通过.Net Core 自带的IHttpClientFactory,启用Http请求。并在请求前后执行一段逻辑,通过 Microsoft.Extensions.Http.Polly 处理异常学习笔记
一、介绍
以生成出站请求中间件管道。 每个处理程序都可以在出站请求前后执行工作。通过Polly 的处理程序,以表达策略处理重试、断路器、超时、隔离和回退。
二、使用http请求
1.配置注册
var host = new HostBuilder()
.ConfigureServices((context, services) => {
services.AddHttpClient();
services.AddHostedService<MyHostedService>();
})
.UseConsoleLifetime()
.Build();
2.请求的后台服务
public Task StartAsync(CancellationToken cancellationToken)
{
return Task.Run(async () =>
{
var request = new HttpRequestMessage(HttpMethod.Post, "http://www.baidu.com");
request.Headers.Add("Accept", "application/json");//设置请求头
request.Properties.Add("id","123");//设置请求参数
var client = _clientFactory.CreateClient();
var response = await client.SendAsync(request);
string result = null;
if (response.IsSuccessStatusCode)
{
result = await response.Content.ReadAsStringAsync();
}
});
}
3.执行时控制台输入日志
二、以客户端的方式使用
在客户端中配置,默认请求Url地址和默认的header。
public class HaosRequestService
{
public HttpClient Client { get; }
public HaosRequestService(HttpClient client)
{
//配置默认值
client.BaseAddress = new Uri("http://www.baidu.com/");
client.DefaultRequestHeaders.Add("Accept","application/json");
Client = client;
}
/// <summary>
/// 封装常用方法
/// </summary>
/// <param name="key"></param>
/// <returns></returns>
public async Task<string> SeachAsync(string key)
{
var content = new FormUrlEncodedContent(new[] {
new KeyValuePair<string,string>("w","关键字"),
});
var response = await Client.PostAsync("/s",content);
response.EnsureSuccessStatusCode();
return await response.Content.ReadAsStringAsync();
}
}
在IServiceCollection中注册
var host = new HostBuilder()
.ConfigureServices((context, services) => {
services.AddHttpClient<HaosRequestService>();
services.AddHostedService<MyHostedService>();
})
三、处理出站 HTTP 请求
要创建处理程序,先定义一个继承 DelegatingHandler
的类。 重写 SendAsync
方法,在将请求传递至管道中的下一个处理程序之前
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;
namespace Haos.Develop.HttpRequest.Samples
{
public class ColationDelegatingHandler:DelegatingHandler
{
protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
{
//此处实现过滤逻辑
return base.SendAsync(request, cancellationToken);
}
}
}
var Host = new HostBuilder()
.ConfigureAppConfiguration(builder =>
{
builder.AddCommandLine(args);
})
.ConfigureServices((context, services) =>
{
services.AddHttpClient<RequestClient>()
//注册过滤程序
.AddHttpMessageHandler<ColationDelegatingHandler>();
})
.UseConsoleLifetime()
.Build();
四、基于Polly的处理程序
Polly 以表达策略,例如以流畅且线程安全的方式处理重试、断路器、超时、Bulkhead 隔离和回退。Microsoft.Extensions.Http.Polly NuGet 包中提供 Polly 扩展实现将 Polly 策略用于配置的 HttpClient 实例。
Polly 添加策略分为三种
1. AddTransientHttpErrorPolicy:是处理Http请求的错误,如HTTP 5XX 的状态码,HTTP 408 的状态码 以及System.Net.Http.HttpRequestException异常
2. AddPolicyHandler:添加自定义策列
3. AddPolicyHandlerFromRegistry:从Policy注册表集合里面选择添加
a. AddTransientHttpErrorPolicy
.ConfigureServices((context, services) =>
{
services.AddHttpClient<RequestClient>()
.AddTransientHttpErrorPolicy(builder => builder.WaitAndRetryAsync(3, t => TimeSpan.FromMilliseconds(500)))
//或。上下都是定义了,错误重试上面是间隔都是500毫秒,下面则定义了每次重试的时间间隔
.AddTransientHttpErrorPolicy(builder => builder.WaitAndRetryAsync(new[] {
TimeSpan.FromSeconds(1),
TimeSpan.FromSeconds(5),
TimeSpan.FromSeconds(10)
}));
})
b. AddPolicyHandler
先定义策略,在通过AddPolicyHandler方法添加,改方法接收一个泛型的IAsyncPolicy<HttpResponseMessage>。HttpResponseMessage我理解为出站请求上下文
.ConfigureServices((context, services) =>
{
var retryPolicy = Policy.Handle<HttpRequestException>()
.OrResult<HttpResponseMessage>(response => {
//此处实现处理改异常的逻辑
return true;
}).WaitAndRetryAsync(3,t => TimeSpan.FromMilliseconds(50));
services.AddHttpClient<RequestClient>()
.AddPolicyHandler(retryPolicy);
})
retryPolicy:发生HttpRequestException的异常,并且OrResult返回结果为true,采用这个策略
c. AddPolicyHandlerFromRegistry
先注册策略表服务,为策略表添加策略,最后通过AddPolicyHandlerFromRegistry方法选用某个或几个策略
.ConfigureServices((context, services) =>
{
//注册,策略表服务
var registry = services.AddPolicyRegistry();
//创建策略
var retryPolicy = Policy.Handle<HttpRequestException>()
.OrResult<HttpResponseMessage>(response => {
//此处实现处理改异常的逻辑
return true;
}).WaitAndRetryAsync(3, t => TimeSpan.FromMilliseconds(50));
registry.Add("registry1", retryPolicy);
services.AddHttpClient<RequestClient>()
.AddPolicyHandlerFromRegistry("registry1");
})
添加多个 Polly 处理程序嵌套 Polly 策略以增强功
分别定义三种策略,timeoutPolicy,noOpPolicy,retryPolicy 通过策略表的方式和自定义。添加多个策略。
.ConfigureServices((context, services) =>
{
//注册,策略表服务
var registry = services.AddPolicyRegistry();
//创建策略
var timeoutPolicy = Policy.TimeoutAsync<HttpResponseMessage>(10);//10秒超时
var noOpPolicy = Policy.NoOpAsync().AsAsyncPolicy<HttpResponseMessage>();//有时我们也需要一个没有任何行为的策略,Polly系统默认提供了一个.
var retryPolicy = Policy.Handle<HttpRequestException>()
.OrResult<HttpResponseMessage>(response => {
//此处实现处理改异常的逻辑
return true;
}).WaitAndRetryAsync(3, t => TimeSpan.FromMilliseconds(50));
registry.Add("registry1", retryPolicy);
registry.Add("registry2", timeoutPolicy);
services.AddHttpClient<RequestClient>()
.AddPolicyHandlerFromRegistry("registry1")
.AddPolicyHandler(retryPolicy)
.AddPolicyHandler(timeoutPolicy);
})