Forge 1.12.2 latest recommended version starts refusing to open out of nowhere.

[Slyshi]

Hi, I was making a Forge server for me and a group of friends and everything went smoothly for the past week.

I turned the server off when I went to bed, and once I woke up, I restarted the server only for it to instantly close. I have no idea what is causing this.

Spoiler

D:\server>java -Xmx4096M -Xms4096M -jar forge-1.12.2-14.23.1.2555-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(Unknown Source)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
        at java.base/java.lang.reflect.Method.invoke(Unknown Source)
        at net.minecraftforge.fml.relauncher.ServerLaunchWrapper.run(ServerLaunchWrapper.java:62)
        at net.minecraftforge.fml.relauncher.ServerLaunchWrapper.main(ServerLaunchWrapper.java:31)
Caused by: java.lang.ClassCastException: java.base/jdk.internal.loader.ClassLoaders$AppClassLoader cannot be cast to java.base/java.net.URLClassLoader
        at net.minecraft.launchwrapper.Launch.<init>(Launch.java:34)
        at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
        ... 6 more

I tried everything. Reinstalling, making a new server, deleting each and every single mod I was using, and no luck. I've been trying to fix this for over 2 hours and I have no idea what is going on. As a last resort I decided to make an account here in hope that someone will help me fix the issue. Thanks

Edited January 27, 2018 by Slyshi

[Choonster]

1 hour ago, Slyshi said:

Caused by: java.lang.ClassCastException: java.base/jdk.internal.loader.ClassLoaders$AppClassLoader cannot be cast to java.base/java.net.URLClassLoader

 

You're using Java 9, which isn't supported by Forge. You need to use Java 8 instead.