.Net中的Interception一个简单的AOP框架学习

最近翻手头的dll文件时无意中发现了一个Interception实现，这个框架比起目前流行的AOP框架显的比较简漏，但却很好的体现出了.net下AOP是怎么实现的，于是就整理出来。

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

view sourceprint?

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

view sourceprint?

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

view sourceprint?

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:

view sourceprint?

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

view sourceprint?

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);

    }

}

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