重置HttpClient的处理程序或在方法中设置其属性

Question

我想像在本article中那样使用HttpClient时减少连接数量，而不用在HttpClient语句中包装using的创建。但是我需要针对不同的请求使用不同的证书。

我在基类中将HttpsClient设为静态，并在静态构造函数中创建了该实例以及静态WebRequestHandler的实例。为方法SetHandler添加了证书并设置了处理程序的其他属性。然后在ExecuteRequestAsync中调用SetHandler，我希望它可以将属性填充到HttpClient处理程序的静态实例中。

    private static readonly WebRequestHandler _handler;
    private static readonly HttpClient _httpClient;

    private readonly string _uri;
    private readonly IDictionary<string, string> _headers;
    private readonly string _customContentType;
    private readonly int _timeout;
    private readonly X509Certificate _clientCertificate;
    private readonly X509Certificate _trustedServerCertificate;
    private readonly bool _allowAutoRedirect;
    private readonly bool _allowErrorStatusCodes;
    private readonly CookieContainer _cookie;
    private readonly IProtocolLogger _logger;

    static ProtocolHttpService()
    {
        _handler = new WebRequestHandler();
        _httpClient = new HttpClient(_handler);
    }

    public ProtocolHttpService(
        string uri,
        IDictionary<string, string> headers = null,
        string customContentType = null,
        int timeout = MAX_TIMEOUT,
        X509Certificate clientCertificate = null,
        X509Certificate trustedServerCertificate = null,
        bool allowAutoRedirect = false,
        bool allowErrorStatusCodes = false,
        CookieContainer cookie = null,
        IProtocolLogger logger = null)
    {
        _uri = uri;
        _headers = headers;
        _customContentType = customContentType;
        _timeout = timeout;
        _clientCertificate = clientCertificate;
        _trustedServerCertificate = trustedServerCertificate;
        _allowAutoRedirect = allowAutoRedirect;
        _allowErrorStatusCodes = allowErrorStatusCodes;
        _cookie = cookie;
        _logger = logger;
    }

    static ProtocolHttpService()
    {
        _handler = new WebRequestHandler();
        _httpClient = new HttpClient(_handler);
    }

    private async Task<CommunicationStats> ExecuteRequestAsync(HttpMethod method, string requestText)
    {
        var sw = Stopwatch.StartNew();

        using (var cancellationTokenSource = new CancellationTokenSource(_timeout))
        {
            var cancellationToken = cancellationTokenSource.Token;

            var request = new HttpRequestMessage
            {
                Method = method,
                RequestUri = new Uri(_uri)
            };

            if (!string.IsNullOrEmpty(requestText))
            {
                request.Content = new StringContent(requestText, Encoding.UTF8, _customContentType);
            }
            AddHeaders(request);
            SetHandler();

            var response = await _httpClient.SendAsync(request, cancellationToken);
            var responseText = await response.Content.ReadAsStringAsync();
            return CommunicationStats.Create(response.StatusCode, _uri, requestText, responseText, sw.Elapsed);

        }

    private void SetHandler()
    {
        if (_cookie != null)
        {
            _handler.CookieContainer = _cookie;
        }

        if (_clientCertificate != null &&
            !_handler.ClientCertificates.Contains(_clientCertificate))
        {
            _handler.ClientCertificates.Add(_clientCertificate);
        }

        _handler.AllowAutoRedirect = _allowAutoRedirect;
    }

在调试过程中，我发现HttpClient的处理程序属性未设置为应在SetHandler中设置。