真实代理(RealProxy)在WCF中的运用
在WCF中,当我们在调用服务端的方法时,一般有两点需要考虑:1、捕获服务端的异常信息,记录日志;2、及时关闭会话信道,当调用超时或调用失败时及时中断会话信道。我们一般会像下面这样处理(以CalculatorService为例):
using (ChannelFactory<ICalculatorService> channelFactory = new ChannelFactory<ICalculatorService>("CalculatorService")) { ICalculatorService proxy = channelFactory.CreateChannel(); var commObj = proxy as ICommunicationObject; try { Console.WriteLine("x + y = {2} when x = {0} and y = {1}", 1, 2, proxy.Add(1, 2)); commObj.Close(); } catch (CommunicationException) { commObj.Abort(); } catch (TimeoutException) { commObj.Abort(); } catch (Exception) { //TODO:记录异常到日志 commObj.Abort(); throw; } }
以上这种处理方式完全可以满足我们的需要,但存在一个问题,每次调用服务端的方法时都需要手工加上这些异常捕获代码,如果服务有很多方法时,这样势必会存在大量功能重复的代码,可复用性很差。我们可以借鉴一下AOP的思想,具体来说就是对服务端方法调用进行拦截。对于.Net应用来说,自定义RealProxy是实现方法调用拦截最简单的一种方式。下面是一个自定义RealProxy的例子:
public class CalculatorServiceRealProxy : RealProxy { public CalculatorServiceRealProxy():base(typeof(ICalculatorService)){} public override IMessage Invoke(IMessage msg) { IMethodReturnMessage methodReturn = null; IMethodCallMessage methodCall = (IMethodCallMessage)msg; var client = new ChannelFactory<ICalculatorService>("CalculatorService"); var channel = client.CreateChannel(); try { object[] copiedArgs = Array.CreateInstance(typeof(object), methodCall.Args.Length) as object[]; methodCall.Args.CopyTo(copiedArgs, 0); object returnValue = methodCall.MethodBase.Invoke(channel, copiedArgs); methodReturn = new ReturnMessage(returnValue, copiedArgs, copiedArgs.Length, methodCall.LogicalCallContext, methodCall); //TODO:Write log } catch (Exception ex) { var exception = ex; if (ex.InnerException != null) exception = ex.InnerException; methodReturn = new ReturnMessage(exception, methodCall); } finally { var commObj = channel as ICommunicationObject; if (commObj != null) { try { commObj.Close(); } catch (CommunicationException) { commObj.Abort(); } catch (TimeoutException) { commObj.Abort(); } catch (Exception) { commObj.Abort(); //TODO:Logging exception throw; } } } return methodReturn; } }
方法调用:
static void Main(string[] args) { ICalculatorService proxy = (ICalculatorService)new CalculatorServiceRealProxy().GetTransparentProxy(); Console.WriteLine("x + y = {2} when x = {0} and y = {1}", 1, 2, proxy.Add(1, 2)); Console.WriteLine("x - y = {2} when x = {0} and y = {1}", 1, 2, proxy.Subtract(1, 2)); Console.WriteLine("x * y = {2} when x = {0} and y = {1}", 1, 2, proxy.Multiply(1, 2)); Console.WriteLine("x / y = {2} when x = {0} and y = {1}", 1, 2, proxy.Divide(1, 2)); Console.ReadKey(); }
通过自定义的RealProxy创建TransparentProxy供客户端代码调用,对于通过TransparentProxy的每一次调用,都会被RealProxy接管,这样我们就可以在RealProxy中加入异常捕获、记录日志等非业务逻辑代码,这些代码在每次调用服务端方法时都会被调用。
源代码下载 (工程ConsoleHosting为服务端,工程Client3为客户端)
作者:陈 锋
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