I'm using Drools 5.4.0 with Java 8 beta 89 and all works perfect. Very simple use of Drools: KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder(); kbuilder.add(ResourceFactory.newClassPathResource("CFL_Advisor.dsl", getClass() ), ResourceType.DSL); kbuilder.add( ResourceFactory.newClassPathResource( "CFL_Advisor.dslr", getClass() ), ResourceType.DSLR ); Now I've just upgraded to Java 8 beta 104 and Drools stopped working. I have tried with Java 8 beta 101 with the same error. I have tried also with Drools 5.5.0 and Drools 6.0.0 RC3 and the error is the same. Java 8 beta 89 works also well for all the previous Drools versions. I need to use lastest Java 8 beta releases because we are developing an experimental system that needs last releases of Java FX. And I suppose that it is important that Drools (any versión) will support Java 8. I get this error: Exception in thread "main" java.lang.RuntimeException: wrong class format at org.drools.commons.jci.compilers.EclipseJavaCompiler$2.findType(EclipseJavaCompiler.java:263) at org.drools.commons.jci.compilers.EclipseJavaCompiler$2.findType(EclipseJavaCompiler.java:203) at org.eclipse.jdt.internal.compiler.lookup.LookupEnvironment.askForType(LookupEnvironment.java:102) at org.eclipse.jdt.internal.compiler.lookup.UnresolvedReferenceBinding.resolve(UnresolvedReferenceBinding.java:49) at org.eclipse.jdt.internal.compiler.lookup.BinaryTypeBinding.resolveType(BinaryTypeBinding.java:122) at org.eclipse.jdt.internal.compiler.lookup.LookupEnvironment.getTypeFromTypeSignature(LookupEnvironment.java:1188) at org.eclipse.jdt.internal.compiler.lookup.BinaryTypeBinding.cachePartsFrom(BinaryTypeBinding.java:317) at org.eclipse.jdt.internal.compiler.lookup.LookupEnvironment.createBinaryTypeFrom(LookupEnvironment.java:640) at org.eclipse.jdt.internal.compiler.lookup.LookupEnvironment.createBinaryTypeFrom(LookupEnvironment.java:619) at org.eclipse.jdt.internal.compiler.Compiler.accept(Compiler.java:295) at org.eclipse.jdt.internal.compiler.lookup.LookupEnvironment.askForType(LookupEnvironment.java:107) at org.eclipse.jdt.internal.compiler.lookup.UnresolvedReferenceBinding.resolve(UnresolvedReferenceBinding.java:49) at org.eclipse.jdt.internal.compiler.lookup.BinaryTypeBinding.resolveType(BinaryTypeBinding.java:122) at org.eclipse.jdt.internal.compiler.lookup.LookupEnvironment.getTypeFromTypeSignature(LookupEnvironment.java:1188) at org.eclipse.jdt.internal.compiler.lookup.BinaryTypeBinding.createFields(BinaryTypeBinding.java:355) at org.eclipse.jdt.internal.compiler.lookup.BinaryTypeBinding.cachePartsFrom(BinaryTypeBinding.java:326) at org.eclipse.jdt.internal.compiler.lookup.LookupEnvironment.createBinaryTypeFrom(LookupEnvironment.java:640) at org.eclipse.jdt.internal.compiler.lookup.LookupEnvironment.createBinaryTypeFrom(LookupEnvironment.java:619) at org.eclipse.jdt.internal.compiler.Compiler.accept(Compiler.java:295) at org.eclipse.jdt.internal.compiler.lookup.LookupEnvironment.askForType(LookupEnvironment.java:107) at org.eclipse.jdt.internal.compiler.lookup.UnresolvedReferenceBinding.resolve(UnresolvedReferenceBinding.java:49) at org.eclipse.jdt.internal.compiler.lookup.BinaryTypeBinding.resolveType(BinaryTypeBinding.java:122) at