Groovy - WARNING: An illegal reflective access operation has occurred

Question

I am pretty much new to java and groovy. I have installed groovy 3.0 on my windows 10 laptop (64 bit) and when tried to run groovy getting following warning:

>groovy -v
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.codehaus.groovy.reflection.CachedClass (file:/C:/groovy-3.0.0-alpha-1/lib/groovy-3.0.0-alpha-1.jar) to method java.lang.Object.finalize()
WARNING: Please consider reporting this to the maintainers of org.codehaus.groovy.reflection.CachedClass
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
Groovy Version: 3.0.0-alpha-1 JVM: 9.0.1 Vendor: Oracle Corporation OS: Windows 10

And the java version is:

java --version
java 9.0.1
Java(TM) SE Runtime Environment (build 9.0.1+11)
Java HotSpot(TM) 64-Bit Server VM (build 9.0.1+11, mixed mode)

Any help to resolve this.

Answer 1

To disable the warnings you can pass --add-opens to the JVM, see details here. Unfortunately Groovy requires a lot of modules/packages to be opened, see this (currently reverted) commit (source). Just tested these with AdoptOpenJDK 11.

Answer 2

It is more than a 'warning' for me: I cannot get Groovy scripts to run (on macOS) with the current JVM 9, much less 10. The workaround (until a compatible version of Groovy is available) is to install jenv and an earlier version of Java, so you can switch when needed.

Answer 3

Although my environment is Linux, after struggling some days to setup Groovy on Grails environment I feel like I know the answer: use JDK 8 for now. I was fiddling with JDK 9, and I thought it was too far behind so I tried JDK 11, which made things even worse, I got actual crashes. It seems like that Groovy / Grails is heavily lagging behind in terms of Java version compatibility.

Once the new Groovy will be released (said to be end of this year) then newer JDK can be used as well.