Mindustry/core/src/mindustry/mod/ModClassLoader.java

package mindustry.mod;

import arc.struct.*;

public class ModClassLoader extends ClassLoader{
    private Seq<ClassLoader> children = new Seq<>();
    private ThreadLocal<Boolean> inChild = new ThreadLocal<>(){
        @Override
        protected Boolean initialValue(){
            return Boolean.FALSE;
        }
    };

    public ModClassLoader(ClassLoader parent){
        super(parent);
    }

    public void addChild(ClassLoader child){
        children.add(child);
    }

    @Override
    protected Class<?> findClass(String name) throws ClassNotFoundException{
        //a child may try to delegate class loading to its parent, which is *this class loader* - do not let that happen
        if(inChild.get()){
            inChild.set(false);
            throw new ClassNotFoundException(name);
        }

        ClassNotFoundException last = null;
        int size = children.size;

        //if it doesn't exist in the main class loader, try all the children
        for(int i = 0; i < size; i++){
            try{
                try{
                    inChild.set(true);
                    return children.get(i).loadClass(name);
                }finally{
                    inChild.set(false);
                }
            }catch(ClassNotFoundException e){
                last = e;
            }
        }

        throw (last == null ? new ClassNotFoundException(name) : last);
    }
}