org.eclipse.jdt.internal.compiler.lookup.ParameterizedTypeBinding.resolve(ParameterizedTypeBinding.java:851) at org.eclipse.jdt.internal.compiler.lookup.BinaryTypeBinding.resolveType(BinaryTypeBinding.java:100) at org.eclipse.jdt.internal.compiler.lookup.BinaryTypeBinding.superclass(BinaryTypeBinding.java:1062) at org.eclipse.jdt.internal.compiler.lookup.Scope.findMethod(Scope.java:1256) at org.eclipse.jdt.internal.compiler.lookup.Scope.findMethod(Scope.java:1181) at org.eclipse.jdt.internal.compiler.lookup.Scope.getMethod(Scope.java:2237) at org.eclipse.jdt.internal.compiler.ast.MessageSend.resolveType(MessageSend.java:401) at org.eclipse.jdt.internal.compiler.ast.MessageSend.resolveType(MessageSend.java:357) at org.eclipse.jdt.internal.compiler.ast.Expression.resolve(Expression.java:913) at org.eclipse.jdt.internal.compiler.ast.AbstractMethodDeclaration.resolveStatements(AbstractMethodDeclaration.java:447) at org.eclipse.jdt.internal.compiler.ast.MethodDeclaration.resolveStatements(MethodDeclaration.java:189) at org.eclipse.jdt.internal.compiler.ast.AbstractMethodDeclaration.resolve(AbstractMethodDeclaration.java:406) at org.eclipse.jdt.internal.compiler.ast.TypeDeclaration.resolve(TypeDeclaration.java:1131) at org.eclipse.jdt.internal.compiler.ast.TypeDeclaration.resolve(TypeDeclaration.java:1219) at org.eclipse.jdt.internal.compiler.ast.CompilationUnitDeclaration.resolve(CompilationUnitDeclaration.java:528) at org.eclipse.jdt.internal.compiler.Compiler.process(Compiler.java:759) at org.eclipse.jdt.internal.compiler.Compiler.compile(Compiler.java:464) at org.drools.commons.jci.compilers.EclipseJavaCompiler.compile(EclipseJavaCompiler.java:389) at org.drools.commons.jci.compilers.AbstractJavaCompiler.compile(AbstractJavaCompiler.java:49) at org.drools.rule.builder.dialect.java.JavaDialect.compileAll(JavaDialect.java:371) at org.drools.compiler.DialectCompiletimeRegistry.compileAll(DialectCompiletimeRegistry.java:46) at org.drools.compiler.PackageRegistry.compileAll(PackageRegistry.java:102) at org.drools.compiler.PackageBuilder.compileAll(PackageBuilder.java:1006) at org.drools.compiler.PackageBuilder.compileAllRules(PackageBuilder.java:842) at org.drools.compiler.PackageBuilder.addPackage(PackageBuilder.java:831) at org.drools.compiler.PackageBuilder.addPackageFromDrl(PackageBuilder.java:467) at org.drools.compiler.PackageBuilder.addKnowledgeResource(PackageBuilder.java:673) at org.drools.builder.impl.KnowledgeBuilderImpl.add(KnowledgeBuilderImpl.java:45) at org.drools.builder.impl.KnowledgeBuilderImpl.add(KnowledgeBuilderImpl.java:34) at es.indra.ifocucs.drools.CflAdvisor.getKnowledgeBase(CflAdvisor.java:28) at es.indra.ifocucs.drools.CflAdvisor.(CflAdvisor.java:52) at es.indra.ifocucs.drools.CflAdvisor.main(CflAdvisor.java:79) Caused by: org.eclipse.jdt.internal.compiler.classfmt.ClassFormatException at org.eclipse.jdt.internal.compiler.classfmt.ClassFileReader.(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) ... 53 more -- View this message in context: http://drools.46999.n3.nabble.com/Drools-doesn-t-works-with-latest-beta-r... 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