创建一个名为HttpClientTest的Web API项目

新建Clients文件夹，用于存放自定义的HttpClient

在Clients下新建一个MyHttpClient类

代码为：

namespace HttpClientTest.Clients
{
    public class MyHttpClient
    {
        private readonly HttpClient _client;

        public MyHttpClient(HttpClient client)
        {
            _client = client;
        }

        public async Task<string> ShowAsync()
        {
            return await _client.GetStringAsync("https://www.baidu.com");
        }
    }
}

将自定义的MyHttpClient服务注册进容器中

services.AddHttpClient<MyHttpClient>();

新建一个TestController来对我们的MyHttpClient做一个测试

using HttpClientTest.Clients;
using Microsoft.AspNetCore.Mvc;

namespace HttpClientTest.Controllers
{
    [ApiController]
    [Route("[controller]/[action]")]
    public class TestController : ControllerBase
    {
        private readonly MyHttpClient _myHttpClient;

        public TestController(MyHttpClient myHttpClient)
        {
            _myHttpClient = myHttpClient;
        }

        [HttpGet]
        public async Task<object> GetAsync()
        {
            return await _myHttpClient.ShowAsync();
        }
    }
}

访问GetAsync接口，发现成功返回了百度首页的html内容

很多时候，我们希望通过相对路径的方式来对远程服务进行访问

可以把MyHttpClient改为：

namespace HttpClientTest.Clients
{
    public class MyHttpClient
    {
        private readonly HttpClient _client;

        public MyHttpClient(HttpClient client)
        {
            _client = client;
        }

        public async Task<string> ShowAsync()
        {
	        //return await _client.GetStringAsync("https://www.baidu.com");
            return await _client.GetStringAsync("/");
        }
    }
}

在注册服务时就要配置基地址

services.AddHttpClient<MyHttpClient>(client =>
{
    client.BaseAddress = new Uri("https://www.baidu.com");
});