如下

DownloadManager downloadManager = (DownloadManager) MainActivity.this.getSystemService(DOWNLOAD_SERVICE);
Uri uri = Uri.parse(url);
DownloadManager.Request request = new DownloadManager.Request(uri);              
long download_id = downloadManager.enqueue(request);
//返回值download_id是一个比较重要的参数，主要用来查询

直接调用系统自带的下载器