第壹種方式
直接在創建的HttpClient對象的DefaultRequestHeaders集合中添加報頭。
class Program
{undefined
static Task Main()=> SendAsync1();
private static async Task SendAsync1()
{undefined
var httpClient = new HttpClient();
AddDefaultHeaders(httpClient);
await httpClient.GetStringAsync("http://localhost:5000/");
}
private static void AddDefaultHeaders(HttpClient httpClient)
{undefined
httpClient.DefaultRequestHeaders.Add("x-www-foo", "123");
httpClient.DefaultRequestHeaders.Add("x-www-bar", "456");
httpClient.DefaultRequestHeaders.Add("x-www-baz", "789");
}
}
第二種方式
對於.NET Core應用來說，我們更推薦的做法是采用依賴註入的方式，利用IHttpClientFactory來創建HttpClient對象，那麽我們在進行相關服務註冊的時候就可以設置默認請求報頭。
class Program
{undefined
static Task Main()=> SendAsync2();
private static async Task SendAsync2()
{undefined
var services = new ServiceCollection();
services.AddHttpClient("", AddDefaultHeaders);
var httpClient = services
.BuildServiceProvider()
.GetRequiredService()
.CreateClient();
await httpClient.GetStringAsync("http://localhost:5000/");
}
private static void AddDefaultHeaders(HttpClient httpClient)
{undefined
httpClient.DefaultRequestHeaders.Add("x-www-foo", "123");
httpClient.DefaultRequestHeaders.Add("x-www-bar", "456");
httpClient.DefaultRequestHeaders.Add("x-www-baz", "789");
}
}
第三種方式
由於HttpClient在發送請求的時候會利用DiagnosticSource對象發送相應的診斷事件，並且將作為請求的HttpRequestMessage對象作為請求事件內容負載。我們可以訂閱該事件，在請求被發送之前將其攔截下來，並添加相應的請求頭即可。
class Program
{undefined
static Task Main()=> SendAsync3();
private static async Task SendAsync3()
{undefined
Func requestAccessor = null;
DiagnosticListener.AllListeners.Subscribe(listener =>
{undefined
if (listener.Name == "HttpHandlerDiagnosticListener")
{undefined
listener.Subscribe(kv =>
{undefined
if (kv.Key == "System.Net.Http.HttpRequestOut.Start")
{undefined
requestAccessor ?= BuildRequestAccessor(kv.Value.GetType());
var request = requestAccessor(kv.Value);
AddDefaultHeaders(request);
}
});
}
});
var httpClient = new HttpClient();
await httpClient.GetStringAsync("http://localhost:5000/");
static Func BuildRequestAccessor(Type payloadType)
{undefined
var property = payloadType.GetProperty("Request", BindingFlags.Instance | BindingFlags.Public);
var payload = Expression.Parameter(typeof(object));
var convertedPayload = Expression.Convert(payload, payloadType);
var getRequest = Expression.Call(convertedPayload, property.GetMethod);
var convert = Expression.Convert(getRequest, typeof(HttpRequestMessage));
return Expression.Lambda>(convert, payload).Compile();
}
}
private static void AddDefaultHeaders(HttpRequestMessage request)
{undefined
request.Headers.Add("x-www-foo", "123");
request.Headers.Add("x-www-bar", "456");
request.Headers.Add("x-www-baz", "789");
}
}
第四種方式
上面這種方式可以采用強類型編程方式，具體的代碼如下。
class Program
{undefined
static Task Main()=> SendAsync4();
private static async Task SendAsync4()
{undefined
DiagnosticListener.AllListeners.Subscribe(listener =>
{undefined
if (listener.Name == "HttpHandlerDiagnosticListener")
{undefined
listener.SubscribeWithAdapter(new HttpClientListener());
}
});
var httpClient = new HttpClient();
await httpClient.GetStringAsync("http://localhost:5000/");
}
private sealed class HttpClientListener
{undefined
[DiagnosticName("System.Net.Http.HttpRequestOut.Start")]
public void OnSend(HttpRequestMessage request) => AddDefaultHeaders(request);
//Must subscribute the System.Net.Http.HttpRequestOut event.
[DiagnosticName("System.Net.Http.HttpRequestOut")]
public void OnSend() { }
}
private static void AddDefaultHeaders(HttpRequestMessage request)
{undefined
request.Headers.Add("x-www-foo", "123");
request.Headers.Add("x-www-bar", "456");
request.Headers.Add("x-www-baz", "789");
}
}