private void downloadFile(String apk){

        //下载进度条设置
        if(this.progress==null){
            this.progress = new ProgressDialog(this);
            this.progress .setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
            this.progress .setTitle("更新包下载");
            this.progress.setMax(100);
            //设置ProgressDialog 是否可以按退回按键取消
            this.progress.setCancelable(true);
            this.progress.setCanceledOnTouchOutside(false);
            //显示
            this.progress.show();
        }

        //url设置，okhttp设置
        final String url =apk;
        final long startTime = System.currentTimeMillis();
        Log.i("DOWNLOAD","startTime="+startTime);
        OkHttpClient okHttpClient = new OkHttpClient();

        //CALL 请求
        Request request = new Request.Builder().url(url).build();
        okHttpClient.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                // 下载失败
                e.printStackTrace();
            }
            @Override
            public void onResponse(Call call, Response response) throws IOException {
                InputStream is = null;
                byte[] buf = new byte[2048];
                int len = 0;
                FileOutputStream fos = null;
                // 储存下载文件的目录
                String savePath = Environment.getExternalStorageDirectory().getAbsolutePath();
                try {
                    is = response.body().byteStream();
                    long total = response.body().contentLength();
                    File file = new File(savePath, url.substring(url.lastIndexOf("/") + 1));
                    fos = new FileOutputStream(file);
                    long sum = 0;
                    while ((len = is.read(buf)) != -1) {
                        fos.write(buf, 0, len);
                        sum += len;
                        int progress = (int) (sum * 1.0f / total * 100);
                        // 下载中
                        loading(progress);
                    }
                    fos.flush();
                    // 下载完成
                    loadingFinish(file.getPath());
                } catch (Exception e) {
                    e.printStackTrace();
                    loadingFailure();
                } finally {
                    try {
                        if (is != null)
                            is.close();
                    } catch (IOException e) {
                    }
                    try {
                        if (fos != null)
                            fos.close();
                    } catch (IOException e) {
                    }
                }
            }
        });
    }

public void loading(int progress) {
        this.progress.setProgress( progress);
    }

    public void loadingFinish(String path) {
        this.progress.dismiss();

        String fileName = path;
        Intent i = new Intent();
        i.setAction(Intent.ACTION_VIEW);
        i.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        i.setDataAndType(Uri.fromFile(new File(fileName) ), "application/vnd.android.package-archive");
        startActivity(i);
    }

    public void loadingFailure() {
        this.progress.dismiss();
    }