org.drools.runtime.StatefulKnowledgeSession Maven / Gradle / Ivy
package org.drools.runtime;
import org.drools.KnowledgeBase;
import org.drools.runtime.process.StatefulProcessSession;
import org.drools.runtime.rule.StatefulRuleSession;
/**
* StatefulKnowledgeSession is the most common way to interact with a rules engine. A StatefulKnowledgeSession
* allows the application to establish an iterative conversation with the engine, where the reasoning process
* may be triggered multiple times for the same set of data. After the application finishes using the session,
* though, it must call the dispose() method in order to free the resources and used memory.
*
*
* Simple example showing a stateful session executing for a given collection of java objects.
*
*
* KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();
* kbuilder.add( ResourceFactory.newFileSystemResource( fileName ), ResourceType.DRL );
* assertFalse( kbuilder.hasErrors() );
* if (kbuilder.hasErrors() ) {
* System.out.println( kbuilder.getErrors() );
* }
* KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase();
* kbase.addKnowledgePackages( kbuilder.getKnowledgePackages() );
*
* StatefulKnowledgeSession ksession = kbase.newStatefulKnowledgeSession();
* for( Object fact : facts ) {
* ksession.insert( fact );
* }
* ksession.fireAllRules();
* ksession.dispose();
*
*
*
* StatefulKnowledgeSessions support globals. Globals are used to pass information into the engine and receive callbacks
* from your rules, but they should not be used to reason over. If you need to reason over your data, make sure you insert
* it as a fact, not a global.
* Globals are shared among ALL your rules, so be especially careful of (and avoid as much as possible) mutable globals.
* Also, it is a good practice to set your globals before inserting your facts. Rules engines evaluate rules at fact insertion
* time, and so, if you are using a global to constraint a fact pattern, and the global is not set, you may receive a
* NullPointerException.
* Globals can be resolved in two ways. The StatefulKnowledgeSession supports setGlobalResolver() and setGlobal().
* Calling of setGlobal(String, Object) will set the global on an internal Collection. Identifiers in this internal
* Collection will have priority over the externally supplied GlobalResolver. If an identifier cannot be found in
* the internal Collection, it will then check the externally supplied Global Resolver, if one has been set.
*
*
* Code snippet for setting a global:
*
* StatefulKnowledgeSession ksession = kbase.newStatefulKnowledgeSession();
* ksession.setGlobal( "hbnSession", hibernateSession ); // sets a global hibernate session, that can be used for DB interactions in the rules.
* for( Object fact : facts ) {
* ksession.insert( fact );
* }
* ksession.fireAllRules(); // this will now execute and will be able to resolve the "hbnSession" identifier.
* ksession.dispose();
*
*
* @see org.drools.runtime.GlobalResolver
*/
public interface StatefulKnowledgeSession
extends
StatefulRuleSession,
StatefulProcessSession,
KnowledgeRuntime {
/**
* Sets a global value on the internal collection
* @param identifer the global identifier
* @param value the value assigned to the global identifier
*/
void setGlobal(String identifier,
Object object);
/**
* Delegate used to resolve any global names not found in the global map.
* @param globalResolver
*/
void setGlobalResolver(GlobalResolver globalResolver);
/**
* Returns the KnowledgeBase reference from which this stateful session was created.
*
* @return
*/
KnowledgeBase getKnowledgeBase();
/**
* Releases all the current session resources, setting up the session for garbage collection.
* This method must always be called after finishing using the session, or the engine
* will not free the memory used by the session.
*/
void dispose();
}