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[原创]WCF后续之旅（8）：通过WCF Extension 实现与MS Enterprise Library Policy Injection Application Block 的集成

2008-07-29 09:16 831 查看

在上一篇文章中，我们通过自定义InstanceProvider实现了WCF和微软Enterprise Library Unity Application Block的集成，今天我们已相同的方式实现WCF与Enterprise Library的另一个Application Block的集成：Policy Injection Application Block (PIAB)。

PIAB，通过Method Interception的机制实现了AOP(Aspect Oriented Programing)。按照PIAB的编程方式，我们将非业务逻辑，比如Caching、Authorization、Transaction Enlist、Auditing、ExceptionHandling扽等等，定义在一个个的CallHandler，这些CallHandler通过Attribute或者Configuration的方式应用到目标方法上。关于PIAB的详细介绍，我们参考我的PIAB系列（http://www.cnblogs.com/artech/archive/2008/01/29/1057379.html）。

由于PIAB特殊的实现机制(PIAB实现原理),我们需要通过PIAB的PolicyInjector来创建新的对象或者包装现有的目标对象。只有调用这种能够方式的对象，应用在上面的CallHandler才能被执行。所以WCF和PIAB的核心问题就是如何通过PIAB PolicyInjector来创建新的Service Instance，或者包装已经生成的service instance。在上面一篇文章中，我们通过Unity Container重新定义了InstanceProvider，我们今天的实现方案也是通过自定义InstanceProvider的方式来实现，不是我们需需要通过PolicyInjector来进行对象的创建。

1、创建基于PolicyInjection的InstanceProvider

下面是我们新的InstanceProvider（PolicyInjectionInstanceProvider ）的定义

namespace Artech.WCFExtensions

{

    public class PolicyInjectionInstanceProvider : IInstanceProvider

    {

        private Type _serviceContractType;

        private string _policyInjectorName;

        public PolicyInjectionInstanceProvider(Type serviceContractType, string policyInjectorName)

        {

            this._serviceContractType = serviceContractType;

            this._policyInjectorName = policyInjectorName;

        }

        #region IInstanceProvider Members

        public object GetInstance(InstanceContext instanceContext, Message message)

        {

            PolicyInjector policyInjector = null;

            if (string.IsNullOrEmpty(this._policyInjectorName))

            {

                policyInjector = new PolicyInjectorFactory().Create();

            }

            else

            {

                policyInjector = new PolicyInjectorFactory().Create(this._policyInjectorName);

            }

            Type serviceType = instanceContext.Host.Description.ServiceType;

            object serviceInstance = Activator.CreateInstance(serviceType);

            if (!this._serviceContractType.IsInterface && !serviceType.IsMarshalByRef && policyInjector is RemotingPolicyInjector)

            {

                return serviceInstance;

            }

            return policyInjector.Wrap(serviceInstance, this._serviceContractType);

        }

        public object GetInstance(InstanceContext instanceContext)

        {

            return this.GetInstance(instanceContext, null);

        }

        public void ReleaseInstance(InstanceContext instanceContext, object instance)

        {

            IDisposable disposable = instance as IDisposable;

            if (disposable != null)

            {

                disposable.Dispose();

            }

        }

        #endregion

    }

}

我们对PolicyInjectionInstanceProvider 的实现进行简单的说明：在PIAB中真正用于创建对象的是PolicyInjector，虽然PIAB中仅仅定义了一种基于Remoting的RemotingPolicyInjector，但是我们可以根据我们的需要实现一些不同Injection方式，比如IL Injection。所以我们定义了一个字段_policyInjectorName在配置中定位我们需要的PolicyInjector。该字段如果为null或者empty，将使用默认的PolicyInjector。PolicyInjection的获取通过下面的代码实现：

PolicyInjector policyInjector = null;

if (string.IsNullOrEmpty(this._policyInjectorName))

{

    policyInjector = new PolicyInjectorFactory().Create();

}

else

{

    policyInjector = new PolicyInjectorFactory().Create(this._policyInjectorName);

}

能够被RemotingPolicyInjector创建的对象不是满足下面两个条件中的一个：

Target type实现一个Interface。

Target Type直接或者间接集成System.MarshalByRefObject.

