Detecting new new items in a RSS feed

15
votes

What is the best way to detect when a feed has been updated? Say I have an application which polls the feed every 15 minutes. How do I find out if new content has been added or not? For RSS as well as Atom feeds.

3
xmlrssfeedatom-feed

3 Answers

6
votes

Each item in RSS 2 and Atom has a GUID/ID that may be flagged as unique. If it's flagged as unique you can use it to identify items and match against the previous items.

4
votes

Check the Last-Modified and ETag fields of the http response when requesting the field. Even better, use the If-Modified-Since and If-None-Match tags in your request, and you will only get a 304 response if the feed hasn't been modified. (see: http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html)

1
votes

I am using etags on my project, computed in a servlet filter as shown here http://www.infoq.com/articles/etags

This would work for rss, atom or any other resource hosted on your webserver.