eShopOnContainers学习系列（三）：RabbitMQ消息总线实践

今天研究了下eShopOnContainers里的RabbitMQ的使用，在项目里是以封装成消息总线的方式使用的，但是仍然是以其发布、订阅两个方法作为基础封装的，我们今天就来实际使用一下。

为了简单起见，就在同一个API项目里实现发布订阅。

新建API项目 RabbitMQ_Bus_Test ，类库 EventBus、EventBusRabbitMQ，这两个类库中将会实现消息总线最主要的方法、发布订阅。

在EventBus中新增消息事件类：IntegrationEvent，这个类在事件里是作为一个消息父类，所有的消息类都需要继承这个类，在实际项目里按需修改。

public class IntegrationEvent
    {
        public IntegrationEvent()
        {
            Id = Guid.NewGuid();
            CreationDate = DateTime.UtcNow;
        }

        [JsonConstructor]
        public IntegrationEvent(Guid id, DateTime createDate)
        {
            Id = id;
            CreationDate = createDate;
        }

        [JsonProperty]
        public Guid Id { get; private set; }

        [JsonProperty]
        public DateTime CreationDate { get; private set; }
    }

新增泛型接口类：IIntegrationEventHandler.cs，通过消息队列发送的消息需要有处理程序，而这个接口则是作为一个约束类存在，所有的处理程序都需要继承这个泛型接口类：

    public interface IIntegrationEventHandler<in TIntegrationEvent> : IIntegrationEventHandler
            where TIntegrationEvent : IntegrationEvent
    {
        Task Handle(TIntegrationEvent @event);
    }

    public interface IIntegrationEventHandler
    {
    }

新增事件订阅管理接口：IEventBusSubscriptionsManager，从类名就可以看出这个是专门用来管理消息处理方法的，我们这里主要看AddSubscription这个订阅方法，它的作用是绑定消息类和消息处理程序，即哪一个消息被哪一个方法消费，当然这里有两个约束，消息类需要继承IntegrationEvent，处理类需要继承IIntegrationEventHandler：

public interface IEventBusSubscriptionsManager
    {
        bool IsEmpty { get; }
        event EventHandler<string> OnEventRemoved;
        void AddDynamicSubscription<TH>(string eventName)
            where TH : IDynamicIntegrationEventHandler;

        void AddSubscription<T, TH>()
           where T : IntegrationEvent
           where TH : IIntegrationEventHandler<T>;

        void RemoveSubscription<T, TH>()
            where TH : IIntegrationEventHandler<T>
            where T : IntegrationEvent;

        void RemoveDynamicSubscription<TH>(string eventName)
            where TH : IDynamicIntegrationEventHandler;

        bool HasSubscriptionsForEvent<T>() where T : IntegrationEvent;
        bool HasSubscriptionsForEvent(string eventName);
        Type GetEventTypeByName(string eventName);
        void Clear();
        IEnumerable<SubscriptionInfo> GetHandlersForEvent<T>() where T : IntegrationEvent;
        IEnumerable<SubscriptionInfo> GetHandlersForEvent(string eventName);
        string GetEventKey<T>();
    }

接着新增它的实现类InMemoryEventBusSubscriptionsManager.cs，从类名可以看出订阅的管理都是在内存中处理的，在生产项目里我们可以使用Redis来进行存储：

public partial class InMemoryEventBusSubscriptionsManager: IEventBusSubscriptionsManager
    {
        private readonly Dictionary<string, List<SubscriptionInfo>> _handlers;
        private readonly List<Type> _eventTypes;

        public event EventHandler<string> OnEventRemoved;

        public InMemoryEventBusSubscriptionsManager()
        {
            _handlers = new Dictionary<string, List<SubscriptionInfo>>();
            _eventTypes = new List<Type>();
        }

        public bool IsEmpty => !_handlers.Keys.Any();
        public void Clear() => _handlers.Clear();

        public bool HasSubscriptionsForEvent(string eventName) => _handlers.ContainsKey(eventName);

        public void AddDynamicSubscription<TH>(string eventName)
            where TH : IDynamicIntegrationEventHandler
        {
            DoAddSubscription(typeof(TH), eventName, isDynamic: true);
        }

        public void AddSubscription<T,TH>()
            where T:IntegrationEvent
            where TH:IIntegrationEventHandler<T>
        {
            var eventName = GetEventKey<T>();

