c# - 如何使用 autofac 注册类型化的 httpClient 服务？

Question

我正在创建 MVC Web 应用程序，它使用 .net core 2.2 使用单独的 HttpClient 调用 api s 调用每个 Controller (相同的 api)。

前任:

对于用户 Controller 操作:UserService (httpclient)

对于后期 Controller 操作: PostService (httpclient)

在 startup.cs 我使用 DI 作为:

services.AddHttpClient<IUserService, UserService>();
services.AddHttpClient<IPostService, PostService>();

在我的处理程序中:

public class CommandHandler : IRequestHandler<Command, BaseResponse>
{
    private readonly IUserService _userService;

    public CommandHandler(IUserService userService)
    {
        _userService = userService;
    }

    public Task<BaseResponse> Handle(Command request, CancellationToken cancellationToken)
    {
        throw new System.NotImplementedException();
    }
}

但是当调用命令处理程序时，我得到了这个错误:

None of the constructors found with 'Autofac.Core.Activators.Reflection.DefaultConstructorFinder' on type 'xxx.Application.Services.Users.UserService' can be invoked with the available services and parameters: Cannot resolve parameter 'System.Net.Http.HttpClient httpClient' of constructor 'Void .ctor(System.Net.Http.HttpClient, xxx.Application.Configurations.IApplicationConfigurations, Microsoft.Extensions.Logging.ILogger`1[xxx.Application.Services.Users.UserService])'.

但是我已经在 autofac 模块中注册了服务:

public class ServiceModule : Module
{
    protected override void Load(ContainerBuilder builder)
    {
        builder.RegisterAssemblyTypes(typeof(ServiceModule).Assembly)
                .Where(t => t.Namespace.StartsWith("xxx.Application.Services"))
                .AsImplementedInterfaces().InstancePerLifetimeScope();
    }
}

这是我的UserService类构造函数:

public UserService (HttpClient httpClient, IApplicationConfigurations applicationConfig, ILogger<UserService> logger)
{
    _httpClient = httpClient;
    _applicationConfig = applicationConfig;
    _logger = logger;

    _remoteServiceBaseUrl = $"{_applicationConfig.WebApiBaseUrl}";
}

我有两个问题:

上面的错误是什么意思？

为 api 中的不同 Controller 使用单独的 httpclients 是一种好习惯吗？

Answer 1

通过做

services.AddHttpClient<IUserService, UserService>();  

您将配置 native .net 核心依赖注入(inject)以注入(inject) HttpClient至UserService当一个 IUserService被要求。

然后你做

builder.RegisterAssemblyTypes(typeof(ServiceModule).Assembly)
       .Where(t => t.Namespace.StartsWith("xxx.Application.Services"))
       .AsImplementedInterfaces().InstancePerLifetimeScope();

这将删除 IUserService 的 native 依赖注入(inject)配置. IUserService现已注册 UserService没有任何HttpClient心里。

添加HttpClient的最简单方法将是这样注册它:

builder.Register(c => new HttpClient())
       .As<HttpClient>();

或者

services.AddHttpClient(); // register the .net core IHttpClientFactory 
builder.Register(c => c.Resolve<IHttpClientFactory>().CreateClient())
       .As<HttpClient>(); 

如果您想为特定服务配置 httpclient，您可以创建一个 autofac 模块，该模块添加如下参数:

public class HttpClientModule<TService> : Module
{
    public HttpClientModule(Action<HttpClient> clientConfigurator)
    {
        this._clientConfigurator = clientConfigurator;
    }

    private readonly Action<HttpClient> _clientConfigurator;

    protected override void AttachToComponentRegistration(IComponentRegistry componentRegistry, IComponentRegistration registration)
    {
        base.AttachToComponentRegistration(componentRegistry, registration);

        if (registration.Activator.LimitType == typeof(TService))
        {
            registration.Preparing += (sender, e) =>
            {
                e.Parameters = e.Parameters.Union(
                  new[]
                  {
                    new ResolvedParameter(
                        (p, i) => p.ParameterType == typeof(HttpClient),
                        (p, i) => {
                            HttpClient client = i.Resolve<IHttpClientFactory>().CreateClient();
                            this._clientConfigurator(client);
                            return client;
                        }
                    )
                  });
            };
        }
    }
}

然后

builder.RegisterModule(new HttpClientModule<UserService>(client =>
{
    client.BaseAddress = new Uri("https://api.XXX.com/");
    client.DefaultRequestHeaders.Add("Accept", "application/vnd.XXX.v3+json");
    client.DefaultRequestHeaders.Add("User-Agent", "HttpClientFactory-XXX");
}));