一个简单的AOP框架学习

在.Net Unity2.0中的Interception，按三种方式实现:

1.TransparentProxy/RealProxy Interceptor 即Remoting代理机制。

2.Interface Interceptor 即动态代码（Emit编程)实现

3.Virtual Method Interceptor 也是动态代码实现，Emit编程基本类似于IL编程了。

实例拦截与类型拦截

1.实例拦截

TransparentProxy 与 Interface Interceptor 属于实例拦截，所谓实例拦截就是被拦截对象完整而独立的在内参中存在。Client端通过代理类与被拦截对象发生通信（方法调用）。

2.类型拦截

Virtual Method 方式属于类型拦截，内参中不存在被拦截类型的实例，拦截框架通过动态代码生成被拦截类型的子类型程序集，该程序集被加载后对应的子类型被实例化于内存中与Client发生通信

下面针对TransparentProxy/RealProxy 与 Interface Interceptor帖出手头上dll实现的代码

1.TransparentProxy/RealProxy实现

using System.Reflection; 

using System.Runtime.Remoting.Proxies; 

using System.Runtime.Remoting.Messaging; 

using System.Runtime.Remoting; 

internal class TransparentProxy : RealProxy 

{ 

    // Fields 

    private readonly MarshalByRefObject m_Target; 

    // Methods 

    public TransparentProxy(MarshalByRefObject target) 

        : base(target.GetType()) 

    { 

        this.m_Target = target; 

    } 

    public static object GetProxy(MarshalByRefObject target) 

    { 

        TransparentProxy proxy = new TransparentProxy(target); 

        return proxy.GetTransparentProxy(); 

    } 

    public override IMessage Invoke(IMessage msg) 

    { 

        IMessage message = null; 

        IMethodCallMessage callMsg = msg as IMethodCallMessage; 

        if (callMsg != null) 

        { 

            object[] customAttributes = callMsg.MethodBase.GetCustomAttributes(true); 

            this.InvokeBeforeAttribute(customAttributes, callMsg); 

            try

            { 

                message = RemotingServices.ExecuteMessage(this.m_Target, callMsg); 

            } 

            catch (Exception exception) 

            { 

                this.InvokeExceptionAttribute(customAttributes, callMsg, exception); 

                throw; 

            } 

            this.InvokeAfterAttribute(customAttributes, callMsg, ((ReturnMessage)message).ReturnValue); 

        } 

        return message; 

    } 

  //.......... 

  //............ 

}

类TransproxyProxy中维护着一个到target类实例的引用(必须是MarshalByRefObject类型的子类），最终的方法调用会通过消息机制到达target实例--语句RemotingServices.ExecuteMessage(this.m_Target, callMsg);,在调用目标对象的目标方法之前会调用InvokeBeforeAttribute，错误时会调用InvokeExceptionAttribute,而完成后调用InvokeAfterAttribute.这里需要注意的是Unity2.0 Interception 中将要调用的InterceptionBehavior构建成管道模型，编程时会有Scop样的开闭结构，而这里的实现只是顺序的调用，这点需要加以区分。InvokeBeforeAttribute等方法实现如下

private void InvokeAfterAttribute(object[] attributes, IMethodCallMessage callMsg, object result) 

{ 

    foreach (object obj2 in attributes) 

    { 

        AfterAttribute attribute = obj2 as AfterAttribute; 

        if (attribute != null) 

        { 

            attribute.Invoke(this.m_Target, callMsg.MethodBase, callMsg.InArgs, result); 

        } 

    } 

    List<IInterception> interceptionList = ProxyBuilder.GetInterceptionList(this.m_Target.GetType().FullName + "." + callMsg.MethodName, InterceptionType.After); 

    if (interceptionList != null) 

    { 

        foreach (IInterception interception in interceptionList) 

        { 

            interception.Invoke(this.m_Target, callMsg.MethodBase, callMsg.InArgs, result); 

        } 

    } 

}

2.Interface Interceptor 代码

public static object GetProxyInstance(object target, Type interfaceType) 

   { 

       return Activator.CreateInstance(GetProxyType(target.GetType(), interfaceType), new object[] { target, interfaceType }); 

   } 

   private static Type GetProxyType(Type targetType, Type interfaceType) 

   { 

       AppDomain domain = Thread.GetDomain(); 

       AssemblyName name = new AssemblyName(); 

       name.Name = "TempAssemblyInjection"; 

       AssemblyName name2 = name; 

       AssemblyBuilder assemblyBuilder = domain.DefineDynamicAssembly(name2, AssemblyBuilderAccess.Run); 

