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>
WCF后续之旅：
WCF后续之旅(1): WCF是如何通过Binding进行通信的
WCF后续之旅(2): 如何对Channel Layer进行扩展——创建自定义Channel
WCF后续之旅(3): WCF Service Mode Layer 的中枢—Dispatcher
WCF后续之旅(4)：WCF Extension Point 概览
WCF后续之旅(5): 通过WCF Extension实现Localization
WCF后续之旅(6): 通过WCF Extension实现Context信息的传递
WCF后续之旅(7)：通过WCF Extension实现和Enterprise Library Unity Container的集成
WCF后续之旅(8)：通过WCF Extension 实现与MS Enterprise Library Policy Injection Application Block 的集成
WCF后续之旅(9)：通过WCF的双向通信实现Session管理[Part I]
WCF后续之旅(9): 通过WCF双向通信实现Session管理[Part II]
WCF后续之旅(10): 通过WCF Extension实现以对象池的方式创建Service Instance
WCF后续之旅(11): 关于并发、回调的线程关联性（Thread Affinity）
WCF后续之旅(12): 线程关联性（Thread Affinity）对WCF并发访问的影响
WCF后续之旅(13): 创建一个简单的WCF SOAP Message拦截、转发工具[上篇]
WCF后续之旅(13)：创建一个简单的SOAP Message拦截、转发工具[下篇]
WCF后续之旅(14)：TCP端口共享
WCF后续之旅(15): 逻辑地址和物理地址
WCF后续之旅(16): 消息是如何分发到Endpoint的--消息筛选(Message Filter)
WCF后续之旅(17)：通过tcpTracer进行消息的路由
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