Auditing Interceptor Example

auditinginterceptor.cs

using System;
using System.Linq;
using System.Reflection;
using Castle.Core;
using Castle.DynamicProxy;
using Castle.MicroKernel.Proxy;
using Castle.MicroKernel.Registration;
using Castle.Windsor;

namespace WindsorExamples
{

    [AttributeUsage(AttributeTargets.Method)]
    public class AuditAttribute : Attribute
    {
        public string Message { get; set; }

        public AuditAttribute(string message)
        {
            Message = message;
        }
    }

    public interface ICustomerService
    {
        void DeleteStaleCustomer();
    }

    public class CustomerService : ICustomerService
    {
        [Audit("Audit of delete customers which are stale")]
        public void DeleteStaleCustomer()
        {
            Console.WriteLine("Deleting stale customers");
        }
    }

    public class AuditInterceptor : IInterceptor
    {
        public void Intercept(IInvocation invocation)
        {

            var attribute = invocation.MethodInvocationTarget.GetCustomAttribute(typeof(AuditAttribute),false);
            if (attribute != null)
                Console.WriteLine(attribute.As<AuditAttribute>().Message);

            invocation.Proceed();
        }
    }

    public class AuditInterceptorSelector : IModelInterceptorsSelector
    {
        public bool HasInterceptors(ComponentModel model)
        {
            var result = model.Implementation.GetMethods(BindingFlags.Public | BindingFlags.Instance)
                .Any(method => method.GetCustomAttributes(false).Any(attribute=> attribute.GetType() == typeof (AuditAttribute)));
            return result;
        }

        public InterceptorReference[] SelectInterceptors(ComponentModel model, InterceptorReference[] interceptors)
        {
            return new[]
                       {
                           InterceptorReference.ForType<AuditInterceptor>()
                       };
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            var container = new WindsorContainer();
            container.Kernel.ProxyFactory.AddInterceptorSelector(new AuditInterceptorSelector());
            container.Register(Component.For<AuditInterceptor>());
            container.Register(Component.For<ICustomerService>().ImplementedBy<CustomerService>().LifeStyle.Singleton);

            var element = container.Resolve<ICustomerService>();
            element.DeleteStaleCustomer();

        }
    }

    public static class ExtensionMethods
    {
        public static T As<T>(this object o)
        {
            return (T)o;
        }
    }
}