public class HomeController : Controller { private IHttpClientFactory _httpClientFactory; private readonly ILogger<HomeController> _logger; public HomeController(ILogger<HomeController> logger, IHttpClientFactory httpClientFactory) { _logger = logger; _httpClientFactory = httpClientFactory; } }
在Action中挪用HttpClient要通过利用IHttpClientFactory建设HttpClient，应该挪用CreateClient要领。一旦HttpClient实例可用，就可以在HomeController类的index要领中利用以下代码来挪用ValuesController类的Get要领。
public async Task<IActionResult> Index() { HttpClient httpClient = _httpClientFactory.CreateClient(); httpClient.BaseAddress = new Uri("http://localhost:1810/"); var response = await httpClient.GetAsync("/api/values"); string str = await response.Content.ReadAsStringAsync(); List<string> data = JsonSerializer.Deserialize<List<string>>(str); return View(data); }
利用IHttpClientFactory在ASP.NET Core中建设和打点HttpClient实例有几种要领可以在应用措施中利用IHttpClientFactory。这包罗直接利用IHttpClientFactory、利用定名client和范例client。
根基的或一般的利用模式，即直接利用IHttpClientFactory—在前面的小节中已经接头过了。请参考“注册一个IHttpClientFactory实例”一节，该节接头了如何注册HttpClient实例。
假如你想利用差异设置的HttpClient实例，以下是一个不错的选择。下面的代码片断说明白如何建设。
services.AddHttpClient("github", c => { c.BaseAddress = new Uri("https://api.github.com/"); c.DefaultRequestHeaders.Add("Accept", "application/vnd.github.v3+json"); c.DefaultRequestHeaders.Add("User-Agent", "This is a test user agent"); });
第二种要领是利用包装了HttpClient实例的自界说类，该自界说类封装了通过HTTP协议挪用所有终结点的逻辑。下面的代码片断说明白如何界说自界说HttpClient类。
public class ProductService : IProductService { private IHttpClientFactory _httpClientFactory; private readonly HttpClient _httpClient; private readonly string _baseUrl = "http://localhost:1810/"; public ProductService(HttpClient httpClient) { _httpClient = httpClient; } public async Task<Catalog> GetAllProducts() { _httpClient = _httpClientFactory.CreateClient(); _httpClient.BaseAddress = new Uri(_baseUrl); var uri = "/api/products"; var result = await _httpClient.GetStringAsync(uri); return JsonConvert.DeserializeObject<Product>(result); } }
通过以下代码注册自界说的client：
services.AddHttpClient<IProductService, ProductService>();
将MessageHandler添加到定名管道中MessageHandler是扩展自HttpMessageHandler类，它可以接管HTTP请求并返回HTTP响应。假如你想构建本身的MessageHandler，你应该建设一个担任DelegatingHandler的类。
你可以将HttpMessageHandler添加到请求处理惩罚管道中。可以在Startup类的ConfigureServices要领中利用以下代码将HttpMessageHandler添加到管道中。
public void ConfigureServices(IServiceCollection services) { services.AddHttpClient("github", c => { c.BaseAddress = new Uri("https://api.github.com/"); }) .AddHttpMessageHandler<DemoHandler>(); services.AddTransient<DemoHandler>(); }
IHttpClientFactory是一个自.net Core 2.1以来就可用的工场类。假如你利用IHttpClientFactory来建设HttpClient实例，那么底层HttpClientMessagehandler实例的池化和生命周期将自动打点。IHttpClientFactory还认真处理惩罚一些常见问题，好比日志记录。
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