       ModuleBuilder builder = assemblyBuilder.DefineDynamicModule("TempClassInjection"); 

       Type type = builder.GetType("TempAssemblyInjection__Proxy" + interfaceType.Name + targetType.Name); 

       if (type != null) 

       { 

           return type; 

       } 

       m_TypeBuilder = builder.DefineType("TempAssemblyInjection__Proxy" + interfaceType.Name + targetType.Name, TypeAttributes.Public, targetType.BaseType, new Type[] { interfaceType }); 

       m_Target = m_TypeBuilder.DefineField("target", interfaceType, FieldAttributes.Private); 

       m_Interface = m_TypeBuilder.DefineField("iface", typeof(Type), FieldAttributes.Private); 

       CreateConstructor(m_TypeBuilder, m_Target, m_Interface); 

       foreach (MethodInfo info in interfaceType.GetMethods()) 

       { 

           CreateProxyMethod(info, m_TypeBuilder); 

       } 

       return m_TypeBuilder.CreateType(); 

   }

上面代码通过Emit编程动态构建程序集，程序集中包括一个到目标类的代理类,针对给定接口中的方法签名逐个创建代理方法--语句CreateProxyMethod(info, m_TypeBuilder);
另外可以看到代理类型的程序集只在第一次访问时被创建
--语句
Type type = builder.GetType("TempAssemblyInjection__Proxy" + interfaceType.Name + targetType.Name);
   if (type != null)
    {
         return type;
     }

建立的代理类定义类似如下代码:

public class TempAssemblyInjection__ProxyIAnimalDog : IAnimal 

{ 

    // Fields 

    private Type iface; 

    private IAnimal target; 

    // Methods 

    public TempAssemblyInjection__ProxyIAnimalDog(object obj1, Type type1) 

    { 

        this.target = (IAnimal) obj1; 

        this.iface = type1; 

    } 

    public override int Run(int num1, int num2) 

    { 

        object[] parameters = new object[] { num1, num2 }; 

        return (int) DynamicProxy.InterceptHandler(this.target, <BR>           Helper.GetMethodFromType(this.target.GetType(), MethodBase.GetCurrentMethod()),<BR>           parameters, <BR>           Helper.AspectUnion(Helper.GetMethodFromType(this.iface, MethodBase.GetCurrentMethod()).GetCustomAttributes(typeof(AspectAttribute), true))<BR>      ); 

    } 

}

DynamicProxy.InterceptHandler的代码

public static object InterceptHandlerMethod(object target, MethodBase method, object[] parameters, AspectAttribute[] attributes) 

{ 

    object obj2; 

    foreach (AspectAttribute attribute in attributes) 

    { 

        if (attribute is BeforeAttribute) 

        { 

            attribute.Invoke(target, method, parameters, null); 

        } 

    } 

    foreach (IInterception interception in ProxyBuilder.GetInterceptionList(target.GetType().FullName + "." + method.Name, InterceptionType.Before)) 

    { 

        interception.Invoke(target, method, parameters, null); 

    } 

    try

    { 

        obj2 = target.GetType().GetMethod(method.Name).Invoke(target, parameters); 

    } 

    catch (Exception exception) 

    { 

        foreach (AspectAttribute attribute2 in attributes) 

        { 

            if (attribute2 is ExceptionAttribute) 

            { 

                attribute2.Invoke(target, method, parameters, exception); 

            } 

        } 

        foreach (IInterception interception2 in ProxyBuilder.GetInterceptionList(target.GetType().FullName + "." + method.Name, InterceptionType.Exception)) 

        { 

            interception2.Invoke(target, method, parameters, exception); 

        } 

        throw; 

    } 

    foreach (AspectAttribute attribute3 in attributes) 

    { 

        if (attribute3 is AfterAttribute) 

        { 

            attribute3.Invoke(target, method, parameters, obj2); 

        } 

    } 

    foreach (IInterception interception3 in ProxyBuilder.GetInterceptionList(target.GetType().FullName + "." + method.Name, InterceptionType.After)) 

    { 

        interception3.Invoke(target, method, parameters, obj2); 

    } 

    return obj2; 

} 

// Properties 

public static Callback InterceptHandler 

{ 

    get

    { 

        return new Callback(DynamicProxy.InterceptHandlerMethod); 

    } 

}

完成代码与使用Demo请下载演示包

==================================点这里下载=========================

http://www.cnblogs.com/wdfrog/archive/2011/03/18/1988091.html