所以如果不能满足这个条件，我们直接通过反射创建service instance：

Type serviceType = instanceContext.Host.Description.ServiceType;

object serviceInstance = Activator.CreateInstance(serviceType);

if (!this._serviceContractType.IsInterface && !serviceType.IsMarshalByRef && policyInjector is RemotingPolicyInjector)

{

         return serviceInstance;

}
最后我们通过policyInjector 的Wrap方法对service instance进行封装并返回：

return policyInjector.Wrap(serviceInstance, this._serviceContractType);

2、为PolicyInjectionInstanceProvider创建Behavior

我们可以通过ContractBehavior或者EndpointBehavior应用我们定义的PolicyInjectionInstanceProvider 。

I、ContractBehavior：PolicyInjectionBehaviorAttribute

namespace Artech.WCFExtensions

{

    public class PolicyInjectionBehaviorAttribute:Attribute, IContractBehavior

    {

        public string PolicyInjectorName

        { get; set; }

        #region IContractBehavior Members

        public void AddBindingParameters(ContractDescription contractDescription, ServiceEndpoint endpoint, BindingParameterCollection bindingParameters)

        {}

        public void ApplyClientBehavior(ContractDescription contractDescription, ServiceEndpoint endpoint, ClientRuntime clientRuntime)

        {}

        public void ApplyDispatchBehavior(ContractDescription contractDescription, ServiceEndpoint endpoint, DispatchRuntime dispatchRuntime)

        {

            Type serviceContractType = contractDescription.ContractType;

            dispatchRuntime.InstanceProvider = new PolicyInjectionInstanceProvider(serviceContractType, this.PolicyInjectorName);
        }

        public void Validate(ContractDescription contractDescription, ServiceEndpoint endpoint)

        {}

        #endregion

    }

}

我们在ApplyDispatchBehavior，通过contractDescription.ContractType获得service contract type，然后创建我们的PolicyInjectionInstanceProvider，并将其指定成当前DispatchRuntime 的InstanceProvider 。PolicyInjector通过属性PolicyInjectorName进行设置。

II、Endpoint Behavior & Behavior Extension: PolicyInjectionBehavior

namespace Artech.WCFExtensions

{

public class PolicyInjectionBehavior:IEndpointBehavior

    {

        private string _policyInjectorName;

        public PolicyInjectionBehavior(string policyInjectorName)

        {

            this._policyInjectorName = policyInjectorName;

        }

        #region IEndpointBehavior Members

        public void AddBindingParameters(ServiceEndpoint endpoint, BindingParameterCollection bindingParameters)

        {}

        public void ApplyClientBehavior(ServiceEndpoint endpoint, ClientRuntime clientRuntime)

        {}

        public void ApplyDispatchBehavior(ServiceEndpoint endpoint, EndpointDispatcher endpointDispatcher)

        {

            Type serviceContractType = endpoint.Contract.ContractType;

            endpointDispatcher.DispatchRuntime.InstanceProvider = new PolicyInjectionInstanceProvider(serviceContractType, this._policyInjectorName);
        }

        public void Validate(ServiceEndpoint endpoint)

        {}

        #endregion

    }

}

当前DispatchRuntime的InstanceProvider 在ApplyDispatchBehavior方法中指定，PolicyInjectorName通过配置文件配置。该配置节通过下面的PolicyInjectionBehaviorElement定义：

namespace Artech.WCFExtensions

{

    public class PolicyInjectionBehaviorElement:BehaviorExtensionElement

    {

        [ConfigurationProperty("policyInjectorName",IsRequired = false, DefaultValue = "")]

        public string PolicyInjectorName

        {

            get

            {

                return this["policyInjectorName"] as string;

            }

            set

            {

                this["policyInjectorName"] = value;

            }

        }

        public override Type BehaviorType

        {

            get { return typeof(PolicyInjectionBehavior); }

        }

        protected override object CreateBehavior()

        {

            return new PolicyInjectionBehavior(this.PolicyInjectorName);

        }

    }

}

3、应用我们的PolicyInjectionBehavior

现在模拟一个WCF的场景来应用我们创建的PolicyInjectionBehavior。为了直观我们我们创建一个Timeservice，用于返回当前的系统之间，然后我们运用PIAB的CachingCallHandler。那么我们可以通过返回值是否反映真正的当前时间来判断Policy Injection是否起作用了。

我们依然采用我们的4层结构程序构架：

I、Artech.TimeService.Contract

namespace Artech.TimeService.Contract

{

    [ServiceContract]

