Drools: Compiling rules (or loading compiled rules) fails with obscure exceptions in JamVM

Question

I'm developing a framework that, as one of its features, enables robots to use a rule based system. We began with Jess as the RBS, and now wanted to implement drools (using Drools 5.2.0 final), which works on our development machines running on OpenJDK 6.

Our robot controller runs ARM Linux and JamVM, previously 1.4.3, but I recently compiled 1.5.4 because it was missing classes needed by drools. After failures, I installed JamVM in a virtual machine using the same configurations as when I compiled it for the controller, and there it failed with the same exceptions.

A little research showed that there are bug reports for Drools + JamVM, but this also means that it generally does work.

When Running the framework with precompiled rules with the following code...

kBase = KnowledgeBaseFactory.newKnowledgeBase();

ObjectInputStream in;
Collection<KnowledgePackage> kpkgs;
try {
    in = new ObjectInputStream(Thread.currentThread().getContextClassLoader().getResourceAsStream(
            packageFile));
    kpkgs = (Collection<KnowledgePackage>) in.readObject();
    in.close();
} catch(IOException e) {
    throw new DisboticsException("Couldn't read drools knowledge package file!", e);
} catch(ClassNotFoundException e) {
    throw new DisboticsException("Drools knowledge package file didn't contain expected instance.", e);
}

kBase.addKnowledgePackages(kpkgs);
kSession = kBase.newStatefulKnowledgeSession();

...I got this exception:

java.lang.UnsupportedOperationException
   at java.util.AbstractList.add(AbstractList.java:131)
   at java.util.AbstractList.add(AbstractList.java:152)
   at org.drools.rule.JavaDialectRuntimeData.write(JavaDialectRuntimeData.java:383)
   at org.drools.rule.JavaDialectRuntimeData.merge(JavaDialectRuntimeData.java:266)
   at org.drools.rule.JavaDialectRuntimeData.clone(JavaDialectRuntimeData.java:251)
   at org.drools.rule.DialectRuntimeRegistry.merge(DialectRuntimeRegistry.java:110)
   at org.drools.common.AbstractRuleBase.addPackages(AbstractRuleBase.java:496)
   at org.drools.reteoo.ReteooRuleBase.addPackages(ReteooRuleBase.java:427)
   at org.drools.impl.KnowledgeBaseImpl.addKnowledgePackages(KnowledgeBaseImpl.java:149)
   at disbotics.core.config.DroolsRulesPlugin.initialize(DroolsRulesPlugin.java:76)
   at disbotics.core.common.DisboticsCore.startFramework(DisboticsCore.java:109)
   at disbotics.core.common.DisboticsCore.main(DisboticsCore.java:56)
Exception in thread "main" org.drools.RuntimeDroolsException: java.lang.UnsupportedOperationException
   at org.drools.rule.JavaDialectRuntimeData.write(JavaDialectRuntimeData.java:386)
   at org.drools.rule.JavaDialectRuntimeData.merge(JavaDialectRuntimeData.java:266)
   at org.drools.rule.JavaDialectRuntimeData.clone(JavaDialectRuntimeData.java:251)
   at org.drools.rule.DialectRuntimeRegistry.merge(DialectRuntimeRegistry.java:110)
   at org.drools.common.AbstractRuleBase.addPackages(AbstractRuleBase.java:496)
   at org.drools.reteoo.ReteooRuleBase.addPackages(ReteooRuleBase.java:427)
   at org.drools.impl.KnowledgeBaseImpl.addKnowledgePackages(KnowledgeBaseImpl.java:149)
   at disbotics.core.config.DroolsRulesPlugin.initialize(DroolsRulesPlugin.java:76)
   at disbotics.core.common.DisboticsCore.startFramework(DisboticsCore.java:109)
   at disbotics.core.common.DisboticsCore.main(DisboticsCore.java:56)
Caused by: java.lang.UnsupportedOperationException
   at java.util.AbstractList.add(AbstractList.java:131)
   at java.util.AbstractList.add(AbstractList.java:152)
   at org.drools.rule.JavaDialectRuntimeData.write(JavaDialectRuntimeData.java:383)
   ...9 more

...which works in OpenJDK. weirdly, it turns out that the list in question in JavaDialectRuntimeData is obtained via Collections.emptyList() and is never changed again (or so eclipse suggests...).

