Forge Server not booting

[SheepHead]

Hello,

I recently upgraded my server completely and everything works except that every single version of forge doesn't work. I tried the installer(The forge recommended installer NOT the universal although it says so in the installation folder "forge-1.12.2-14.23.5.2768-universal.jar") to install a fresh new server. doesn't work, it loads the GUI, I follow the installation and try to run the server through the terminal with this command "java -Xmx48000M -jar forge-(inserting here the forge version)-universal.jar". I copied the server files from my previous server(and I tested it on the old server and it all works) and it doesn't work on the new server. But vanilla Minecraft server works perfectly.

I get this error

theserver@TheServer:~/Server 1.12.2$ java -Xmx48000M -jar forge-1.12.2-14.23.5.2768-universal.jar
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:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    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.<init>(Launch.java:34)
    at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
    ... 6 more

 

(this is the java version)
theserver@TheServer:~/Server 1.12.2$ java -version
java version "11.0.2" 2019-01-15 LTS
Java(TM) SE Runtime Environment 18.9 (build 11.0.2+9-LTS)
Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.2+9-LTS, mixed mode)
 

I'm running Ubuntu 18.04 LTS

What can I do to fix this error?

 

Already thank you.

 

 

[DaemonUmbra]

You must use Java 8 for Forge 1.12.2 and earlier.

[SheepHead]

Thank you very very much, it works