            DoAddSubscription(typeof(TH), eventName, isDynamic: false);

            if(!_eventTypes.Contains(typeof(T)))
            {
                _eventTypes.Add(typeof(T));
            }
        }

        public void DoAddSubscription(Type handlerType,string eventName,bool isDynamic)
        {
            if(!HasSubscriptionsForEvent(eventName))
            {
                _handlers.Add(eventName, new List<SubscriptionInfo>());
            }

            if(_handlers[eventName].Any(s=>s.HandlerType==handlerType))
            {
                throw new ArgumentException($"Handler Type {handlerType.Name} already registered for '{eventName}'", nameof(handlerType));
            }

            if(isDynamic)
            {
                _handlers[eventName].Add(SubscriptionInfo.Dynamic(handlerType));
            }
            else
            {
                _handlers[eventName].Add(SubscriptionInfo.Typed(handlerType));
            }
        }

        public void RemoveDynamicSubscription<TH>(string eventName)
            where TH: IDynamicIntegrationEventHandler
        {
            var handlerToRemove = FindDynamicSubscriptionToRemove<TH>(eventName);
            
        }

        private SubscriptionInfo FindDynamicSubscriptionToRemove<TH>(string eventName)
            where TH:IDynamicIntegrationEventHandler
        {
            return DoFindSubscriptionToRemove(eventName, typeof(TH));
        }


        private SubscriptionInfo DoFindSubscriptionToRemove(string eventName,Type handlerType)
        {
            if(!HasSubscriptionsForEvent(eventName))
            {
                return null;
            }

            return _handlers[eventName].SingleOrDefault(s => s.HandlerType == handlerType);
        }

        public void DoRemoveHandler(string eventName, SubscriptionInfo subsToRemove)
        {
            if(subsToRemove!=null)
            {
                _handlers[eventName].Remove(subsToRemove);
                if(!_handlers[eventName].Any())
                {
                    _handlers.Remove(eventName);
                    var eventType = _eventTypes.SingleOrDefault(e => e.Name == eventName);
                    if(eventType!=null)
                    {
                        _eventTypes.Remove(eventType);
                    }
                    RaiseOnEventRemoved(eventName);
                }
            }
        }

        public void RaiseOnEventRemoved(string eventName)
        {
            var handler = OnEventRemoved;
            if(handler!=null)
            {
                OnEventRemoved(this, eventName);
            }
        }

        public void RemoveSubscription<T, TH>()
            where T : IntegrationEvent
            where TH : IIntegrationEventHandler<T>
        {
            var handlerToRemove = FindSubscriptionToRemove<T, TH>();
            var eventName = GetEventKey<T>();
            DoRemoveHandler(eventName, handlerToRemove);
        }

        private SubscriptionInfo FindSubscriptionToRemove<T,TH>()
            where T:IntegrationEvent
            where TH:IIntegrationEventHandler<T>
        {
            var eventName = GetEventKey<T>();
            return DoFindSubscriptionToRemove(eventName, typeof(TH));
        }

        public Type GetEventTypeByName(string eventName) => _eventTypes.SingleOrDefault(t => t.Name == eventName);

        public IEnumerable<SubscriptionInfo> GetHandlersForEvent<T>() where T : IntegrationEvent
        {
            var key = GetEventKey<T>();
            return GetHandlersForEvent(key);
        }

        public IEnumerable<SubscriptionInfo> GetHandlersForEvent(string eventName) => _handlers[eventName];

        public string GetEventKey<T>()
        {
            return typeof(T).Name;
        }

        public bool HasSubscriptionsForEvent<T>() where T : IntegrationEvent
        {
            var key = GetEventKey<T>();
            return HasSubscriptionsForEvent(key);
        }
    }

