Junit tests not working with Drools 5.4.0.Final and JDK 8

Question

I recently started upgrading my application JDK version from jdk1.7.0_121_x64 to jdk1.8.0_202_x64. I have some legacy code using Drools 5.4.0.Final. This code is working with JDK version jdk1.7.0_121_x64 without any issue.

Maven dependencies are:

<dependency>     <groupId>org.drools</groupId>     <artifactId>drools-core</artifactId>     <version>5.4.0.Final</version> </dependency> <dependency>     <groupId>org.drools</groupId>     <artifactId>drools-decisiontables</artifactId>     <version>5.4.0.Final</version> </dependency> 

DRL files are loaded as:

final KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase(); final KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder(); kbuilder.add(resource, ResourceType.DRL); knowledgeBase.addKnowledgePackages(kbuilder.getKnowledgePackages()); 

I was aware that there are issues using Drools with JDK 8. I referrred to other SO thread to start with.

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When I built my application and executed Junit tests using JDK 8, tests failed with error:

testRunRule(com.company.app.RuleTest)  Time elapsed: 0.073 sec  <<< ERROR! java.lang.RuntimeException: java.lang.RuntimeException: wrong class format     at org.eclipse.jdt.internal.compiler.classfmt.ClassFileReader.<init>(ClassFileReader.java:372)     at org.drools.commons.jci.compilers.EclipseJavaCompiler$2.createNameEnvironmentAnswer(EclipseJavaCompiler.java:287)     at org.drools.commons.jci.compilers.EclipseJavaCompiler$2.findType(EclipseJavaCompiler.java:258) 

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As mentioned in SO thread, I found reference to this bugfix ticket DROOLS-329.

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Based on approaches mentioned in this bugfix ticket, I tried to use JANINO compiler:

Added following maven dependency:

<dependency>     <groupId>org.codehaus.janino</groupId>     <artifactId>janino</artifactId>     <version>2.5.16</version> </dependency> 

I added following VM argument (I was running tests from eclipse, so in eclipse launch configuration in JRE VM argument added the argument):

-Ddrools.dialect.java.compiler=JANINO 

I could still see the wrong class format error. So I modified my code to load DRL files as:

final KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase(); final Properties props = new Properties(); props.setProperty("drools.dialect.java.compiler", "JANINO"); final KnowledgeBuilderConfiguration config = KnowledgeBuilderFactory.newKnowledgeBuilderConfiguration(props, null); final KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder(config); kbuilder.add(resource, ResourceType.DRL); knowledgeBase.addKnowledgePackages(kbuilder.getKnowledgePackages()); 

It didn't help. I could still see the wrong class format error.

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I followed another apprroach mentioned in this external link. I updated added/updated maven dependencies as:

<dependency>     <groupId>org.drools</groupId>     <artifactId>drools-core</artifactId>     <version>5.4.0.Final</version>     <exclusions>       <exclusion>           <groupId>org.mvel</groupId>           <artifactId>mvel2</artifactId>       </exclusion>    </exclusions> </dependency> <dependency>     <groupId>org.drools</groupId>     <artifactId>drools-decisiontables</artifactId>     <version>5.4.0.Final</version>     <exclusions>       <exclusion>           <groupId>org.eclipse.jdt.core.compiler</groupId>           <artifactId>ecj</artifactId>       </exclusion>       <exclusion>           <groupId>org.mvel</groupId>           <artifactId>mvel2</artifactId>       </exclusion>    </exclusions> </dependency> <dependency>     <groupId>org.mvel</groupId>     <artifactId>mvel2</artifactId>     <version>2.1.9.Final</version> </dependency> <dependency>    <groupId>org.eclipse.jdt.core.compiler</groupId>    <artifactId>ecj</artifactId>    <version>4.6.1</version> </dependency> 

mvel2 patch is built using: https://github.com/mkornipati/mvel/tree/2.1.9.Final.Patch

With this wrong class format error is gone. But my tests are now failing with following error:

testRunRule(com.company.app.RuleTest))  Time elapsed: 4.684 sec  <<< ERROR! java.lang.RuntimeException: org.drools.rule.InvalidRulePackage: Rule Compilation error : [Rule name='ruleCheck']     org/drools/template/parser/Rule_ruleCheck_8eb4621227714a36b7b84c8b764527e4.java (2:80) : Only a type can be imported. java.util.Map resolves to a package     org/drools/template/parser/Rule_ruleCheck_8eb4621227714a36b7b84c8b764527e4.java (2:101) : Only a type can be imported. java.util.HashMap resolves to a package     org/drools/template/parser/Rule_ruleCheck_8eb4621227714a36b7b84c8b764527e4.java (6:299) : org.drools.spi.KnowledgeHelper cannot be resolved to a type     org/drools/template/parser/Rule_ruleCheck_8eb4621227714a36b7b84c8b764527e4.java (6:339) : org.drools.template.parser.Row cannot be resolved to a type     org/drools/template/parser/Rule_ruleCheck_8eb4621227714a36b7b84c8b764527e4.java (6:373) : org.drools.FactHandle cannot be resolved to a type     org/drools/template/parser/Rule_ruleCheck_8eb4621227714a36b7b84c8b764527e4.java (6:411) : org.drools.template.parser.DefaultGenerator cannot be resolved to a type     org/drools/template/parser/Rule_ruleCheck_8eb4621227714a36b7b84c8b764527e4.java (6:487) : org.drools.runtime.rule.RuleContext cannot be resolved to a type     at org.drools.rule.Package.checkValidity(Package.java:445) 

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I don't know how to proceed further. Please let me know if you are able to make Drools 5.4 work with JDK 8.

Answer 1

I used Drools 7.7.0 with Java 8 and worked great for me. I am not sure what is the oldest Drools version that is compatible with Java 8. That said, Drools 5.4.0 was released in 2011. Java 8 was released in 2014, so you can assume it won't be compatible. Java 7 was released in July 2011. Depending on when 5.4.0 was released it might or might not be. Based on that, I expect Drools 5.4.0 to be compatible with Java 6 or earlier. If you want to use Java 8 with Drools, I don't see how you can without upgrading. I think the earliest compatible version is 6.1.0 download.jboss.org/drools/release.

In summary: Either downgrade your project to Java 6 to use Drools 5.4.0 or Upgrade Drools to use 6.1.0. Better yet, upgrade to latest Drools and then figure out what is the latest Java version it supports.