.Net Core 1.1 HttpClient with DI

Question

以下是我正在使用的代码：

namespace MySite.Api
{
using System.Collections.Specialized;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Text;
using System.Threading.Tasks;
using Microsoft.Extensions.Configuration;
using Newtonsoft.Json;
using System;
using System.Net.Http.Headers;
using Microsoft.Extensions.Logging;
/// <summary>
/// API query execution helper
/// </summary>
public class ApiQuery : IApiQuery
{
/// <summary>
/// configuration reference
/// </summary>
private IConfiguration config;
private HmacAuthenticationUtils hmacUtils;
private readonly ILogger logger;
private static readonly HttpClient httpClient = new HttpClient();
private static readonly HttpClient httpClientHMAC = new HttpClient();
/// <summary>
/// Initializes a new instance of the <see cref="ApiQuery"/> class.
/// </summary>
/// <param name="inConfig">injected configuration</param>
public ApiQuery(IConfiguration inConfig, HmacAuthenticationUtils hmacUtils, ILoggerFactory loggerFactory)
{
this.config = inConfig;
this.hmacUtils = hmacUtils;
this.logger = loggerFactory.CreateLogger("perfLogger");
}
/// <summary>
/// HTTP verb post
/// </summary>
/// <param name="requestUrl">API url</param>
/// <param name="requestData">request data</param>
/// <returns>HTTP response message</returns>
public virtual async Task<string> Post(string requestUrl, object requestData, HttpClient client = null)
{
return await PostBypassCache(requestUrl, requestData, client);
}
/// <summary>
/// HTTP verb post, specifically to bypass cache
/// </summary>
/// <param name="requestUrl">API url</param>
/// <param name="requestData">request data</param>
/// <returns>HTTP response message</returns>
public async Task<string> PostBypassCache(string requestUrl, object requestData, HttpClient client = null)
{
DateTime perfStart = DateTime.Now;
string customerJson = string.Empty;
if (requestData is string)
{
customerJson = requestData.ToString();
}
else
{
customerJson = JsonConvert.SerializeObject(requestData);
}
////just some template output to test which I'm getting back.
string resultJson = "{ 'status':'No Content'}";
if (client == null)
{
client = httpClient;
}
var response = await httpClient.PostAsync(requestUrl, new StringContent(customerJson, Encoding.UTF8, "application/json"));
if (response.StatusCode == HttpStatusCode.OK)
{
resultJson = await response.Content.ReadAsStringAsync();
}
logger.LogInformation("response time: " + (DateTime.Now - perfStart).TotalMilliseconds + "ms. Resource:" + requestUrl);
return resultJson;
}
/// <summary>
/// HTTP verb post
/// </summary>
/// <param name="requestUrl">API url</param>
/// <param name="requestData">request data</param>
/// <param name="headerset">header data</param>
/// <returns>string data</returns>
public async Task<string> PostHmacAuth(string requestUrl, string requestData)
{
var httpRequest = new HttpRequestMessage(HttpMethod.Post, requestUrl);
httpRequest.Content = new StringContent(requestData, Encoding.UTF8, "application/json");
var signature = await Utils.GenerateAuthenticationString(httpRequest);
httpClientHMAC.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(HmacAuthenticationUtils.HmacHeader, signature);
return await PostBypassCache(requestUrl, requestData, httpClientHMAC);
}
}
}

在Startup.cs中，我将其注入

services.AddTransient<IApiQuery, ApiQuery>();

我最近做了这些更改，因为之前代码实际上是在每个方法中实例化httpClient，即。，var client=新HttpClient((；

在某些地方，情况是这样的：使用(var client=new HttpClient(((｛｝

我认为由于这样的代码，appPool显示了错误，导致我的IIS挂起，只有重新启动appPool才能解决这个问题。当我阅读了许多其他文章时，我认为这是一个问题。我无法得出的结论是，将ApiQuery服务作为单例本身注入是否是个好主意。注射它会更好吗？

由于我现在将IApiQuery作为一种临时服务注入到每个业务服务中，这是个好主意吗？任何想法

Answer 1

HttpClient应该是单例作用域。您的计算机上可用的连接数量有限，由于HttpClient保留了它创建的连接，因此让多个实例四处浮动可能会迅速耗尽您的连接池。

从ASP.NET Core 2.1开始，就有了IHttpClientFactory，它提供了一种简单且可重用的方法来注入范围正确的HttpClient实例。但是，由于您使用的是1.1，因此您无法使用它。建议的路径是将您的项目升级到2.1。ASP.NET Core的1.X行简直就是垃圾。尽管它是官方发布的，但还没有准备好投入生产使用。

如果您坚持使用1.1，那么您将需要实现自己的重用HttpClient实例的方法。最简单的方法是使用"访问器"类，然后可以使用这些类将不同的HttpClient注入到不同的对象中。例如：

public class ApiHttpClientAccessor : IDisposable
{
public ApiHttpClientAccessor()
{
HttpClient = new HttpClient
{
BaseAddress = new Uri("https://foo.com")
};
}
public HttpClient HttpClient { get; }
private bool _disposed;
public virtual void Dispose(bool disposing)
{
if (disposing && !_disposed)
{
HttpClient.Dispose();
}
_disposed = true;
}
public bool Dispose() =>
Dispose(true);        
}

然后，您可以将此访问器类注册为singleton，这意味着它将只创建一次(因此所包含的HttpClient也将只创建一遍(。然后，将类设置为在其构造函数中接受此访问器：

public class ApiQuery : IApiQuery
{
private readonly HttpClient _client;
public ApiQuery(ApiHttpClientAccessor httpClientAccessor)
{
_client = (httpClientAccessor ?? throw new ArgumentNullException(nameof(httpClientAccessor))).HttpClient;
}
...
}

并且在Startup.cs:中

services.AddSingleton<ApiHttpClientAccessor>();
services.AddTransient<IApiQuery, ApiQuery>();