I recognise the docs say “17+” but I wonder if Java 21 is part of the test
suite.
Drools 10.1.0 rule compilation fails on Java 21 (OpenJDK) with an
UnsupportedOperationException during parallel rule compilation when creating a
KieSession from a KJAR.
Environment
Java: OpenJDK 21
Drools: 10.1.0
OS: Windows
Maven: 3.x
Steps to Reproduce
1. Build a KJAR with Drools 10.1.0
2. Load via KieServices.Factory.get().getKieClasspathContainer() and create a
KieSession from a KJAR
3. Trigger parallel rule compilation
Error Details
java.lang.RuntimeException: Rules compilation failed or interrupted at
org.drools.compiler.builder.impl.processors.ImmutableRuleCompilationPhase.compileRulesLevel(ImmutableRuleCompilationPhase.java:285)
... (parallel execution stack trace using atomic primitives)
Root cause:
java.lang.UnsupportedOperationException: null
at
org.drools.compiler.rule.builder.ConstraintBuilder$DummyConstraintBuilder.setExprInputs(ConstraintBuilder.java:210)
Stack Trace Highlights
The failure occurs in parallel execution via ForkJoinPool:
at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateParallel
at
org.drools.compiler.builder.impl.processors.ImmutableRuleCompilationPhase.lambda$compileRulesLevel$4
Indicates a failure during parallel compilation using Java 21's stream
framework.
Workarounds Attempted (None Successful)
1. System.setProperty("drools.parallelExecutionAllowed", "false") – not honored
in 10.x
2. System.setProperty("drools.multithreadEvaluation", "false") – no effect
3. Downgrade to Drools 8.44 – DRL incompatibility with 10.x-compiled rules
4. -Djdk.reflect.useDirectMethodHandle=false – still fails with native
reflection
Expected Behavior
Rules compile and execute successfully on Java 21 without errors.
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Douglas Whitfield | Enterprise Architect, OpenLogic
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