提供XML文件供asp.net c＃中的大量記錄下載

Question

我需要提供xml文件以便下載6,00,000條記錄（數據可能會增加）但不允許將文件保存在磁盤上。 我直接將xml寫入流然后提供下載時遇到問題，所以我首先在磁盤上創建了xml文件並將數據寫入其中並嘗試讀取它並提供下載然后從磁盤中刪除文件。 但是在“Byte [] b = File.ReadAllBytes（filepath）;”中獲取“system.outofmemoryexception”。

以下是我的代碼：

string name = string.Format("{0:yyyyMMddHHmmss}", DateTime.Now);
string filename = "TestFile.xml";

string filepath = ConfigurationManager.AppSettings["XmlFiles"] + "\\" + filename;


DataTable dataTable = dsData.Tables[0];             

FileStream fs =new FileStream(filepath, FileMode.Create);
XmlWriterSettings xws = new XmlWriterSettings { OmitXmlDeclaration = true };
using (XmlWriter xmlWriter = XmlWriter.Create(fs,xws))
{

  xmlWriter.WriteStartElement("root");

  foreach (DataRow dataRow in dataTable.Rows)
  {
    xmlWriter.WriteStartElement("datanode");
    foreach (DataColumn dataColumn in dataTable.Columns)
    {
     xmlWriter.WriteElementString(dataColumn.ColumnName.Replace("\n\r", " ")
                                  .Replace("\n", " ").Replace("\r", " "), Convert.ToString(dataRow[dataColumn]).Replace("\n\r", " ").Replace("\n", " ").Replace("\r", " "));
                        }

         xmlWriter.WriteEndElement();
     }
     xmlWriter.WriteEndElement();
     xmlWriter.Flush();
     xmlWriter.Close();
   }

   fs.Close();
   Byte[] b = File.ReadAllBytes(filepath);                
   if (File.Exists(filepath))
      File.Delete(filepath);

string s = string.Format("{0:yyyyMMddHHmmss}", DateTime.Now);
HttpContext.Current.Response.ContentType = "application/xml";
HttpContext.Current.Response.ContentEncoding = System.Text.Encoding.UTF8;
HttpContext.Current.Response.AppendHeader("Content-Disposition", "attachment; filename=" + s + ".xml" + "");
HttpContext.Current.Response.BinaryWrite(b);
HttpContext.Current.Response.End();

還有其他方法可以處理大量記錄嗎？

Answer 1

您可以直接將XmlWriter連接到Response OutputStream，而無需中間文件。 通過將BufferOutput設置為false可以在發送到客戶端之前阻止完整的repsonse緩沖服務器端。

請注意，多個Replace語句將導致額外的內存壓力/更多字符串被GC編輯。

string name = string.Format("attachment; filename={0:yyyyMMddHHmmss}.xml", DateTime.Now);
HttpContext.Current.Response.ContentType = "application/xml";
HttpContext.Current.Response.ContentEncoding = System.Text.Encoding.UTF8;

HttpContext.Current.Response.BufferOutput = false; //start streaming immideately

HttpContext.Current.Response.AppendHeader("Content-Disposition", name);

DataTable dataTable = dsData.Tables[0];             

XmlWriterSettings xws = new XmlWriterSettings { OmitXmlDeclaration = true };

using (XmlWriter xmlWriter = XmlWriter.Create(
         HttpContext.Current.Response.OutputStream,  // The OutputStream of the HttpResponse
         xws))
{
  xmlWriter.WriteStartElement("root");

  var cleanedColNames = new Dictionary<DataColumn, string>();
  foreach (DataColumn dataColumn in dataTable.Columns)
  {
      cleanedColNames.Add(dataColumn, 
          dataColumn.ColumnName.Replace("\n\r", " ")
                               .Replace("\n", " ")
                               .Replace("\r", " "));
  }

  foreach (DataRow dataRow in dataTable.Rows)
  {
    xmlWriter.WriteStartElement("datanode");
    foreach (DataColumn dataColumn in dataTable.Columns)
    {
         xmlWriter.WriteElementString(
             cleanedColNames[dataColumn],  
             Convert.ToString(dataRow[dataColumn]).Replace("\n\r", " ")
                                                  .Replace("\n", " ")
                                                  .Replace("\r", " "));
                        }
         xmlWriter.WriteEndElement();
     }
     xmlWriter.WriteEndElement();
     xmlWriter.Flush();
     xmlWriter.Close();
   }

HttpContext.Current.Response.End();