[1.7.10] ScriptEngineManager is Returning Null for JavaScript

[angellus]

This is not an issue that is directly related to Forge, but it is something someone here might be able to help me with.

 

When we updated our mod to 1.7.10, we noticed some people started having issues with running our content scripts which we use for mob drops and some other things. Well, now, it is happening to everything. I am pretty sure now that everyone is on Java 8, it does not work for anyone. It does not even work in our dev environment anymore for intelliJ.

 

This is the code that is messing up and it seems that it is a pretty standard way of doing things. "getEngineByName" is returning null which is only support to happen if that Engine does not exist. Except JavaScript should exist.

 

import javax.script.*;
new ScriptEngineManager().getEngineByName("JavaScript");

 

UPDATE: After a lot more research, it looks like in Java 8 that nashorn.jar, which contains the JavaScript engine, is a Java Extension and it is not being loaded by the Minecraft Launcher. Does anyone know how to force load this extension using either Gradle or the code or something else? The mod is being built with JDK8 targeting JRE 8. If I load it inside of IntelliJ it all works fine, it is simply because the extension is not being loaded by the launcher.

[angellus]

Java 8 targeting 7.

[larsgerrits]

Try targeting Java 8.

[angellus]

It looks like it is a classpath issue. It was not set up right. I finally got it working now though. Thanks guys!

[angellus]

Updated OP.

[angellus]

Yeah, nashorn is definitely there. I am pretty sure the Minecraft launcher it just not loading it. I know you can do classpath injection, but I do not really know how. Can I force Java to load it somehow?

[angellus]

For IntelliJ? No. It is just there. It should just be there.

[angellus]

It looks like it might be modloader that is causing the issue.

 

The following code works in Java 7 in both IntelliJ AND Minecraft, whereas in Java 8, it only works in IntelliJ

import javax.script.*;
new ScriptEngineManager().getEngineByName("JavaScript");

 

However, if I tell ScriptEngineManager to use the Forge Mod Loader, it only works in Java 7 and no longer in Java 8 at all.

 

import cpw.mods.fml.common.Loader;
import javax.script.*;
new ScriptEngineManager(Loader.instance().getModClassLoader()).getEngineByName("JavaScript");

 

 

In Java 7, rhino.jar is located inside of JRE\lib, in Java 8, nashorn.jar is located in JRE\lib\ext. It looks like Forge is not loading the Java extension Jars.

[angellus]

In that case, is it possible to get Forge to load a jar from a Maven repo if it cannot find it?

 

i.e. Can I upload and host a copy of rhino.jar that it needs to use Rhino and make it so Forge will download and use it if it is on Java 8+?

[angellus]

I just determined it is not. Forge is not loading it. Nashorn is a Java Extension and it is not loading it.