Number of hits per document

Hi,

I would like to get the hits per document using lucene search, example:

If a document has

Hello world, How are doing
Hello world, Good
Hello world, This is lucene world

I can get 4 hits for "world"(using termdocs), but if I want to search "Hello world". how do I work for it?
Any ideas will be very helpful..

Thanks,
Sharma