从 Static 工厂访问 ASP.NET 核心 DI 容器 Class

Question

我创建了一个 ASP.NET Core MVC/WebApi 网站，该网站有一个 RabbitMQ 订阅者，基于 James Still 的博客文章Real-World PubSub Messaging with RabbitMQ 。

在他的文章中，他使用 static class 来启动队列订阅者并为排队事件定义事件处理程序。 这个 static 方法然后通过 static 工厂 class 实例化事件处理程序类。

using RabbitMQ.Client;
using RabbitMQ.Client.Events;
using System;
using System.Text;

namespace NST.Web.MessageProcessing
{
    public static class MessageListener
    {
        private static IConnection _connection;
        private static IModel _channel;

        public static void Start(string hostName, string userName, string password, int port)
        {
            var factory = new ConnectionFactory
            {
                HostName = hostName,
                Port = port,
                UserName = userName,
                Password = password,
                VirtualHost = "/",
                AutomaticRecoveryEnabled = true,
                NetworkRecoveryInterval = TimeSpan.FromSeconds(15)
            };

            _connection = factory.CreateConnection();
            _channel = _connection.CreateModel();
            _channel.ExchangeDeclare(exchange: "myExchange", type: "direct", durable: true);

            var queueName = "myQueue";

            QueueDeclareOk ok = _channel.QueueDeclare(queueName, true, false, false, null);

            _channel.QueueBind(queue: queueName, exchange: "myExchange", routingKey: "myRoutingKey");

            var consumer = new EventingBasicConsumer(_channel);
            consumer.Received += ConsumerOnReceived;

            _channel.BasicConsume(queue: queueName, noAck: false, consumer: consumer);

        }

        public static void Stop()
        {
            _channel.Close(200, "Goodbye");
            _connection.Close();
        }

        private static void ConsumerOnReceived(object sender, BasicDeliverEventArgs ea)
        {
            // get the details from the event
            var body = ea.Body;
            var message = Encoding.UTF8.GetString(body);
            var messageType = "endpoint";  // hardcoding the message type while we dev...

            // instantiate the appropriate handler based on the message type
            IMessageProcessor processor = MessageHandlerFactory.Create(messageType);
            processor.Process(message);

            // Ack the event on the queue
            IBasicConsumer consumer = (IBasicConsumer)sender;
            consumer.Model.BasicAck(ea.DeliveryTag, false);
        }

    }
}

它工作得很好，直到我现在需要在我的消息处理器工厂中解析服务，而不是仅仅写入控制台。

using NST.Web.Services;
using System;

namespace NST.Web.MessageProcessing
{
    public static class MessageHandlerFactory
    {
        public static IMessageProcessor Create(string messageType)
        {
            switch (messageType.ToLower())
            {
                case "ipset":
                    // need to resolve IIpSetService here...
                    IIpSetService ipService = ???????

                    return new IpSetMessageProcessor(ipService);

                case "endpoint":
                    // need to resolve IEndpointService here...
                    IEndpointService epService = ???????

                    // create new message processor
                    return new EndpointMessageProcessor(epService);

                default:
                    throw new Exception("Unknown message type");
            }
        }
    }
}

有没有办法访问 ASP.NET 核心 IoC 容器来解决依赖关系？ 我真的不想手动启动整个依赖项堆栈:(

或者，有没有更好的方法从 ASP.NET 核心应用程序订阅 RabbitMQ？ 我找到了 RestBus但它没有针对 Core 1.x 进行更新

Answer 1

您可以避免使用静态类并始终结合使用依赖注入：

• 每当应用程序启动/停止时，使用IApplicationLifetime来启动/停止侦听器。
• 使用IServiceProvider创建消息处理器的实例。

首先，让我们将配置移动到可以从 appsettings.json 填充的自己的类中：

public class RabbitOptions
{
    public string HostName { get; set; }
    public string UserName { get; set; }
    public string Password { get; set; }
    public int Port { get; set; }
}

// In appsettings.json:
{
  "Rabbit": {
    "hostName": "192.168.99.100",
    "username": "guest",
    "password": "guest",
    "port": 5672
  }
}

接下来，将MessageHandlerFactory转换为接收IServiceProvider作为依赖项的非静态类。 它将使用服务提供者来解析消息处理器实例：

public class MessageHandlerFactory
{
    private readonly IServiceProvider services;
    public MessageHandlerFactory(IServiceProvider services)
    {
        this.services = services;
    }

    public IMessageProcessor Create(string messageType)
    {
        switch (messageType.ToLower())
        {
            case "ipset":
                return services.GetService<IpSetMessageProcessor>();                
            case "endpoint":
                return services.GetService<EndpointMessageProcessor>();
            default:
                throw new Exception("Unknown message type");
        }
    }
}

通过这种方式，您的消息处理器类可以在构造函数中接收它们需要的任何依赖项（只要您在Startup.ConfigureServices配置它们）。 例如，我将一个 ILogger 注入到我的一个示例处理器中：

public class IpSetMessageProcessor : IMessageProcessor
{
    private ILogger<IpSetMessageProcessor> logger;
    public IpSetMessageProcessor(ILogger<IpSetMessageProcessor> logger)
    {
        this.logger = logger;
    }

    public void Process(string message)
    {
        logger.LogInformation("Received message: {0}", message);
    }
}

