How to get session information for service?

[Nattanicha Rittammanart]

Hi all,
   I need to implement lock for transaction (manual pessimistic
locking). I need to use sessionid to be one of parameters for lock. How
can I get session information for the transaction in Java Service. Or
can I have another way to do this. Finally, I knew that OFBiz provide
only optimistic lock for us, right?

Thanks in advance,
Nattanicha