When running with bare .drl files using this code:

Properties props = new Properties();
props.put("drools.dialect.java.compiler", "JANINO");

KnowledgeBuilderConfiguration kbConfig = KnowledgeBuilderFactory.newKnowledgeBuilderConfiguration(props,
        (ClassLoader[]) null);
KnowledgeBuilder kBuilder = KnowledgeBuilderFactory.newKnowledgeBuilder(kbConfig);

kBuilder.add(ResourceFactory.newClassPathResource("disbotics/core/rules/drools/function.drl",
        DroolsRulesPlugin.class), ResourceType.DRL);
kBuilder.add(ResourceFactory.newClassPathResource(rulesFile, DroolsRulesPlugin.class), ResourceType.DRL);

if(kBuilder.hasErrors()) {
    String errorMessage = "";
    for(KnowledgeBuilderError error:kBuilder.getErrors())
        errorMessage = errorMessage + error.getMessage() + "\n";
    throw new DisboticsException(errorMessage);
}

kBase = KnowledgeBaseFactory.newKnowledgeBase();
kBase.addKnowledgePackages(kBuilder.getKnowledgePackages());
kSession = kBase.newStatefulKnowledgeSession();

... I get these (unexpected) exceptions from the rules compiler:

Exception in thread "main" disbotics.core.common.DisboticsException: Line 2:8 unexpected exception at input '"mvel"'. Exception: java.lang.UnsupportedOperationException. Stack trace:
 java.lang.UnsupportedOperationException
   at java.util.AbstractList.add(AbstractList.java:131)
   at java.util.AbstractList.add(AbstractList.java:152)
   at org.drools.lang.descr.PackageDescr.addAttribute(PackageDescr.java:138)
   at org.drools.lang.api.impl.PackageDescrBuilderImpl.attribute(PackageDescrBuilderImpl.java:93)
   at org.drools.lang.ParserHelper.start(ParserHelper.java:684)
   at org.drools.lang.DRLParser.stringAttribute(DRLParser.java:1289)
   at org.drools.lang.DRLParser.attribute(DRLParser.java:1062)
   at org.drools.lang.DRLParser.statement(DRLParser.java:276)
   at org.drools.lang.DRLParser.compilationUnit(DRLParser.java:155)
   at org.drools.compiler.DrlParser.compile(DrlParser.java:225)
   at org.drools.compiler.DrlParser.parse(DrlParser.java:136)
   at org.drools.compiler.DrlParser.parse(DrlParser.java:141)
   at org.drools.compiler.PackageBuilder.addPackageFromDrl(PackageBuilder.java:352)
   at org.drools.compiler.PackageBuilder.addKnowledgeResource(PackageBuilder.java:538)
   at org.drools.builder.impl.KnowledgeBuilderImpl.add(KnowledgeBuilderImpl.java:28)
   at disbotics.core.config.DroolsRulesPlugin.initialize(DroolsRulesPlugin.java:55)
   at disbotics.core.common.DisboticsCore.startFramework(DisboticsCore.java:109)
   at disbotics.core.common.DisboticsCore.main(DisboticsCore.java:56)

