ASP.NET Core – HttpClient

前言

以前写过的文章 Asp.net core 学习笔记 ( HttpClient ).

其实 HttpClient 内容是挺多的, 但是我自己用到的很少. 所以这篇记入一下自己用到的就好了.

参考

3 ways to use HTTPClientFactory in ASP.NET Core 2.1

Docs – Make HTTP requests using IHttpClientFactory in ASP.NET Core

3 大用法介绍

其实是 4 种哦, 只是第 4 种我不熟就忽略掉呗.

Basic usage 的方式是注入 HttpClientFactory > 创建 HttpClient > 发 request

Named clients 的方式是先在 program.cs provide 好 config, 比如 Uri, default header 等等. 然后注入 HttpClientFactory > 创建 HttpClient with named config > 发 request.

如果你要发多个不同的 path 但是相同的 origin 的话, 这个管理方式会比 Basic usage 好.

Typed clients 的方式是先做一个 service class, 在 constructor 注入 HttpClient 然后配置 config, 提供各做方法里面使用 HttpClient 发 request. 

这个方式主要就是封装了所以对这个 client 的请求, 外部只要 call service 的 method 就好. 

对比 3 大用法

可以看出来, 主要就是在管理上的区别. 个人建议, 如果只是 1 个请求, 那么直接用 basic 就好了, 如果多个请求, 或者多个地方用到, 那么就用 Type clients. 至于 Named clients 感觉有点不上不下就不要用了.

Get Request (Basic usage)

要到这里 Github – CountryCodes.json 请求 Country Code JSON

Provide HttpClient

builder.Services.AddHttpClient();

注入 HttpClientFactory

private readonly IHttpClientFactory _httpClientFactory;

public IndexModel(
    IHttpClientFactory httpClientFactory
)
{
    _httpClientFactory = httpClientFactory;
}

创建 Request Message

var httpRequestMessage = new HttpRequestMessage
{
    RequestUri = new Uri("https://gist.githubusercontent.com/Goles/3196253/raw/9ca4e7e62ea5ad935bb3580dc0a07d9df033b451/CountryCodes.json"),
    Method = HttpMethod.Get,
};
httpRequestMessage.Headers.Add("Accept", "application/json; charset=utf-8");

调用 HttpClient 发请求

var httpClient = _httpClientFactory.CreateClient();
var response = await httpClient.SendAsync(httpRequestMessage);
if (response.IsSuccessStatusCode)
{
    var json = await response.Content.ReadAsStringAsync();
}

以上就是 basic usage 的方式. 类似发 SMTP 请求那样.

解析 JSON response

另外, 也可以直接解析 JSON response

public class Country
{
    public string Name { get; set; } = "";

    [JsonPropertyName("dial_code")]
    public string DialCode { get; set; } = "";

    public string Code { get; set; } = "";
}

var counties = await response.Content.ReadFromJsonAsync<List<Country>>();

Get Request (Typed clients)

创建 Client

public class CountryCodeHttpClient
{
    private readonly HttpClient _httpClient;
    public CountryCodeHttpClient(
           HttpClient httpClient
       )
    {
        _httpClient = httpClient;
        _httpClient.BaseAddress = new Uri("https://gist.githubusercontent.com");
        _httpClient.DefaultRequestHeaders.Add("Accept", "application/json; charset=utf-8");
    }

    public async Task<List<Country>> GetCountriesAsync()
    {
        var response = await _httpClient.GetAsync("/Goles/3196253/raw/9ca4e7e62ea5ad935bb3580dc0a07d9df033b451/CountryCodes.json");
        if (response.IsSuccessStatusCode)
        {
            return (await response.Content.ReadFromJsonAsync<List<Country>>())!;
        }
        else
        {
            throw new Exception("error");
        }
    }
}

通常 Client 在 construtor 会配置通用的 URI 和 Header. 在方法内则控制 path 和 extra Header.

Provide HttpClient

builder.Services.AddHttpClient<CountryCodeHttpClient>();

调用

var counties = await _countryCodeHttpClient.GetCountriesAsync();

TODO post request 等等...