Startup Issue with Minecraft - Minecraft 1.12.2 server with forge does not start

Technical Support
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1

System Information

Field Value
Operating System Linux - Debian GNU/Linux 11 on x86_64
Product AMP ‘Decadeus’ v2.4.6.6 (Mainline)
Virtualization QEMU_KVM
Application Minecraft
Module MinecraftModule
Running in Container No
Current State Failed

Yes, Java 8 is selected.
No there’s no mods installed yet

Issue

Error:

A problem occurred running the Server launcher.java.lang.reflect.InvocationTargetException
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:568)
at net.minecraftforge.fml.relauncher.ServerLaunchWrapper.run(ServerLaunchWrapper.java:70)
at net.minecraftforge.fml.relauncher.ServerLaunchWrapper.main(ServerLaunchWrapper.java:34)
Caused by: java.lang.ClassCastException: class jdk.internal.loader.ClassLoaders$AppClassLoader cannot be cast to class java.net.URLClassLoader (jdk.internal.loader.ClassLoaders$AppClassLoader and java.net.URLClassLoader are in module java.base of loader ‘bootstrap’)
at net.minecraft.launchwrapper.Launch.(Launch.java:34)
at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
… 6 more

Reproduction Steps

  • Opened Game Panel
  • Installed Forge 14.23.5.2859 (1.12.2)
  • Started the server
2

so some times java doesn’t kick over so try this first, switch your java to something like 16 or 17 and then wait a min, then switch it back. its a know java problem and there isn’t a fix for it on the books right now.

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