Is there any library available to parse KML ?
You'll be making your own library, but you won't be writing any code.
I suggest looking at http://code.google.com/apis/kml/documentation/kmlreference.html. From there you can get the XML Schema. Once you've got the schema you can use JAXB to generate an object tree to easily parse and write KML.
This may also be a good resource, looks like someone else has already done it!