为了实现下载文件，在AndroidManifest中添加了权限：
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
但是运行时，始终报错未获得权限，查资料了解到运行时权限，于是在活动中进行查询并获取权限：
if (ContextCompat.checkSelfPermission(VoiceActivity.this,permission.WRITE_EXTERNAL_STORAGE)!=PackageManager.PERMISSION_GRANTED){
ActivityCompat.requestPermissions(VoiceActivity.this,
new String[]{permission.WRITE_EXTERNAL_STORAGE},
REQUESTCODE);
}
参考：
https://developer.android.com/training/permissions/requesting
