/** 下载pdf文件 */
    private String updateContentName;//文件名
    private Call call;
    private boolean isSuccess = true;//是否下载成功
    File target = null;

    protected void download(String downloadUrl) {
        showLoading();

        target = new File(Environment.getExternalStorageDirectory() + "/ZyHealthy/PDF", updateContentName);
        if (!target.getParentFile().exists()) {
            target.getParentFile().mkdirs();
        }

        OkHttpClient client = new OkHttpClient();
        //构造请求
        FormBody body = new FormBody.Builder()
                .build();
        final Request request1 = new Request.Builder()
                .url(downloadUrl)
                .post(body)
                .build();

        //包装Response使其支持进度回调
        call = ProgressHelper.addProgressResponseListener(client, uiProgressResponseListener).newCall(request1);
        call.enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                DesityUtil.showToast("下载失败，请尝试重新下载"+e);
                closeLoading();
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {

//                //方案一 String型的byte数组
//                int n = 1024;
//                String bodyStr = response.body().string();
//                try {
//                    String decodedString = new String(Base64Utils.decode(bodyStr));
//                    byte[] bytes = gson.fromJson(decodedString, new TypeToken<byte []>(){}.getType());
//                    FileOutputStream fos  = new FileOutputStream(target, true);
//                    int length = bytes.length;
//                    int start = 0;
//                    while (length > start+n) {
//                        fos.write(bytes, start, n);
//                        start = start+n;
//                    }
//                    if (length != start+n) {
//                        n = length-start;
//                        fos.write(bytes, start, n);
//                    }
//                    fos.flush();
//                    fos.close();
//                } catch (Exception e) {
//                    e.printStackTrace();
//                }


                //方案二 io流
                InputStream is = response.body().byteStream();
                FileOutputStream fos = new FileOutputStream(target, true);
                byte[] buffer = new byte[2048];//缓冲数组2kB
                int len;
                while ((len = is.read(buffer)) != -1) {
                    fos.write(buffer, 0, len);
                }
                fos.flush();
                is.close();
                fos.close();


                closeLoading();

                if (target.exists()) {
                    dialogFragment = new PromptDialogFragment();
                    dialogFragment
                            .setTitle(getResources().getString(R.string.tjbb_exportPDF) + "  /ZyHealthy/PDF/" + updateContentName)
                            .setMissVisibility(View.GONE)
                            .setSureOnClickListener(new NoDoubleClickListener() {

                                @Override
                                protected void onNoDoubleClick(View v) {
                                    dialogFragment.dismiss();
                                }
                            });
                    dialogFragment.show(getFragmentManager(), "FullScreenDownPDFFragment");
                } else {
                    DesityUtil.showToast("下载失败，请尝试重新下载");
                }
            }
        });
    }

    //这个是ui线程回调，可直接操作UI
    PromptDialogFragment dialogFragment;
    UIProgressListener uiProgressResponseListener = new UIProgressListener() {
        @Override
        public void onUIProgress(long bytesRead, long contentLength, boolean done) {
            isSuccess = done;
            NumberFormat formatter = new DecimalFormat("00.#");
//            String format = formatter.format(Float.valueOf(bytesRead) / contentLength * 100);
            // 下载完成 弹框提示
            if (100 <= (Float.valueOf(bytesRead) / contentLength * 100)) {
//                DesityUtil.showToast("下载完成");
            }
        }

        @Override
        public void onUIStart(long bytesRead, long contentLength, boolean done) {
            super.onUIStart(bytesRead, contentLength, done);
        }

        @Override
        public void onUIFinish(long bytesRead, long contentLength, boolean done) {
            super.onUIFinish(bytesRead, contentLength, done);
            isSuccess = done;
        }
    };


    public void showLoading() {
        if (loadingFragment != null)
            loadingFragment.show(getFragmentManager(), "loading");
    }

    public void closeLoading() {
        if (loadingFragment != null)
            loadingFragment.dismiss();
    }

通过接口返回数据下载文件的两种返回数据类型方法