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）