这个实现类里有许多关于订阅事件的处理方法，我们本次需要关注的有两个地方，这里使用字典Dictionary<string, List<SubscriptionInfo>>存储消息类和消息处理类，这里有个事件资源类订阅信息类，存储两个属性，一个是否是动态的，另一个是处理程序类型：

public class SubscriptionInfo
    {
        public bool IsDynamic { get; }
        public Type HandlerType { get; }

        private SubscriptionInfo(bool isDynamic, Type handlerType)
        {
            IsDynamic = isDynamic;
            HandlerType = handlerType;
        }

        public static SubscriptionInfo Dynamic(Type handlerType)
        {
            return new SubscriptionInfo(true, handlerType);
        }

        public static SubscriptionInfo Typed(Type handlerType)
        {
            return new SubscriptionInfo(false, handlerType);
        }
    }

简单描述一下消息的处理流程，在程序初次加载时会将消息类和对应的处理类进行绑定，当消息发送的时候从根据发送的消息类从字典里查找对应的处理类，通过反射进行加载调用。

OK，关于消息资源方面的方法就这些，下面我们看下关于RabbitMQ的封装，新增事件总线接口，这里面有两个最重要的方法，发布和订阅：

public interface IEventBus
    {
        void Publish(IntegrationEvent @event);

        void Subscribe<T, TH>()
            where T : IntegrationEvent
            where TH : IIntegrationEventHandler<T>;

        void SubscribeDynamic<TH>(string eventName)
            where TH : IDynamicIntegrationEventHandler;

        void UnsubscribeDynamic<TH>(string eventName)
            where TH : IDynamicIntegrationEventHandler;

        void Unsubscribe<T, TH>()
            where TH : IIntegrationEventHandler<T>
            where T : IntegrationEvent;
    }

看一下它的实现类EventBusRabbitMQ.cs，这里我们只看最重要的两个方法Publish和Subscribe：

public class EventBusRabbitMQ : IEventBus, IDisposable
    {
        const string BROKER_NAME = "eshop_event_bus";

        private readonly IRabbitMQPersistentConnection _persistentConnection;
        private readonly ILogger<EventBusRabbitMQ> _logger;
        private readonly IEventBusSubscriptionsManager _subsManager;
        private readonly ILifetimeScope _autofac;
        private readonly string AUTOFAC_SCOPE_NAME = "eshop_event_bus";
        private readonly int _retryCount;

        private IModel _consumerChannel;
        private string _queueName;


        public EventBusRabbitMQ(IRabbitMQPersistentConnection persistentConnection, ILogger<EventBusRabbitMQ> logger,
    ILifetimeScope autofac, IEventBusSubscriptionsManager subsManager, string queueName = null, int retryCount = 5)
        {
            _persistentConnection = persistentConnection ?? throw new ArgumentNullException(nameof(persistentConnection));
            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
            _subsManager = subsManager ?? new InMemoryEventBusSubscriptionsManager();
            _queueName = queueName;
            _consumerChannel = CreateConsumerChannel();
            _autofac = autofac;
            _retryCount = retryCount;
            _subsManager.OnEventRemoved += SubsManager_OnEventRemoved;
        }

        private void SubsManager_OnEventRemoved(object sender, string eventName)
        {
            if (!_persistentConnection.IsConnected)
            {
                _persistentConnection.TryConnect();
            }

            using (var channel = _persistentConnection.CreateModel())
            {
                channel.QueueUnbind(queue: _queueName, exchange: BROKER_NAME, routingKey: eventName);

                if (_subsManager.IsEmpty)
                {
                    _queueName = string.Empty;
                    _consumerChannel.Close();
                }
            }
        }

        public void Publish(IntegrationEvent @event)
        {
            if (!_persistentConnection.IsConnected)
            {
                _persistentConnection.TryConnect();
            }

            var policy = RetryPolicy.Handle<BrokerUnreachableException>()
                .Or<SocketException>()
                .WaitAndRetry(_retryCount, retryAttempt => TimeSpan.FromSeconds(Math.Pow(2, retryAttempt)), (ex, time) =>
                {
                    _logger.LogWarning(ex.ToString());
                });

            using (var channel = _persistentConnection.CreateModel())
            {
                var eventName = @event.GetType()
                    .Name;

