OkHttp实现带进度条上传文件

在 OkHttp 中实现带进度条上传文件，可以使用 RequestBody 的子类 ProgressRequestBody 来实现，具体代码如下：

public class ProgressRequestBody extends RequestBody {
    private RequestBody requestBody;
    private UploadProgressListener progressListener;

    public ProgressRequestBody(RequestBody requestBody, UploadProgressListener progressListener) {
        this.requestBody = requestBody;
        this.progressListener = progressListener;
    }

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

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

    @Override
    public void writeTo(BufferedSink sink) throws IOException {
        BufferedSink bufferedSink;
        if (sink instanceof Buffer) {
            bufferedSink = sink;
        } else {
            bufferedSink = Okio.buffer(sink);
        }

        CountingSink countingSink = new CountingSink(bufferedSink);
        BufferedSink progressSink = Okio.buffer(countingSink);

        requestBody.writeTo(progressSink);

        progressSink.flush();

        progressListener.onProgress(countingSink.getContentLength());
    }

    private class CountingSink extends ForwardingSink {
        private long contentLength;
        private long bytesWritten;

        public CountingSink(Sink delegate) {
            super(delegate);
            contentLength = -1;
            bytesWritten = 0;
        }

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

            if (contentLength == -1) {
                contentLength = contentLength();
            }

            bytesWritten += byteCount;
        }

        public long getContentLength() {
            return contentLength;
        }

        public long getBytesWritten() {
            return bytesWritten;
        }
    }
}

其中，UploadProgressListener 为上传进度监听器，代码如下：

public interface UploadProgressListener {
    void onProgress(long bytesWritten);
}

在上传文件的时候，将 ProgressRequestBody 作为 RequestBody 使用即可：

OkHttpClient client = new OkHttpClient();
File file = new File("path/to/file");
RequestBody requestBody = new MultipartBody.Builder()
        .setType(MultipartBody.FORM)
        .addFormDataPart("file", file.getName(), new ProgressRequestBody(RequestBody.create(MediaType.parse("application/octet-stream"), file), new UploadProgressListener() {
            @Override
            public void onProgress(long bytesWritten) {
                // 更新上传进度
            }
        }))
        .build();
Request request = new Request.Builder()
        .url("http://localhost/upload")
        .post(requestBody)
        .build();
Response response = client.newCall(request).execute();

在 ProgressRequestBody 中，每次写入数据的时候，都会回调 onProgress 方法，可以在这里更新上传进度。