Weka is the best tool for doing this. It takes the texts in form of string attributes and converts using TF-IDF logic. There are many different parameter setting that you can choose.

Thanks Chandrima. Yes, I saw. But is there any other way to do this thing? Because I need it separately and will add my system.

The only other way related to weka is that , you can use weka jar files in your own code (java) and do this task.

:) yes, that is last option

There are lots of tools nowadays. The predominant of those are WEKA, Rapidminer and Lightside and this stringtowordvector class is very common.