                channel.ExchangeDeclare(exchange: BROKER_NAME, type: "direct");

                var message = JsonConvert.SerializeObject(@event);
                var body = Encoding.UTF8.GetBytes(message);

                try
                {
                    policy.Execute(() =>
                    {
                        var properties = channel.CreateBasicProperties();
                        properties.DeliveryMode = 2; // persistent
                        channel.BasicPublish(exchange: BROKER_NAME, routingKey: eventName, mandatory: false, basicProperties: properties, body: body);
                    });
                }
                catch(Exception ex)
                {
                    Console.WriteLine(ex.Message);
                }
            }
        }

        /// <summary>
        /// 订阅动态
        /// </summary>
        public void SubscribeDynamic<TH>(string eventName)
    where TH : IDynamicIntegrationEventHandler
        {
            DoInternalSubscription(eventName);
            _subsManager.AddDynamicSubscription<TH>(eventName);
        }


        /// <summary>
        /// 订阅
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <typeparam name="TH"></typeparam>
        public void Subscribe<T, TH>()
            where T : IntegrationEvent
            where TH : IIntegrationEventHandler<T>
        {
            var eventName = _subsManager.GetEventKey<T>();
            DoInternalSubscription(eventName);
            _subsManager.AddSubscription<T, TH>();
        }

       /// <summary>
        /// 进行内部订阅
        /// </summary>
        /// <param name="eventName"></param>
        private void DoInternalSubscription(string eventName)
        {
            var containsKey = _subsManager.HasSubscriptionsForEvent(eventName);
            if(!containsKey)
            {
                if(!_persistentConnection.IsConnected)
                {
                    _persistentConnection.TryConnect();
                }

                using (var channel = _persistentConnection.CreateModel())
                {
                    channel.QueueBind(queue: _queueName, exchange: BROKER_NAME, routingKey: eventName);
                }
            }
        }

        /// <summary>
        /// 取消订阅
        /// </summary>
        public void Unsubscribe<T,TH>()
            where TH:IIntegrationEventHandler<T>
            where T:IntegrationEvent
        {
            _subsManager.RemoveSubscription<T, TH>();
        }

        /// <summary>
        /// 取消订阅动态
        /// </summary>
        public void UnsubscribeDynamic<TH>(string eventName)
    where TH : IDynamicIntegrationEventHandler
        {
            _subsManager.RemoveDynamicSubscription<TH>(eventName);
        }

        /// <summary>
        /// 释放资源
        /// </summary>
        public void Dispose()
        {
            if(_consumerChannel!=null)
            {
                _consumerChannel.Dispose();
            }

            _subsManager.Clear();
        }

          /// <summary>
        /// 创建消费者通道
        /// </summary>
        private IModel CreateConsumerChannel()
        {
            if (!_persistentConnection.IsConnected)
            {
                _persistentConnection.TryConnect();
            }

            var channel = _persistentConnection.CreateModel();

            channel.ExchangeDeclare(exchange: BROKER_NAME, type: "direct");

            channel.QueueDeclare(queue: _queueName
                , durable: true,
                exclusive: false,
                autoDelete: false,
                arguments: null);

            var consumer = new EventingBasicConsumer(channel);
            consumer.Received += async (model, ea) =>
            {
                var eventName = ea.RoutingKey;
                var message = Encoding.UTF8.GetString(ea.Body);

                await ProcessEvent(eventName, message);

                channel.BasicAck(ea.DeliveryTag, multiple: false);
            };
            channel.BasicConsume(queue: _queueName, autoAck: false, consumer: consumer);

            channel.CallbackException += (sender, ea) =>
            {
                _consumerChannel.Dispose();
                _consumerChannel = CreateConsumerChannel();
            };

