JarFileLoader.java

package common;

import java.io.File;
import java.io.FilenameFilter;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;

public class JarFileLoader extends URLClassLoader {

	public JarFileLoader() {
		super(new URL[] {});
	}
	
	public JarFileLoader withFile(String jarFile) {
		return withFile(new File(jarFile));
	}
	
	public JarFileLoader withFile(File jarFile) {
		try {
			addURL(new URL("jar:file://" + jarFile.getAbsolutePath() + "!/"));
		} catch (MalformedURLException e) {
			throw new IllegalArgumentException(e);
		}
		return this;
	}
	
	public JarFileLoader withLibDir(String path) {
		// JAVA 8 to the rescue ;-)
		// stream(new File(path).listFiles(f -> f.getName().endsWith(".jar"))).forEach(this::withFile);
		for (File jarFile : new File(path).listFiles(new FilenameFilter() {
			public boolean accept(File dir, String name) {
				return name.endsWith(".jar");
			}
		})) {
			withFile(jarFile);
		}
		return this;
	}
}

Line 30 for the J8 version it is : Stream.of(new File...);

And to make it work :

		String path = "libs";
		List<URL> urls = new ArrayList<URL>();
		Stream.of(new File(path).listFiles(f -> f.getName().endsWith(".jar"))).forEach(f -> {
			try {
				urls.add(f.toURI().toURL());
			} catch (MalformedURLException e) {
				e.printStackTrace();
			}
		});
		URLClassLoader child = new URLClassLoader(urls.toArray(new URL[urls.size()]));
		Class theClass = Class.forName("ClassToLoad", true, child);
		Method method = theClass .getDeclaredMethod("getInstance");
		final Object theClassInstance = method.invoke(theClass );