indexing algorithm to use for free form text

I am tasked with working on an app to index free form text, for fast look-up. I am sure this is an area that has been researched to death. However I am not sure where to start, any help开发者_如何学编程 is greatly appreciated.

There's even an open-source tool that is well regarded. http://lucene.apache.org/java/docs/index.html

Look up Inverted index. There are a few implementations over the link.