Removing illegal reflective access warnings in Grails 4
Tags: grails, groovy
Published: 2019-07-15 14:53:57

When using JDK11 with Grails 4 you likely have seen these messages:

```
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.codehaus.groovy.reflection.CachedConstructor$1 (file:/Users/erichelgeson/.gradle/caches/modules-2/files-2.1/org.codehaus.groovy/groovy/2.5.6/6936e700f0fb1b50bac0698ada4347a769d40199/groovy-2.5.6.jar) to constructor com.sun.jmx.mbeanserver.JmxMBeanServer(java.lang.String,javax.management.MBeanServer,javax.management.MBeanServerDelegate)
WARNING: Please consider reporting this to the maintainers of org.codehaus.groovy.reflection.CachedConstructor$1
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
```

This is because Groovy 2.5 uses reflection. In Groovy 3 they've already made [great strides on this](https://opencollective.com/friends-of-groovy/updates/progressing-towards-groovy-3-0-0-with-greatly-reduced-illegal-access-errors). 

For now we can add the correct packages to the `--add-opens` JVM args to get rid of them.

**NOTE:** This is the same way Groovy 2.5 removes them when calling `groovy` with the [`GROOVY_TURN_OFF_JAVA_WARNINGS`](https://github.com/apache/groovy/commit/a7f7cdd352a40dd7acd2def999eb560c2b76904e) environment variable.

