Java動態代理可以通過以下幾種方式實現：

1. 使用java.lang.reflect.Proxy類：Proxy類提供了一個靜態方法newProxyInstance()，可以通過傳入目標對象的類加載器、目標對象實現的接口和InvocationHandler接口的實現類來創建代理對象。InvocationHandler接口的實現類負責處理代理對象的方法調用。代理對象在調用方法時，會把方法調用轉發給InvocationHandler的invoke()方法，從而實現代理功能。

public interface Subject {
    void doSomething();
}

public class RealSubject implements Subject {
    public void doSomething() {
        System.out.println("RealSubject doSomething");
    }
}

public class MyInvocationHandler implements InvocationHandler {
    private Subject target;

    public MyInvocationHandler(Subject target) {
        this.target = target;
    }

    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("Before method invoke");
        Object result = method.invoke(target, args);
        System.out.println("After method invoke");
        return result;
    }
}

public class Main {
    public static void main(String[] args) {
        Subject realSubject = new RealSubject();
        Subject proxySubject = (Subject) Proxy.newProxyInstance(realSubject.getClass().getClassLoader(),
                realSubject.getClass().getInterfaces(),
                new MyInvocationHandler(realSubject));
        proxySubject.doSomething();
    }
}

2. 使用CGLib庫：CGLib是一個基于ASM框架的字節碼生成庫，它可以在運行時動態生成目標對象的子類，并覆蓋其中的方法以實現代理功能。

public interface Subject {
    void doSomething();
}

public class RealSubject implements Subject {
    public void doSomething() {
        System.out.println("RealSubject doSomething");
    }
}

public class MyMethodInterceptor implements MethodInterceptor {
    public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
        System.out.println("Before method invoke");
        Object result = proxy.invokeSuper(obj, args);
        System.out.println("After method invoke");
        return result;
    }
}

public class Main {
    public static void main(String[] args) {
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(RealSubject.class);
        enhancer.setCallback(new MyMethodInterceptor());
        Subject proxySubject = (Subject) enhancer.create();
        proxySubject.doSomething();
    }
}

需要注意的是，使用CGLib實現動態代理時，目標對象不能是final類或者包含final方法，因為CGLib是通過生成目標對象的子類來實現代理的。

3. 使用ByteBuddy庫：ByteBuddy是一個輕量級的字節碼操作庫，它可以在運行時動態生成目標對象的子類，并覆蓋其中的方法以實現代理功能。

public interface Subject {
    void doSomething();
}

public class RealSubject implements Subject {
    public void doSomething() {
        System.out.println("RealSubject doSomething");
    }
}

public class MyInterceptor implements MethodInterceptor {
    public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
        System.out.println("Before method invoke");
        Object result = proxy.invokeSuper(obj, args);
        System.out.println("After method invoke");
        return result;
    }
}

public class Main {
    public static void main(String[] args) throws Exception {
        Class<? extends Subject> proxyClass = new ByteBuddy()
                .subclass(Subject.class)
                .method(any()).intercept(MethodDelegation.to(MyInterceptor.class))
                .make()
                .load(RealSubject.class.getClassLoader())
                .getLoaded();
        Subject proxySubject = proxyClass.getDeclaredConstructor().newInstance();
        proxySubject.doSomething();
    }
}

需要注意的是，使用ByteBuddy實現動態代理時，需要引入net.bytebuddy:byte-buddy和net.bytebuddy:byte-buddy-agent兩個依賴。