[ERR 107] Line 2:8 mismatched input '"mvel"' expecting one of the following tokens: '[package, import, global, declare, function, rule, query]'.
Line 4:0 unexpected exception at input 'global'. Exception: java.util.EmptyStackException. Stack trace:
 java.util.EmptyStackException
   at java.util.Stack.pop(Stack.java:109)
   at org.drools.lang.ParserHelper.popParaphrases(ParserHelper.java:421)
   at org.drools.lang.ParserHelper.end(ParserHelper.java:732)
   at org.drools.lang.DRLParser.globalStatement(DRLParser.java:401)
   at org.drools.lang.DRLParser.statement(DRLParser.java:261)
   at org.drools.lang.DRLParser.compilationUnit(DRLParser.java:155)
   at org.drools.compiler.DrlParser.compile(DrlParser.java:225)
   at org.drools.compiler.DrlParser.parse(DrlParser.java:136)
   at org.drools.compiler.DrlParser.parse(DrlParser.java:141)
   at org.drools.compiler.PackageBuilder.addPackageFromDrl(PackageBuilder.java:352)
   at org.drools.compiler.PackageBuilder.addKnowledgeResource(PackageBuilder.java:538)
   at org.drools.builder.impl.KnowledgeBuilderImpl.add(KnowledgeBuilderImpl.java:28)
   at disbotics.core.config.DroolsRulesPlugin.initialize(DroolsRulesPlugin.java:55)
   at disbotics.core.common.DisboticsCore.startFramework(DisboticsCore.java:109)
   at disbotics.core.common.DisboticsCore.main(DisboticsCore.java:56)

Parser returned a null Package
Line 2:8 unexpected exception at input '"java"'. Exception: java.lang.UnsupportedOperationException. Stack trace:
 java.lang.UnsupportedOperationException
   at java.util.AbstractList.add(AbstractList.java:131)
   at java.util.AbstractList.add(AbstractList.java:152)
   at org.drools.lang.descr.PackageDescr.addAttribute(PackageDescr.java:138)
   at org.drools.lang.api.impl.PackageDescrBuilderImpl.attribute(PackageDescrBuilderImpl.java:93)
   at org.drools.lang.ParserHelper.start(ParserHelper.java:684)
   at org.drools.lang.DRLParser.stringAttribute(DRLParser.java:1289)
   at org.drools.lang.DRLParser.attribute(DRLParser.java:1062)
   at org.drools.lang.DRLParser.statement(DRLParser.java:276)
   at org.drools.lang.DRLParser.compilationUnit(DRLParser.java:155)
   at org.drools.compiler.DrlParser.compile(DrlParser.java:225)
   at org.drools.compiler.DrlParser.parse(DrlParser.java:136)
   at org.drools.compiler.DrlParser.parse(DrlParser.java:141)
   at org.drools.compiler.PackageBuilder.addPackageFromDrl(PackageBuilder.java:352)
   at org.drools.compiler.PackageBuilder.addKnowledgeResource(PackageBuilder.java:538)
   at org.drools.builder.impl.KnowledgeBuilderImpl.add(KnowledgeBuilderImpl.java:28)
   at disbotics.core.config.DroolsRulesPlugin.initialize(DroolsRulesPlugin.java:57)
   at disbotics.core.common.DisboticsCore.startFramework(DisboticsCore.java:109)
   at disbotics.core.common.DisboticsCore.main(DisboticsCore.java:56)

[ERR 107] Line 2:8 mismatched input '"java"' expecting one of the following tokens: '[package, import, global, declare, function, rule, query]'.
Line 4:0 unexpected exception at input 'import'. Exception: java.util.EmptyStackException. Stack trace:
 java.util.EmptyStackException
   at java.util.Stack.pop(Stack.java:109)
   at org.drools.lang.ParserHelper.popParaphrases(ParserHelper.java:421)
   at org.drools.lang.ParserHelper.end(ParserHelper.java:732)
   at org.drools.lang.DRLParser.importStatement(DRLParser.java:349)
   at org.drools.lang.DRLParser.statement(DRLParser.java:258)
   at org.drools.lang.DRLParser.compilationUnit(DRLParser.java:155)
   at org.drools.compiler.DrlParser.compile(DrlParser.java:225)
   at org.drools.compiler.DrlParser.parse(DrlParser.java:136)
   at org.drools.compiler.DrlParser.parse(DrlParser.java:141)
   at org.drools.compiler.PackageBuilder.addPackageFromDrl(PackageBuilder.java:352)
   at org.drools.compiler.PackageBuilder.addKnowledgeResource(PackageBuilder.java:538)
   at org.drools.builder.impl.KnowledgeBuilderImpl.add(KnowledgeBuilderImpl.java:28)
   at disbotics.core.config.DroolsRulesPlugin.initialize(DroolsRulesPlugin.java:57)
   at disbotics.core.common.DisboticsCore.startFramework(DisboticsCore.java:109)
   at disbotics.core.common.DisboticsCore.main(DisboticsCore.java:56)

