CacioExtension fails when running under OpenJDK 21 on Linux

[jbloomfield2008]

The CacioExtension fails to run under Linux with X11 libraries loaded. I've tried both under Ubuntu and Rocky Linux 9.5 running Xfce. In both cases, Cacio runs fine when started from a command-line with a DISPLAY environment variable set, but as soon as it's run from a session with no DISPLAY set then it fails with the following error:

java.lang.ExceptionInInitializerError: Exception java.lang.UnsatisfiedLinkError: 'void java.awt.Component.initIDs()' [in thread "main"]
at java.desktop/java.awt.Component.initIDs(Native Method)
at java.desktop/java.awt.Component.(Unknown Source)
at java.desktop/javax.swing.ImageIcon$2.run(Unknown Source)
at java.desktop/javax.swing.ImageIcon$2.run(Unknown Source)
at java.base/java.security.AccessController.doPrivileged(Unknown Source)
at java.desktop/javax.swing.ImageIcon.createNoPermsComponent(Unknown Source)
at java.desktop/javax.swing.ImageIcon$1.run(Unknown Source)
at java.desktop/javax.swing.ImageIcon$1.run(Unknown Source)
at java.base/java.security.AccessController.doPrivileged(Unknown Source)
at java.desktop/javax.swing.ImageIcon.(Unknown Source)

I've confirmed that both Toolkit / GraphicsEnviroment have been replaced with the Cacio versions. The error above seems to be deep within the native code of the JVM.

[jbloomfield2008]

Any idea what's going on?

[gschrader]

Sorry for the late response, did you make any progress on this? I need to re-figure out the github action, it was running against Mac/Windows and Linux, so I'm not sure where this would have started to fail, maybe its because no tests use an ImageIcon. I'll hopefully have some more cycles to spend on this project soon.

[gschrader]

I was able to add an ImageIcon test and get it to run with GitHub actions under Ubuntu 24.04.2. I'm at a bit of a loss as to why it's not working for you. Are you able to run this repositories tests on your linux environment to see if they run ok?

[jbloomfield2008]

You are correct, the tests run just fine under Ubuntu and that extends to our tests. So it looks like it has something to do with Rocky Linux or potentially XFCE. I will do some more tests to hopefully narrow down what's going on.

[mtf90]

I ran into the same issue on 17.0.17+10 so it does not seem to be specifically related to Java 21. What eventually helped was explicitly setting

<systemPropertyVariables>
    <java.awt.headless>false</java.awt.headless>
</systemPropertyVariables>

It seems that the JDK picks up on the missing DISPLAY variable and decides to not load specific subsystems.

So the only issue seems to be that the README.md falsely claims for Java 17 and later that

The system properties are no longer supported or needed in pom.xml or build.gradle.

[gschrader]

Thanks for the diagnosis @mtf90, you're right that the README contradicted itself. The "Java 17 and later" section claimed system properties were no longer needed, but the pom example just above it still sets java.awt.headless=false. I've clarified that section on the v2 branch (PR #22): eaa4876

Net of the change:

• awt.toolkit and java.awt.graphicsenv are auto-applied by @CacioTest / CacioExtension and don't need to be set.
• java.awt.headless=false is still required in environments without a DISPLAY (headless Linux CI, Rocky/XFCE, etc.). Without it the JDK skips loading native AWT and you hit UnsatisfiedLinkError: Component.initIDs().

@jbloomfield2008, does adding <java.awt.headless>false</java.awt.headless> to your surefire <systemPropertyVariables> resolve it on Rocky? If so I'll close this issue once 2.0 ships.