Proxy and Enhancement

/**
 * Primary class for creating enhanced/proxied subclasses
 */
public class Enhancer {
    // Static factory methods for simple use cases
    public static Object create(Class type, Callback callback);
    public static Object create(Class superclass, Class[] interfaces, Callback callback);
    public static Object create(Class superclass, Class[] interfaces, 
                              CallbackFilter filter, Callback[] callbacks);
    
    // Instance configuration methods
    public void setSuperclass(Class superclass);
    public void setInterfaces(Class[] interfaces);
    public void setCallback(Callback callback);
    public void setCallbacks(Callback[] callbacks);
    public void setCallbackFilter(CallbackFilter filter);
    public void setUseFactory(boolean useFactory);
    public void setUseCache(boolean useCache);
    
    // Generation methods
    public Object create();
    public Object create(Class[] argumentTypes, Object[] arguments);
    public Class createClass();
    
    // Utility methods
    public static void getMethods(Class superclass, Class[] interfaces, List methods);
    public static void registerCallbacks(Class generatedClass, Callback[] callbacks);
    public static void registerStaticCallbacks(Class generatedClass, Callback[] callbacks);
}

// Simple method interception
Enhancer enhancer = new Enhancer();
enhancer.setSuperclass(MyService.class);
enhancer.setCallback(new MethodInterceptor() {
    public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
        long start = System.currentTimeMillis();
        try {
            return proxy.invokeSuper(obj, args);
        } finally {
            System.out.println(method.getName() + " took " + (System.currentTimeMillis() - start) + "ms");
        }
    }
});
MyService proxy = (MyService) enhancer.create();

// Multiple interfaces with constructor arguments
enhancer = new Enhancer();
enhancer.setSuperclass(DatabaseService.class);
enhancer.setInterfaces(new Class[]{Serializable.class, Auditable.class});
enhancer.setCallback(myInterceptor);
DatabaseService service = (DatabaseService) enhancer.create(
    new Class[]{String.class}, 
    new Object[]{"jdbc:mysql://localhost/db"}
);

// Multiple callbacks with filter
enhancer = new Enhancer();
enhancer.setSuperclass(BusinessObject.class);
enhancer.setCallbacks(new Callback[]{
    methodInterceptor,    // index 0
    NoOp.INSTANCE,       // index 1
    fixedValue           // index 2
});
enhancer.setCallbackFilter(new CallbackFilter() {
    public int accept(Method method) {
        if (method.getName().startsWith("get")) return 1; // NoOp
        if (method.getName().equals("toString")) return 2; // FixedValue
        return 0; // MethodInterceptor
    }
});
BusinessObject obj = (BusinessObject) enhancer.create();

/**
 * Intercepts method calls with full control over invocation
 */
public interface MethodInterceptor extends Callback {
    /**
     * Intercept a method call
     * @param obj The enhanced object
     * @param method The intercepted Method
     * @param args Method arguments
     * @param proxy MethodProxy for invoking super method
     * @return Method return value
     * @throws Throwable Any exception
     */
    Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable;
}

/**
 * Returns a fixed value for all intercepted methods
 */
public interface FixedValue extends Callback {
    /**
     * Return the fixed value
     * @return The value to return for all method calls
     * @throws Exception Any exception
     */
    Object loadObject() throws Exception;
}

/**
 * Loads a delegate object on first access, then delegates all calls to it
 */
public interface LazyLoader extends Callback {
    /**
     * Load the delegate object (called only once)
     * @return The delegate object
     * @throws Exception Any exception
     */
    Object loadObject() throws Exception;
}

/**
 * Loads a delegate object for each method call
 */
public interface Dispatcher extends Callback {
    /**
     * Load the delegate object (called for every method invocation)
     * @return The delegate object
     * @throws Exception Any exception
     */
    Object loadObject() throws Exception;
}

/**
 * Like Dispatcher but provides reference to the proxy object
 */
public interface ProxyRefDispatcher extends Callback {
    /**
     * Load the delegate object with access to the proxy
     * @param proxy The proxy object
     * @return The delegate object
     * @throws Exception Any exception
     */
    Object loadObject(Object proxy) throws Exception;
}

/**
 * No-operation callback - methods proceed normally
 */
public interface NoOp extends Callback {
    // Marker interface - no methods
    NoOp INSTANCE = new NoOp() {};
}

/**
 * JDK-compatible invocation handler for interface proxies
 */
public interface InvocationHandler extends Callback {
    /**
     * Invoke a method on the proxy
     * @param proxy The proxy object
     * @param method The method being invoked
     * @param args Method arguments
     * @return Method return value
     * @throws Throwable Any exception
     */
    Object invoke(Object proxy, Method method, Object[] args) throws Throwable;
}

/**
 * Determines which callback to use for each method
 */
public interface CallbackFilter {
    /**
     * Choose callback index for a method
     * @param method The method being intercepted
     * @return Index of callback to use
     */
    int accept(Method method);
}

/**
 * Faster method invocation alternative to reflection
 */
public class MethodProxy {
    /**
     * Create a MethodProxy
     * @param c1 The enhanced class
     * @param c2 The original class
     * @param desc Method descriptor
     * @param name1 Generated method name
     * @param name2 Super method name
     * @return MethodProxy instance
     */
    public static MethodProxy create(Class c1, Class c2, String desc, String name1, String name2);
    
    /**
     * Invoke the original method on the object
     * @param obj Target object
     * @param args Method arguments
     * @return Method return value
     * @throws Throwable Any exception
     */
    public Object invoke(Object obj, Object[] args) throws Throwable;
    
