C#封裝HttpClient：HTTP請求處理最佳實踐

在現代的.NET應用程序開發中，與外部服務進行HTTP通信是一項常見需求。HttpClient作為.NET框架中處理HTTP請求的核心組件，為我們提供了強大而靈活的API。然而，直接使用原生的HttpClient可能會導致代碼重復、錯誤處理不完善等問題。為了提高代碼的可維護性和可測試性，我們通常會對HttpClient進行封裝。本文將介紹一個完整的HttpRequest類封裝實現，并深入探討HTTP請求處理的最佳實踐。

一、完整的HttpRequest類實現

首先，讓我們來看一下完整的HttpRequest類實現代碼：

using System;
using System.Collections.Generic;
using System.Net;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Text;
using System.Text.Json;
using System.Threading.Tasks;public class Response
{public bool Success { get; set; }public string Message { get; set; }public object Data { get; set; }public HttpStatusCode StatusCode { get; set; }
}public static class JsonConverterExtensions
{public static readonly JsonSerializerOptions SerializerSettings = new JsonSerializerOptions{PropertyNamingPolicy = JsonNamingPolicy.CamelCase,IgnoreNullValues = true,WriteIndented = false};
}public class HttpRequest : IDisposable
{private readonly HttpClient client;private bool disposed = false;public HttpRequest(HttpClient client){this.client = client ?? throw new ArgumentNullException(nameof(client));}public void Dispose(){Dispose(true);GC.SuppressFinalize(this);}protected virtual void Dispose(bool disposing){if (!disposed){if (disposing){client?.Dispose();}disposed = true;}}public async Task<Response> GetAsync(string resource){try{var response = await client.GetAsync(resource);return await ProcessResponseAsync(response);}catch (HttpRequestException ex){return HandleException(ex);}catch (Exception ex){return HandleUnexpectedException(ex);}}public async Task<Response> PostAsync(string resource, object body){try{var content = CreateJsonContent(body);var response = await client.PostAsync(resource, content);return await ProcessResponseAsync(response);}catch (HttpRequestException ex){return HandleException(ex);}catch (Exception ex){return HandleUnexpectedException(ex);}}public async Task<Response> PutAsync(string resource, object body){try{var content = CreateJsonContent(body);var response = await client.PutAsync(resource, content);return await ProcessResponseAsync(response);}catch (HttpRequestException ex){return HandleException(ex);}catch (Exception ex){return HandleUnexpectedException(ex);}}public async Task<Response> DeleteAsync(string resource){try{var response = await client.DeleteAsync(resource);return await ProcessResponseAsync(response);}catch (HttpRequestException ex){return HandleException(ex);}catch (Exception ex){return HandleUnexpectedException(ex);}}public HttpRequest WithBaseAddress(string baseAddress){if (!string.IsNullOrEmpty(baseAddress)){client.BaseAddress = new Uri(baseAddress);}return this;}public HttpRequest WithTimeout(TimeSpan timeout){client.Timeout = timeout;return this;}public HttpRequest WithHeader(string name, string value){if (!client.DefaultRequestHeaders.Contains(name)){client.DefaultRequestHeaders.Add(name, value);}return this;}public HttpRequest WithHeaders(IDictionary<string, string> headers){if (headers != null){foreach (var header in headers){WithHeader(header.Key, header.Value);}}return this;}public HttpRequest WithAuthorization(string scheme, string parameter){client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(scheme, parameter);return this;}public HttpRequest WithBearerToken(string token){return WithAuthorization("Bearer", token);}private StringContent CreateJsonContent(object body){if (body == null){return new StringContent("{}", Encoding.UTF8, "application/json");}var json = JsonSerializer.Serialize(body, JsonConverterExtensions.SerializerSettings);return new StringContent(json, Encoding.UTF8, "application/json");}private async Task<Response> ProcessResponseAsync(HttpResponseMessage response){var responseContent = await response.Content.ReadAsStringAsync();try{// 嘗試解析JSON響應var responseObject = JsonSerializer.Deserialize<Response>(responseContent, JsonConverterExtensions.SerializerSettings);if (responseObject != null){responseObject.StatusCode = response.StatusCode;return responseObject;}}catch (JsonException){// 如果JSON解析失敗，創建一個基于HTTP狀態碼的響應}// 對于非JSON響應或解析失敗的情況return new Response{Success = response.IsSuccessStatusCode,Message = response.ReasonPhrase,StatusCode = response.StatusCode,Data = responseContent};}private Response HandleException(HttpRequestException ex){return new Response{Success = false,Message = $"HTTP請求錯誤: {ex.Message}",StatusCode = ex.StatusCode ?? HttpStatusCode.InternalServerError,Data = ex};}private Response HandleUnexpectedException(Exception ex){return new Response{Success = false,Message = $"處理請求時發生意外錯誤: {ex.Message}",StatusCode = HttpStatusCode.InternalServerError,Data = ex};}
}

