An isolated class loader after http://blog.markturansky.com/archives/21 Usage: javac IsolatedClassLoader.java && java -ea IsolatedClassLoader

IsolatedClassLoader.java

import java.io.File;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.List;

public class IsolatedClassLoader extends URLClassLoader {

    private static URL[] classPathAsURLArray() {
        List<URL> classPathUrls = new ArrayList<>();
        String classpath = System.getProperty("java.class.path");
        try {
            for (String s : classpath.split(";")) {
                classPathUrls.add(new File(s).toURI().toURL());
            }
        } catch (MalformedURLException ex) {
        }
        return classPathUrls.toArray(new URL[classPathUrls.size()]);
    }
    private final String[] isolatedPackages;

    public IsolatedClassLoader(String... isolatedPackages) {
        super(classPathAsURLArray(), ClassLoader.getSystemClassLoader().getParent());
        this.isolatedPackages = isolatedPackages;
    }

    @Override
    public Class<?> loadClass(String name) throws ClassNotFoundException {
        if (isInIsolatedPackage(name)) {
            return super.loadClass(name);
        } else {
            return ClassLoader.getSystemClassLoader().loadClass(name);
        }
    }

    private boolean isInIsolatedPackage(String name) {
        for (String p : isolatedPackages) {
            if (name.contains(p)) {
                return true;
            }
        }
        return false;
    }

    public static void main(String... args) throws ClassNotFoundException {

        Class IsolatedClassLoader2 = new IsolatedClassLoader("").loadClass("IsolatedClassLoader");

        assert IsolatedClassLoader.class != IsolatedClassLoader2;
    }
}