Stateless Vs Stateful Session behavior in drools

[Manish Gandhi]

Hello,

I am new to the drools. I was trying to understand the difference  between Stateless and Stateful sessions provided by Drools. 

As per my initial understanding,

In case of Stateless session, if fact is modified during action execution of any rule then it will not be re-submitted to inference engine to find out the new rules which matches the modified fact.

In case of Stateful session, if fact is modified during action execution of any rule then it will be re-submitted to inference engine to find out the new rules which matches the modified fact and then their corresponding action will be executed.

So when I tried to verify this behavior by writing a sample rule, I found that behavior is exactly same in both the cases. So now I am really confused regarding the difference between Stateful and Stateless sessions. 

I would like to request everyone to help me in understand the correct behavior of Stateful and Stateless sessions. 

For your reference I am pasting my sample code for Stateful and Stateless session along with their output and sample rule.

licenseApplication.drl   (Rule file)

package com.idal.droolsapp

rule "Is of valid age"

no-loop

when

    $a : Applicant( age < 18 )

then

    System.out.println( "Not eligible for license" );

    System.out.println( "Setting Valid to false" );

    modify( $a ) { setValid( false ) };

end

rule "Is of valid false"

salience 100

when

    $a : Applicant( valid == false )

then

    System.out.println( "Second rule fired" );

end

Input object (Fact) Applicant.java

package com.idal.droolsapp;

public class Applicant {

    private String name;

    private int age;

    private boolean valid = true;

public Applicant(String name, int age) {

setName(name);

setAge(age);

}

public void setName(String name) {

this.name = name;

}

public String getName() {

return name;

}

public void setAge(int age) {

this.age = age;

}

public int getAge() {

return age;

}

public void setValid(boolean valid) {

this.valid = valid;

}

public boolean isValid() {

return valid;

}

@Override

public String toString() {

return "Applicant [name=" + name + ", age=" + age + ", valid=" + valid

+ "]";

}

}

StatelessSessionExample.java  (Stateless Session test code)

package com.idal.droolsapp;

import org.drools.KnowledgeBase;

import org.drools.KnowledgeBaseFactory;

import org.drools.builder.KnowledgeBuilder;

import org.drools.builder.KnowledgeBuilderFactory;

import org.drools.builder.ResourceType;

import org.drools.io.ResourceFactory;

import org.drools.runtime.StatelessKnowledgeSession;

public class StatelessSessionExample {

/**

 * @param args

 */

public static void main(String[] args) {

KnowledgeBuilder kbuilder = KnowledgeBuilderFactory

.newKnowledgeBuilder();

kbuilder.add(ResourceFactory.newClassPathResource(

"licenseApplication.drl", StatelessSessionExample.class),

ResourceType.DRL);

if (kbuilder.hasErrors()) {

System.err.println(kbuilder.getErrors().toString());

}

KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase();

kbase.addKnowledgePackages(kbuilder.getKnowledgePackages());

StatelessKnowledgeSession ksession = kbase.newStatelessKnowledgeSession();

Applicant applicant = new Applicant( "Mr John Smith", 16 );

ksession.execute( applicant );

System.out.println("Updated Applicant = " + applicant);

}

}

Output of Stateless session test code:

Not eligible for license

Setting Valid to false

Second rule fired

Updated Applicant = Applicant [name=Mr John Smith, age=16, valid=false]

StatefulSessionExample.java  (Stateless Session test code)

package com.idal.droolsapp;

import org.drools.KnowledgeBase;

import org.drools.KnowledgeBaseFactory;

import org.drools.builder.KnowledgeBuilder;

import org.drools.builder.KnowledgeBuilderFactory;

import org.drools.builder.ResourceType;

import org.drools.io.ResourceFactory;

import org.drools.runtime.StatefulKnowledgeSession;

public class StatefulSessionExample {

/**

 * @param args

 */

public static void main(String[] args) {

KnowledgeBuilder kbuilder = KnowledgeBuilderFactory

.newKnowledgeBuilder();

kbuilder.add(ResourceFactory.newClassPathResource(

"licenseApplication.drl", StatefulSessionExample.class),

ResourceType.DRL);

if (kbuilder.hasErrors()) {

System.err.println(kbuilder.getErrors().toString());

}

KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase();

kbase.addKnowledgePackages(kbuilder.getKnowledgePackages());

StatefulKnowledgeSession ksession = kbase.newStatefulKnowledgeSession();

Applicant applicant = new Applicant( "Mr John Smith", 16 );

ksession.insert( applicant );

ksession.fireAllRules();

ksession.dispose();

System.out.println("Updated Applicant = " + applicant);

}

}

Output of Stateful session test code:

Not eligible for license

Setting Valid to false

Second rule fired

Updated Applicant = Applicant [name=Mr John Smith, age=16, valid=false]

Once again requesting everyone to help me in understanding the correct behavior of Stateful and Stateless sessions. 

Thanks in advance,

Manish Gandhi

[amitsingh chandele]

Your understanding of stateful vs stateless is wrong.

As per my knowledge :

Stateful : "Inserted data objects will be part of working memory & can be reused later for further rule execution."

Stateless : "Inserted data objects will not be stored in working memory after rules execution". 

And if rules should be evaluated after data modification is controlled by update / modify calls in rules then part.

Hope this helps. Please let me know if I have got this wrong.

[Manish Gandhi]

Thanks for the clarification. Its clear now