    [PolicyInjectionBehavior]

    public interface ITime

    {

        [OperationContract]

        DateTime GetCurrentTime();

    }

}

我们先试验ContractBehavior，我们仅仅需要将PolicyInjectionBehaviorAttribute应用到ServiceContract上。

II、Artech.TimeService.Service

namespace Artech.TimeService.Service

{

    public class TimeService:ITime

    {

        #region ITime Members

       [CachingCallHandler]
        public DateTime GetCurrentTime()

        {

            return DateTime.Now;

        }

        #endregion

    }

}

我们在GetCurrentTime方法上应用了CachingCallHandlerAttribute，那么在第一次执行该方法的时候，方法返回的结果会被缓存，缓存的Key将会是方法和参数值的列表。后续的执行，将会直接从Cache中获取已经执行过的结果。

III、Artech.TimeService.Hosting

<?xml version="1.0" encoding="utf-8" ?>

<configuration>

    <system.serviceModel>

        <services>

            <service name="Artech.TimeService.Service.TimeService">

                <endpoint behaviorConfiguration="" binding="basicHttpBinding"

                    contract="Artech.TimeService.Contract.ITime" />

                <host>

                    <baseAddresses>

                        <add baseAddress="http://127.0.0.1/timeservice" />

                    </baseAddresses>

                </host>

            </service>

        </services>

    </system.serviceModel>

</configuration>

namespace Artech.TimeService.Hosting

{

    class Program

    {

        static void Main(string[] args)

        {

            using (ServiceHost host = new ServiceHost(typeof(Artech.TimeService.Service.TimeService)))

            {

                host.Opened += delegate

                {

                    Console.WriteLine("Time service has been started up!");

                };

                host.Open();

                Console.Read();

            }

        }

    }

}

IV、Artech.TimeService.Client

<?xml version="1.0" encoding="utf-8" ?>

<configuration>

    <system.serviceModel>

        <client>

            <endpoint address="http://127.0.0.1/timeservice" binding="basicHttpBinding"

                contract="Artech.TimeService.Contract.ITime" name="timeservice" />

        </client>

    </system.serviceModel>

</configuration>

namespace Artech.TimeService.Client

{

    class Program

    {

        static void Main(string[] args)

        {

            using (ChannelFactory<ITime> channelFactory = new ChannelFactory<ITime>("timeservice"))

            {

                ITime proxy = channelFactory.CreateChannel();

                for (int i = 0; i < 10; i++)

                {

                    Console.WriteLine(proxy.GetCurrentTime());

                   Thread.Sleep(1000);
                }

            }

            Console.Read();

        }

    }

}

下面是最终输出的结果：

从返回的时间都是相同的，我们可以确认caching发挥了作用，如何我们将Contract上[PolicyInjectionBehavior]注释掉。

namespace Artech.TimeService.Contract

{

    [ServiceContract]

   //[PolicyInjectionBehavior]
    public interface ITime

    {

        [OperationContract]

        DateTime GetCurrentTime();

    }

}

我们将会得到这样的结果：

上面我们演示了ContractBehavior的应用，我们接着来演示EndpointBehavior的应用。我们仅仅需要修改Hosting的cnonfiguration就可以了：

<?xml version="1.0" encoding="utf-8" ?>

<configuration>

    <system.serviceModel>

        <behaviors>

            <endpointBehaviors>

                <behavior name="PolicyInjectionBehavior">

                    <PolicyInjectionBehaviorExtension />

                </behavior>

            </endpointBehaviors>

        </behaviors>

        <extensions>

            <behaviorExtensions>

                <add name="PolicyInjectionBehaviorExtension" type="Artech.WCFExtensions.PolicyInjectionBehaviorElement, Artech.WCFExtensions, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" />

            </behaviorExtensions>

        </extensions>

        <services>

            <service name="Artech.TimeService.Service.TimeService">

                <endpoint behaviorConfiguration="PolicyInjectionBehavior" binding="basicHttpBinding"

                    contract="Artech.TimeService.Contract.ITime" />

                <host>

                    <baseAddresses>

                        <add baseAddress="http://127.0.0.1/timeservice" />

                    </baseAddresses>

                </host>

            </service>

        </services>

    </system.serviceModel>

</configuration>

此时运行我们的程序一样可以得到被返回值被Cache的结果：

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标签： wcf extension application library service serialization

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