            return channel;
        }

/// <summary>
        /// 流程事件
        /// </summary>
        private async Task ProcessEvent(string eventName, string message)
        {
            if (_subsManager.HasSubscriptionsForEvent(eventName))
            {
                using (var scope = _autofac.BeginLifetimeScope(AUTOFAC_SCOPE_NAME))
                {
                    var subscriptions = _subsManager.GetHandlersForEvent(eventName);
                    foreach (var subscription in subscriptions)
                    {
                        if (subscription.IsDynamic)
                        {
                            var handler = scope.ResolveOptional(subscription.HandlerType) as IDynamicIntegrationEventHandler;
                            if (handler == null) continue;
                            dynamic eventData = JObject.Parse(message);
                            await handler.Handle(eventData);
                        }
                        else
                        {
                            var handler = scope.ResolveOptional(subscription.HandlerType);
                            if (handler == null) continue;
                            var eventType = _subsManager.GetEventTypeByName(eventName);
                            var integrationEvent = JsonConvert.DeserializeObject(message, eventType);
                            var concreteType = typeof(IIntegrationEventHandler<>).MakeGenericType(eventType);
                            await (Task)concreteType.GetMethod("Handle").Invoke(handler, new object[] { integrationEvent });
                        }
                    }
                }
            }
        }
    }

首先是发布流程，当调用发布方法的时候首先会检查RabbitMQ是否连接，关于RabbitMQ连接的操作，项目里又封装了一个单独和接口和实现，下面贴一下代码：

    public interface IRabbitMQPersistentConnection:IDisposable
    {
        bool IsConnected { get; }
        bool TryConnect();
        IModel CreateModel();
    }

 public class DefaultRabbitMQPersistentConnection:IRabbitMQPersistentConnection
    {
        private readonly IConnectionFactory _connectionFactory;
        private readonly ILogger<DefaultRabbitMQPersistentConnection> _logger;
        private readonly int _retryCount;
        IConnection _connection;
        bool _disposed;

        object sync_root = new object();

        public DefaultRabbitMQPersistentConnection(IConnectionFactory connectionFactory,ILogger<DefaultRabbitMQPersistentConnection> logger,int retryCount=5)
        {
            _connectionFactory = connectionFactory ?? throw new ArgumentNullException(nameof(connectionFactory));
            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
            _retryCount = retryCount;
        }

        public bool IsConnected
        {
            get
            {
                return _connection != null && _connection.IsOpen && !_disposed;
            }
        }

        public IModel CreateModel()
        {
            if(!IsConnected)
            {
                throw new InvalidOperationException("No RabbitMQ connections are available to perform this action");
            }

            return _connection.CreateModel();
        }


        public void Dispose()
        {
            if (_disposed) return;

            _disposed = true;

            try
            {
                _connection.Dispose();
            }
            catch(IOException ex)
            {
                _logger.LogCritical(ex.ToString());
            }
        }


        public bool TryConnect()
        {
            _logger.LogInformation("RabbitMQ Client is trying to connect");

            lock(sync_root)
            {
                var policy = RetryPolicy.Handle<SocketException>()
                    .Or<BrokerUnreachableException>()
                    .WaitAndRetry(_retryCount, retryAttempt => TimeSpan.FromSeconds(Math.Pow(2, retryAttempt)), (ex, time) =>
                    {
                        _logger.LogWarning(ex.ToString());
                    });

                policy.Execute(() =>
                {
                    _connection = _connectionFactory
                          .CreateConnection();
                });

                if(IsConnected)
                {
                    _connection.ConnectionShutdown += OnConnectionShutdown;
                    _connection.CallbackException += OnCallbackException;
                    _connection.ConnectionBlocked += OnConnectionBlocked;

                    _logger.LogInformation($"RabbitMQ persistent connection acquired a connection {_connection.Endpoint.HostName} and is subscribed to failure events");

                    return true;
                }
                else
                {
                    _logger.LogCritical("FATAL ERROR: RabbitMQ connections could not be created and opened");

                    return false;
                }
            }
        }


        private void OnConnectionBlocked(object sender, ConnectionBlockedEventArgs e)
        {
            if (_disposed) return;

            _logger.LogWarning("A RabbitMQ connection is shutdown. Trying to re-connect...");

            TryConnect();
        }

        void OnCallbackException(object sender, CallbackExceptionEventArgs e)
        {
            if (_disposed) return;

            _logger.LogWarning("A RabbitMQ connection throw exception. Trying to re-connect...");

