Specifying java version usage for Minecraft Server with flag

Question

Problem

I want to run two servers, one in 1.17 using Java 16 and the other in 1.12.2 using Java 8.

The argument I want to use in the .bat file is "C:\Program Files\Java\jre1.8.0_291\lib" -jar but it doesn't work.

.bat

The full .bat is as such.

@ECHO OFF
java -Xms10G -Xmx10G -XX:+UseG1GC -XX:+ParallelRefProcEnabled -XX:MaxGCPauseMillis=200 -XX:+UnlockExperimentalVMOptions -XX:+DisableExplicitGC -XX:-OmitStackTraceInFastThrow -XX:+AlwaysPreTouch  -XX:G1NewSizePercent=30 -XX:G1MaxNewSizePercent=40 -XX:G1HeapRegionSize=8M -XX:G1ReservePercent=20 -XX:G1HeapWastePercent=5 -XX:G1MixedGCCountTarget=8 -XX:InitiatingHeapOccupancyPercent=15 -XX:G1MixedGCLiveThresholdPercent=90 -XX:G1RSetUpdatingPauseTimePercent=5 -XX:SurvivorRatio=32 -XX:MaxTenuringThreshold=1 -Dusing.aikars.flags=true -Daikars.new.flags=true "C:\Program Files\Java\jre1.8.0_291\bin\java.exe" -jar forge-1.12.2-14.23.5.2855.jar --nogui
pause

Error message

The error given is:

Error: Could not find or load main class C:\Program Files\Java\jre1.8.0_291\bin\java.exe
Caused by: java.lang.ClassNotFoundException: C:\Program Files\Java\jre1.8.0_291\bin\java.exe

I don't know how to resolve the error of the java class not being found.

Additional details

I am running JRE 16 and Java 8 on the same computer. Only the 1.17 servers start with this installation set up.

The 1.12.2 server starts when I uninstall JRE 16.

Answer 1

You need to use the correct binaries.

Suppose Java 15 is in your PATH variable. Then executing the plain java command will execute with the Java 15 binary.

C:\Program Files\Java\jre1.8.0_291\bin\java.exe is your java 8 binary.

Thus, to execute forge on Java 8, you don't want to execute the plain java command, since that is java 15. You will need to qualify the whole path to your Java 8 executable, with the command:

C:\Program Files\Java\jre1.8.0_291\bin\java.exe -jar <path to forge jar>

Answer 2

Potential answer

Context

I've installed 2 versions of java, 8 and 16. When I type java -version in command prompt, java 16 shows up.

The following is my .bat file for forge 1.12.2

@ECHO OFF
java -Xms10G -Xmx10G -XX:+UseG1GC -XX:+ParallelRefProcEnabled -XX:MaxGCPauseMillis=200 -XX:+UnlockExperimentalVMOptions -XX:+DisableExplicitGC -XX:-OmitStackTraceInFastThrow -XX:+AlwaysPreTouch  -XX:G1NewSizePercent=30 -XX:G1MaxNewSizePercent=40 -XX:G1HeapRegionSize=8M -XX:G1ReservePercent=20 -XX:G1HeapWastePercent=5 -XX:G1MixedGCCountTarget=8 -XX:InitiatingHeapOccupancyPercent=15 -XX:G1MixedGCLiveThresholdPercent=90 -XX:G1RSetUpdatingPauseTimePercent=5 -XX:SurvivorRatio=32 -XX:MaxTenuringThreshold=1 -Dusing.aikars.flags=true -Daikars.new.flags=true -jar forge-1.12.2-14.23.5.2855.jar --nogui
pause

When trying to run a 1.12.2 forger server in this state, the following error message appears.

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:78)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/java.lang.reflect.Method.invoke(Method.java:567)
        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

Solution?

I take the java.exe from where I've installed Java 8: C:\Program Files\Java\jre1.8.0_291\bin.

I put it inside my minecraft folder, in the same file level as the forge jar and bat file.

I use the same .bat as shown above, no modifications.

I run it, and the server turns on.

Answer 3

Replace the word java at the beginning with "<path\java.exe>", if you leave the word java at the beginning it will choose a java automatically.

The correct format would look like this:

"<path\java.exe>" <some arguments> -jar <forge jar>

Don't forget ""

I had the same problem and looking at the posts here I could understand what was happening, I know this has already been answered, but I wanted to leave the answer in a more didactic way for the next ones who come looking.

Answer 4

Use this:

@ECHO OFF
"C:\Program Files\Java\jre1.8.0_291\bin\java.exe" -Xms10G -Xmx10G  
-XX:+UseG1GC -XX:+ParallelRefProcEnabled -XX:MaxGCPauseMillis=200 
-XX:+UnlockExperimentalVMOptions -XX:+DisableExplicitGC 
-XX:-OmitStackTraceInFastThrow -XX:+AlwaysPreTouch  
-XX:G1NewSizePercent=30 -XX:G1MaxNewSizePercent=40 
-XX:G1HeapRegionSize=8M -XX:G1ReservePercent=20 
-XX:G1HeapWastePercent=5 -XX:G1MixedGCCountTarget=8 
-XX:InitiatingHeapOccupancyPercent=15 -XX:G1MixedGCLiveThresholdPercent=90 
-XX:G1RSetUpdatingPauseTimePercent=5 -XX:SurvivorRatio=32 
-XX:MaxTenuringThreshold=1 -Dusing.aikars.flags=true 
-Daikars.new.flags=true -jar forge-1.12.2-14.23.5.2855.jar --nogui
pause