadProgressInterceptor(CountingRequestBody.Listener progressListener) {
    this.progressListener = progressListener;
  }

  @Override public Response intercept(Chain chain) throws IOException {
    Request originalRequest = chain.request();

    if (originalRequest.body() == null) {
      return chain.proceed(originalRequest);
    }

    Request progressRequest = originalRequest.newBuilder()
        .method(originalRequest.method(),
            new CountingRequestBody(originalRequest.body(), progressListener))
        .build();

    return chain.proceed(progressRequest);
  }
}

====

使用方式：

如果只是在okhttp中使用，上传可以使用CountingRequestBody类，下载可以把DownloadProgressResponseBody单独抽出来使用。使用时new出来，传入相应参数即可。

如果是在retrofit 2中使用，可以使用拦截器的方式。类似DownloadProgressInterceptor，UpLoadProgressInterceptor，关键代码如下：

OkHttpClientManager.getInstance()
    .getOkHttpClient()
    .networkInterceptors()
    .add(upLoadProgressInterceptor);

/*上传图片请求*/
  @Multipart @POST(ConstantsNetInterface.COURSE_UPLOAD_PIC) Call<UploadPicBean> uploadPic(
      @PartMap Map<String, ?> params);

RequestBody fileBody = RequestBody.create(MediaType.parse("image/*"), imgFile);
        mParams = new HashMap<>();//请求参数
        mParams.put("file\"; filename=\"" + imgFile.getName() + "", fileBody);

===

关于Batow提的问题（为方便例子使用了Rxjava,不使用Rxjava则是用下面的Call来处理）：

@GET("{path}") @Streaming Call<ResponseBody> download(@Path("path") String path);

@GET("{path}") @Streaming Observable<ResponseBody> downloadFile(@Path("path") String path);

public static void downloadFile(final String path, final Subscriber<Boolean> subscriber) {

  RetrofitManager.getInstance()
      .createDownloadApiService(Api.class)
      .downloadFile(path)
      .map(new Func1<ResponseBody, Boolean>() {
        @Override public Boolean call(ResponseBody responseBody) {
          return writeFileToSD(path, responseBody);
        }
      })
      .subscribeOn(Schedulers.io())
      .observeOn(AndroidSchedulers.mainThread())
      .subscribe(subscriber);
}

private static boolean writeFileToSD(String pathName, ResponseBody responseBody) {
  String sdStatus = Environment.getExternalStorageState();
  if (!sdStatus.equals(Environment.MEDIA_MOUNTED)) {
    Logger.d("SD card is not avaiable/writeable right now.");
    return false;
  }
  try {

    String fileName = pathName.substring(pathName.lastIndexOf("/"));

    Logger.d("fileName-->" + fileName);

    File path = Environment.getExternalStorageDirectory();
    File file = new File(path.getPath() + fileName);

    if (!file.exists()) {
      Logger.d("Create the file:" + file.getPath());
      file.createNewFile();
    }
    FileOutputStream stream = new FileOutputStream(file);
    byte[] buf = responseBody.bytes();
    stream.write(buf);
    stream.close();

    return true;
  } catch (Exception e) {
    Logger.e("Error on writeFilToSD.");
    e.printStackTrace();
  }
  return false;
}

NetworkWrapper.downloadFile(path, new Subscriber<Boolean>() {
  @Override public void onCompleted() {
    Logger.d("onCompleted");
  }

  @Override public void onError(Throwable e) {
    Logger.d("onError:" + e);
  }

  @Override public void onNext(Boolean aBoolean) {
    Logger.d("onNext" + aBoolean);

    if (aBoolean) {
      Toast.makeText(DownloadActivity.this, "pic download finish", Toast.LENGTH_LONG)
          .show();
    }
  }
});

===

enjoy it！