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?
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?