How to access a Portal User Info from a J2EE application?

Hi,

I have deployed a j2ee application in portal and its running fine.

from that application i need to assign some roles to some users.i have the user id.

so my doubt is can i access the portal user info from this j2ee application?i have some servlets in the j2ee application....can i get the portal user info from this servlet?

plz help me

regards,

Visweswar