Proxy Generation

import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;
import net.sf.cglib.proxy.Callback;
import net.sf.cglib.proxy.CallbackFilter;
import net.sf.cglib.proxy.Factory;
import net.sf.cglib.proxy.FixedValue;
import net.sf.cglib.proxy.NoOp;
import net.sf.cglib.proxy.LazyLoader;
import net.sf.cglib.proxy.Dispatcher;
import net.sf.cglib.proxy.ProxyRefDispatcher;
import net.sf.cglib.proxy.InvocationHandler;
import net.sf.cglib.proxy.UndeclaredThrowableException;
import net.sf.cglib.core.NamingPolicy;
import java.lang.reflect.Method;
import java.io.Serializable;

/**
 * Main class for creating enhanced subclasses and proxy objects
 */
public class Enhancer extends AbstractClassGenerator {
    /**
     * Set the class to be enhanced (superclass of generated class)
     * @param superclass - The class to extend
     */
    public void setSuperclass(Class superclass);
    
    /**
     * Set interfaces to be implemented by generated class
     * @param interfaces - Array of interfaces to implement
     */
    public void setInterfaces(Class[] interfaces);
    
    /**
     * Set single callback for all methods
     * @param callback - Callback to handle method calls
     */
    public void setCallback(Callback callback);
    
    /**
     * Set multiple callbacks for different methods
     * @param callbacks - Array of callbacks
     */
    public void setCallbacks(Callback[] callbacks);
    
    /**
     * Set filter to determine which callback to use for each method
     * @param filter - CallbackFilter implementation
     */
    public void setCallbackFilter(CallbackFilter filter);
    
    /**
     * Create instance using default constructor
     * @return Enhanced instance
     */
    public Object create();
    
    /**
     * Create instance using specific constructor
     * @param argumentTypes - Constructor parameter types
     * @param arguments - Constructor arguments
     * @return Enhanced instance
     */
    public Object create(Class[] argumentTypes, Object[] arguments);
    
    /**
     * Set naming policy for generated classes
     * @param namingPolicy - Strategy for naming generated classes
     */
    public void setNamingPolicy(NamingPolicy namingPolicy);
    
    /**
     * Set class loader for generated classes
     * @param loader - ClassLoader to use
     */
    public void setClassLoader(ClassLoader loader);
}

import net.sf.cglib.proxy.*;
import java.lang.reflect.Method;

// Basic method interception
Enhancer enhancer = new Enhancer();
enhancer.setSuperclass(UserService.class);
enhancer.setCallback(new MethodInterceptor() {
    @Override
    public Object intercept(Object obj, Method method, Object[] args, 
                          MethodProxy proxy) throws Throwable {
        System.out.println("Before: " + method.getName());
        Object result = proxy.invokeSuper(obj, args);
        System.out.println("After: " + method.getName());
        return result;
    }
});

UserService service = (UserService) enhancer.create();

// Multiple callbacks with filter
enhancer.setCallbacks(new Callback[] {
    new MethodInterceptor() { /* logging interceptor */ },
    NoOp.INSTANCE  // no interception
});
enhancer.setCallbackFilter(new CallbackFilter() {
    @Override
    public int accept(Method method) {
        return method.getName().startsWith("get") ? 1 : 0;
    }
});

/**
 * Callback for intercepting method calls on proxy objects
 */
public interface MethodInterceptor extends Callback {
    /**
     * Intercept method calls on proxy objects
     * @param obj - Enhanced object instance
     * @param method - Method being called
     * @param args - Method arguments
     * @param proxy - MethodProxy for efficient super calls
     * @return Method result
     * @throws Throwable - Any exception from method execution
     */
    Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) 
        throws Throwable;
}

/**
 * Callback that returns a fixed value for all method calls
 */
public interface FixedValue extends Callback {
    Object loadObject() throws Exception;
}

/**
 * Callback that performs no operation, allowing original method execution
 */
public interface NoOp extends Callback {
    NoOp INSTANCE = new NoOp() {};
}

/**
 * Callback for lazy initialization of proxy objects
 */
public interface LazyLoader extends Callback {
    Object loadObject() throws Exception;
}

/**
 * Callback that dispatches calls to different objects
 */
public interface Dispatcher extends Callback {
    Object loadObject() throws Exception;
}

/**
 * Dispatcher that receives reference to proxy object
 */
public interface ProxyRefDispatcher extends Callback {
    Object loadObject(Object proxy) throws Exception;
}

/**
 * JDK-compatible invocation handler interface
 */
public interface InvocationHandler extends Callback {
    Object invoke(Object proxy, Method method, Object[] args) throws Throwable;
}

/**
 * Interface for determining which callback to use for each method
 */
public interface CallbackFilter {
    /**
     * Determine callback index for given method
     * @param method - Method to filter
     * @return Index of callback to use (corresponds to callbacks array)
     */
    int accept(Method method);
}

/**
 * Interface implemented by enhanced classes for callback management
 */
public interface Factory {
    /**
     * Create new instance with single callback
     * @param callback - Callback to use
     * @return New instance
     */
    Object newInstance(Callback callback);
    
    /**
     * Create new instance with multiple callbacks
     * @param callbacks - Array of callbacks
     * @return New 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 instance
     */
    Object newInstance(Class[] types, Object[] args, Callback[] callbacks);
    
    /**
     * Set callback at specific index
     * @param index - Callback index
     * @param callback - Callback to set
     */
    void setCallback(int index, Callback callback);
    
    /**
     * Set all callbacks
     * @param callbacks - Array of callbacks
     */
    void setCallbacks(Callback[] callbacks);
    
    /**
     * Get callback at specific index
     * @param index - Callback index
     * @return Callback at index
     */
    Callback getCallback(int index);
    
    /**
     * Get all callbacks
     * @return Array of all callbacks
     */
    Callback[] getCallbacks();
}

/**
 * Efficient method invocation mechanism for proxy objects
 */
public class MethodProxy {
    /**
     * Invoke super method implementation
     * @param obj - Object instance
     * @param args - Method arguments
     * @return Method result
     * @throws Throwable - Any exception from method execution
     */
    public Object invokeSuper(Object obj, Object[] args) throws Throwable;
    
    /**
     * Invoke original method (may cause infinite recursion if not careful)
     * @param obj - Object instance
     * @param args - Method arguments
     * @return Method result
     * @throws Throwable - Any exception from method execution
     */
    public Object invoke(Object obj, Object[] args) throws Throwable;
    
    /**
     * Get name of super method
     * @return Super method name
     */
    public String getSuperName();
    
    /**
     * Get index of super method
     * @return Super method index
     */
    public int getSuperIndex();
}