OKHttp附件下载实现，进度监听

1.创建请求request

Request request = new Request.Builder().url(url).build();

2.获取response，由于是耗时操作，所以需要异步获取

 new Thread(new Runnable() {
            @Override
            public void run() {
                ...
                try {
                    Response response = okHttpClient.newCall(request).execute();
                    if (!response.isSuccessful() || response == null || response.body() == null) {
                        sendMessage(1, 0, 0, "");
                    } else {
                        //处理response
                        ...
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                    sendMessage(1, 0, 0, "");
                }
            }
        }).start();

3.处理获取的response，并进行进度监听

InputStream is = null;
byte[] buf = new byte[2048];
int len = 0;
FileOutputStream fos = null;
try {
    is = response.body().byteStream();
    int last = 0;
    final long total = response.body().contentLength();
    long sum = 0;
    fos = new FileOutputStream(new File(apkPath));
    while ((len = is.read(buf)) != -1) {
        sum += len;
        fos.write(buf, 0, len);
        int now = (int) (sum * 100 / total);
        if (last < now) {
            LogUtils.d("current:" + last + ";total:" + 100);
            sendMessage(3, last, 100, "");
            last = now;
        }
    }
    fos.flush();
    sendMessage(2, 0, 0, "");
} catch (IOException e) {
    e.printStackTrace();
    sendMessage(1, 0, 0, "");
} finally {
    try {
        if (is != null) {
           is.close();
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
    try {
        if (fos != null) {
           fos.close();
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
}

4.通知主线程进行相应的处理

public void sendMessage(int what, long current, long total, String msg) {
        Message message = Message.obtain();
        message.what = what;
        message.arg1 = (int) current;
        message.arg2 = (int) total;
        message.obj = msg;
        handler.sendMessage(message);
    }
     private Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            switch (msg.what) {
                case 1:
                    //下载失败
                    ...
                    break;
                case 2:
                    //下载成功
                    ...
                    break;
                case 3:
                    //下载进度
                    int current = msg.arg1;
                    int total = msg.arg2;
                    ...
                    break;
            }
        }
    };