自己实现简单的AOP（二）引入Attribute 为方法指定增强对象

    /// <summary>
    /// 为方法标记指定的增强对象
    /// <para>指定的增强，可通过代理 DelayProxy 织入</para>
    /// </summary>
    [AttributeUsage(AttributeTargets.Method, Inherited = false, AllowMultiple = false)]
    public sealed class AdviceAttribute : Attribute
    {
        /// <summary>
        /// 增强对象
        /// </summary>
        public AdviceAbstract Advice { get; private set; }

        /// <summary>
        /// 使用指定类型的默认增强对象
        /// <para>如果类型为空 则不使用任何增强</para>
        /// </summary>
        /// <param name="type"></param>
        public AdviceAttribute(Type type)
            : this(type, string.Empty)
        {

        }

        /// <summary>
        /// 使用公有静态方法名初始化指定类型的增强对象
        /// <para>如果类型为空 则不使用任何增强</para>
        /// </summary>
        /// <param name="type">类型</param>
        /// <param name="methodName">
        /// 公有静态方法名
        /// <para>如果方法名为空，调用默认构造函数</para>
        /// </param>
        public AdviceAttribute(Type type, string methodName)
        {
            // 如果类型为空 则不使用任何增强
            if (type == null)
            {
                this.Advice = null;
                return;
            }

            if (string.IsNullOrWhiteSpace(methodName))
            {
                this.Advice = Activator.CreateInstance(type) as AdviceAbstract;
                return;
            }

            this.Advice = type.InvokeMember(
                methodName,
                System.Reflection.BindingFlags.InvokeMethod | System.Reflection.BindingFlags.Public
                | System.Reflection.BindingFlags.Static,
                null, null, null) as AdviceAbstract;
        }





        #region 以下两种方式效果不是很好，不推荐使用，故 构造函数私有化

        /// <summary>
        /// 使用参数列表初始化指定类型的增强对象
        /// </summary>
        /// <param name="type">类型</param>
        /// <param name="objs">参数列表</param>
        private AdviceAttribute(Type type, params object[] objs)
        {
            this.Advice = Activator.CreateInstance(type, objs) as AdviceAbstract;
        }

        /// <summary>
        /// 使用命名参数初始化指定类型的增强对象
        /// </summary>
        /// <param name="namedParameter">
        /// 以 冒号 和 分号 分割的形参的命名参数列表
        /// <para>支持的数据类型有：string, int, bool 及 可通过静态方法Parse 反序列化的类型</para>
        /// </param>
        /// <param name="type"></param>
        private AdviceAttribute(string namedParameter, Type type)
        {
            this.Advice = ReflectionUtil.InvokeConstructor(type, namedParameter) as AdviceAbstract;
        }

        #endregion

    }

    /// <summary>
    /// 抽象的增强类
    /// </summary>
    public abstract class AdviceAbstract
    {
        public abstract IMessage Invoke(MarshalByRefObject target, IMethodCallMessage callMessage);
    }


    public class MyAdvice : AdviceAbstract
    {
        public override IMessage Invoke(MarshalByRefObject target, IMethodCallMessage callMessage)
        {
            this.BeforeInvoke(target);

            IMessage message = DelayProxyUtil.InvokeBeProxy(target, callMessage);

            this.AfterInvoke(target);

            return message;
        }

        protected virtual void BeforeInvoke(MarshalByRefObject target)
        {
            Console.WriteLine("Before");
        }

        protected virtual void AfterInvoke(MarshalByRefObject target)
        {
            Console.WriteLine("After");
        }


    }

    /// <summary>
    /// 支持泛型、支持延迟初始化的代理类， 可为 MarshalByRefObject 的子类型提供代理
    /// <para>在执行代理的过程中，获取 AdviceAttribute 所指定的增强，并织入该增强</para>
    /// </summary>
    public class DelayProxy<T> : RealProxy where T : MarshalByRefObject
    {
        private static object objLock = new object();

        /// <summary>
        /// 被代理的对象
        /// </summary>
        private T target;

        /// <summary>
        /// 是否延迟初始化
        /// <para>True：延迟, False: 不延迟</para>
        /// </summary>
        private readonly bool delay;

        public DelayProxy(T target, bool delay)
            : base(typeof(T))
        {
            this.target = target;
            this.delay = delay;
        }

        /// <summary>
        /// 调用被代理对象
        /// <para>支持 out ref 参数</para>
        /// </summary>
        /// <param name="msg"></param>
        /// <returns></returns>
        public override IMessage Invoke(IMessage msg)
        {
            if (this.delay && this.target == null)
            {
                lock (objLock)
                {
                    if (this.delay && this.target == null)
                    {
                        T instance = Activator.CreateInstance(typeof(T)) as T;

                        // 自动装配属性
                        // 为属性对象启用代理，并延迟初始化被代理的对象
                        // DelayProxyUtil.AutowiredProperties(instance);

                        this.target = instance;
                    }
                }
            }

            IMethodCallMessage callMessage = (IMethodCallMessage)msg;

            AdviceAttribute attri = ReflectionUtil.GetCustomAttribute<AdviceAttribute>(callMessage.MethodBase);

            if (attri != null && attri.Advice != null)
            {
                return attri.Advice.Invoke(this.target, callMessage);
            }

            return DelayProxyUtil.InvokeBeProxy(this.target, callMessage);
        }

    }