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HttpClient 处理错误与异常

根据客户端的创建方法不周，有不同的错误与异常处理方式。推荐类型化客户端、工厂和Polly库中统一处理！

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初始化

#!import ./Ini.ipynb

常规方法

直接实例化客户端时，可以用Try Catch或者EnsureSuccessStatusCode方法简单处理, 这种是最不推荐的方式！

推荐使用后面介绍的 Pipeline 管道方式

• try catch

/*try catch 处理异常
*/
try
{var requestUri = new Uri(webApiBaseUri, "/api/ErrorDemo/Error500");using(var client = new HttpClient()){//发送请求var response = await client.GetAsync(requestUri);if(response.IsSuccessStatusCode){Console.WriteLine($"远程请求成功,响应码 {response.StatusCode}");}else{Console.WriteLine($"远程请求失败,响应码 {response.StatusCode}");}}
}
catch(Exception ex)
{Console.WriteLine($"远程调用异常：{ex.Message}");
}
finally
{//清理业务
}

• Response的EnsureSuccessStatusCode方法

{ //EnsureSuccessStatusCode方法var requestUri = new Uri(webApiBaseUri, "/api/ErrorDemo/Error500");using(var client = new HttpClient()){//发送请求var response = await client.GetAsync(requestUri);//确保响应码正确,否则异常response.EnsureSuccessStatusCode();//输出响应码Console.WriteLine($"远程请求成功,响应码 {response.StatusCode}");}
}

静态或工具类中处理

静态类或工具类，可以在内部方法里使用 Try Catch 等常规方法进行异常处理。

注意：推荐使用后面介绍的 Pipeline 管道方式

• 内部处理

//静态类中处理异常
public class HttpClientHelper
{public readonly static HttpClient StaticClient;static HttpClientHelper(){SocketsHttpHandler handler = new SocketsHttpHandler(){PooledConnectionLifetime = TimeSpan.FromSeconds(30),};StaticClient = new HttpClient(handler){//统一设置: 基础UriBaseAddress = new Uri(WebApiConfigManager.GetWebApiConfig().BaseUrl),};//统一设置：请求头等StaticClient.DefaultRequestHeaders.Add("x-custom-time","12ms");//统一错误处理：可以在Pipline中统一设置，后面有单独章节} public static async Task<HttpResponseMessage> GetAsync(string url){//异常处理try{return await StaticClient.GetAsync(url);}catch(Exception ex){Console.WriteLine($"远程调用发生异常：{ex.Message}");return await Task.FromResult(new HttpResponseMessage(HttpStatusCode.ExpectationFailed));}finally{//清理业务}}public static async Task<string> GetStringAsync(string url){var response = await StaticClient.GetAsync(url);//异常处理response.EnsureSuccessStatusCode();return await response.Content.ReadAsStringAsync();}public static async Task<HttpResponseMessage> PostAsync(string url, HttpContent content){//异常处理try{return await StaticClient.PostAsync(url, content);}catch(Exception ex){Console.WriteLine($"远程调用发生异常：{ex.Message}");return await Task.FromResult(new HttpResponseMessage(HttpStatusCode.ExpectationFailed));}finally{//清理业务}}
}{   //正常请求var response = await HttpClientHelper.GetAsync("/api/Config/GetApiConfig");var content = await response.Content.ReadAsStringAsync();Console.WriteLine($"正常请求结果：{content}");//异常请求var response2 = await HttpClientHelper.GetAsync("/api/ErrorDemo/Error500");Console.WriteLine($"异常请求结果：{response2}");
}

• 添加异常Pipeline管道（下面专项介绍）

类型化客户端中处理

类型化客户端有三种方法：一是类内部处理；二是Pipeline，统一处理；三是结合IoC/工厂和Polly库，初始设置时统一处理。

推荐第二、第三种，后面有专项介绍。

• 内部处理，类似静态或工具类

// 类型化客户端A HttpClient
public class HttpClientServiceA
{public HttpClient Client { get; }public HttpClientServiceA(HttpClient client){Client = client;Console.WriteLine("HttpClientServiceA => 构造函数执行一次");}//常规方法：异常可在方法内处理public async Task<string> GetAsync(){var response = await Client.GetAsync("/api/ErrorDemo/Error500");var content = await response.Content.ReadAsStringAsync();return content;}
}// 使用类型化客户端
{var services = new ServiceCollection();services.AddHttpClient<HttpClientServiceA>().ConfigureHttpClient(client=>{client.BaseAddress = new Uri(webApiBaseUrl);});var builder = services.BuildServiceProvider();var serverA = builder.GetRequiredService<HttpClientServiceA>();var dataA = await serverA.GetAsync();Console.WriteLine(dataA);
}

