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Drools the Business Logic Integration Platform provides an knowledge centric api, where rules and processes are first class citizens.



The most common interfaces you will use are:

org.drools.builder.KnowledgeBuilder
org.drools.KnowledgeBase
org.drools.agent.KnowledgeAgent
org.drools.runtime.StatefulKnowledgeSession
org.drools.runtime.StatelessKnowledgeSession




Factory classes, with static methods, provide instances of the above interfaces. A pluggable provider approach is used to allow provider implementations to
be wired up to the factories at runtime. The Factories you will most commonly used are:

org.drools.builder.KnowledgeBuilderFactory
org.drools.io.ResourceFactory
org.drools.KnowledgeBaseFactory
org.drools.agent.KnowledgeAgentFactory




A Typical example to load a rule resource.
KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();
kbuilder.add( ResourceFactory.newUrlResource( url ),
                      ResourceType.DRL );
if ( kbuilder.hasErrors() ) {
    System.err.println( builder.getErrors().toString() );
}                     

KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase();
kbase.addKnowledgePackages( builder.getKnowledgePackages() );

StatefulKnowledgeSession ksession = knowledgeBase.newStatefulKnowledgeSession();
ksession.insert( new Fibonacci( 10 ) );
ksession.fireAllRules();

ksession.dispose();




A Typical example to load a process resource. Notice the ResourceType is changed, in accordance with the Resource type.
KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();
kbuilder.add( ResourceFactory.newUrlResource( url ),
              ResourceType.DRF );
if ( kbuilder.hasErrors() ) {
    System.err.println( builder.getErrors().toString() );
}                     

KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase();
kbase.addKnowledgePackages( builder.getKnowledgePackages() );

StatefulKnowledgeSession ksession = knowledgeBase.newStatefulKnowledgeSession();
ksession.startProcess( "Buy Order Process" );

ksession.dispose();




'kbuilder', 'kbase', 'ksession' are the variable identifiers often used, the k prefix is for 'knowledge'.



It is also possible to configure a KnowledgeBase using configuration, via a xml change set, instead of programmatically. Here is a simple change set:

<change-set xmlns='http://drools.org/drools-5.0/change-set'
           xmlns:xs='http://www.w3.org/2001/XMLSchema-instance'
           xs:schemaLocation='http://drools.org/drools-5.0/change-set change-set-5.0.xsd' >
    <add>
	    <resource source='classpath:org/domain/someRules.drl' type='DRL' />
	    <resource source='classpath:org/domain/aFlow.drf' type='DRF' />
    </add>      
</change-set>



And it is added just like any other ResourceType

KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();
kbuilder.add( ResourceFactory.newUrlResource( url ),
              ResourceType.ChangeSet );



The majority of Drools API is considered stable and should not change, experimental classes and apis will be marked as such.