How to Resolve IntelliJ 2023.3 Groovyc ClassNotFoundError After JDK 21 Upgrade

The 2023.3 release of IntelliJ, which improves JDK 21 virtual‑thread support, may fail with a Groovyc compilation error like

java.lang.NoClassDefFoundError: com/intellij/util/containers/IntObjectHashMap$ArrayProducer

. The stack trace shows the failure occurs during the Groovy stub generation phase, indicating that IntelliJ’s internal class loader cannot locate required IntelliJ utility classes.

The issue was first reported on the IntelliJ official forum on December 9 and is linked to the IJPL‑126 migration that replaces custom IntelliJ interfaces with standard JDK APIs.

Affected builds include:

2023.3 Beta (233.11799.6), 2023.3 Beta 2 (233.11799.30), 2023.3 Beta 3 (233.11799.67), 2023.3 RC (233.11799.196), 2023.3 (233.11799.241)

Three possible solutions are provided:

Downgrade IntelliJ to a previous version where the issue does not exist.

Enable the JVM option -Dgroovyc.in.process=true in the shared build process VM options.

Wait for the next IntelliJ update, expected around December 19.

Explanation of the JVM option:

The system property -Dgroovyc.in.process=true tells the Groovy compiler to run inside the current Java process instead of spawning a separate process. Running in‑process can improve performance and reduce resource consumption, especially when Groovy compilation is invoked repeatedly.

However, using this option may affect application behavior, resource usage, and performance characteristics. It is recommended to test thoroughly in the intended environment before adopting it in production.