Missing Dependency Injection in Bean called by Drools event rule
leutenmayr May 8, 2012 5:12 AMHello,
I am developing a Seam application that enables users to trade shares on a virtual market. In this application, I want to employ Drools for triggering actions given certain patterns in the stream of trading events. I use Seam 2.2.0 and JBoss 4.2. In this version of Seam, the provided Drools can only be used as a rule base end engine but not for processing event streams as this requires the usage of the Drools knowledge base and working memory entry points. I already replaced the Seam provided Drools jars with the Drools 5.2 jars. However, Seam does not provide for configuring knowledge bases, only rule bases. Thus, I manually create the required knowledge base, knowledge session and working memory entry points in an application scoped bean (tradeExecutionBean). Upon executing a trade, I insert the trade event into the working memory entry point and the rule engine executes the matching rule. A call to System.out.println works fine from the rule. However, I want to trigger another execution of a trade by calling executeTransaction from within the rule. Thus, I made the tradeExecutionBean available to the session by setGlobal. The method is then executed, but the entityManager does not get injected to the tradeExecutionBean, but resolves to null. How should I best trigger the execution of this method from within the rule? Should I try to get the entityManager injected, or should I follow a different approach not calling the method from within the rule?
Thank you
Stephan
{code}
@Name("tradeExecutionBean")
@Scope(ScopeType.APPLICATION)
@Startup
@Synchronized
public class TradeExecutionBean
{
@In
private EntityManager entityManager;
private StatefulKnowledgeSession kSession;
private WorkingMemoryEntryPoint tradeEntryPoint;
@Create
public void create()
{
KnowledgeAgent agent = KnowledgeAgentFactory.newKnowledgeAgent("knowledgeAgent");
agent.monitorResourceChangeEvents(true);
agent.applyChangeSet(ResourceFactory.newClassPathResource("changeset.xml"));
KnowledgeBase kbase = agent.getKnowledgeBase();
kSession = kbase.newStatefulKnowledgeSession();
kSession.setGlobal("tradeExecutionBean", this);
tradeEntryPoint = kSession.getWorkingMemoryEntryPoint("transactionStream");
// Fire rules in session until halt in a separate thread
new Thread(new Runnable()
{
public void run()
{
kSession.fireUntilHalt();
}
}).start();
}
@Transactional(TransactionPropagationType.REQUIRED)
public void executeTransaction(..)
{
int holdingsQuantity;
try
{
System.out.println(entityManager);
holdingsQuantity = (Integer) entityManager.createQuery("SELECT h.quantity FROM Holdings AS h WHERE h.person.id = :personid AND h.stock.id = :stockid").setParameter("stockid", stock.getId()).setParameter("personid", person.getId()).getSingleResult();
}
catch (NoResultException e)
{
holdingsQuantity = 0;
}
//create transaction event here..
tradeEntryPoint.insert(transaction);
}
}
{code}
{code}
rule TransactionNotification
when
t: Transaction() from entry-point "transactionStream"
then
tradeExecutionBean.executeTransaction(..);
end
{code}