Pritam wrote: As I understood it, a stateless session behaves as if the only object known to it is the one you just inserted. Personally, I look at it like: stateless -> propositional logic stateful -> first-order logic I'm not sure that's 100% true though. In any case, it depends on the kind of questions you like to ask. If you're not sure, test it. Cheers, Simon

On 20/01/2010 11:41, Simon Thum wrote: I prefer to look at it as turning a drools session into a function. It can do eveything a normal stateful session can do, just you have to do it all within the scope of a single execute call. Mark

I'm planning to use the following approach in my webtier: High level design: Each http request for a page on our site has an average of 5 separate requests to process rules before finally rendering. Each time, servlet handler calls runRule(<some context object>). Essentially, rules is serving as a filtering process and while Stateless ksession would have done the trick, I needed to control the execution of rules based on agenda-order and salience, hence the stateful ksession. The rules themselves are pretty st forward and I don't see the need to insert facts "dynamically" during a long web conversation (at least for now). protected void runRule(MyContect context) { try { KnowledgeBase kbase = loadKnowledgeBase(context); StatefulKnowledgeSession kSession = kbase.newStatefulKnowledgeSession(); // set some globals here // pop groups into agenda's stack for controlling execution order kSession.getAgenda().getAgendaGroup("<page-id>").setFocus(); kSession.getAgenda().getAgendaGroup("<section-id>).setFocus(); kSession.getAgenda().getAgendaGroup("site-global").setFocus(); kSession.insert(context); kSession.fireAllRules(); // at this point context is updated by rules for the servlet to handle after the call; kSession.dispose(); } catch (Exception e) { e.printStackTrace(); throw new RuntimeException("Error occured in processing Drools rules", e); } } public KnowledgeBase loadKnowledgeBase() throws DroolsParserException, IOException { if(kbase != null) { // singleton instance return kbase; } KnowledgeBuilder knowledgeBuilder = KnowledgeBuilderFactory.newKnowledgeBuilder(); knowledgeBuilder.add(ResourceFactory.newClassPathResource("dsl/global.dsl"), ResourceType.DSL); knowledgeBuilder.add(ResourceFactory.newClassPathResource("rules/"), ResourceType.DSLR); if (knowledgeBuilder.hasErrors()) { throw new RuntimeException(knowledgeBuilder.getErrors().toString()); } kbase = KnowledgeBaseFactory.newKnowledgeBase(); kbase .addKnowledgePackages(knowledgeBuilder.getKnowledgePackages()); return kbase ; } Michael Bali's book has an entire chapter on Stateful Session in which it recommended to create a StatefulSession Service with a dedicated writeObject and readObject and "warns" about thread safety. I'm still not clear about the unsafe threading issues with using a stateful ksession inside a webtier. And would the approach 1 in the above work, assuming multiple users are executing the same rules at the same time? Thanks public class DroolsService implements Serializable { private static final long serialVersionUID = 6623448115053519253L; private transient KnowledgeBase knowledgeBase; private transient StatefulKnowledgeSession statefulSession; public DroolsService(KnowledgeBase knowledgeBase) { this.knowledgeBase = knowledgeBase; statefulSession = createKnowledgeSession(); } private StatefulKnowledgeSession createKnowledgeSession() { StatefulKnowledgeSession session = knowledgeBase .newStatefulKnowledgeSession(); return session; } public void insertOrUpdate(Object fact) { if (fact == null) { return; } FactHandle factHandle = statefulSession.getFactHandle(fact); if (factHandle == null) { statefulSession.insert(fact); } else { statefulSession.update(factHandle, fact); } } public void executeRules() { statefulSession.fireAllRules(); } public void terminate() { statefulSession.dispose(); } private void writeObject(ObjectOutputStream out) throws IOException { out.defaultWriteObject(); DroolsObjectOutputStream droolsOut = new DroolsObjectOutputStream( (OutputStream) out); droolsOut.writeObject(knowledgeBase); Marshaller marshaller = createSerializableMarshaller(knowledgeBase); marshaller.marshall(droolsOut, statefulSession); } private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException { in.defaultReadObject(); DroolsObjectInputStream droolsIn = new DroolsObjectInputStream( (InputStream) in); this.knowledgeBase = (KnowledgeBase) droolsIn.readObject(); Marshaller marshaller = createSerializableMarshaller(knowledgeBase); statefulSession = marshaller.unmarshall(droolsIn); } private Marshaller createSerializableMarshaller(KnowledgeBase knowledgeBase) { ObjectMarshallingStrategyAcceptor acceptor = MarshallerFactory .newClassFilterAcceptor(new String[] { "*.*" }); ObjectMarshallingStrategy strategy = MarshallerFactory .newSerializeMarshallingStrategy(acceptor); Marshaller marshaller = MarshallerFactory.newMarshaller(knowledgeBase, new ObjectMarshallingStrategy[] { strategy }); return marshaller; } } -- View this message in context: http://n3.nabble.com/Stateless-Vs-Stateful-Sessions-in-Webtier-tp130284p1... Sent from the Drools - User mailing list archive at Nabble.com.

On 27/01/2010 13:09, Simon Thum wrote: you can use agenda and ruleflow from within the stateless session. Mark

[quote] you can use agenda and ruleflow from within the stateless session.[/quote] How? The api doesn't seem to support at the moment (5.0.1) -- View this message in context: http://n3.nabble.com/Stateless-Vs-Stateful-Sessions-in-Webtier-tp130284p1... Sent from the Drools - User mailing list archive at Nabble.com.