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.访问网络权限
android.permission.INTERNET
访问SCARD
1.得到当前设备SD卡目录
Environment.getExternalStorageDirectory()
2.访问SD卡的权限
android.permission.WRITE_EXTERNAL_STORAGE
