Question

我正在尝试向Web服务发送一个简单的HTTP POST请求并读取响应。我需要在.NET项目中执行此操作，但调用始终失败。我测试过用Java调用相同的Web服务，它没有任何问题。

这是我在C＃中的代码：

HttpRequestMessage requestMessage = new HttpRequestMessage(HttpMethod.Post, "web service URI");


        string json = "some json input";
        requestMessage.Content = new StringContent(json, Encoding.UTF8, "application/json");            
        HttpClient httpClient = new HttpClient();       
        httpClient.DefaultRequestHeaders.Add("User-Agent", "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2) Gecko/20100115 Firefox/3.6 (.NET CLR 3.5.30729)");
        httpClient.DefaultRequestHeaders.Add("Accept-Language", "en");
        httpClient.DefaultRequestHeaders.Add("Accept", "image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, */*");                                                                                                                    
        httpClient.DefaultRequestHeaders.Add("Accept-Encoding", "gzip, deflate");
        httpClient.DefaultRequestHeaders.Add("Cache-Control", "no-cache");
        httpClient.DefaultRequestHeaders.Add("Connection", "Keep-Alive");
        httpClient.DefaultRequestHeaders.ExpectContinue = false;

        try
        {               
            Task<HttpResponseMessage> httpRequest = httpClient.SendAsync(requestMessage, HttpCompletionOption.ResponseContentRead
                , CancellationToken.None);

            HttpResponseMessage httpResponse = httpRequest.Result;
            HttpStatusCode statusCode = httpResponse.StatusCode;
            HttpContent responseContent = httpResponse.Content;
            if (responseContent != null)
            {
                Task<string> stringContentTask = responseContent.ReadAsStringAsync();
                string stringContent = stringContentTask.Result;
                return stringContent;
            }
            else
            {
                throw new Exception("Response content is null.");
            }
        }
        catch (AggregateException ae)
        {
            List<Exception> innerExceptions = ae.InnerExceptions.ToList();
            StringBuilder sb = new StringBuilder();
            foreach (Exception e in innerExceptions)
            {
                sb.Append(e.Message).Append(Environment.NewLine);
                if (e.InnerException != null)
                {
                    sb.Append(e.InnerException.Message).Append(Environment.NewLine);
                }
            }
            Console.WriteLine(sb.ToString());
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.Message);
        }

当我调用httpRequest.Result时代码失败。最终的异常消息如下：

“无法从传输连接读取数据：连接已关闭。”

但是，当我在Java中尝试相同时，它可以完美地运行。这是我的Java代码：

String url = "web service URI";
        URL obj = new URL(url);
        HttpURLConnection connection = (HttpURLConnection) obj.openConnection();
        connection.setRequestMethod("POST");
        connection.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2) Gecko/20100115 Firefox/3.6 (.NET CLR 3.5.30729)");
        connection.setRequestProperty("Accept-Language", "en");
        connection.setRequestProperty("Accept", "image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, */*");
        connection.setRequestProperty("Accept-Encoding", "gzip, deflate");
        connection.setRequestProperty("Content-Type", "application/json");
        connection.setRequestProperty("Cache-Control", "no-cache");
        connection.setRequestProperty("Connection", "Close");
        String content = "some json";
        connection.setDoOutput(true);
        DataOutputStream wr = new DataOutputStream(connection.getOutputStream());
        wr.writeBytes(content);
        wr.flush();
        wr.close();

        int responseCode = connection.getResponseCode();
        System.out.println("\nSending 'POST' request to URL : " + url);
        System.out.println("Post parameters : " + content);
        System.out.println("Response Code : " + responseCode);

        BufferedReader in = new BufferedReader(
                new InputStreamReader(connection.getInputStream()));
        String inputLine;
        StringBuilder response = new StringBuilder();

        while ((inputLine = in.readLine()) != null)
        {
            response.append(inputLine);
        }
        in.close();

        //print result
        System.out.println(response.toString());

对于C＃部分，我在.NET中测试了其他与http相关的对象：HttpWebRequest和WebClient，只是为了获得相同的异常消息。

我怀疑.NET对象添加了某种类型的标头或默认设置，必须禁用它，但我不知道它是什么。

供参考：
- 即使我删除了对setRequestProperty的所有调用，Java代码仍然有效，因此代码在没有明确设置“User-Agent”，“Accept-Language”等的情况下通过。 - 设置Web服务以在通信结束后立即关闭连接，即没有保持活动可用。我似乎记得.NET Web客户端对象“不喜欢”这个功能，但我不打赌我的生活。 - 你会注意到我在C＃中将ExpectContinue设置为false，而在Java中则没有。在Java中，显然没有必要，而我必须在其他C＃项目中关闭它以使调用工作。我测试将其设置为true而结果没有任何差异。

欢迎任何建议。我无法控制Web服务设置，因此请不要提出任何需要进行此类更改的建议。

谢谢，安德拉斯

Answer 1

我建议不要添加连接头。首先，如果您想要请求服务器在请求后关闭连接，请使用HttpClient

   httpClient.DefaultRequestHeaders.ConnectionClose = true;

Http 1.1默认使用keep-alive，因此无需发送标头。如果服务器返回Connection: close，则客户端应该处理该问题。

当您开始弄乱它想要控制的标题时，HttpClient确实有点不高兴。

Answer 2

您可能想尝试Fiddler Web调试代理。找到HTTP流量（fiddler2.com）的差异可能会有所帮助。

Answer 3

试试这个

        HttpWebRequest request = (HttpWebRequest)WebRequest.Create("Your URL");
        byte[] data = Encoding.UTF8.GetBytes("Post Input");
        request.Method = "POST";
        request.Accept = "application/json"; //you can set application/xml
        request.ContentType = "application/json";// you can set application/xml
        Stream dataStream = request.GetRequestStream();
        dataStream.Write(data, 0, data.Length);
        dataStream.Close();
        HttpWebResponse resp = (HttpWebResponse)request.GetResponse();
        StreamReader result = new StreamReader(resp.GetResponseStream());
        if( result !=null)
        {
        if(!string.IsNullorEmpty(result.ReadToEnd().ToString()))
        {
          MessageBox.Show(result.ReadToEnd().ToString());
        }
        }

Http POST请求在Java中成功但在C＃中失败

3 个答案: