我正在创建 MVC Web 应用程序，它使用 .net core 2.2 调用 api，使用单独的
HttpClient例如：
在
startup.csservices.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，我收到此错误：
没有找到任何构造函数 类型上的“Autofac.Core.Activators.Reflection.DefaultConstructorFinder” 'xxx.Application.Services.Users.UserService' 可以通过以下方式调用 可用的服务和参数：无法解析参数 构造函数“Void”的“System.Net.Http.HttpClient httpClient” .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
UserServicepublic UserService (HttpClient httpClient, IApplicationConfigurations applicationConfig, ILogger<UserService> logger)
{
_httpClient = httpClient;
_applicationConfig = applicationConfig;
_logger = logger;
_remoteServiceBaseUrl = $"{_applicationConfig.WebApiBaseUrl}";
}
我有两个问题：
通过做
services.AddHttpClient<IUserService, UserService>();
您将配置本机 .net core 依赖项注入，以便在请求
HttpClientUserServiceIUserService然后你就可以了
builder.RegisterAssemblyTypes(typeof(ServiceModule).Assembly)
.Where(t => t.Namespace.StartsWith("xxx.Application.Services"))
.AsImplementedInterfaces().InstancePerLifetimeScope();
这将删除
IUserServiceIUserServiceUserServiceHttpClient添加
HttpClientbuilder.Register(c => new HttpClient())
.As<HttpClient>();
或
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，其中添加如下参数：
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");
}));
Cyril 使用 Autofac 模块的实现效果非常好，但不幸的是与 Autofac 6.0+ 不兼容。
为了在 Autofac 6.0+ 中为特定服务配置
HttpClientpublic class HttpClientMiddleware<TService> : IResolveMiddleware
{
private readonly Action<HttpClient> _clientConfigurator;
public HttpClientMiddleware(Action<HttpClient> clientConfigurator)
{
_clientConfigurator = clientConfigurator;
}
public PipelinePhase Phase => PipelinePhase.ParameterSelection;
public void Execute(ResolveRequestContext context, Action<ResolveRequestContext> next)
{
if (context.Registration.Activator.LimitType == typeof(TService))
{
context.ChangeParameters(context.Parameters.Union(
new[]
{
new ResolvedParameter(
(p, _) => p.ParameterType == typeof(HttpClient),
(_, i) => {
var client = i.Resolve<IHttpClientFactory>().CreateClient();
_clientConfigurator(client);
return client;
}
)
}));
}
next(context);
}
}
然后可以利用中间件注册服务：
builder.RegisterType<UserService>()
.As<IUserService>()
.ConfigurePipeline(p =>
{
p.Use(new HttpClientMiddleware<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");
}));
});
您可以按照以下扩展方法向 httpclient 注册任何类型。
public static ContainerBuilder RegisterWithHttpClient<TInterface, TClass>(this ContainerBuilder builder, Action<IComponentContext, HttpClient> config)
where TClass: class
{
builder
.RegisterType<TClass>()
.AsSelf()
.As<TInterface>()
.WithParameter(new ResolvedParameter(
(info, context) => info.ParameterType.IsAssignableFrom(typeof(HttpClient)),
(info, context) =>
{
var httpClient = context.Resolve<IHttpClientFactory>().CreateClient();
config.Invoke(context, httpClient);
return httpClient;
}
))
.InstancePerLifetimeScope();
return builder;
}
并注册您的类型。
//in startup.cs or autofac module.
public void ConfigureContainer(ContainerBuilder container)
{
container.RegisterWithHttpClient<IEmailSender, MyEmailSender>((context, client) =>
{
var settings = context.Resolve<IOptionsSnapshot<EmailSenderSettings>>().Value;
client.BaseAddress = new Uri($"{settings.ApiBaseUrl.TrimEnd('/')}/");
client.Timeout = TimeSpan.FromSeconds(settings.TimeoutSeconds);
});
}
根据https://autofac.readthedocs.io/en/latest/integration/netcore.html#quick-start页面，最简单、最正确的方法是：
// Generate a ServiceCollection to directly add elements to.
var serviceCollection = new ServiceCollection();
// Add the HTTP Client as per the extension.
serviceCollection.AddHttpClient();
serviceCollection.AddHttpClient<IUserService, UserService>();
serviceCollection.AddHttpClient<IPostService, PostService>();
// Build the ContainerBuilder.
var containerBuilder = new ContainerBuilder();
// Populate the builder from the ServiceCollection.
containerBuilder.Populate(serviceCollection);
// Continue with the AutoFac registrations after this point.