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参考
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https://www.cnblogs.com/deepthought/p/11303015.html
https://www.cnblogs.com/willick/p/net-core-httpclient.html
技术译民翻译的博客 https://www.cnblogs.com/ittranslator/p/making-http-requests-in-blazor-webassembly-apps.html
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直接使用 HttpClient 的问题
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HttpClient 类所在库为 System.Net.Http,
Blazor webassembly 默认模版已经自动将HttpClient 注册到DI 容器中了, 使用起来非常方便. Program.Main 函数注册DI容器代码:
builder.Services.AddScoped(sp => new HttpClient { BaseAddress = new Uri(builder.HostEnvironment.BaseAddress) });
直接使用 HttpClient 问题有:
- HttpClient 主要问题是, 即使 Dispose 之后, 也不能即时关闭 socket 连接, 在 windows 下, 默认需要等 240秒之后才能关闭 socket. 短时大量使用 HttpClient, 会将客户端和服务器端 socket 连接消耗殆尽, 详见参考文档1的分析. 所以, 客户端应用程序一般使用单例模式使用 HttpClient 类. Blazor webassembly 也是如此.
- 如果使用单例模式, 如要为 不同url 设置不同的 header, 就很不方便.
- HttpClient 还会缓存 IP, 如果 DNS 之后有更新, HttpClient 仍会使用老的 IP
Net Core2.1 提供的 IHttpClientFactory 解决了直接使用HttpClient的所有问题, IHttpClientFactory 提供了更优雅 Http Client 功能.
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IHttpClientFactory 简单方法生成 HttpClient
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IHttpClientFactory 所在的类库是 Microsoft.Extensions.Http , 将它加到blazor wasm 项目的依赖中,
Program.Main 函数必须使用 AddHttpClient 完成DI容器注册, 这样DI容器就能为我们注入 IHttpClientFactory 实例.
builder.Services.AddHttpClient();
Razor 页面使用 IHttpClientFactory 的实例生成 HttpClient 对象.
@page "/hello" @inject IHttpClientFactory HttpClientFactory <div> _statusCode: @_statusCode </div> @code{ private string _statusCode = ""; protected override async Task OnInitializedAsync() { var httpClient = HttpClientFactory.CreateClient(); //gorest.co.in 网站已经开启 CORS 共享, 所以我们用它来测试, 而不是 https://www.baidu.com httpClient.BaseAddress=new Uri("https://gorest.co.in"); var result = await httpClient.GetAsync("/public/v1/users"); _statusCode = result.StatusCode.ToString(); } }
使用这个简单的方式, IHttpClientFactory 注入的实例未经任何初始化, 比如未设置BaseAddress参数, 需要在使用该实例时候, 进行各种设置, 代码复用性较差.
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IHttpClientFactory 采用命名方式生成 HttpClient
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命名方式在使用友好性方面比简单方式好很多.
注册DI容器时, AddHttpClient()传入名称, 同时还可以为将来的HttpClient对象设置各种参数.
使用时, 先获取注入的 IHttpClientFactory HttpClient实例, 然后CreateClient()传入命名值即可得到经过预设的HttpClient对象对象 , 不需要再进行参数设置.
builder.Services.AddHttpClient(name: "gorest", c => { c.BaseAddress = new Uri("https://gorest.co.in"); } );
@page "/hello" @inject IHttpClientFactory HttpClientFactory <div> _statusCode: @_statusCode </div> @code{ private string _statusCode = ""; protected override async Task OnInitializedAsync() { var httpClient = HttpClientFactory.CreateClient(name: "gorest"); var result = await httpClient.GetAsync("/public/v1/users"); _statusCode = result.StatusCode.ToString(); } }
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IHttpClientFactory 采用类型化方式生成 HttpClient
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类型化方式比命名方式更进一步, 注册DI容器时, AddHttpClient()传入一个泛型类型, 将HttpClient的各种设置转移到泛型类中
这样的好处时, AddHttpClient() 方法更简单, 代码内聚性更好.
包装了 HttpClient 的泛型类:
public class GorestHttpService { private readonly HttpClient _httpClient; public GorestHttpService(HttpClient httpClient) { _httpClient = httpClient; _httpClient.BaseAddress = new Uri("https://gorest.co.in"); } public async Task<string> GetStatusCodeAsync() { var result = await _httpClient.GetAsync("/public/v1/users"); return result.StatusCode.ToString(); } }
Program.Main 函数 AddHttpClient 完成DI容器注册
builder.Services.AddHttpClient<GorestHttpService>();
Razor 代码:
@page "/hello" @inject GorestHttpService gorestHttpService <div> _statusCode: @_statusCode </div> @code{ private string _statusCode = ""; protected override async Task OnInitializedAsync() { var result = await gorestHttpService.GetStatusCodeAsync(); _statusCode = result; } }
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为 HttpClient 增加 Header
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如需要增加 Bearer Header, 可以通过为 httpClient.DefaultRequestHeaders.Authorization 属性赋值.
public class GorestHttpService { private readonly HttpClient _httpClient; public GorestHttpService(HttpClient httpClient) { _httpClient = httpClient; _httpClient.BaseAddress = new Uri("https://gorest.co.in"); string token = "changeMe"; _httpClient.DefaultRequestHeaders.Authorization= new AuthenticationHeaderValue("Bearer", token); } public async Task<string> GetStatusCodeAsync() { var result = await _httpClient.GetAsync("/public/v1/users"); return result.StatusCode.ToString(); } }
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开放的 Rest api 服务
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示例中使用了 GoRest 网站, 它是 Online REST API for Testing and Prototyping https://gorest.co.in/
一些简单的api网站 https://mixedanalytics.com/blog/list-actually-free-open-no-auth-needed-apis/