說明：本篇不是說明HttpClient怎麼使用，而以分享在asp.net core mini api框架下，HttpClient的引入和使用方式。

　　我們在業務開發中，免不了呼叫三方的服務，這時就會用到HttpClient，在早期的asp.net core框架中，一般是通過new HttpClient來實現對三方的請求，現在，可以通過HttPClientFactory來實現，這樣的好處是可以池化連線，節省資源。

　　基礎使用方法很簡單：

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddHttpClient();

 
var app = builder.Build();

app.MapGet("/test", async (IHttpClientFactory clientFactory) =>
 {
     var client = clientFactory.CreateClient();
     var content = await client.GetStringAsync("https://www.google.com");
 });

app.Run();

　　當專案中有多個三方服務請求，為了區分各個三方服務，可以採用命名方式

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddHttpClient(
 
"Google", httpClient =>
{
    httpClient.BaseAddress = new Uri("https://www.google.com/");
});
builder.Services.AddHttpClient("BaiDu", httpClient =>
{
    httpClient.BaseAddress = new Uri("https://www.baidu.com/");
});
var app = builder.Build();

app.MapGet("/testgoogle", async (IHttpClientFactory clientFactory) =>
 {
     
 
var googleClient = clientFactory.CreateClient("Google");
     return await googleCclient.GetStringAsync("search?q=桂素偉");
 });
app.MapGet("/testbaidu", async (IHttpClientFactory clientFactory) =>
{
    var baiduClient = clientFactory.CreateClient("BaiDu");
    return await lient .GetStringAsync("s?wd=桂素偉");
});
app.Run();

　　還可以專案中每個服務的請求各自封裝，各用各的HttpClient:

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddHttpClient<IGoogleService, GoogleService>();
builder.Services.AddHttpClient<IBaiDuService, BaiDuService>(httpClient =>
{
    httpClient.BaseAddress = new Uri("https://www.baidu.com/");
});

var app = builder.Build();

app.MapGet("/testgoogle", async (IGoogleService google) =>
 {
     return await google.GetContentAsync();
 });
app.MapGet("/testbaidu", async (IBaiDuService baidu) =>
{
    return await baidu.GetContentAsync();
});
app.Run();

interface IGoogleService
{
    Task<string> GetContentAsync();
}
class GoogleService : IGoogleService
{
    private readonly HttpClient _httpClient;
    public GoogleService(HttpClient httpClient)
    {
        _httpClient = httpClient;
        _httpClient.BaseAddress = new Uri("https://www.google.com/");

    }
    public async Task<string> GetContentAsync()
    {
        return await _httpClient.GetStringAsync("search?q=桂素偉");
    }
}
interface IBaiDuService
{
    Task<string> GetContentAsync();
}
class BaiDuService : IBaiDuService
{
    private readonly HttpClient _httpClient;
    public BaiDuService(HttpClient httpClient)
    {
        _httpClient = httpClient;
    }
    public async Task<string> GetContentAsync()
    {
        return await _httpClient.GetStringAsync("s?wd=桂素偉");
    }
}