文件下载步骤

1、创建一个HttpURLConnection对象

     HttpURLConnection urlConn = （HttpURLConnection）url.openConnection();

2、获得一个InputStream对象

     urlConn.getInputStream();

3、访问网络的权限

     android.permission.INTERNET

4、访问SDCARD

     得到当前设备SD卡的目录

     Environment.getExternalStorageDirectory()

5、访问SD卡的权限

     android.permission.WRITE_EXTERNAL_STORAGE

//根据URL得到输入流

public InputStream getInputStreamFromUrl(String urlStr)

throws MalformedURLException,IOException{

url = new URL(urlStr);

HttpURLConnection urlConn = (HttpURLConnection) url.openConnection();

InputStream inputStream = urlConn.getInputStream();

return inputStream;

}