二、設計思路與實現要點

1. 依賴注入與生命周期管理

這個封裝類采用了依賴注入模式，通過構造函數接收一個HttpClient實例。這樣做有幾個重要好處：

遵循單一職責原則，HttpRequest類專注于HTTP請求處理
便于單元測試，可以輕松注入模擬的HttpClient
利用.NET的IHttpClientFactory進行正確的HttpClient生命周期管理，避免資源泄漏

同時，類實現了IDisposable接口，確保在不再需要時正確釋放HttpClient資源。

2. 流暢接口設計

為了提供更友好的API體驗，封裝類實現了流暢接口模式：

var response = await new HttpRequest(httpClient).WithBaseAddress("https://api.example.com").WithBearerToken("your-token-here").WithHeader("X-Custom-Header", "value").PostAsync("/resource", new { Key = "value" });

這種鏈式調用方式使代碼更加簡潔易讀，同時保持了良好的可擴展性。

3. 統一的錯誤處理

在每個HTTP方法中，我們都實現了統一的異常處理機制：

捕獲HttpRequestException處理HTTP特定錯誤
捕獲其他異常處理意外錯誤
將所有錯誤轉換為統一的Response對象
保留原始異常信息以便調試

這種統一的錯誤處理方式使上層調用代碼更加簡潔，無需重復處理各種異常情況。

4. 靈活的響應處理

ProcessResponseAsync方法負責處理HTTP響應，它嘗試將響應內容解析為JSON格式的Response對象：

如果解析成功，返回包含完整信息的Response對象
如果解析失敗，創建一個基于HTTP狀態碼的Response對象
始終保留原始響應內容和狀態碼信息

這種設計使封裝類能夠處理各種類型的HTTP響應，同時提供一致的返回格式。

三、實際使用示例

下面是一個使用這個封裝類的完整示例：

using System;
using System.Net.Http;
using System.Threading.Tasks;public class Program
{public static async Task Main(){try{// 創建HttpClient實例（實際應用中建議使用IHttpClientFactory）using var httpClient = new HttpClient();// 創建請求實例并配置var request = new HttpRequest(httpClient).WithBaseAddress("https://api.example.com").WithBearerToken("your-auth-token");// 發送GET請求var getResponse = await request.GetAsync("/api/users");Console.WriteLine($"GET請求結果: {getResponse.Success}, 狀態碼: {getResponse.StatusCode}");// 發送POST請求var postData = new { Name = "John Doe", Email = "john@example.com" };var postResponse = await request.PostAsync("/api/users", postData);Console.WriteLine($"POST請求結果: {postResponse.Success}, 狀態碼: {postResponse.StatusCode}");// 發送PUT請求var putData = new { Id = 1, Name = "Jane Doe" };var putResponse = await request.PutAsync("/api/users/1", putData);Console.WriteLine($"PUT請求結果: {putResponse.Success}, 狀態碼: {putResponse.StatusCode}");// 發送DELETE請求var deleteResponse = await request.DeleteAsync("/api/users/1");Console.WriteLine($"DELETE請求結果: {deleteResponse.Success}, 狀態碼: {deleteResponse.StatusCode}");}catch (Exception ex){Console.WriteLine($"發生未處理的異常: {ex.Message}");}}
}

四、HttpClient使用最佳實踐

在使用HttpClient和這個封裝類時，還需要注意以下最佳實踐：

1. 使用IHttpClientFactory：在ASP.NET Core應用中，始終使用IHttpClientFactory創建HttpClient實例，避免直接實例化HttpClient。
1. 設置合理的超時時間：默認情況下，HttpClient的超時時間是100秒，根據實際需求調整這個值，防止長時間阻塞。
1. 處理取消請求：考慮實現請求取消機制，通過CancellationToken參數傳遞取消令牌。
1. 處理重試邏輯：對于臨時性網絡錯誤，考慮實現重試機制。可以使用Polly等庫來簡化重試策略的實現。
1. 監控HTTP請求性能：記錄HTTP請求的執行時間、成功率等指標，便于性能分析和問題排查。