Java: How to Load Classes at Runtime from Jar or Class Files

I wrote java program for loading classes at runtime from jar file or class files
Hope this post will help somebody...

package com.dukesoftware.utils.reflect;

import java.io.File;
import java.io.FileFilter;
import java.io.IOException;
import java.net.URI;
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 DynamicClassLoader {
    
    public static List<Class<?>> readAllClassesFormJarFile(File jarFilePath) throws IOException{
        List<Class<?>> classes = new ArrayList<>();
        URL[] urls = { new URL("jar:" + jarFilePath.toURI().toURL() + "!/") };
        URLClassLoader loader = URLClassLoader.newInstance(urls);
        for(Enumeration<JarEntry> en = new JarFile(jarFilePath).entries(); en.hasMoreElements();){
            final String name = en.nextElement().getName();
            if(name.endsWith(".class")){
                try {
                    classes.add(loader.loadClass(toClassName(name)));
                } catch (ClassNotFoundException e) {
                    throw new IllegalStateException("Should not happen:", e);
                }
            }
        }
        return classes;
    }

    public static List<Class<?>> readAllClasses(File rootClasspathDirectory) throws IOException{
        URI rootURI = rootClasspathDirectory.toURI();
        List<Class<?>> classes = new ArrayList<>();
        URLClassLoader loader = new URLClassLoader(new URL[]{ rootURI.toURL()});
        for(File classFile : listFiles(rootClasspathDirectory, acceptExtensionOnly("class"))){
            URI uri = rootURI.relativize(classFile.toURI());
            final String clazz = uri.toString();
            try {
                classes.add(loader.loadClass(toClassName(clazz)));
            } catch (ClassNotFoundException e) {
                throw new IllegalStateException("Should not happen:", e);
            }
        }
        return classes;
    }

    private static String toClassName(String uri) {
        return uri.substring(0, uri.lastIndexOf(".class")).replaceAll("/", ".");
    }
    

    // list files
    public static List<File> listFiles(File file, FileFilter filter){
        ArrayList<File> result = new ArrayList<>();
        listFiles(file, filter, result);
        return result;
    }
    
    public static void listFiles(File file, FileFilter filter, List<File> result){
        if(file.isDirectory()){
            final File[] files = file.listFiles();
            if(files != null){
                for(File child: files){
                    result.add(child);
                }
            }
        }
        else{
            if(filter.accept(file)){
                listFiles(file, filter, result);
            }
        }
        
    }
    
    // file filter which only accepts given extension
    public static FileFilter acceptExtensionOnly(final String ext){
        return new FileFilter() {
            
            @Override
            public boolean accept(File pathname) {
                return pathname.getName().endsWith("." + ext);
            }
        };
    }
}