• 与工厂和Polly库统合，统一处理（下面专项介绍）
• 添加异常Pipeline管道（下面专项介绍）

在管道中，添加异常中间件

不管那种方式创建的客户端，都可以配置Pipeline，专门添加异常管道中间件进行异常统一处理，也很推荐这种方式。

• 准备异常处理中间件

//异常中间件(管道)类
public class ExceptionDelegatingHandler : DelegatingHandler
{protected override HttpResponseMessage Send(HttpRequestMessage request, CancellationToken cancellationToken){Console.WriteLine("ExceptionDelegatingHandler -> Send -> Before");HttpResponseMessage response;try {response = base.Send(request, cancellationToken);response.EnsureSuccessStatusCode();}catch(Exception ex){Console.WriteLine($"异常管道中间件，监控到异常：{ex.Message}");response = new HttpResponseMessage(HttpStatusCode.ExpectationFailed);}finally{//清理业务}Console.WriteLine("ExceptionDelegatingHandler -> Send -> After");return response;}protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken){Console.WriteLine("ExceptionDelegatingHandler -> SendAsync -> Before");HttpResponseMessage response;try {response = response = await base.SendAsync(request, cancellationToken);response.EnsureSuccessStatusCode();}catch(Exception ex){Console.WriteLine($"异常管道中间件，监控到异常：{ex.Message}");response = new HttpResponseMessage(HttpStatusCode.ExpectationFailed);}finally{//清理业务}Console.WriteLine("ExceptionDelegatingHandler -> SendAsync -> After");return response;}
}

• 直接创建客户端时，加入异常管道

{//构建管道(加入异常中间件)var handler = new ExceptionDelegatingHandler(){//相当于下一个中间件(管道)//最后中间件必须是SocketsHttpHandlerInnerHandler = new SocketsHttpHandler() {AllowAutoRedirect = true}};//构造中传入管道对象using(var client = new HttpClient(handler){BaseAddress = new Uri(webApiBaseUrl)}){//发送请求var response = await client.GetAsync("/api/ErrorDemo/Error500");if(response.IsSuccessStatusCode){Console.WriteLine($"远程请求成功,响应码 {response.StatusCode}");}else{Console.WriteLine($"远程请求失败,响应码 {response.StatusCode}");}}
}

• 静态或工具类，加入异常管道

//静态类中处理异常
public class HttpClientHelper2
{public readonly static HttpClient StaticClient;static HttpClientHelper2(){//构建管道(加入异常中间件)var handler = new ExceptionDelegatingHandler(){//相当于下一个中间件(管道)//最后中间件必须是SocketsHttpHandlerInnerHandler = new SocketsHttpHandler() {AllowAutoRedirect = true,PooledConnectionLifetime = TimeSpan.FromSeconds(30),}};StaticClient = new HttpClient(handler){//统一设置: 基础UriBaseAddress = new Uri(WebApiConfigManager.GetWebApiConfig().BaseUrl),};//统一设置：请求头等StaticClient.DefaultRequestHeaders.Add("x-custom-time","12ms");//统一错误处理：可以在Pipline中统一设置，后面有单独章节} public static async Task<HttpResponseMessage> GetAsync(string url){return await StaticClient.GetAsync(url);}public static async Task<string> GetStringAsync(string url){var response = await StaticClient.GetAsync(url);//无异常处理return await response.Content.ReadAsStringAsync();}public static async Task<HttpResponseMessage> PostAsync(string url, HttpContent content){//无异常处理return await StaticClient.PostAsync(url,content);}
}{   //正常请求var response = await HttpClientHelper2.GetAsync("/api/Config/GetApiConfig");var content = await response.Content.ReadAsStringAsync();Console.WriteLine($"正常请求结果：{content}");//异常请求var response2 = await HttpClientHelper2.GetAsync("/api/ErrorDemo/Error500");Console.WriteLine($"异常请求结果：{response2}");
}