现在将MessageListener转换为依赖于IOptions<RabbitOptions>和MessageHandlerFactory的非静态类。它与你原来的非常相似，我只是用选项依赖替换了 Start 方法的参数，处理程序工厂现在是一个依赖而不是静态类：

public class MessageListener
{
    private readonly RabbitOptions opts;
    private readonly MessageHandlerFactory handlerFactory;
    private IConnection _connection;
    private IModel _channel;

    public MessageListener(IOptions<RabbitOptions> opts, MessageHandlerFactory handlerFactory)
    {
        this.opts = opts.Value;
        this.handlerFactory = handlerFactory;
    }

    public void Start()
    {
        var factory = new ConnectionFactory
        {
            HostName = opts.HostName,
            Port = opts.Port,
            UserName = opts.UserName,
            Password = opts.Password,
            VirtualHost = "/",
            AutomaticRecoveryEnabled = true,
            NetworkRecoveryInterval = TimeSpan.FromSeconds(15)
        };

        _connection = factory.CreateConnection();
        _channel = _connection.CreateModel();
        _channel.ExchangeDeclare(exchange: "myExchange", type: "direct", durable: true);

        var queueName = "myQueue";

        QueueDeclareOk ok = _channel.QueueDeclare(queueName, true, false, false, null);

        _channel.QueueBind(queue: queueName, exchange: "myExchange", routingKey: "myRoutingKey");

        var consumer = new EventingBasicConsumer(_channel);
        consumer.Received += ConsumerOnReceived;

        _channel.BasicConsume(queue: queueName, noAck: false, consumer: consumer);

    }

    public void Stop()
    {
        _channel.Close(200, "Goodbye");
        _connection.Close();
    }

    private void ConsumerOnReceived(object sender, BasicDeliverEventArgs ea)
    {
        // get the details from the event
        var body = ea.Body;
        var message = Encoding.UTF8.GetString(body);
        var messageType = "endpoint";  // hardcoding the message type while we dev...
        //var messageType = Encoding.UTF8.GetString(ea.BasicProperties.Headers["message-type"] as byte[]);

        // instantiate the appropriate handler based on the message type
        IMessageProcessor processor = handlerFactory.Create(messageType);
        processor.Process(message);

        // Ack the event on the queue
        IBasicConsumer consumer = (IBasicConsumer)sender;
        consumer.Model.BasicAck(ea.DeliveryTag, false);
    }
}

几乎在那里，您将需要更新Startup.ConfigureServices方法，以便它了解您的服务和选项（如果需要，您可以为侦听器和处理程序工厂创建接口）：

public void ConfigureServices(IServiceCollection services)
{            
    // ...

    // Add RabbitMQ services
    services.Configure<RabbitOptions>(Configuration.GetSection("rabbit"));
    services.AddTransient<MessageListener>();
    services.AddTransient<MessageHandlerFactory>();
    services.AddTransient<IpSetMessageProcessor>();
    services.AddTransient<EndpointMessageProcessor>();
}

最后，更新Startup.Configure方法以获取额外的IApplicationLifetime参数并在ApplicationStarted / ApplicationStopped事件中启动/停止消息侦听器（尽管我不久前注意到使用 IISExpress 的 ApplicationStopping 事件存在一些问题，如本问题所示）：

public MessageListener MessageListener { get; private set; }
public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory, IApplicationLifetime appLifetime)
{
    appLifetime.ApplicationStarted.Register(() =>
    {
        MessageListener = app.ApplicationServices.GetService<MessageListener>();
        MessageListener.Start();
    });
    appLifetime.ApplicationStopping.Register(() =>
    {
        MessageListener.Stop();
    });

    // ...
}

Answer 2

尽管使用依赖注入是一个更好的解决方案，但在某些情况下你必须使用静态方法（比如在扩展方法中）。

对于这些情况，您可以向静态类添加静态属性并在 ConfigureServices 方法中对其进行初始化。

例如：

public static class EnumExtentions
{
    static public IStringLocalizerFactory StringLocalizerFactory { set; get; }

    public static string GetDisplayName(this Enum e)
    {
        var resourceManager = StringLocalizerFactory.Create(e.GetType());
        var key = e.ToString();
        var resourceDisplayName = resourceManager.GetString(key);

        return resourceDisplayName;
    }
}

并在您的 ConfigureServices 中：

EnumExtentions.StringLocalizerFactory = services.BuildServiceProvider().GetService<IStringLocalizerFactory>();

Answer 3

我知道我的回答晚了，但我想分享我是如何做到的。

首先：使用ServiceLocator是反模式，所以尽量不要使用它。 在我来说，我需要它来打电话MediatR我的DomainModel内实现DomainEvents逻辑。

