Question

我对一个返回任务的webapi客户端进行了多次调用像这样的东西

public async Task<TResp> GetMyThingAsync(TReq req)
{
    using (HttpClient client = new HttpClient())
    {
        client.BaseAddress = new Uri(BaseURI);
        client.DefaultRequestHeaders.Accept.Clear();
        client.DefaultRequestHeaders.Accept.Add(new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("application/json"));
        client.DefaultRequestHeaders.Accept.Add(new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("application/xml"));

        await HttpRuntime.Cache.GetToken().ContinueWith((t) =>
        {
            client.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("XXX", t.Result);
        });

        var httpResponseMessage = await client.PostAsXmlAsync<TReq>("This/That/", req);
        httpResponseMessage.EnsureSuccessStatusCode();
        var resp = await httpResponseMessage.Content.ReadAsAsync<TResp>();
        return resp;
    }
}

对api的调用当然可以返回500或其他一些问题。如果类似的事情发生，EnsureSuccessStatusCode()显然会抛出，但是对于响应中的任何信息做任何事都为时已晚。有一个很好的方法来处理这个？我知道你可以在客户端添加一个messageHandler，比如 HttpClient client = HttpClientFactory(new ErrorMessageHandler()) ..

var customHandler = new ErrorMessageHandler()
        { InnerHandler = new HttpClientHandler()};
HttpClient client = new HttpClient(customHandler);

这是要走的路吗？ ErroMessageHandler会是什么样子，并且会向调用控制器返回一些有用的东西......？

非常感谢

NAT

Answer 1

创建自定义处理程序可以成为记录异常或验证响应的优雅解决方案。如果遇到异常，我不确定被叫控制器是否正在等待来自客户端的有意义的响应。我认为真正重要的部分是确保您（客户端）优雅地处理Web apis错误。

这可以通过以下两种方式完成：

您可以在调用方法中本地处理异常。您可以使用HttpResponseMessage.IsSuccessStatusCode属性指示是否返回错误响应而不是调用引发异常的httpResponseMessage.EnsureSuccessStatusCode()，并返回自定义ErrorResponse（或执行您决定的任何操作）：

var client = new HttpClient() // No need to dispose HttpClient

client.BaseAddress = new Uri(BaseURI);
client.DefaultRequestHeaders.Accept.Clear();

client.DefaultRequestHeaders.Accept.Add(new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("application/json"));
client.DefaultRequestHeaders.Accept.Add(new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("application/xml"));

var token = await HttpRuntime.Cache.GetToken();
client.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("XXX", token);

var httpResponseMessage = await client.PostAsXmlAsync<TReq>("This/That/", req);
if (!httpResponseMessage.IsSuccessStatusCode)
{
   return Task.FromResult(new ErrorResponse()) // Create some kind of error response to indicate failure
}

var resp = await httpResponseMessage.Content.ReadAsAsync<TResp>();
return resp;

创建一个ErrorLoggingHandler，它可以记录从web api收到的异常（或做其他事情）：

public class ErrorLoggingHandler : DelegatingHandler
{
   private readonly StreamWriter _writer; // As a sample, log to a StreamWriter

   public ErrorLoggingHandler(Stream stream)
   {
      _writer = new StreamWriter(stream);
   }

   protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, System.Threading.CancellationToken cancellationToken)
   {
      var response = await base.SendAsync(request, cancellationToken);

      if (!response.IsSuccessStatusCode)
      {
          // This would probably be replaced with real error 
          // handling logic (return some kind of special response etc..)
          _writer.WriteLine("{0}\t{1}\t{2}", request.RequestUri,
            (int) response.StatusCode, response.Headers.Date);
      }

      return response;
   }

   protected override void Dispose(bool disposing)
   {
      if (disposing)
      {
         _writer.Dispose();
      }

      base.Dispose(disposing);
   }
}

然后，您可以使用HttpClient创建HttpClientFactory：

var httpclient = HttpClientFactory.Create(new ErrorLoggingHandler(new FileStream(@"Location", FileMode.OpenOrCreate)));

处理类型化的Web API HttpClient调用中的错误

1 个答案: