WCF以其灵活的可扩展架构为开发者提供了方便,其中对行为的扩展或许是应用中最为常见的。自 定义对行为的扩展并不复杂,但仍有许多细节需要注意。在服务端,一般是对DispatchRuntime和DispatchOperation进行扩展, 扩展点包括了对参数和消息的检查,以及操作调用程序,它们对应的接口分别为 IParameterInspector,IDispatchMessageInspector以及IOperationInvoker。而在客户端,则 是对ClientRuntime和ClientOperation进行扩展,扩展点包括对参数和消息的检查,对应的接口分别为 IParameterInspector和IClientMessageInspector。这些接口类型均被定义在 System.ServiceModel.Dispatcher命名空间下,其中IParameterInspector接口可以同时作用在服务端和客户 端。

对这些接口的实现,有点类似于AOP的实现,可以对方法调用前和调用后注入一些额外的逻辑,所以通常会将这些扩展称为侦听器。例如IParameterInspector接口,就定义了如下方法:
        void AfterCall(string operationName, object[] outputs, object returnValue, object correlationState);       
        object BeforeCall(string operationName, object[] inputs);

在调用服务对象的目标方法前,会调用BeforeCall方法,而在调用后则会调用AfterCall方法。例如我们可在方法调用前检验计算方法的参数是否小于0,如果小于0则抛出异常:
public class CalculatorParameterInspector:IParameterInspector
{
    public void BeforeCall(string operationName, object[] inputs)
    {
        int x = inputs[0] as int;
        int y = inputs[1] as int;
        if (x <0 || y < 0)
        {
           throw new FaultException("The number can not be less than zero.");
        }
        return null;
    }

    public void AfterCall(string operationName, object[] outputs, object returnValue, object correlationState)
    {
        //empty;
    }
}

对消息的检查区分了服务端和客户端,接口方法根据消息传递的顺序刚好相反[注]。我们可以通过接口方法对消息进行处理,例如打印消息的Header:
    public class PrintMessageInterceptor : IDispatchMessageInspector
    {
        #region IDispatchMessageInspector Members

        public object AfterReceiveRequest(ref System.ServiceModel.Channels.Message request, IClientChannel channel, InstanceContext instanceContext)
        {
            MessageBuffer buffer = request.CreateBufferedCopy(Int32.MaxValue);
            request = buffer.CreateMessage();

            Console.WriteLine("After Receive Request:");
            foreach (MessageHeader header in request.Headers)
            {
                Console.WriteLine(header);
            }
            Console.WriteLine(new string('*', 20));
            return null;
        }

        public void BeforeSendReply(ref System.ServiceModel.Channels.Message reply, object correlationState)
        {
            MessageBuffer buffer = reply.CreateBufferedCopy(Int32.MaxValue);
            reply = buffer.CreateMessage();

            Console.WriteLine("Before Send Request:");
            foreach (MessageHeader header in reply.Headers)
            {
                Console.WriteLine(header);
            }
            Console.WriteLine(new string('*', 20));
        }

        #endregion
    }

WCF提供了四种类型的行为:服务行为、终结点行为、契约行为和操作行为。 这四种行为分别定义了四个接口:IServiceBehavior,IEndpointBehavior,IContractBehavior以及 IOperationBehavior。虽然是四个不同的接口,但它们的接口方法却基本相同,分别为 AddBindingParameters(),ApplyClientBehavior()以及ApplyDispatchBehavior()。注 意,IServiceBehavior由于只能作用在服务端,因此并不包含ApplyClientBehavior()方法

我们可以定义自己的类实现这些接口,但需要注意几点:
1、行为的作用范围,可以用如下表格表示:

作用域

接口

影响范围

服务

终结点

契约

操作

服务

IServiceBehavior

Y

Y

Y

Y

终结点

IEndpointBehavior

 

Y

Y

Y

契约

IContractBehavior

 

 

Y

Y

操作

IOperationBehavior

 

 

 

Y

2、可以利用自定义特性的方式添加扩展的服务行为、契约行为和操作行为,但不能添加终结点行为;可以利用配置文件添加扩展服务行为和终结点行为,但不能添加契约行为和操作行为。但这些扩展的行为都可以通过ServiceDescription添加

利用特性添加行为,意味着我们在定义自己的扩展行为时,可以将其派生自Attribute类,然后以特性方式添加。例如:
[AttributeUsage(AttributeTargets.Class|AttributeTargets.Interface)]
public class MyServiceBehavior:Attribute, IServiceBehavior...

[MyServiceBehavior]
public interface IService...

如果以配置文件的方式添加行为,则必须定义一个类继承自BehaviorExtensionElement(属 于命名空间System.ServiceModel.Configuration),然后重写属性BehaviorType以及 CreateBehavior()方法。BehaviorType属性返回的是扩展行为的类型,而CreateBehavior()方法则负责创建该扩展 行为的对象实例:
    public class MyBehaviorExtensionElement:BehaviorExtensionElement
    {
        public MyBehaviorExtensionElement() { }
        public override Type BehaviorType
        {
            get { return typeof(MyServiceBehavior); }
        }

        protected override object CreateBehavior()
        {
            return new MyServiceBehavior();
        }
    }

如果配置的Element添加了新的属性,则需要为新增的属性应用ConfigurationPropertyAttribute,例如:
    [ConfigurationProperty("providerName",IsRequired = true)]
    public virtual string ProviderName
    {
        get
        {
            return this["ProviderName"] as string;
        }
        set
        {
            this["ProviderName"] = value;
        }
    }

配置文件中的配置方法如下所示:
<configuration>
  <system.serviceModel>   
    <services>
      <service name="MessageInspectorDemo.Calculator">
        <endpoint behaviorConfiguration="messageInspectorBehavior"
                  address="http://localhost:801/Calculator"                  
                  binding="basicHttpBinding"
                  contract="MessageInspectorDemo.ICalculator"/>
      </service>
    </services>
    <behaviors>
      <serviceBehaviors>
        <behavior name="messageInspectorBehavior">
          <myBehaviorExtensionElement providerName="Test"/>
        </behavior>
      </serviceBehaviors>
    </behaviors>
    <extensions>
      <behaviorExtensions>
        <add name="myBehaviorExtensionElement"
             type="MessageInspectorDemo.MyBehaviorExtensionElement, MessageInspectorDemo, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null"/>
      </behaviorExtensions>
    </extensions>

  </system.serviceModel>
</configuration>

注 意,在<serviceBehaviors>一节中,<behavior>下 的<myBehaviorExtensionElement>就是我们扩展的行为,providerName则是 MyBehaviorExtensionElement增加的属性。如果扩展了IEndpointBehavior,则配置节的名称 为<endpointBehaviors>。<extensions>节负责添加自定义行为的扩展。其 中,<add>中的name值与<behavior>下 的<myBehaviorExtensionElement>对应。

特别注意的是<extensions>下的 type值,必须是类型的full name。第一个逗点前的内容为完整的类型名(包括命名空间),第二部分为完整的命名空间。Version,Culture以及 PublicKeyToken也是缺一不可的。每个逗点后必须保留一个空格,否则无法正确添加扩展行为的配置。这与反射有关,但太容易让人忽略这一小细节。希望微软能在后来的版本中修订这个瑕疵。

3、在行为扩展的适当方法中,需要添加参数检查、消息检查或操作调用程序的扩展。这之间存在一定的对应关系。对于参数检查,我们需要在IOperationBehavior接口类型中的ApplyClientBehavior()以及ApplyDispatchBehavior()中添加。例如对于之前的CalculatorParameterInspector,我们可以定义一个类CalculatorParameterValidation:
public class CalculatorParameterValidation:Attribute, IOperationBehavior
{
        #region IOperationBehavior Members
        public void AddBindingParameters(OperationDescription operationDescription,
            BindingParameterCollection bindingParameters)
        {
        }

        public void ApplyClientBehavior(OperationDescription operationDescription,
            ClientOperation clientOperation)
        {
            CalculatorParameterInspector inspector = new CalculatorParameterInspector();
            clientOperation.ParameterInspectors.Add(inspector);

        }

        public void ApplyDispatchBehavior(OperationDescription operationDescription,
            DispatchOperation dispatchOperation)
        {
            CalculatorParameterInspector inspector = new CalculatorParameterInspector();
            dispatchOperation.ParameterInspectors.Add(inspector);

        }

        public void Validate(OperationDescription operationDescription)
        {
        }
        #endregion
}

如果检查器与扩展行为在职责上没有分离的必要,一个更好的方法是定义一个类同时实现IParameterInspector和IOperationBehavior接口,例如:
public class CalculatorParameterValidation:Attribute, IParameterInspector, IOperationBehavior
{
        #region IParameterInspector Members
        public void BeforeCall(string operationName, object[] inputs)
        {
            int x = inputs[0] as int;
            int y = inputs[1] as int;
            if (x <0 || y < 0)
            {
               throw new FaultException("The number can not be less than zero.");
            }
            return null;
        }

        public void AfterCall(string operationName, object[] outputs, object returnValue, object correlationState)
        {
            //empty;
        }
        #endregion


        #region IOperationBehavior Members
        public void AddBindingParameters(OperationDescription operationDescription,
            BindingParameterCollection bindingParameters)
        {
        }

        public void ApplyClientBehavior(OperationDescription operationDescription,
            ClientOperation clientOperation)
        {
            CalculatorParameterInspector inspector = new CalculatorParameterInspector();
            clientOperation.ParameterInspectors.Add(thisinspector);
        }

        public void ApplyDispatchBehavior(OperationDescription operationDescription,
            DispatchOperation dispatchOperation)
        {
            CalculatorParameterInspector inspector = new CalculatorParameterInspector();
            dispatchOperation.ParameterInspectors.Add(thisinspector);
        }

        public void Validate(OperationDescription operationDescription)
        {
        }
        #endregion
}

操作调用程序虽然通过IOperationBehavior进行关联,但确是通过DispatchOperation的Invoker属性。假定我们已经定义了一个实现IOperationInvoker的类MyOperationInvoker,则关联的方法为:
    public class MyOperationInvokerBehavior : Attribute, IOperationBehavior
    {
        #region IOperationBehavior Members
        public void AddBindingParameters(OperationDescription operationDescription,
            BindingParameterCollection bindingParameters)
        {
        }
        public void ApplyClientBehavior(OperationDescription operationDescription,
            ClientOperation clientOperation)
        {           
        }
        public void ApplyDispatchBehavior(OperationDescription operationDescription,
            DispatchOperation dispatchOperation)
        {
            dispatchOperation.Invoker = new MyOperationInvoker(dispatchOperation.Invoker);
        }
        public void Validate(OperationDescription operationDescription)
        {
        }
        #endregion
    }

至 于对Dispatch的消息检查,则可以通过IServiceBehavior,IEndpointBehavior或 IContractBehavior中DispatchRuntime的MessageInspectors添加;而对Client的消息检查则可以通过 IEndpointBehavior或IContractBehavior中ClientRuntime的MessageInspectors添加(注 意,此时与IServiceBehavior无关,因为它不会作用于客户端代理)。例如:
    public class PrintMessageInspectorBehavior : IDispatchMessageInspector,IEndpointBehavior
    {
        //略去IDispatchMessageInspector接口成员的实现;

        #region IEndpointBehavior Members
        public void AddBindingParameters(ServiceEndpoint endpoint, BindingParameterCollection bindingParameters)
        {
            //empty;
        }
        public void ApplyClientBehavior(ServiceEndpoint endpoint, ClientRuntime clientRuntime)
        {
              clientRuntime.MessageInspectors.Add(this);
        }
        public void ApplyDispatchBehavior(ServiceEndpoint endpoint, EndpointDispatcher endpointDispatcher)
        {
            endpointDispatcher.DispatchRuntime.MessageInspectors.Add(this);
        }
        public void Validate(ServiceEndpoint endpoint)
        {
            //empty;
        }
        #endregion
    }

如果实现的是IServiceBehavior接口,则需要遍历ApplyDispatchBehavior()方法中的ServiceHostBase对象:
        public void ApplyDispatchBehavior(ServiceDescription serviceDescription, ServiceHostBase serviceHostBase)
        {
            foreach (ChannelDispatcher channelDispatcher in serviceHostBase.ChannelDispatchers)
            {
                foreach (EndpointDispatcher endpointDispatcher in channelDispatcher .Endpoints)
                {
                    endpointDispatcher.DispatchRuntime.MessageInspectors.Add(this);
                }
            }
        }

注:IDispatchMessageInspector 接口的方法为BeforeSendReply()和AfterReceiveRequest();而IClientMessageInspector接口 的方法则为BeforeSendRequest()和AfterReceiveReply()。