使用AOP微型框架的例子
在前面的系列文章中，我介绍了消息、代理与AOP的关系，这次将我自己实现的一个AOP微型框架拿出来和大家交流一下。AOP的最基本功能就是实现特定的预处理和后处理，我通过代理实现了此微型框架。先来看看构成此微型框架的4个.cs文件。1.CommonDef.cs 用于定义最基本的AOP接口************************************* CommonDef.cs **************************
using System;using System.Runtime.Remoting.Messaging;namespace EnterpriseServerBase.Aop{ /// <summary> /// IAopOperator AOP操作符接口，包括前处理和后处理 /// 2005.04.12 /// </summary> public interface IAopOperator { void PreProcess(IMessage requestMsg); void PostProcess(IMessage requestMsg, IMessage Respond); } /// <summary> /// IAopProxyFactory 用于创建特定的Aop代理的实例，IAopProxyFactory的作用是使AopProxyAttribute独立于具体的AOP代理类。 /// </summary> public interface IAopProxyFactory { AopProxyBase CreateAopProxyInstance(MarshalByRefObject obj, Type type); }}2. AopProxyBase AOP代理的基类，所有自定义AOP代理类都从此类派生，覆写IAopOperator接口，实现具体的前/后处理 。using System;using System.Runtime.Remoting;using System.Runtime.Remoting.Proxies;using System.Runtime.Remoting.Messaging;using System.Runtime.Remoting.Services;using System.Runtime.Remoting.Activation;namespace EnterpriseServerBase.Aop{ /// <summary> /// AopProxyBase 所有自定义AOP代理类都从此类派生，覆写IAopOperator接口，实现具体的前/后处理 。 /// 2005.04.12 /// </summary> public abstract class AopProxyBase : RealProxy, IAopOperator { private readonly MarshalByRefObject target; //默认透明代理 public AopProxyBase(MarshalByRefObject obj, Type type) : base(type) { this.target = obj; } #region Invoke public override IMessage Invoke(IMessage msg) { bool useAspect = false; IMethodCallMessage call = (IMethodCallMessage)msg; //查询目标方法是否使用了启用AOP的MethodAopSwitcherAttribute foreach (Attribute attr in call.MethodBase.GetCustomAttributes(false)) { MethodAopSwitcherAttribute mehodAopAttr = attr as MethodAopSwitcherAttribute; if (mehodAopAttr != null) { if (mehodAopAttr.UseAspect) { useAspect = true; break; } } } if (useAspect) { this.PreProcess(msg); } //如果触发的是构造函数，此时target的构建还未开始 IConstructionCallMessage ctor = call as IConstructionCallMessage; if (ctor != null) { //获取最底层的默认真实代理 RealProxy default_proxy = RemotingServices.GetRealProxy(this.target); default_proxy.InitializeServerObject(ctor); MarshalByRefObject tp = (MarshalByRefObject)this.GetTransparentProxy(); //自定义的透明代理 this return EnterpriseServicesHelper.CreateConstructionReturnMessage(ctor, tp); } IMethodReturnMessage result_msg = RemotingServices.ExecuteMessage(this.target, call); //将消息转化为堆栈，并执行目标方法，方法完成后，再将堆栈转化为消息 if (useAspect) { this.PostProcess(msg, result_msg); } return result_msg; } #endregion #region IAopOperator 成员 public abstract void PreProcess(IMessage requestMsg); public abstract void PostProcess(IMessage requestMsg, IMessage Respond); #endregion }}3. AopProxyAttribute AOP代理特性****************************** AopProxyAttribute ************************************using System;using System.Runtime.Remoting;using System.Runtime.Remoting.Proxies;namespace EnterpriseServerBase.Aop{ /// <summary> /// AopProxyAttribute /// AOP代理特性，如果一个类想实现具体的AOP，只要实现AopProxyBase和IAopProxyFactory，然后加上该特性即可。 /// 2005.04.11 /// </summary> [AttributeUsage(AttributeTargets.Class, AllowMultiple = false)] public class AopProxyAttribute : ProxyAttribute { private IAopProxyFactory proxyFactory = null; public AopProxyAttribute(Type factoryType) { this.proxyFactory = (IAopProxyFactory)Activator.CreateInstance(factoryType); } #region CreateInstance /// <summary> /// 获得目标对象的自定义透明代理 /// </summary> public override MarshalByRefObject CreateInstance(Type serverType)//serverType是被AopProxyAttribute修饰的类 { //未初始化的实例的默认透明代理 MarshalByRefObject target = base.CreateInstance(serverType); //得到位初始化的实例（ctor未执行） object[] args = { target, serverType }; //AopProxyBase rp = (AopProxyBase)Activator.CreateInstance(this.realProxyType ,args) ; //Activator.CreateInstance在调用ctor时通过了代理，所以此处将会失败 //得到自定义的真实代理 AopProxyBase rp = this.proxyFactory.CreateAopProxyInstance(target, serverType);//new AopControlProxy(target ,serverType) ; return (MarshalByRefObject)rp.GetTransparentProxy(); } #endregion }}4 .MethodAopSwitcherAttribute.cs**************************** MethodAopSwitcherAttribute.cs *************************using System;namespace EnterpriseServerBase.Aop{ /// <summary> /// MethodAopSwitcherAttribute 用于决定一个被AopProxyAttribute修饰的class的某个特定方法是否启用截获 。 /// 创建原因：绝大多数时候我们只希望对某个类的一部分Method而不是所有Method使用截获。 /// 使用方法：如果一个方法没有使用MethodAopSwitcherAttribute特性或使用MethodAopSwitcherAttribute(false)修饰， /// 都不会对其进行截获。只对使用了MethodAopSwitcherAttribute(true)启用截获。 /// 2005.05.11 /// </summary> [AttributeUsage(AttributeTargets.Method, AllowMultiple = false)] public class MethodAopSwitcherAttribute : Attribute { private bool useAspect = false; public MethodAopSwitcherAttribute(bool useAop) { this.useAspect = useAop; } public bool UseAspect { get { return this.useAspect; } } }}在基于前两篇文章给出的AOP微型框架的实现的基础上，我们可以写个例子来测试一下了：）public class AopControlProxyFactory : IAopProxyFactory{ #region IAopProxyFactory 成员 public AopProxyBase CreateAopProxyInstance(MarshalByRefObject obj, Type type) { return new AopControlProxy(obj, type); } #endregion}//自定义真实代理public class AopControlProxy : AopProxyBase{ public AopControlProxy(MarshalByRefObject obj, Type type) : base(obj, type) { } public override void PreProcess(IMessage requestMsg) { Console.Write("Begin Aop !"); } public override void PostProcess(IMessage requestMsg, IMessage Respond) { Console.Write("End Aop !"); }}[AopProxyAttribute(typeof(AopControlProxyFactory))] //将自己委托给AOP代理AopControlProxypublic class Example : ContextBoundObject//放到特定的上下文中，该上下文外部才会得到该对象的透明代理{ private string name; public Example(string a) { this.name = a; } [MethodAopSwitcherAttribute(true)] public void say_hello() { Console.WriteLine("hello ! " + name); } public void sayByeBye() { Console.WriteLine("Bye ! " + name); }}
