Android中的Drools（JavafxPorts）

Question

I created a simple JavaFX Application to be deployed on Android. I was trying to execute Drools in my application but there was an expected error occurred:

java.lang.NullPointerException: parentLoader == null && !nullAllowed

Can somebody tell me how to resolve this?

Here's the code:

package com.rameses.waterworks.drools;

import java.util.Properties;
import org.drools.KnowledgeBase;
import org.drools.KnowledgeBaseFactory;
import org.drools.builder.KnowledgeBuilder;
import org.drools.builder.KnowledgeBuilderConfiguration;
import org.drools.builder.KnowledgeBuilderError;
import org.drools.builder.KnowledgeBuilderErrors;
import org.drools.builder.KnowledgeBuilderFactory;
import org.drools.builder.ResourceType;
import org.drools.io.ResourceFactory;
import org.drools.runtime.StatefulKnowledgeSession;

public class TestReports {


    public static void main(String[] args) throws Exception {
         Properties properties = new Properties();
         properties.setProperty( "drools.dialect.java.compiler", "JANINO" );
         KnowledgeBuilderConfiguration conf = KnowledgeBuilderFactory.newKnowledgeBuilderConfiguration(properties,TestReports.class.getClassLoader());
         KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder(conf);
        kbuilder.add(ResourceFactory.newClassPathResource("test/reports/test.drl"), ResourceType.DRL);
         KnowledgeBuilderErrors errors = kbuilder.getErrors();
         if (errors.size() > 0) {
            for (KnowledgeBuilderError error: errors) {
               System.err.println(error);
            }
            throw new IllegalArgumentException("Could not parse knowledge.");
         }
         KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase();
         kbase.addKnowledgePackages(kbuilder.getKnowledgePackages());
         StatefulKnowledgeSession ksession = null;

         try {
             ksession = kbase.newStatefulKnowledgeSession();
             ksession.insert(new SampleBean("Hello Drools!"));
             ksession.fireAllRules();
         }
         catch(Exception  e){

         }   
         finally {
             ksession.dispose();
         }
    }     
}

I executed it using the following code:

TestReports.main(null);

Answer 1

It may seem strange, but this issue may depend on which version of Drools libraries set you use. For example, I used the JARs from this site (following this tutorial). The tutorial was written for desktop Drools application, and when I tried to move some of this JARs to my Android project, I got java.lang.NullPointerException: parentLoader == null && !nullAllowed . So I found another example (you can find it here: Integration of Drools (Expert System) with Android Projects ) and took JARs from there. This made the error stopped appearing. To be exact, this example isn't perfect as it doesn't work as I'd like it to, but it may be some help for you.