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

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。

一、创建基于PolicyInjection的InstanceProvider

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

1: namespace Artech.WCFExtensions

2: {

3:     public class PolicyInjectionInstanceProvider : IInstanceProvider

4:     {

5:         private Type _serviceContractType;

6:         private string _policyInjectorName;

7: 

8:         public PolicyInjectionInstanceProvider(Type serviceContractType, string policyInjectorName)

9:         {

10:             this._serviceContractType = serviceContractType;

11:             this._policyInjectorName = policyInjectorName;

12:         }

13:         public object GetInstance(InstanceContext instanceContext, Message message)

14:         {

15:             PolicyInjector policyInjector = null;

16:             if (string.IsNullOrEmpty(this._policyInjectorName))

17:             {

18:                 policyInjector = new PolicyInjectorFactory().Create();

19:             }

20:             else

21:             {

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

23:             }

24: 

25:             Type serviceType = instanceContext.Host.Description.ServiceType;

26:             object serviceInstance = Activator.CreateInstance(serviceType);

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

28:             {

29:                 return serviceInstance;

30:             }

31: 

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

33:         }

34: 

35:         public object GetInstance(InstanceContext instanceContext)

36:         {

37:             return this.GetInstance(instanceContext, null);

38:         }

39: 

40:         public void ReleaseInstance(InstanceContext instanceContext, object instance)

41:         {

42:             IDisposable disposable = instance as IDisposable;

43:             if (disposable != null)

44:             {

45:                 disposable.Dispose();

46:             }

47:         }

48:     }

49: }

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：

1: PolicyInjector policyInjector = null;

2: if (string.IsNullOrEmpty(this._policyInjectorName))

3: {

4:     policyInjector = new PolicyInjectorFactory().Create();

5: }

6: else

7: {

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

9: }

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：

1: Type serviceType = instanceContext.Host.Description.ServiceType;

2: object serviceInstance = Activator.CreateInstance(serviceType);

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

4: {

5:          return serviceInstance;

6: }

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

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

二、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

1: namespace Artech.WCFExtensions

2: {

3:     public class PolicyInjectionBehaviorAttribute : Attribute, IContractBehavior

4:     {

5:         public string PolicyInjectorName{ get; set; }

6:         public void AddBindingParameters(ContractDescription contractDescription, ServiceEndpoint endpoint, BindingParameterCollection bindingParameters){ }

7:         public void ApplyClientBehavior(ContractDescription contractDescription, ServiceEndpoint endpoint, ClientRuntime clientRuntime){ }

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

9:         {

10:             Type serviceContractType = contractDescription.ContractType;

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

12:         }

13:         public void Validate(ContractDescription contractDescription, ServiceEndpoint endpoint){

14:     }

15: }

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

1: namespace Artech.WCFExtensions

2: {

3:     public class PolicyInjectionBehavior : IEndpointBehavior

4:     {

5:         private string _policyInjectorName;

6:         public PolicyInjectionBehavior(string policyInjectorName)

7:         {

8:             this._policyInjectorName = policyInjectorName;

9:         }

10:         public void AddBindingParameters(ServiceEndpoint endpoint, BindingParameterCollection bindingParameters){ }

11:         public void ApplyClientBehavior(ServiceEndpoint endpoint, ClientRuntime clientRuntime){ }

12:         public void ApplyDispatchBehavior(ServiceEndpoint endpoint, EndpointDispatcher endpointDispatcher)

13:         {

14:             Type serviceContractType = endpoint.Contract.ContractType;

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

16:         }

17:         public void Validate(ServiceEndpoint endpoint){ }

18:     }

19: }

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：

1: namespace Artech.WCFExtensions

2: {

3:     public class PolicyInjectionBehaviorElement:BehaviorExtensionElement

4:     {

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

6:         public string PolicyInjectorName

7:         {

8:             get

9:             {

10:                 return this["policyInjectorName"] as string;

11:             }

12:             set

13:             {

14:                 this["policyInjectorName"] = value;

15:             }

16:         } 

17: 

18:         public override Type BehaviorType

19:         {

20:             get { return typeof(PolicyInjectionBehavior); }

21:         }

22: 

23:         protected override object CreateBehavior()

24:         {

25:             return new PolicyInjectionBehavior(this.PolicyInjectorName);

26:         }

27:     }

28: }

29: 

三、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

1: namespace Artech.TimeService.Contract

2: {

3:     [ServiceContract]

4:     [PolicyInjectionBehavior]

5:     public interface ITime

6:     {

7:         [OperationContract]

8:         DateTime GetCurrentTime();

9:     }

10: }

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

II、Artech.TimeService.Service

1: namespace Artech.TimeService.Service

2: {

3:     public class TimeService:ITime

4:     {

5:        [CachingCallHandler]

6:         public DateTime GetCurrentTime()

7:         {

8:             return DateTime.Now;

9:         } 

10:     }

11: }

 

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

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

2: <configuration>

3:     <system.serviceModel>

4:         <services>

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

6:                 <endpoint behaviorConfiguration="" binding="basicHttpBinding"

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

8:                 <host>

9:                     <baseAddresses>

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

11:                     </baseAddresses>

12:                 </host>

13:             </service>

14:         </services>

15:     </system.serviceModel>

16: </configuration>

1: namespace Artech.TimeService.Hosting

2: {

3:     class Program

4:     {

5:         static void Main(string[] args)

6:         {

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

8:             {

9:                 host.Opened += delegate

10:                 {

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

12:                 };

13:                 host.Open();

14: 

15:                 Console.Read();

16:             }

17:         }

18:     }

19: }

20: 

 

 

 

 

IV、Artech.TimeService.Client

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

2: <configuration>

3:     <system.serviceModel>

4:         <client>

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

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

7:         </client>

8:     </system.serviceModel>

9: </configuration>

 

 

1: namespace Artech.TimeService.Client

2: {

3:     class Program

4:     {

5:         static void Main(string[] args)

6:         {

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

8:             {

9:                 ITime proxy = channelFactory.CreateChannel();

10: 

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

12:                 {

13:                     Console.WriteLine(proxy.GetCurrentTime());

14:                    Thread.Sleep(1000);

15:                 }

16:             } 

17: 

18:             Console.Read();

19:         }

20:     }

21: }

22: 

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。

1: namespace Artech.TimeService.Contract

2: {

3:     [ServiceContract]

4:    //[PolicyInjectionBehavior]

5:     public interface ITime

6:     {

7:         [OperationContract]

8:         DateTime GetCurrentTime();

9:     }

10: }

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：

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

2: <configuration>

3:     <system.serviceModel>

4:         <behaviors>

5:             <endpointBehaviors>

6:                 <behavior name="PolicyInjectionBehavior">

7:                     <PolicyInjectionBehaviorExtension />

8:                 </behavior>

9:             </endpointBehaviors>

10:         </behaviors>

11:         <extensions>

12:             <behaviorExtensions>

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

14:             </behaviorExtensions>

15:         </extensions>

16:         <services>

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

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

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

20:                 <host>

21:                     <baseAddresses>

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

23:                     </baseAddresses>

24:                 </host>

25:             </service>

26:         </services>

27:     </system.serviceModel>

28: </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：

 

 

 





作者：Artech
出处：http://artech.cnblogs.com
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