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Is it possible to write a universal multiplexer in Java?

I have many listeners that are registered using setListener methods, not addListener. Therefore, in order to allow multiple listeners to register for an object, I have to use multiplexers. This is good, but now I need to create a multiplexer for each listener interface that I have. So my question is: is it possible to implement Mux.create () as required for the following code?

AppleListener appleListener1 = new AppleProcessorA();
AppleListener appleListener2 = new AppleProcessorB();
AppleListener appleListenerMux = Mux.create(appleListener1, appleListener2);
Apple apple = new Apple();
apple.setListener(appleListenerMux);

OrangeListener orangeListener1 = new OrangeProcessorA();
OrangeListener orangeListener2 = new OrangeProcessorB();
OrangeListener orangeListenerMux = Mux.create(orangeListener1, orangeListener2);
Orange apple = new Orange();
orange.setListener(orangeListenerMux);

class Mux {
   public static <T> T create(T... outputs) { }
}

I suggest that this is possible through reflection. Is there any reason using reflection would be a bad idea? (performance comes to mind)

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3 answers

Proxy.

- Mux.create(). , ( , - ).

:

public class Mux {

    /**
     * @param targetInterface
     *            the interface to create a proxy for
     * @param instances
     *            the concrete instances to delegate to
     * @return a proxy that'll delegate to all the arguments
     */
    @SuppressWarnings("unchecked")
    public static <T> T create(Class<T> targetInterface, final T... instances) {
        ClassLoader classLoader = targetInterface.getClassLoader();
        InvocationHandler handler = new InvocationHandler() {
            @Override
            public Object invoke(Object proxy, Method m, Object[] args)
                    throws Throwable {
                for (T instance : instances) {
                    m.invoke(instance, args);
                }
                return null;
            }
        };
        return (T) Proxy.newProxyInstance(classLoader,
                new Class<?>[] { targetInterface }, handler);
    }
}

, , :

Apple apple = new Apple();
AppleListener l1 = new AppleListenerA();
AppleListener l2 = new AppleListenerB();
apple.setListener(Mux.create(AppleListener.class, l1, l2));
apple.doSomething(); // will notify all listeners

, Proxy, T. InvocationHandler, .

, , , , T... instances , , instances , "( " args , ").

, , ( ) , handler null . , .

instances, , , , newProxyInstance(). Mux.create() .

/**
 * @param instances
 *            the arguments
 * @return a proxy that'll delegate to all the arguments
 */
@SuppressWarnings("unchecked")
public static <T> T create(final T... instances) {

    // Inspect common interfaces
    final Set<Class<?>> commonInterfaces = new HashSet<Class<?>>();
    commonInterfaces.addAll(Arrays.asList(instances[0].getClass()
            .getInterfaces()));

    // Or skip instances[0]
    for (final T instance : instances) {
        commonInterfaces.retainAll(Arrays.asList(instance.getClass()
                .getInterfaces()));
    }

    // Or use ClassLoader.getSystemClassLoader();
    final ClassLoader classLoader = instances[0].getClass().getClassLoader();

    // magic
    final InvocationHandler handler = new InvocationHandler() {
        @Override
        public Object invoke(final Object proxy, final Method m, final Object[] args)
                throws Throwable {
            for (final T instance : instances) {
                m.invoke(instance, args);
            }
            return null;
        }
    };

    final Class<?>[] targetInterfaces = commonInterfaces
            .toArray(new Class<?>[commonInterfaces.size()]);
    return (T) Proxy.newProxyInstance(classLoader, targetInterfaces,
            handler);
}
+9

, " " Factory. , Java, :

0

.

AppleListener appleListener1 = new AppleProcessorA();
AppleListener appleListener2 = new AppleProcessorB();
CompositeListener composite = CompositeListener.for(appleListener1, appleListener2);
Apple apple = new Apple();
apple.setListener(composite);

, AppleListener OrangeListener Listener, . CompositeListener .

0

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