[rules-users] How can I access the updated JAR file in DRL file ???

[Vijeth Raj]

Hi ,

    Recently i was working on a drools project where i came across certain
issues and i need some help.

In my project i access jar at runtime by making use of the
URLClassLoader.Here is the code :



 Object object=*null*;

 Class myclass=*null*;

 URL jarPath=*null*;

 *try*{

      jarPath=*new* File("lib/Billing.jar").toURI().toURL();

      URLClassLoader loader = *new* URLClassLoader(*new* URL[] { jarPath },*
ClassLoader.*getClassLoader());

      myclass = loader.loadClass("dynamicclasses.Billing");

      object = myclass.newInstance();

}

*catch* (Exception e) {e.printStackTrace}



After getting the class instance I will set the values and pass the object
to my drools class



new DroolsClass().fireRules(object);



The drools class contain the following code :



public class DroolsClass {



*public* *void* fireRules(Object object){

            *try* {

                  KnowledgeBase kbase = *readKnowledgeBase*();

                  StatefulKnowledgeSession ksession =
kbase.newStatefulKnowledgeSession();

                  KnowledgeRuntimeLogger logger =
KnowledgeRuntimeLoggerFactory.*newFileLogger*(ksession, "test");

                  ksession.insert(object);

                  ksession.fireAllRules();

                  logger.close();



            } *catch* (Throwable t) {

                  t.printStackTrace();

            }



}

*private* *static* KnowledgeBase readKnowledgeBase() *throws* Exception {



            KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.*
newKnowledgeBuilder*();

            kbuilder.add(ResourceFactory.*newFileResource*(
"./rulefiles/testing.drl"), ResourceType.*DRL*);

            KnowledgeBuilderErrors errors = kbuilder.getErrors();

            // *------ some code*

            KnowledgeBase kbase = KnowledgeBaseFactory.*newKnowledgeBase*();

            kbase.addKnowledgePackages(kbuilder.getKnowledgePackages());

            *return* kbase;

}





Next I have a drl file testing.drl which is present in the file directoty
and which accesses the same class dynamicclasses.Billing which is present in
Billing.jar



Here is the drl file content :



*import* dynamicclasses.Billing;



*rule* "rule 3"



*salience* 10

*dialect* "mvel"

*no-loop* *true*

*when*

     m : Billing(bplan=="plan1")

*then*

      System.out.println("You have opted for plan1");

*end*

* *

The problem I encounter is when the jar i.e  Billing.jar get updated at
runtime the drl file i.e testing.drl



The following things i am trying to do.



1) I will create jar at runtime and update it if required.

2) I will create a drl file at runtime which will import the class present
in the jar i.e. dynamicclasses.Billing



I am able to access the updated jar contents in my java class ussing
URLClassLoader .But once i pass the object to my drools class i get the
following exception



Unable to resolve ObjectType 'Billing' : [Rule name='rule 3']



Error importing : 'dynamicclasses.Billing'

*java.lang.IllegalArgumentException*: Could not parse knowledge.





If i restart my application i get no exception since the jar is already
present but the object doesn't seem to pass to the drl and i get no result.



I made the following adjustment to the code :



URLClassLoader loader = new URLClassLoader(new URL[] { jarPath
},this.getClass().getClassLoader());



Here I get the same exception initially. But after I restart my application
it works fine and the rule get fired and I will get the result.



But again if I update the jar it will access only the previous content.



So it’s clear that the DRL file is not able to access the jar initially or
even after updating.

Is there any way so that I can make it work?



Thanks.
-- 

Thanks & Regards,

Vijeth Raj K

Email : vijethrajk at gmail.com
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