How to fix UnsupportedClassVersionError on a Java server¶

The error¶

When starting the server, you may see one of these errors:

Caused by: java.lang.UnsupportedClassVersionError: net/minecraft/bundler/Main
has been compiled by a more recent version of the Java Runtime (class file
version 69.0), this version of the Java Runtime only recognizes class file
versions up to 65.0

Exception in thread "ServerMain" java.lang.UnsupportedClassVersionError:
org/bukkit/craftbukkit/Main has been compiled by a more recent version of
the Java Runtime (class file version 65.0), this version of the Java Runtime
only recognizes class file versions up to 61.0

This happens because the server jar requires a newer Java version than the one currently selected in the Docker Image.

Steps¶

1. Open https://panel.nexuscloud.id/.
2. If you are using a phone, click the hamburger menu (=) to open the panel navigation.
3. Scroll down and click Startup.
4. Find the Docker Image dropdown.
5. Change the Docker Image to the highest Java version available. For example, Minecraft 1.26.x requires Java 25 Temurin.
6. Start the server. The error should be resolved.

Cheers, Team NexusCloud