Line 6:0 unexpected exception at input 'rule'. Exception: java.util.EmptyStackException. Stack trace:
 java.util.EmptyStackException
   at java.util.Stack.pop(Stack.java:109)
   at org.drools.lang.ParserHelper.popParaphrases(ParserHelper.java:421)
   at org.drools.lang.ParserHelper.end(ParserHelper.java:732)
   at org.drools.lang.DRLParser.rule(DRLParser.java:886)
   at org.drools.lang.DRLParser.statement(DRLParser.java:267)
   at org.drools.lang.DRLParser.compilationUnit(DRLParser.java:155)
   at org.drools.compiler.DrlParser.compile(DrlParser.java:225)
   at org.drools.compiler.DrlParser.parse(DrlParser.java:136)
   at org.drools.compiler.DrlParser.parse(DrlParser.java:141)
   at org.drools.compiler.PackageBuilder.addPackageFromDrl(PackageBuilder.java:352)
   at org.drools.compiler.PackageBuilder.addKnowledgeResource(PackageBuilder.java:538)
   at org.drools.builder.impl.KnowledgeBuilderImpl.add(KnowledgeBuilderImpl.java:28)
   at disbotics.core.config.DroolsRulesPlugin.initialize(DroolsRulesPlugin.java:57)
   at disbotics.core.common.DisboticsCore.startFramework(DisboticsCore.java:109)
   at disbotics.core.common.DisboticsCore.main(DisboticsCore.java:56)

Parser returned a null Package

   at disbotics.core.config.DroolsRulesPlugin.initialize(DroolsRulesPlugin.java:63)
   at disbotics.core.common.DisboticsCore.startFramework(DisboticsCore.java:109)
   at disbotics.core.common.DisboticsCore.main(DisboticsCore.java:56)

again, compiling the rules worked just fine in OpenJDK. We're using Janino, and it is properly referenced on the classpath (the classpath used at runtime is created by the Maven build, so contains all jars referenced by drools/janino/ anything else)

Does anyone know what's going on here and/or how to get Drools working with JamVM?

score 2 · Accepted Answer · answered Nov 24 '11 at 12:24

2

Are you compiling the knowledge packages using OpenJDK 1.6? and then trying to load it with 1.5.4? You should try compiling the original packages using 1.5.4 and see if you have the same errors.

For the stack trace, it looks like you are trying to add something to an unmodifiable list right?

Basically you are getting the exception here: kBase.addKnowledgePackages(kpkgs); Right?

answered Nov 24 '11 at 12:24

salaboy

4,123
1
14
15

1) Yes and yes - I also tried to compile the rules at runtime, i.e. using the JamVM, but that also gave me simmilarly strange errors. I'll post that too ASAP... 2) yes and yes - The thing is that (unless Drools doesn't call that code in OpenJDK) the error is specific to JamVM, although the code doesn't suggest that it replaces the empty list with a modifiable one (unless some heavy advanced reflection is used here) – Silly Freak Nov 28 '11 at 13:58
1

It looks like JamVM is not supporting that unmodifiable list method. Different JVM implementations can omit these kind of things. We should read a little bit more about why JamVM is throwing this exception and see how we can fix it: java.lang.UnsupportedOperationException at java.util.AbstractList.add(AbstractList.java:131) – salaboy Dec 03 '11 at 13:54
Thanks for your help! I hope you can find out what's wrong with the lists on JamVM. For so long, we'll try to stay with Jess or switch the VM and hope it works! – Silly Freak Dec 06 '11 at 10:26
Let me know if you switch the VM and still have problems, The Unsupported Operation Exception is part of the VM implementation, so we should try with another one.Cheers – salaboy Dec 06 '11 at 13:55

Drools: Compiling rules (or loading compiled rules) fails with obscure exceptions in JamVM

1 Answers1