Hello,
I'm trying to use the forge installer to install a modded server on my computer. I've tried about 5 separate times now (each time in a different folder) to install the server yet it crashes each time I try to run it. The unmodded vanilla server .jar file downloaded through the installer runs just fine, however trying to run the forge server .jar (with or without my batch file) produces the following error:

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C:\Users\DIRECTORYSTUCTURE\>java -Xmx1024M -Xms1024M -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

C:\Users\DIRECTORYSTRUCTURE\>pause
Press any key to continue . . .

The contents of the batch file I'm trying to use are as follows:

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java -Xmx1024M -Xms1024M -jar forge-1.12.2-14.23.1.2555-universal.jar
pause

Any idea what's up? Thanks.

 

EDIT: Forge installer version is 1.12.2-14.23.1.2555

Edited January 27, 20187 yr by impromptutriplet

Having the same issue. No idea what's going on.

1 hour ago, impromptutriplet 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.

6 hours ago, Choonster said:

 

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

That fixed it! For anyone else having this problem you don't need to uninstall Java 9, if you have 9 and 8 installed you can specify which version of Java to run by entering the full directory in your batch file like so:

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"C:\Program Files\Java\jre1.8.0_151\bin\java" -Xmx1024M -Xms1024M -jar forge-1.12.2-14.23.1.2555-universal.jar
pause

Note the quotes around the directory, they're necessary if there are any spaces (like in the folder "Program Files").

 

Thanks for the help!