c# - 当通过 .NET Compact 从 C# 向同一 Java 服务器发出两个 HttpWebRequest 时，出现 "Request timed out"

Question

我有一个在 .NETCF 3.5 设备上使用 C# 运行的客户端应用程序，并发送到位于远程的 Java servlet。在对同一个 servlet 进行第三次 HTTP POST 期间，我收到“请求超时”消息。例如，如果 servlet 管理对 Java 服务器的登录，则来自客户端的前两次登录尝试将通过(同一客户端设备)，当我尝试第三次时，它将返回“请求超时”异常。服务器。我注意到这种情况总是发生，但我无法找出问题所在。我读到，C# 默认情况下会在 HTTP header 中发送请求 100 继续，因此我使用 ServicePointManager 将请求 100 设置为 false，但无济于事。

这是引发此错误的代码:

            serverUrl = url;
            string responseFromServer = "";
            try
            {
                System.Net.ServicePointManager.Expect100Continue = false;
                int tmp = ServicePointManager.DefaultConnectionLimit;
                // Create a request using a URL that can receive a post. 
                request = (HttpWebRequest)WebRequest.Create(url);
                // Set the Method property of the request to POST.
                request.Method = "POST";
                // Create POST data and convert it to a byte array.            
                byte[] byteArray = System.Text.Encoding.UTF8.GetBytes(url);
                // Set the ContentType property of the WebRequest.
                request.ContentType = "application/x-www-form-urlencoded";                
                // Set the ContentLength property of the WebRequest.
                request.ContentLength = byteArray.Length;
                request.Timeout = (50 * 100);
                request.Proxy = System.Net.GlobalProxySelection.GetEmptyWebProxy();
                // Get the request stream.
                Stream dataStream = request.GetRequestStream();
                // Write the data to the request stream.
                dataStream.Write(byteArray, 0, byteArray.Length);
                // Close the Stream object.
                dataStream.Close();
                // Get the response.
                response = (HttpWebResponse)request.GetResponse();
                // Get the stream containing content returned by the server.
                dataStream = response.GetResponseStream();
                // Open the stream using a StreamReader for easy access.
                StreamReader reader = new StreamReader(dataStream);
                // Read the content.
                responseFromServer = reader.ReadToEnd();
                // Clean up the streams.
                reader.Close();
                dataStream.Close();
                response.Close();

                return responseFromServer;
            }
            catch (Exception WebExp)
            {
                Logging.Instance.Log(Logging.Levels.Error, "Error in DoPost while retrieving : "+url+ " " + WebExp.Message.ToString());
                Logging.Instance.Log(Logging.Levels.Error, WebExp.StackTrace.ToString());
                throw WebExp;
            }

任何帮助将不胜感激。谢谢!

Answer 1

此行为是由于对 WebResponse 的错误异常处理造成的。您必须始终处理响应并关闭它。否则，第三次尝试 HTTP Webrequest 将会失败，并出现超时(受 WinCE 限制)。

以下源代码是安全的:

HttpWebResponse response = null;
try
{
    //...
    response = (HttpWebResponse)request.GetResponse();
    //...
}
catch(Exception e)
{
    // logging, etc.
    throw e;
}
finally
{
    if(response!=null)
    {
        response.Close();
    }
}