            TryConnect();
        }

        void OnConnectionShutdown(object sender,ShutdownEventArgs reason)
        {
            if (_disposed) return;

            _logger.LogWarning("A RabbitMQ connection is on shutdown. Trying to re-connect...");

            TryConnect();
        }
    }

首在程序加载的时候会创建一个消费者通道，同时给通道的Received委托注册了一个消费方法，这个消费方法的关键点是调用了ProcessEvent方法，完成后就发送一个ack确认：

private IModel CreateConsumerChannel()
        {
            if (!_persistentConnection.IsConnected)
            {
                _persistentConnection.TryConnect();
            }

            var channel = _persistentConnection.CreateModel();

            channel.ExchangeDeclare(exchange: BROKER_NAME, type: "direct");

            channel.QueueDeclare(queue: _queueName
                , durable: true,
                exclusive: false,
                autoDelete: false,
                arguments: null);

            var consumer = new EventingBasicConsumer(channel);
            consumer.Received += async (model, ea) =>
            {
                var eventName = ea.RoutingKey;
                var message = Encoding.UTF8.GetString(ea.Body);

                await ProcessEvent(eventName, message);

                channel.BasicAck(ea.DeliveryTag, multiple: false);
            };
            channel.BasicConsume(queue: _queueName, autoAck: false, consumer: consumer);

            channel.CallbackException += (sender, ea) =>
            {
                _consumerChannel.Dispose();
                _consumerChannel = CreateConsumerChannel();
            };

            return channel;
        }

我们看一下ProcessEvent方法，这个方法是专门用来消费MQ的，前面我们看过，通过字典记录了每个消息类对应的消费类Handler，这个方法的逻辑就是从字典里根据消息类查找对应的消费Handler并通过反射调用：

private async Task ProcessEvent(string eventName, string message)
        {
            if (_subsManager.HasSubscriptionsForEvent(eventName))
            {
                using (var scope = _autofac.BeginLifetimeScope(AUTOFAC_SCOPE_NAME))
                {
                    var subscriptions = _subsManager.GetHandlersForEvent(eventName);
                    foreach (var subscription in subscriptions)
                    {
                        if (subscription.IsDynamic)
                        {
                            var handler = scope.ResolveOptional(subscription.HandlerType) as IDynamicIntegrationEventHandler;
                            if (handler == null) continue;
                            dynamic eventData = JObject.Parse(message);
                            await handler.Handle(eventData);
                        }
                        else
                        {
                            var handler = scope.ResolveOptional(subscription.HandlerType);
                            if (handler == null) continue;
                            var eventType = _subsManager.GetEventTypeByName(eventName);
                            var integrationEvent = JsonConvert.DeserializeObject(message, eventType);
                            var concreteType = typeof(IIntegrationEventHandler<>).MakeGenericType(eventType);
                            await (Task)concreteType.GetMethod("Handle").Invoke(handler, new object[] { integrationEvent });
                        }
                    }
                }
            }
        }

方法看起来一堆变量名有点乱，其实梳理一下就会发现很简单，方法需要传入一个消息类名eventName和消息内容message,首先会根据eventName判断字典里是注册了当前消息体，如果没有，则直接跳过，并返回ack确认，相当于丢弃该消息。如果字典里存在，则从字典中取出这些处理方法，通过反射加载调用。

OK，那问题来了，字典里的内容是什么时候存进去的呢，那就是再调用订阅方法的时候存进去的，这个订阅方法是在启动类里调用的，我们看一下：

        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            ConfigureEventBus(app);

            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseMvcWithDefaultRoute();
        }

        private void ConfigureEventBus(IApplicationBuilder app)
        {
            var eventBus = app.ApplicationServices.GetRequiredService<IEventBus>();
            eventBus.Subscribe<PublisherIntegrationEvent, OrderStatusChangedValidationIntegrationEventHandle>();
        }

这个是在Startup.cs的Configure方法里调用的，这里就是通过调用订阅方法Subscribe绑定消息类和处理类：

public void Subscribe<T, TH>()
            where T : IntegrationEvent
            where TH : IIntegrationEventHandler<T>
        {
            var eventName = _subsManager.GetEventKey<T>();
            DoInternalSubscription(eventName);
            _subsManager.AddSubscription<T, TH>();
        }