In our `build.gradle` file we can define a list of modules to open:

```groovy
def jvmOpenModulesArgs = [
        "--add-opens=java.management/com.sun.jmx.mbeanserver=ALL-UNNAMED",
        "--add-opens=java.base/java.io=ALL-UNNAMED",
        "--add-opens=java.base/java.lang=ALL-UNNAMED",
        "--add-opens=java.base/java.lang.annotation=ALL-UNNAMED",
        "--add-opens=java.base/java.lang.invoke=ALL-UNNAMED",
        "--add-opens=java.base/java.lang.module=ALL-UNNAMED",
        "--add-opens=java.base/java.lang.ref=ALL-UNNAMED",
        "--add-opens=java.base/java.lang.reflect=ALL-UNNAMED",
        "--add-opens=java.base/java.math=ALL-UNNAMED",
        "--add-opens=java.base/java.net=ALL-UNNAMED",
        "--add-opens=java.base/java.net.spi=ALL-UNNAMED",
        "--add-opens=java.base/java.nio=ALL-UNNAMED",
        "--add-opens=java.base/java.nio.channels=ALL-UNNAMED",
        "--add-opens=java.base/java.nio.channels.spi=ALL-UNNAMED",
        "--add-opens=java.base/java.nio.charset=ALL-UNNAMED",
        "--add-opens=java.base/java.nio.charset.spi=ALL-UNNAMED",
        "--add-opens=java.base/java.nio.file=ALL-UNNAMED",
        "--add-opens=java.base/java.nio.file.attribute=ALL-UNNAMED",
        "--add-opens=java.base/java.nio.file.spi=ALL-UNNAMED",
        "--add-opens=java.base/java.security=ALL-UNNAMED",
        "--add-opens=java.base/java.security.acl=ALL-UNNAMED",
        "--add-opens=java.base/java.security.cert=ALL-UNNAMED",
        "--add-opens=java.base/java.security.interfaces=ALL-UNNAMED",
        "--add-opens=java.base/java.security.spec=ALL-UNNAMED",
        "--add-opens=java.base/java.text=ALL-UNNAMED",
        "--add-opens=java.base/java.text.spi=ALL-UNNAMED",
        "--add-opens=java.base/java.time=ALL-UNNAMED",
        "--add-opens=java.base/java.time.chrono=ALL-UNNAMED",
        "--add-opens=java.base/java.time.format=ALL-UNNAMED",
        "--add-opens=java.base/java.time.temporal=ALL-UNNAMED",
        "--add-opens=java.base/java.time.zone=ALL-UNNAMED",
        "--add-opens=java.base/java.util=ALL-UNNAMED",
        "--add-opens=java.base/java.util.concurrent=ALL-UNNAMED",
        "--add-opens=java.base/java.util.concurrent.atomic=ALL-UNNAMED",
        "--add-opens=java.base/java.util.concurrent.locks=ALL-UNNAMED",
        "--add-opens=java.base/java.util.function=ALL-UNNAMED",
        "--add-opens=java.base/java.util.jar=ALL-UNNAMED",
        "--add-opens=java.base/java.util.regex=ALL-UNNAMED",
        "--add-opens=java.base/java.util.spi=ALL-UNNAMED",
        "--add-opens=java.base/java.util.stream=ALL-UNNAMED",
        "--add-opens=java.base/java.util.zip=ALL-UNNAMED",
        "--add-opens=java.datatransfer/java.awt.datatransfer=ALL-UNNAMED",
        "--add-opens=java.desktop/java.applet=ALL-UNNAMED",
        "--add-opens=java.desktop/java.awt=ALL-UNNAMED",
        "--add-opens=java.desktop/java.awt.color=ALL-UNNAMED",
        "--add-opens=java.desktop/java.awt.desktop=ALL-UNNAMED",
        "--add-opens=java.desktop/java.awt.dnd=ALL-UNNAMED",
        "--add-opens=java.desktop/java.awt.dnd.peer=ALL-UNNAMED",
        "--add-opens=java.desktop/java.awt.event=ALL-UNNAMED",
        "--add-opens=java.desktop/java.awt.font=ALL-UNNAMED",
        "--add-opens=java.desktop/java.awt.geom=ALL-UNNAMED",
        "--add-opens=java.desktop/java.awt.im=ALL-UNNAMED",
        "--add-opens=java.desktop/java.awt.im.spi=ALL-UNNAMED",
        "--add-opens=java.desktop/java.awt.image=ALL-UNNAMED",
        "--add-opens=java.desktop/java.awt.image.renderable=ALL-UNNAMED",
        "--add-opens=java.desktop/java.awt.peer=ALL-UNNAMED",
        "--add-opens=java.desktop/java.awt.print=ALL-UNNAMED",
        "--add-opens=java.desktop/java.beans=ALL-UNNAMED",
        "--add-opens=java.desktop/java.beans.beancontext=ALL-UNNAMED",
        "--add-opens=java.instrument/java.lang.instrument=ALL-UNNAMED",
        "--add-opens=java.logging/java.util.logging=ALL-UNNAMED",
        "--add-opens=java.management/java.lang.management=ALL-UNNAMED",
        "--add-opens=java.prefs/java.util.prefs=ALL-UNNAMED",
        "--add-opens=java.rmi/java.rmi=ALL-UNNAMED",
        "--add-opens=java.rmi/java.rmi.activation=ALL-UNNAMED",
        "--add-opens=java.rmi/java.rmi.dgc=ALL-UNNAMED",
        "--add-opens=java.rmi/java.rmi.registry=ALL-UNNAMED",
        "--add-opens=java.rmi/java.rmi.server=ALL-UNNAMED",
        "--add-opens=java.sql/java.sql=ALL-UNNAMED"
]
```

Then add them to our `bootRun` task:

```groovy
bootRun {
    jvmArgs('-noverify',
            '-XX:TieredStopAtLevel=1',
            '-Xmx1024m')
    jvmArgs(jvmOpenModulesArgs)
    // ...
}
```

And any task with `GroovyCompile` & `Test`

```groovy
tasks.withType(GroovyCompile) {
    options.forkOptions.jvmArgs = jvmOpenModulesArgs
}
tasks.withType(Test) {
    jvmArgs = jvmOpenModulesArgs
}
```

That's it - no more pesky reflective access warnings when the JVM starts up. Thanks to Daniel Sun helping me find the right modules.