Generate certificates, public and private keys with Java

I'm looking for a java library or code to generate certificates, public and private keys on the fly without to use third party programs (such as openssl).

I think something that is doeing keytool+openssl but from Java code.

Consider a java servlet based web application secured with ssl and client authentification. I want the servlet container generate client certificates (eg. pkcs12 format) on request only with Java code.