Java - InvocationHandler Examples

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Arrays;

public class MyInvocationHandler implements InvocationHandler {

    @Override
    public Object invoke (Object proxy, Method method, Object[] args) throws Throwable {

         Arrays.stream(Thread.currentThread()
                            .getStackTrace())
              .forEach(System.out::println);
        System.out.println(method);


        System.out.println("the invoked method: " + method);
        return null;
    }

    public static void main (String[] args) {
        MyInvocationHandler handler = new MyInvocationHandler();

        MyInterface o = (MyInterface) Proxy.newProxyInstance(
                            MyInvocationHandler.class.getClassLoader(),
                            new Class[]{MyInterface.class}, handler);
        o.doSomething();
    }
}

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Arrays;

public class MyInvocationHandler implements InvocationHandler {

    private String theString;

    public MyInvocationHandler (String theString) {
        this.theString = theString;
    }

    @Override
    public Object invoke (Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("before method call : " + method.getName());
        Object result = method.invoke(theString, args);
        System.out.println("after method call : " + method.getName());
        return result;
    }

    public static void main (String[] args) {

        MyInvocationHandler handler = new MyInvocationHandler("the example string");

        CharSequence o = (CharSequence) Proxy.newProxyInstance(
                            MyInvocationHandler.class.getClassLoader(),
                            new Class[]{CharSequence.class}, handler);
        System.out.println(o.length());
        System.out.println(o.subSequence(4, 8));
    }
}

public class GenericCacheDecorator implements InvocationHandler {

    private Map<String, Object> cachedData = new HashMap<>();
    private Object EMPTY = new Object();
    private Object obj;

    private GenericCacheDecorator (Object obj) {
        this.obj = obj;
        try {
            BeanInfo beanInfo = Introspector.getBeanInfo(obj.getClass());
            for (PropertyDescriptor desc : beanInfo.getPropertyDescriptors()) {
                cachedData.put(desc.getReadMethod()
                                   .getName(), EMPTY);
            }

        } catch (IntrospectionException e) {
            e.printStackTrace();
        }
    }

    public static <I, T extends I> I decorate (T t, Class<I> interfaceClass) {
        GenericCacheDecorator cacheableDecorator = new GenericCacheDecorator(t);
        return (I) Proxy.newProxyInstance(interfaceClass.getClassLoader(),
                                          new Class[]{interfaceClass}, cacheableDecorator);

    }

    public Object invoke (Object proxy, Method method, Object[] args) throws Throwable {
        if (cachedData.containsKey(method.getName())) {
            Object o = cachedData.get(method.getName());
            if (o == EMPTY) {
                Object returned = method.invoke(obj, args);
                cachedData.put(method.getName(), returned);
                return returned;
            } else {
                return o;
            }
        }
        return method.invoke(args);
    }

    public static void main (String[] args) {
        MyObject object = new MyObject();
        IObject iObject = GenericCacheDecorator.decorate(object, IObject.class);
        System.out.println(iObject.getData());
        System.out.println(iObject.getData());
    }
}