public String getSDPath(){

  File sdDir = null;

  boolean sdCardExist = Environment.getExternalStorageState()

  .equals(android.os.Environment.MEDIA_MOUNTED); //判断sd卡是否存在

  if (sdCardExist)

  {

  sdDir = Environment.getExternalStorageDirectory();//获取跟目录

  }

  return sdDir.toString();

 }