Need clarification on usage of StringUtils in the applications

Hi,

I have been using the StringUtils functions in the spring based applications for sometime now and was surprised when a colleague mentioned about the below message in the documentation of the API.

"Mainly for internal use within the framework; consider Jakarta's Commons Lang for a more comprehensive suite of String utilities."

http://static.springsource.org/sprin...ringUtils.html

Just wondering why it's been explicitly discouraged to use the Utils API in the applications?

Thanks,
Arks