正确使用 HttpClient

使用 HttpClient 注意事项

1. HttpClient默认最大并发连接数是2
2. 本机测试(被请求的WebApi部署在本机)HttpClient不会被限制最大并发连接数
3. 使用HttpClient要写个工厂类，因为HttpClient不能频繁创建
4. HttpClient类提供的方法是线程安全的

HttpClient 工厂类

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Factory
{
    /// <summary>
    /// HttpClient工厂类
    /// 注意：
    /// 1. HttpClient默认最大并发连接数是2
    /// 2. 本机测试HttpClient不会被限制最大并发连接数
    /// </summary>
    public class HttpClientFactory
    {
        private int _httpClientCount;

        private readonly HttpClient[] _httpClientArray;

        private int _index = -1;

        private readonly object _lock = new object();

        private static readonly HttpClientFactory _instance = new HttpClientFactory();

        public static HttpClientFactory Instance
        {
            get
            {
                return _instance;
            }
        }

        public HttpClientFactory(int httpClientCount = 50)
        {
            _httpClientCount = httpClientCount;
            _httpClientArray = new HttpClient[_httpClientCount];
            for (int i = 0; i < _httpClientCount; i++)
            {
                _httpClientArray[i] = new HttpClient();
            }
        }

        public HttpClient Get()
        {
            lock (_lock)
            {
                _index++;
                if (_index == _httpClientCount)
                {
                    _index = 0;
                }
                return _httpClientArray[_index];
            }
        }
    }
}