.NET6之MiniAPI(二十二)：HttpClient

　　说明：本篇不是说明HttpClient怎么使用，而以分享在asp.net core mini api框架下，HttpClient的引入和使用方式。

　　我们在业务开发中，免不了调用三方的服务，这时就会用到HttpClient，在早期的asp.net core框架中，一般是通过new HttpClient来实现对三方的请求，现在，可以通过HttPClientFactory来实现，这样的好处是可以池化连接，节省资源。

　　基础使用方法很简单：

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();

　　当项目中有多个三方服务请求，为了区分各个三方服务，可以采用命名方式

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=桂素伟");
 });
app.MapGet("/testbaidu", async (IHttpClientFactory clientFactory) =>
{
    var baiduClient = clientFactory.CreateClient("BaiDu");
    return await lient .GetStringAsync("s?wd=桂素伟");
});
app.Run();

　　还可以项目中每个服务的请求各自封装，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=桂素伟");
    }
}
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=桂素伟");
    }
}