OkHttp3实现文件下载

一、简单方式

 Request request = new Request.Builder().url(url).build();
        okHttpClient.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                Log.i("myTag", "下载失败");
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                if (response.isSuccessful()) {
                    writeFile(response);
                }
            }
        });

    private void writeFile(Response response) {
        InputStream is = null;
        FileOutputStream fos = null;
        is = response.body().byteStream();
        String path = Environment.getExternalStorageDirectory().getAbsolutePath();
        File file = new File(path, fileName);
        try {
            fos = new FileOutputStream(file);
            byte[] bytes =