Implementing Custom Castle Windsor Facilities

 

If you’ve been following my posts you would know that I love Castle Windsor.

One of the many useful features I have found is the Facility and I’m going to try and give a good example how you can make use of this.

In a recent post I showed how you can add Cross-Cutting concerns to your application by using Interceptors.

Now when configuring the Container you can explicitly configure each Interceptor per Service but when you have lot’s of components it can get pretty hard to maintain after a while and can also introduce subtle issues if someone forgets to configure it correctly.

 

Below is how you would configure your Container without using a Facility. On the last line we are specifying the Interceptor explicitly.

        public void Configure()
        {
            container = new WindsorContainer();

            container.Register(
                Component.For<CacheInterceptor>(),
                Component.For<ICacheProvider>()
                    .ImplementedBy<WebCacheProvider>().LifeStyle.Singleton,
                Component.For<ICatalogQueryService>()
                    .ImplementedBy<CatalogQueryService>()
                    .LifeStyle.Transient
                    .Interceptors(new InterceptorReference(typeof (CacheInterceptor))).Anywhere);
        }

Or the XML version

<?xml version="1.0" encoding="utf-8" ?>
<castle>
  <components>
    <component id="CacheInterceptor"
             service="MyApp.Aop.CacheInterceptor, MyApp"
             type="MyApp.Aop.CacheInterceptor, MyApp"
             lifestyle="transient">
    </component>
    <component id="ICatalogQueryService"
             service="MyApp.Services.ICatalogQueryService, MyApp"
             type="MyApp.Services.Impl.CatalogQueryService, MyApp"
             lifestyle="transient">
      <interceptors>
        <interceptor>${CacheInterceptor}</interceptor>
      </interceptors>
    </component>
    <component id="ICacheProvider"
             service="MyApp.Core.Cache.ICacheProvider, MyApp"
             type="MyApp.Core.Cache.Impl.WebCacheProvider, MyApp"
             lifestyle="transient">
    </component>
  </components>
</castle>

What would be nice would be to be able to specify the Interceptor on all Components automagically and Castle allows for this with Facilities. Below is an implementation which achieves the desired result.

   public class CacheInterceptionFacility : AbstractFacility
   {
       protected override void Init()
       {
           Kernel.ComponentRegistered += Kernel_ComponentRegistered;
       }

       private void Kernel_ComponentRegistered(string key, IHandler handler)
       {
           if (typeof(IMustBeCached).IsAssignableFrom(handler.ComponentModel.Implementation))
           {
               handler.ComponentModel.Interceptors
                   .Add(new InterceptorReference(typeof(CacheInterceptor)));
           }
       }
   }

All you have to do is Inherit from the Castle.MicroKernel.Facilities.AbstractFacility and then override the Init.

You’ll see that we use the Interface IMustBeCached to identify the Component to apply the Interceptor too.

Now in your Bootstrapper all you have to do is call AddFacility on the WindsorContainer and you’re good to go.

        public void Configure()
        {
            container = new WindsorContainer();

            container.Register(
                Component.For<CacheInterceptor>(),
                Component.For<ICacheProvider>()
                    .ImplementedBy<WebCacheProvider>().LifeStyle.Singleton,
                Component.For<ICatalogQueryService>()
                    .ImplementedBy<CatalogQueryService>().LifeStyle.Transient);

            container.AddFacility("CacheInterceptionFacility", new CacheInterceptionFacility()); 

        }

Or the XML version

<?xml version="1.0" encoding="utf-8" ?>
<castle>
  <facilities>
    <facility
      id="CacheInterceptionFacility"
      type="MyApp.Aop.CacheInterceptionFacility, MyApp">
    </facility>
  </facilities>
  <components>
    <component id="CacheInterceptor"
             service="MyApp.Aop.CacheInterceptor, MyApp"
             type="MyApp.Aop.CacheInterceptor, MyApp"
             lifestyle="transient">
    </component>
    <component id="ICatalogQueryService"
             service="MyApp.Services.ICatalogQueryService, MyApp"
             type="MyApp.Services.Impl.CatalogQueryService, MyApp"
             lifestyle="transient">
    </component>
    <component id="ICacheProvider"
             service="MyApp.Core.Cache.ICacheProvider, MyApp"
             type="MyApp.Core.Cache.Impl.WebCacheProvider, MyApp"
             lifestyle="transient">
    </component>
  </components>
</castle>

 

Aside from reducing the configuration overhead another benefit of using this approach is that in your Debug or Test Environments you can easily deploy without any Interceptors and only enable them in your Staging and Production environments.