C# 网络编程-关于HttpClient使用方式（三）

前面有讲到比较底层一点的请求方式C# 网络编程-关于HttpWebRequest使用方式（二）：，官方是推荐使用HttpClient的常用请求方式，可能为了在跨平台兼容吧，HttpClient涵盖GET、POST、PUT、DELETE等方法

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一、基础请求方式

1. GET 请求（获取数据）

using System.Net.Http;
using System.Threading.Tasks;

public async Task<string> GetAsStringAsync(string url)
{
    using (HttpClient client = new HttpClient())
    {
        try
        {
            HttpResponseMessage response = await client.GetAsync(url);
            response.EnsureSuccessStatusCode(); // 检查HTTP状态码（如200）
            return await response.Content.ReadAsStringAsync();
        }
        catch (HttpRequestException ex)
        {
            Console.WriteLine($"请求失败: {ex.Message}");
            return null;
        }
    }
}

2. POST 请求（提交数据）

public async Task<string> PostAsStringAsync(string url, string jsonContent)
{
    using (HttpClient client = new HttpClient())
    {
        try
        {
            // 创建JSON内容
            StringContent content = new StringContent(jsonContent, Encoding.UTF8, "application/json");
            HttpResponseMessage response = await client.PostAsync(url, content);
            response.EnsureSuccessStatusCode();
            return await response.Content.ReadAsStringAsync();
        }
        catch (HttpRequestException ex)
        {
            Console.WriteLine($"请求失败: {ex.Message}");
            return null;
        }
    }
}

3. PUT 请求（更新数据）

public async Task<string> PutAsStringAsync(string url, string jsonContent)
{
    using (HttpClient client = new HttpClient())
    {
        try
        {
            StringContent content = new StringContent(jsonContent, Encoding.UTF8, "application/json");
            HttpResponseMessage response = await client.PutAsync(url, content);
            response.EnsureSuccessStatusCode();
            return await response.Content.ReadAsStringAsync();
        }
        catch (HttpRequestException ex)
        {
            Console.WriteLine($"请求失败: {ex.Message}");
            return null;
        }
    }
}

4. DELETE 请求（删除数据）

public async Task<string> DeleteAsStringAsync(string url)
{
    using (HttpClient client = new HttpClient())
    {
        try
        {
            HttpResponseMessage response = await client.DeleteAsync(url);
            response.EnsureSuccessStatusCode();
            return await response.Content.ReadAsStringAsync();
        }
        catch (HttpRequestException ex)
        {
            Console.WriteLine($"请求失败: {ex.Message}");
            return null;
        }
    }
}

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二、配置与最佳实践

1. 配置超时时间

HttpClient client = new HttpClient();
client.Timeout = TimeSpan.FromSeconds(10); // 设置超时时间为10秒

2. 添加请求头（如Authorization、Content-Type）

client.DefaultRequestHeaders.Add("Authorization", "Bearer your_token");
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

3. 避免重复创建HttpClient实例

• 问题 ：频繁创建HttpClient可能导致Socket资源耗尽。

• 解决方案 ：在应用程序生命周期中重用单个HttpClient实例：

  // 使用单例模式
  private static readonly HttpClient _client = new HttpClient();

4. 使用HttpClientFactory（推荐在ASP.NET Core中使用）

// 在Startup.cs中配置：
services.AddHttpClient<IMyService, MyService>()
    .SetBaseAddress(new Uri("https://api.example.com"))
    .AddPolicyHandler(HttpPolicyRegistry); // 添加重试、超时等策略

// 在服务中注入：
public class MyService : IMyService
{
    private readonly HttpClient _client;
    public MyService(HttpClient client) => _client = client;
}

---

三、处理响应与异常

1. 处理响应内容

• 字符串响应 ：

  string result = await response.Content.ReadAsStringAsync();

• JSON反序列化 ：

  var myObject = await response.Content.ReadFromJsonAsync<MyModel>();
  // 或使用Newtonsoft.Json：
  var myObject = JsonConvert.DeserializeObject<MyModel>(result);

2. 异常处理

try
{
    // 发送请求
}
catch (HttpRequestException ex) when (ex.Message.Contains("404"))
{
    Console.WriteLine("资源未找到");
}
catch (TaskCanceledException ex)
{
    Console.WriteLine("请求超时");
}
catch (Exception ex)
{
    Console.WriteLine($"未知错误: {ex.Message}");
}

---

四、高级用法

1. 上传文件

public async Task UploadFileAsync(string url, string filePath)
{
    using (HttpClient client = new HttpClient())
    {
        var content = new MultipartFormDataContent();
        var fileContent = new ByteArrayContent(File.ReadAllBytes(filePath));
        fileContent.Headers.ContentDisposition = new ContentDispositionHeaderValue("form-data")
        {
            Name = "file",
            FileName = Path.GetFileName(filePath)
        };
        content.Add(fileContent);
        
        await client.PostAsync(url, content);
    }
}

2. 发送表单数据（application/x-www-form-urlencoded）

public async Task PostFormAsync(string url, Dictionary<string, string> formData)
{
    var content = new FormUrlEncodedContent(formData);
    await client.PostAsync(url, content);
}

3. 使用JSON序列化（System.Text.Json）

var myObject = new MyModel { Name = "Test" };
var jsonContent = JsonSerializer.Serialize(myObject);
var content = new StringContent(jsonContent, Encoding.UTF8, "application/json");

---

五、完整示例

public class ApiService
{
    private readonly HttpClient _client;

    public ApiService(HttpClient client)
    {
        _client = client;
    }

    public async Task<T> GetAsync<T>(string endpoint)
    {
        var response = await _client.GetAsync(endpoint);
        response.EnsureSuccessStatusCode();
        return await response.Content.ReadFromJsonAsync<T>();
    }

    public async Task<T> PostAsync<T>(string endpoint, object data)
    {
        var content = new StringContent(JsonSerializer.Serialize(data), Encoding.UTF8, "application/json");
        var response = await _client.PostAsync(endpoint, content);
        response.EnsureSuccessStatusCode();
        return await response.Content.ReadFromJsonAsync<T>();
    }
}

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关键注意事项

1. 异步编程 ：始终使用async/await，避免阻塞。
2. 资源管理 ：重用HttpClient实例，避免创建过多实例。
3. 异常处理 ：捕获HttpRequestException和TaskCanceledException。
4. 安全性 ：对于敏感操作（如身份验证），使用HttpClientFactory和策略模式。