I got it, I have to use Entrypoint in my DRL file otherwise it would give null pointer exception.

I used like this-

rule "Testing EntryPoint"

when

            $cf : CashFlow() from entry-point "TransactionStream"

then

            System.out.println($cf);

            System.out.println("Testing the transaction stream");

end

From: Aman [mailto:boy18nj@gmail.com]
Sent: Sunday, October 03, 2010 9:42 PM
To: 'Rules Users List'
Subject: WorkingMemoryEntryPoint NullpointerException?

memoryEntryPoint is retrieved as null, what could be wrong here or do I need to do some special configuration in order to use working memory point streams?

            StatefulKnowledgeSession knowledgeSession = GivemeStatelessOrStateful

                        .getStatefull("cashflow.drl");

            WorkingMemoryEntryPoint memoryEntryPoint = knowledgeSession

                        .getWorkingMemoryEntryPoint("TransactionStream");