    /**
     * Invoke the super method (recommended for interceptors)
     * @param obj Enhanced object
     * @param args Method arguments
     * @return Method return value
     * @throws Throwable Any exception
     */
    public Object invokeSuper(Object obj, Object[] args) throws Throwable;
    
    /**
     * Get method signature
     * @return Method signature
     */
    public Signature getSignature();
    
    /**
     * Get super method name
     * @return Super method name
     */
    public String getSuperName();
    
    /**
     * Get super method index
     * @return Super method index
     */
    public int getSuperIndex();
}

/**
 * Interface for callback management on enhanced objects
 */
public interface Factory {
    /**
     * Create new instance with single callback
     * @param callback The callback to use
     * @return New enhanced instance
     */
    Object newInstance(Callback callback);
    
    /**
     * Create new instance with multiple callbacks
     * @param callbacks Array of callbacks
     * @return New enhanced instance
     */
    Object newInstance(Callback[] callbacks);
    
    /**
     * Create new instance with constructor arguments and callbacks
     * @param types Constructor parameter types
     * @param args Constructor arguments
     * @param callbacks Array of callbacks
     * @return New enhanced instance
     */
    Object newInstance(Class[] types, Object[] args, Callback[] callbacks);
    
    /**
     * Get callback by index
     * @param index Callback index
     * @return The callback
     */
    Callback getCallback(int index);
    
    /**
     * Set callback by index
     * @param index Callback index
     * @param callback The callback to set
     */
    void setCallback(int index, Callback callback);
    
    /**
     * Set all callbacks
     * @param callbacks Array of callbacks
     */
    void setCallbacks(Callback[] callbacks);
    
    /**
     * Get all callbacks
     * @return Array of callbacks
     */
    Callback[] getCallbacks();
}

/**
 * Creates objects implementing multiple interfaces via delegation
 */
public abstract class Mixin {
    // Style constants
    public static final int STYLE_INTERFACES = 0;
    public static final int STYLE_BEANS = 1;
    public static final int STYLE_EVERYTHING = 2;
    
    /**
     * Create mixin from delegate objects
     * @param delegates Array of delegate objects
     * @return Mixin instance
     */
    public static Mixin create(Object[] delegates);
    
    /**
     * Create mixin with specific interfaces
     * @param interfaces Interfaces to implement
     * @param delegates Delegate objects
     * @return Mixin instance
     */
    public static Mixin create(Class[] interfaces, Object[] delegates);
    
    /**
     * Create new mixin instance with different delegates
     * @param delegates New delegate objects
     * @return New mixin instance
     */
    public abstract Mixin newInstance(Object[] delegates);
}

// Create objects implementing multiple interfaces
interface Readable { String read(); }
interface Writable { void write(String data); }

class Reader implements Readable {
    public String read() { return "data"; }
}

class Writer implements Writable {
    public void write(String data) { System.out.println(data); }
}

// Create mixin implementing both interfaces
Mixin mixin = Mixin.create(new Object[]{new Reader(), new Writer()});
Object combined = mixin.newInstance(new Object[]{new Reader(), new Writer()});

// Use as either interface
Readable readable = (Readable) combined;
Writable writable = (Writable) combined;
readable.read();
writable.write("hello");

/**
 * Drop-in replacement for JDK dynamic proxies
 */
public class Proxy {
    /**
     * Get proxy class for interfaces
     * @param loader ClassLoader to use
     * @param interfaces Interfaces to implement
     * @return Proxy class
     */
    public static Class getProxyClass(ClassLoader loader, Class[] interfaces);
    
    /**
     * Create proxy instance
     * @param loader ClassLoader to use
     * @param interfaces Interfaces to implement
     * @param h InvocationHandler
     * @return Proxy instance
     */
    public static Object newProxyInstance(ClassLoader loader, Class[] interfaces, InvocationHandler h);
    
    /**
     * Check if class is a proxy class
     * @param cl Class to check
     * @return true if proxy class
     */
    public static boolean isProxyClass(Class cl);
    
    /**
     * Get invocation handler from proxy
     * @param proxy Proxy object
     * @return InvocationHandler
     */
    public static InvocationHandler getInvocationHandler(Object proxy);
}

/**
 * Abstract utility for managing multiple callbacks
 */
public abstract class CallbackHelper {
    /**
     * Constructor
     * @param superclass Superclass for enhanced objects
     * @param interfaces Interfaces to implement
     */
    public CallbackHelper(Class superclass, Class[] interfaces);
    
    /**
     * Get callback for a specific method (implement this)
     * @param method The method
     * @return Callback for the method
     */
    protected abstract Object getCallback(Method method);
    
    /**
     * Get all callbacks
     * @return Array of callbacks
     */
    public Callback[] getCallbacks();
    
    /**
     * Get callback filter
     * @return CallbackFilter instance
     */
    public CallbackFilter getFilter();
}

/**
 * Creates new interfaces at runtime
 */
public class InterfaceMaker {
    /**
     * Add method signature to interface
     * @param signature Method signature
     * @param exceptions Exception types
     */
    public void add(Signature signature, Type[] exceptions);
    
    /**
     * Add method to interface
     * @param method Method to add
     */
    public void add(Method method);
    
    /**
     * Add all methods from a class
     * @param clazz Class to copy methods from
     */
    public void add(Class clazz);
    
    /**
     * Create the interface
     * @return Interface class
     */
    public Class create();
}

/**
 * Exception for undeclared checked exceptions
 */
public class UndeclaredThrowableException extends RuntimeException {
    /**
     * Constructor
     * @param t The wrapped exception
     */
    public UndeclaredThrowableException(Throwable t);
    
    /**
     * Get the wrapped exception
     * @return The undeclared throwable
     */
    public Throwable getUndeclaredThrowable();
}