如何获取在线文件的最后修改日期？

Question

I am writting an app for my college and it should alert user when some changes have occured on college's websites. The problem is that I can't change these websites, only read them; yet they don't have "last-modified" in html header.

For now I compare them by downloading the whole html code, then making MD5 checksum out of it, thus seeing if something has changed. But there should be some better(faster) way, or not?

Answer 1

You can check md5 on server every 5 seconds and then just answer for little file with true/false result)).
Also you can connect to servers with ftp and check files status if you have access to it.
I also find this guys - they sends notifications when choosed site has changed.

But i think your variant is much easer).
What is wrong with it? To much time spent for the check?