可以看到这里调用了两个方法，DoInternalSubscription方法是绑定routingKey到指定的交换器和队列：

private void DoInternalSubscription(string eventName)
        {
            var containsKey = _subsManager.HasSubscriptionsForEvent(eventName);
            if(!containsKey)
            {
                if(!_persistentConnection.IsConnected)
                {
                    _persistentConnection.TryConnect();
                }

                using (var channel = _persistentConnection.CreateModel())
                {
                    channel.QueueBind(queue: _queueName, exchange: BROKER_NAME, routingKey: eventName);
                }
            }
        }

而AddSubscription方法则是将消息类和处理类添加到字典中：

public void AddSubscription<T,TH>()
            where T:IntegrationEvent
            where TH:IIntegrationEventHandler<T>
        {
            var eventName = GetEventKey<T>();

            DoAddSubscription(typeof(TH), eventName, isDynamic: false);

            if(!_eventTypes.Contains(typeof(T)))
            {
                _eventTypes.Add(typeof(T));
            }
        }

public void DoAddSubscription(Type handlerType,string eventName,bool isDynamic)
        {
            if(!HasSubscriptionsForEvent(eventName))
            {
                _handlers.Add(eventName, new List<SubscriptionInfo>());
            }

            if(_handlers[eventName].Any(s=>s.HandlerType==handlerType))
            {
                throw new ArgumentException($"Handler Type {handlerType.Name} already registered for '{eventName}'", nameof(handlerType));
            }

            if(isDynamic)
            {
                _handlers[eventName].Add(SubscriptionInfo.Dynamic(handlerType));
            }
            else
            {
                _handlers[eventName].Add(SubscriptionInfo.Typed(handlerType));
            }
        }

这里将消息类名和处理类的类型Type加到了字典里，后面会通过反射来进行调用。

OK，到这里主要的发布订阅方法就梳理完成了，写的有点乱，不过不要紧！！！后面有时间我再重新排版一下！！！！我们现在在新建的项目的试一下，我再ValueController里调用了发布方法，通过MQ发送一个订单号OrderId：

        [HttpGet]
        public IEnumerable<string> Get()
        {
            var @event = new PublisherIntegrationEvent(5);
            _eventBus.Publish(@event);
            _logger.LogError("发送MQ成功！");

            return new string[] { "value1", "value2" };
        }

消息体PublisherIntegrationEvent是这样的：

    public class PublisherIntegrationEvent : IntegrationEvent
    {
        public int OrderId { get; }

        public PublisherIntegrationEvent(int orderId) => OrderId = orderId;
    }

我在启动类里注册了对当前消息类的处理类OrderStatusChangedValidationIntegrationEventHandle：

public class OrderStatusChangedValidationIntegrationEventHandle: IIntegrationEventHandler<PublisherIntegrationEvent>
    {
        private readonly ILogger<OrderStatusChangedValidationIntegrationEventHandle> _logger = null;
        public OrderStatusChangedValidationIntegrationEventHandle(ILogger<OrderStatusChangedValidationIntegrationEventHandle> logger)
        {
            _logger = logger;
        }
        public async Task Handle(PublisherIntegrationEvent @event)
        {
            _logger.LogError("收到MQ" + @event.OrderId);
        }
    }

这里发布和订阅都在一个API里，直接启动：

OK，eShopOnContainers的梳理就到这里，接下来会在.NET Core商城系列里加入消息总线，但是会改一下，使用数据库+Redis存储消息的信息。

在我公司项目里现在也是使用RabbitMQ来实现服务与服务之间的异步通信，但是方式肯定和这里是不一样的，我们是根据RoutingKey与服务地址来绑定，通过windows服务处理消息的发布，根据RoutingKey查找对应的服务地址并进行调用，没有使用RabbitMQ的订阅方法，我们提供了一个web界面专门用来注册，这种方式还是挺好用的。

OK，大功告成，下面我会在商城项目里加入RabbitMQ的使用。