The Collections tutorial at Sun should help. This question doesn't really have anything to do with Servlets though - for future reference you would be better posting a quetion like this in the Beginners' forum. [ February 22, 2005: Message edited by: Paul Sturrock ]
Are you interested in using data structures or creating them? If you just need data structures to use, the most common ones are already implemented in the Collections framework as noted above. (See the link in Paul's message.)
If on the other hand you would like to learn about the inner workings of data structures and possible implement your own, I don't have any links off the top of my head. I would suggest googling for "data structures in java". (Note that "data structure" is two words, not one.) I'm sure there are a lot of resources available. Also, you may want to get a hardcopy textbook on the topic. I learned about data structures in a formal setting at the university. Unfortunately, I am not familiar with any informal sources of the information. I apologize for not being able to help any further.
In your study of data structures, please come back with more quesitons. The more specific they are the more likely we will be able to help.