管道-过滤器模式

     如果项目中的功能要求需要经过一系列的处理。可以采用管道-过滤器模式组织这些处理。每一个处理就是一个过滤器。组织过滤器的管线对象就是管道。

　　管道模式适用于一系列确定/已知的步骤处理。

     原始的管道模型可以像下面这样：

 

 /// <summary>
    /// 处理消息
    /// </summary>
    public abstract class Context
    {
    }

    /// <summary>
    /// 过滤器
    /// </summary>
    /// <typeparam name="T"></typeparam>
    public interface IFilter<T> where T : Context
    {
        T Handle(T message);
    }

    /// <summary>
    /// 管道
    /// </summary>
    /// <typeparam name="T"></typeparam>
    public class PipeBase<T> where T : Context
    {
        protected IList<IFilter<T>> filter = new List<IFilter<T>>();
        public T Message { set; get; }


        public void ProcessHandle()
        {
            foreach (var s in filter)
            {
                s.Handle(Message);
            }
        }

        public void AddFilter( IFilter<T> f )
        {

        }

        public void RemoveFilter(IFilter<T> f)
        {

        }
    }

asp.net的请求事件  就是一个管道-过滤器模式，通过一系列的管道事件处理HttpContext,简要分析下ASP.NET的事件请求管道。

 事件管理：微软的事件管理是构建了一个 EventHandlerList 其实现如下：

public sealed class EventHandlerList : IDisposable
{
    // Fields
    private ListEntry head;
    private Component parent;

    // Methods
    [TargetedPatchingOptOut("Performance critical to inline this type of method across NGen image boundaries")]
    public EventHandlerList();
    [TargetedPatchingOptOut("Performance critical to inline this type of method across NGen image boundaries")]
    internal EventHandlerList(Component parent);
    public void AddHandler(object key, Delegate value);
    public void AddHandlers(EventHandlerList listToAddFrom);
    public void Dispose();
    private ListEntry Find(object key);
    public void RemoveHandler(object key, Delegate value);

    // Properties
    public Delegate this[object key] { get; set; }

    // Nested Types
    private sealed class ListEntry
    {
        // Fields
        internal Delegate handler;
        internal object key;
        internal EventHandlerList.ListEntry next;

        // Methods
        public ListEntry(object key, Delegate handler, EventHandlerList.ListEntry next);
    }
}

HttpAplication中通过采用

  public event EventHandler AcquireRequestState
        {
            add
            {
                this.AddSyncEventHookup(EventAcquireRequestState, value, RequestNotification.AcquireRequestState);
            }
            remove
            {
                this.RemoveSyncEventHookup(EventAcquireRequestState, value, RequestNotification.AcquireRequestState);
            }
        }

把事件加入到事件管理器中。

 

事件发现：

 

 private void RegisterEventSubscriptionsWithIIS(IntPtr appContext, HttpContext context, MethodInfo[] handlers)
        {
            RequestNotification notification;
            RequestNotification notification2;
            this.RegisterIntegratedEvent(appContext, "AspNetFilterModule", RequestNotification.LogRequest | RequestNotification.UpdateRequestCache, 0, string.Empty, string.Empty, true);
            this._moduleCollection = this.GetModuleCollection(appContext);
            if (handlers != null)
            {
                this.HookupEventHandlersForApplicationAndModules(handlers);
            }
            HttpApplicationFactory.EnsureAppStartCalledForIntegratedMode(context, this);
            this._currentModuleCollectionKey = "global.asax";
            try
            {
                this._hideRequestResponse = true;
                context.HideRequestResponse = true;
                this._context = context;
                this.Init();
            }
            catch (Exception exception)
            {
                this.RecordError(exception);
                Exception error = context.Error;
                if (error != null)
                {
                    throw error;
                }
            }
            finally
            {
                this._context = null;
                context.HideRequestResponse = false;
                this._hideRequestResponse = false;
            }
            this.ProcessEventSubscriptions(out notification, out notification2);
            this._appRequestNotifications |= notification;
            this._appPostNotifications |= notification2;
            for (int i = 0; i < this._moduleCollection.Count; i++)
            {
                this._currentModuleCollectionKey = this._moduleCollection.GetKey(i);
                IHttpModule module = this._moduleCollection.Get(i);
                ModuleConfigurationInfo info = _moduleConfigInfo[i];
                module.Init(this);
                this.ProcessEventSubscriptions(out notification, out notification2);
                if ((notification != 0) || (notification2 != 0))
                {
                    this.RegisterIntegratedEvent(appContext, info.Name, notification, notification2, info.Type, info.Precondition, false);
                }
            }
            this.RegisterIntegratedEvent(appContext, "ManagedPipelineHandler", RequestNotification.ExecuteRequestHandler | RequestNotification.MapRequestHandler, RequestNotification.EndRequest, string.Empty, string.Empty, false);
        }

  注意    this.RegisterIntegratedEvent(appContext, "AspNetFilterModule", RequestNotification.LogRequest | RequestNotification.UpdateRequestCache, 0, string.Empty, string.Empty, true);
      this.RegisterIntegratedEvent(appContext, info.Name, notification, notification2, info.Type, info.Precondition, false);
this.RegisterIntegratedEvent(appContext, "ManagedPipelineHandler", RequestNotification.ExecuteRequestHandler | RequestNotification.MapRequestHandler, RequestNotification.EndRequest, string.Empty, string.Empty, false);
this._currentModuleCollectionKey = "global.asax";  

上面就会把在GLOBAL ，Filter,httpmodule 里面定义的事件加入到事件管理列表中。