1.写一个上传监听的接口：

/**

 * Created by Zzm丶Fiona on 2017/7/31.

 */

public interface RetrofitProgressUploadListener {

    /**

     *

     * @param bytesWriting 已经写的字节数

     * @param totalBytes   文件的总字节数

     */

    void onProgress(long bytesWriting, long totalBytes);

}

2.重新写一个类继承于RequesBody:

package zzm.zzmotherthingsshouldknowfortheinterview.upload_progress;

import android.support.annotation.Nullable;

import java.io.IOException;

import okhttp3.MediaType;

import okhttp3.RequestBody;

import okio.Buffer;

import okio.BufferedSink;

import okio.ForwardingSink;

import okio.Okio;

import okio.Sink;

/**

 * Created by Zzm丶Fiona on 2017/7/31.

 */

public class ProgressRequestBody extends RequestBody {

    private final RetrofitProgressUploadListener retrofitProgressUploadListener;

    private final RequestBody requestBody;

    private BufferedSink bufferedSink;

    public ProgressRequestBody(RetrofitProgressUploadListener retrofitProgressUploadListener, RequestBody requestBody) {

        this.retrofitProgressUploadListener = retrofitProgressUploadListener;

        this.requestBody = requestBody;

    }

    @Nullable

    @Override

    public MediaType contentType() {

        return requestBody.contentType();

    }

    @Override

    public long contentLength() throws IOException {

        return requestBody.contentLength();

    }

    //关键方法

    @Override

    public void writeTo(BufferedSink sink) throws IOException {

        if (null == bufferedSink) bufferedSink = Okio.buffer(sink(sink));

        requestBody.writeTo(bufferedSink);

        //必须调用flush，否则最后一部分数据可能不会被写入

        bufferedSink.flush();

    }

    private Sink sink(Sink sink) {

        return new ForwardingSink(sink) {

            long bytesWriting = 0l;

            long contentLength = 0l;

            @Override

            public void write(Buffer source, long byteCount) throws IOException {

                super.write(source, byteCount);

                if (0 == contentLength) contentLength = contentLength();

                bytesWriting += byteCount;

                       //调用接口，把上传文件的进度传过去

                retrofitProgressUploadListener.onProgress(bytesWriting, contentLength);

            }

        };

    }

}

3.封装的方法，返回ProgressRequestBody：

package zzm.zzmotherthingsshouldknowfortheinterview.utils;

import android.os.Handler;

import okhttp3.RequestBody;

import zzm.zzmotherthingsshouldknowfortheinterview.upload_progress.ProgressRequestBody;

import zzm.zzmotherthingsshouldknowfortheinterview.upload_progress.RetrofitProgressUploadListener;

import zzm.zzmotherthingsshouldknowfortheinterview.upload_progress.UploadProgressBean;

/**

 * Created by Zzm丶Fiona on 2017/7/31.

 */

public class RetrofitUploadProgressUtil {

//handler把数据传送到主线程中去处理，展示

    public static ProgressRequestBody getProgressRequesBody(RequestBody requestBody, final Handler handler) {

        return new ProgressRequestBody(new RetrofitProgressUploadListener() {

            UploadProgressBean uploadProgressBean = new UploadProgressBean();

            @Override

            public void onProgress(long bytesWriting, long totalBytes) {

                if (null == uploadProgressBean) uploadProgressBean = new UploadProgressBean();

                uploadProgressBean.setBytesWriting(bytesWriting);

                uploadProgressBean.setTotalBytes(totalBytes);

                handler.sendMessage(handler.obtainMessage(2, uploadProgressBean));

            }

        }, requestBody);

    }

}

4.把自己的写的类继承于RequesBody的ProgressRequestBody传进上传的表单中即可：

/**

 * Created by Zzm丶Fiona on 2017/7/30.

 */

public class UploadThingsByRetrofitActivity extends AppCompatActivity {

    @Override

    protected void onCreate(@Nullable Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        RequestBody requestBody = RequestBody.create(MediaType.parse("multipart/form-data"),你的上传文件-file);

        ProgressRequestBody progressRequestBody = RetrofitUploadProgressUtil.getProgressRequesBody(requestBody, new Handler() {

            @Override

            public void handleMessage(Message msg) {

           //进度的展示：

                super.handleMessage(msg);

                Log.i("zzmzzm", "已读的字节数：  " + ((UploadProgressBean) msg.obj).getTotalBytes());

                Log.i("zzmzzm", "上传的文件的字节总数：  " + ((UploadProgressBean) msg.obj).getTotalBytes());

            }

        });

        UploadThingsByRetrofitInterface uploadThingsByRetrofitInterface = getUploadThingsInterface();

        Call<ResponseBody> upload = uploadThingsByRetrofitInterface.uploadThings(MultipartBody.Part.createFormData(你的key,文件名,progressRequestBody));

        upload.enqueue(new Callback<ResponseBody>() {

            @Override

            public void onResponse(Call<ResponseBody> call, Response<ResponseBody> response) {

 //求情成功的返回

                try {

                    Log.i("zzmzzm", response.body().string());

                } catch (IOException e) {

                    Log.i("zzmzzm", e.toString());

                }

            }

 //求情失败的返回

            @Override

            public void onFailure(Call<ResponseBody> call, Throwable t) {

                Log.i("zzmzzm", t.toString());

            }

        });

    }

    private UploadThingsByRetrofitInterface getUploadThingsInterface() {

        return new Retrofit.Builder()

                .baseUrl("地址")

                .build()

                .create(UploadThingsByRetrofitInterface.class);

    }

}

其中的注解接口：

/**

 * Created by Zzm丶Fiona on 2017/7/30.

 */

public interface UploadThingsByRetrofitInterface {

    @Multipart

    @POST

    Call<ResponseBody> uploadThings(@Part MultipartBody.Part uplodThings);

}

补充说明：

MediaType.parse(String contentType)中参数contentType常见的有：

        text/html ： HTML格式

        text/plain ：纯文本格式

        text/xml ：  XML格式

        text/x-markdown： markdown文档

        image/gif ：gif图片格式

        image/jpeg ：jpg图片格式

        image/png：png图片格式

        以application开头的媒体格式类型：

        application/xhtml+xml ：XHTML格式

        application/xml     ： XML数据格式

        application/atom+xml  ：Atom XML聚合格式

        application/json    ： JSON数据格式

        application/pdf       ：pdf格式

        application/msword  ： Word文档格式

        application/octet-stream ： 二进制流数据（如常见的文件下载）

        application/x-www-form-urlencoded ： <form encType=””>中默认的encType，form表单数据被编码为key/value格式发送到服务器（表单默认的提交数据的格式）

        另外一种常见的媒体格式是上传文件之时使用的：

        multipart/form-data ： 需要在表单中进行文件上传时，就需要使用该格式

        另外的可以参考：http://www.w3school.com.cn/media/media_mimeref.asp