Reflection Utility (Uses ASM)

Reflect.java

import org.objectweb.asm.ClassReader;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.List;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;

public class Reflect {
    private static URL[] urls;
    private static File[] files;

    public final Class<?> superClass;

    public Reflect(Class<?> superClass) throws MalformedURLException {
        this.superClass = superClass;

        if(this.getClass().getClassLoader() instanceof URLClassLoader loader) {
            Reflect.urls = loader.getURLs(); //Quixotic Check
        } else {
            String cp = System.getProperty("java.class.path");
            String[] elements = cp.split(File.pathSeparator);
            if (elements.length == 0) {
                throw new RuntimeException("ClassPath is empty.");
            }

            int index = 0;
            URL[] findUrls = new URL[elements.length];
            File[] findFiles = new File[elements.length];
            for (String el : elements) {
                File file = new File(el);
                URL url = file.toURI().toURL();

                findFiles[index] = file;
                findUrls[index] = url;

                index++;
            }

            Reflect.urls = findUrls;
        }
    }

    public List<Class<?>> getAll(ClassLoader loadWith) throws IOException, ClassNotFoundException {
        List<Class<?>> found = new ArrayList<>();

        for (File f : Reflect.files) {
            JarFile file = new JarFile(f);
            Enumeration<JarEntry> entries = file.entries();

            while(entries.hasMoreElements()) {
                JarEntry current = entries.nextElement();

                if(!current.getName().endsWith(".class")) continue;

                InputStream is = file.getInputStream(current);
                ClassReader reader = new ClassReader(is.readAllBytes());

                if(reader.getSuperName().equals(this.superClass.getName())) {
                    found.add(loadWith.loadClass(reader.getClassName()));
                }

                is.close();
            }

            file.close();
        }

        return found;
    }

    public List<Class<?>> getAll() throws IOException, ClassNotFoundException {
        return this.getAll(this.getClass().getClassLoader());
    }
}