如何拦截.NET MVC3中当前actionresult的输出流？

public class CustomActionFilterAttribute : ActionFilterAttribute
{
    public override void OnActionExecuted(ActionExecutedContext filterContext)
    {
        base.OnActionExecuted(filterContext);
        var result = filterContext.Result as ContentResult;
        if (result != null)
        {
            // 处理输出流
            result.Content = "Hello World!";
        }
    }
}

[CustomActionFilter]
public class HomeController : Controller
{
    public ActionResult Index()
    {
        return Content("This is the original content.");
    }
}

public class CustomHttpModule : IHttpModule
{
    public void Init(HttpApplication context)
    {
        context.PreRequestHandlerExecute += OnPreRequestHandlerExecute;
    }

    private void OnPreRequestHandlerExecute(object sender, EventArgs e)
    {
        var application = (HttpApplication)sender;
        var response = application.Response;
        var filter = new MemoryStream();
        var sw = new StreamWriter(filter);
        var tw = new HtmlTextWriter(sw);
        response.Filter = filter;
        var original = response.Output;
        response.Output = tw;
        response.Flush();
        response.Output.Flush();
        filter.Position = 0;
        var reader = new StreamReader(filter);
        var html = reader.ReadToEnd();
        // 处理输出流
        response.Output.Write(html);
        response.Output.Flush();
    }

    public void Dispose()
    {
    }
}

 <modules>
    <add name="CustomHttpModule" type="YourNamespace.CustomHttpModule, YourAssemblyName"/>
  </modules>
</system.webServer>