• 类型化客户端，加入异常管道

// 类型化客户端A HttpClient
public class HttpClientServiceC
{public HttpClient Client { get; }public HttpClientServiceC(HttpClient client){Client = client;Console.WriteLine("HttpClientServiceC => 构造函数执行一次");}//常规方法：异常可在方法内处理public async Task<string> GetAsync(){var response = await Client.GetAsync("/api/ErrorDemo/Error500");var content = await response.Content.ReadAsStringAsync();return content;}
}// 使用类型化客户端
{var services = new ServiceCollection();services//1、注入异常管道到服务.AddTransient<ExceptionDelegatingHandler>().AddHttpClient<HttpClientServiceC>().ConfigureHttpClient(client=>{client.BaseAddress = new Uri(webApiBaseUrl);})//2、添加异常管道至客户端.AddHttpMessageHandler<ExceptionDelegatingHandler>();var builder = services.BuildServiceProvider();var serverC = builder.GetRequiredService<HttpClientServiceC>();var dataC = await serverC.GetAsync();Console.WriteLine($"响应数据为：{dataC}");
}

• 工厂，加入异常管道

//使用
{var services = new ServiceCollection();//基础配置services//1、注入异常管道到服务.AddTransient<ExceptionDelegatingHandler>()//全局配置.ConfigureHttpClientDefaults(clientBuilder =>{clientBuilder.AddDefaultLogger();clientBuilder.ConfigureHttpClient(client => {client.BaseAddress = new Uri(webApiBaseUrl);});});//默认命名客户端services.AddHttpClient<HttpClient>(string.Empty, config => {config.DefaultRequestHeaders.Add("X-Custom-Demo", "true");})//配置客户端.ConfigureHttpClient(client => {client.BaseAddress = new Uri(webApiBaseUrl);client.Timeout = TimeSpan.FromSeconds(10);})//添加类型化客户端//.AddTypedClient<HttpClientServiceC>()//2、添加异常管道至客户端.AddHttpMessageHandler<ExceptionDelegatingHandler>()//配置SocketsHttpHandler.UseSocketsHttpHandler(config =>{//配置连接池等config.Configure((handler,provider) => {handler.AllowAutoRedirect = true;handler.PooledConnectionIdleTimeout = TimeSpan.FromSeconds(30);handler.PooledConnectionLifetime = TimeSpan.FromSeconds(30);handler.UseProxy = false;handler.UseCookies = true;});})//设置生命周期.SetHandlerLifetime(TimeSpan.FromSeconds(30))//Polly策略配置//.AddPolicyHandler(policy)//便捷配置//.AddTransientHttpErrorPolicy(builder => builder.CircuitBreakerAsync<HttpResponseMessage>(11, TimeSpan.FromSeconds(30)));var factory = services.BuildServiceProvider().GetRequiredService<IHttpClientFactory>();//正常请求var defaultClient = factory.CreateClient();var defaultContent = await defaultClient.GetStringAsync("api/hello/ping");Console.WriteLine(defaultContent);//异常请求var clientA = factory.CreateClient();var responseA = await clientA.GetAsync("/api/ErrorDemo/Error500");Console.WriteLine($"响应码：{responseA.StatusCode}");
}

工厂 + Polly库处理

Polly库提供了多种多样的超时、异常等功能，非常推荐使用(可以配合IoC/工厂)。

下面是简单例子：

//polly策略
var policy = Policy.Handle<HttpRequestException>().OrResult<HttpResponseMessage>(message => message.StatusCode != System.Net.HttpStatusCode.OK)//后备策略，代替异常.FallbackAsync(async fallbackAction =>{Console.WriteLine("运程调用发性异常,Polly进行了回退！");return await Task.FromResult(new HttpResponseMessage(HttpStatusCode.InternalServerError));});//工厂中使用 Polly异常回退策略
{var services = new ServiceCollection();//默认命名客户端services.AddHttpClient<HttpClient>(string.Empty).ConfigureHttpClient(client => {client.BaseAddress = new Uri(webApiBaseUrl);client.Timeout = TimeSpan.FromSeconds(10);})//Polly策略配置.AddPolicyHandler(policy);var factory = services.BuildServiceProvider().GetRequiredService<IHttpClientFactory>();//正常请求var defaultClient = factory.CreateClient();var defaultContent = await defaultClient.GetStringAsync("api/hello/ping");Console.WriteLine($"正常请求, 响应内容： {defaultContent}");//异常请求var clientA = factory.CreateClient();var responseA = await clientA.GetAsync("/api/ErrorDemo/Error500");Console.WriteLine($"异常请求，响应码：{responseA.StatusCode}");
}