概述:
在.NET Framwork中使用HttpClient直接这样使用 using(var client = new HttpClient()){} ,高并发时频繁创建socket,连接来不及释放,socket被耗尽,就会出现问题。HttpClient 实现了 IDispose 接口,但当你 Dispose 它时,它不会立即关闭所使用的 tcp 连接,而是将 tcp 连接置为 TIME_WAIT 状态,240秒(4分钟)后才真正关闭连接。对于高并发的场景,比如每秒 1000 个请求,每个请求都用到 HttpClient ,4分钟内会堆积24万个 tcp 连接,这样的连接爆棚会拖垮服务器。
所以不用频繁创建HttpClient对象,要复用,可以用单例或静态,并且设置成长连接。但这样使用有一点问题是DNS更新会失效
在Core中推荐使用HttpClientFactory创建HttpClient,目的也是复用HttpClient。顾名思义 HttpClientFactory 就是 HttpClient 的工厂,内部已经帮我们处理好了对 HttpClient 的管理,不需要我们人工进行对象释放,同时可命名,支持自定义请求头,支持DNS更新等等等。
HttpClientFacotry内部存放了HttpClient的缓存,并且定时Dispose,防止DNS缓存时间过长
HttpClientFactory使用方法:
案例1,直接使用HttpClientFactory
1、在startup中注册
public void ConfigureServices(IServiceCollection services) { services.AddHttpClient("client_1",config=> //这里指定的 name=client_1 ,可以方便我们后期服用该实例 { config.BaseAddress= new Uri("http://client_1.com"); config.DefaultRequestHeaders.Add("header_1","header_1"); }); services.AddHttpClient("client_2",config=> { config.BaseAddress= new Uri("http://client_2.com"); config.DefaultRequestHeaders.Add("header_2","header_2"); }); services.AddHttpClient(); }
2、Controller中使用
public class TestController : ControllerBase { private readonly IHttpClientFactory _httpClient; public TestController(IHttpClientFactory httpClient) { _httpClient = httpClient; } public async Task<ActionResult> Test() { var client = _httpClient.CreateClient("client_1"); //复用在 Startup 中定义的 client_1 的 httpclient var result = await client.GetStringAsync("/page1.html"); var client2 = _httpClient.CreateClient(); //新建一个 HttpClient var result2 = await client.GetStringAsync("http://www.site.com/XXX.html"); return null; } }
案例2:为单个HttpClient添加DelegatingHandler,拦截请求记录日志
public class LoggingHandler : DelegatingHandler { protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) { if (request.Content != null) { Debug.WriteLine(await request.Content.ReadAsStringAsync()); } HttpResponseMessage response = await base.SendAsync(request, cancellationToken); if (response.Content != null) { Debug.WriteLine(await response.Content.ReadAsStringAsync()); } return response; } }
ConfigureServices中注册:
services.AddHttpClient("baidu", config => { config.BaseAddress = new Uri("https://www.baidu.com"); config.DefaultRequestHeaders.Add("header_1", "header_1"); }).AddHttpMessageHandler(()=>new LoggingHandler());
案例3:设置HttpClientHandler
services.AddHttpClient("client1", client => { client.BaseAddress = new System.Uri("https://www.baidu.com"); }) .ConfigurePrimaryHttpMessageHandler(() => new System.Net.Http.HttpClientHandler() {//设置HttpClientHandler,也就是InnerHandler UseCookies = false });
案例4:注册全局DelegatingHandler,拦截所有httpClient请求
实现接口IHttpMessageHandlerBuilderFilter,并注册。看下面文章
https://blog.csdn.net/weixin_30236595/article/details/101066107
参考:
https://blog.zhuliang.ltd/2019/02/net-core/HttpClient-HttpClientFactory-InNetCore.html
https://blog.csdn.net/weixin_34249367/article/details/86134102
未完待续...