但是，我必须找到一种方法来调用我的 DomainModel 中的静态类，以从 DI 获取某些已注册服务的实例。

所以我决定使用HttpContext来访问IServiceProvider但我需要从静态方法访问它而不在我的域模型中提及它。

让我们这样做：

1-我创建了一个接口来包装 IServiceProvider

public interface IServiceProviderProxy
{
    T GetService<T>();
    IEnumerable<T> GetServices<T>();
    object GetService(Type type);
    IEnumerable<object> GetServices(Type type);
}

2- 然后我创建了一个静态类作为我的 ServiceLocator 访问点

public static class ServiceLocator
{
    private static IServiceProviderProxy diProxy;

    public static IServiceProviderProxy ServiceProvider => diProxy ?? throw new Exception("You should Initialize the ServiceProvider before using it.");

    public static void Initialize(IServiceProviderProxy proxy)
    {
        diProxy = proxy;
    }
}

3- 我为IServiceProviderProxy创建了一个实现，它在内部使用IHttpContextAccessor

public class HttpContextServiceProviderProxy : IServiceProviderProxy
{
    private readonly IHttpContextAccessor contextAccessor;

    public HttpContextServiceProviderProxy(IHttpContextAccessor contextAccessor)
    {
        this.contextAccessor = contextAccessor;
    }

    public T GetService<T>()
    {
        return contextAccessor.HttpContext.RequestServices.GetService<T>();
    }

    public IEnumerable<T> GetServices<T>()
    {
        return contextAccessor.HttpContext.RequestServices.GetServices<T>();
    }

    public object GetService(Type type)
    {
        return contextAccessor.HttpContext.RequestServices.GetService(type);
    }

    public IEnumerable<object> GetServices(Type type)
    {
        return contextAccessor.HttpContext.RequestServices.GetServices(type);
    }
}

4- 我应该像这样在 DI 中注册IServiceProviderProxy

public void ConfigureServices(IServiceCollection services)
{
    services.AddHttpContextAccessor();
    services.AddSingleton<IServiceProviderProxy, HttpContextServiceProviderProxy>();
    .......
}

5- 最后一步是在应用程序启动时使用IServiceProviderProxy实例初始化ServiceLocator

public void Configure(IApplicationBuilder app, IHostingEnvironment env,IServiceProvider sp)
{
    ServiceLocator.Initialize(sp.GetService<IServiceProviderProxy>());
}

因此，现在您可以在您的 DomainModel 类“或和需要的地方”中调用 ServiceLocator 并解析您需要的依赖项。

public class FakeModel
{
    public FakeModel(Guid id, string value)
    {
        Id = id;
        Value = value;
    }

    public Guid Id { get; }
    public string Value { get; private set; }

    public async Task UpdateAsync(string value)
    {
        Value = value;
        var mediator = ServiceLocator.ServiceProvider.GetService<IMediator>();
        await mediator.Send(new FakeModelUpdated(this));
    }
}

Answer 4

对于你的情况，我的看法如下：

如果可能，我会将已解析的服务作为参数发送

public static IMessageProcessor Create(string messageType, IIpSetService ipService)
{
    //
}

否则使用寿命将很重要。

如果服务是单例，我只会设置对配置方法的依赖：

 // configure method
public IApplicationBuilder Configure(IApplicationBuilder app)
{
    var ipService = app.ApplicationServices.GetService<IIpSetService>();
    MessageHandlerFactory.IIpSetService = ipService;
}

// static class
public static IIpSetService IpSetService;

public static IMessageProcessor Create(string messageType)
{
    // use IpSetService
}

如果服务生命周期是范围的，我将使用 HttpContextAccessor：

//Startup.cs
public void ConfigureServices(IServiceCollection services)
{
    services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
}

public IApplicationBuilder Configure(IApplicationBuilder app)
{
    var httpContextAccessor= app.ApplicationServices.GetService<IHttpContextAccessor>();
    MessageHandlerFactory.HttpContextAccessor = httpContextAccessor;
}

// static class
public static IHttpContextAccessor HttpContextAccessor;

public static IMessageProcessor Create(string messageType)
{
    var ipSetService = HttpContextAccessor.HttpContext.RequestServices.GetService<IIpSetService>();
    // use it
}

Answer 5

这是 ServiceLocator 的一个很好的实现，它也使用 Scope。 所以甚至适用于 IHttpContextAccessor！

只需将此类复制到您的代码中即可。 然后注册ServiceLocator

 ServiceActivator.Configure(app.ApplicationServices);

重要说明：ServiceLocator 被视为反模式，因此如果您有任何其他选择，请不要使用它！！！！

Answer 6

关于Wahid Bitar的回答

惊人的。 对于 .Net Core 6，我在Program.cs上执行：

builder.Services.AddSingleton<IServiceProviderProxy, HttpContextServiceProviderProxy>();

ServiceLocator.Initialize(app.Services.GetService<IServiceProviderProxy>());

Answer 7

您可以在Configure获取服务参考：

app.UseMvc();
var myServiceRef = app.ApplicationServices.GetService<MyService>();

然后将它传递给 init 函数或在类上设置静态成员

当然，如其他答案中所述，依赖注入将是更好的解决方案......