我相信很多人在做项目的都碰到过Excel数据导出的需求，我从最开始使用最原始的HTML拼接（将需要导出的数据拼接成TABLE标签）到后来happy的使用开源的NPOI, EPPlus等开源组件导出EXCEL，但不久前，我在一个项目碰到一个需求：要将几个分别有近60多万的数据源导出到Excel中，我们先不要讨论这个需求本身是否合理，客户就是要这样。我先后用NPOI和EPPlus，都发现同一个问题：OutOfMemoryException，我电脑12G内存居然不够用？
的确内存溢出了，但内存还剩下好几个G的，就会溢出，我用 .NET做的网站，开发的时候Host应该是Visual Studio安装的IIS Express, 应该是VS本身的限制，不过在网上查阅资料也没发现这的确也是困扰一些人的，也没查到什么结果，好在还有Google, 跃过墙外，在Stack Overflow上查到资料： OpenXML , 这不是什么新技: Office 2007在设计的时候, 为了更好的和其它应用程序交互，使用了XML + ZIP技术来实现excel, world, PPT等组件的本地保存, 我们所使用xlsx, dox, pptx文件本质上就一个ZIP压缩包，包内是组织好的XML文件，也就是说，我们可以通过生成, 修改, 生成合规的XML文件，再压缩成ZIP包，这就是一个可以被Office识别的文件了。
用图说话：
在园子里其实也有不少人介绍过 Open XML， 我想就多一个视角来介绍Open XML吧，好像也有很长时间没人写关于这个博文。
什么是Office Open XML?
我们来看下维基百科的定义：
Office Open XML (also informally known as OOXML or Microsoft Open XML (MOX)[2) is a zipped, XML-based file format developed by Microsoft[3] for representing spreadsheets, charts, presentations and word processing documents. The format was initially standardized by Ecma (as ECMA-376), and by the ISO and IEC (as ISO/IEC 29500) in later versions.
Starting with Microsoft Office 2007, the Office Open XML file formats have become the default[4] target file format of Microsoft Office.[5][6] Microsoft Office 2010 provides read support for ECMA-376, read/write support for ISO/IEC 29500 Transitional, and read support for ISO/IEC 29500 Strict.[7] Microsoft Office 2013 and Microsoft Office 2016 additionally support both reading and writing of ISO/IEC 29500 Strict.[8]re
refer: https://en.wikipedia.org/wiki/Office_Open_XML
从Office 2007开始，就开始使用XML文件格式作为Microsoft Office的默认保存方式，其实我们通常用的NPOI office 2007部分和EPPlus就是使用Open XML来开发的。
为什么同是使用Open XML， NPOI和EPPLus会出现内存溢出的问题？
这两个开源组件有对Office套件有着很全面的支持，它们会把数据加载到内存中一次性处理，如果碰到数据量过大，就很可能 遇到这个问题，网上EPPlus在20多万条数据的就溢出了，NPOI在11多万的时候就会溢出， 这个是和数据的列数和内容有关系，不管怎样，我们以后可能是会碰到这种大量数据的EXCEL导出，我们不需要很复杂的功能，就是想要导出一个EXCEL列表，这其实是可以做到的。
Open XML怎样做不会内存溢出？
NPOI和EPPlus在导出大量数据 的Excel列表时可能 会发生内存溢出的问题，原因是它们都把数据保存在内存中，因为它们支持各种复杂的功能，那么简单的列表，就是数量超大，我们把它通过文件流写入磁盘，这个问题就解决了。
如何使用OPEN XML?
我们需要去微软官网下载OFFICE OPEN XML的SDK，链接: https://www.microsoft.com/en-hk/download/details.aspx?id=30425，推荐使用NuGet在VISULAL STUDIO直接将引用添加到Project。
在GitHub还有一些示例代码：https://github.com/OfficeDev/Open-XML-SDK
代码实现
说了这么多废话，我们看如何用OPEN XML实现一个EXCEL列表的导出:
从原理上讲就是用OpenXML一个一个把标签写入本地磁盘。
我截取我写的导出类的几个方法来来解释:
/// <summary>/// 指定磁盘路径初始化OpenWorkDoucment/// </summary>/// <param name="fileName"></param>private void OpenWorkDocument(string fileName){ ????document = SpreadsheetDocument.Create(fileName, SpreadsheetDocumentType.Workbook);}///<summary>
///用datatable作为数据源，实际情况可以根据需要调整
///</summary>
public void AddSheet(DataTable dt, string sheetName)
???????{ ???????????if (dt == null || dt.Rows.Count == 0) ???????????{ ???????????????throw new ArgumentNullException(nameof(dt), "data source can not be null"); ???????????} ???????????if (document == null) ???????????{ ???????????????throw new ArgumentNullException(nameof(document), "please init document first"); ???????????} ???????????//this list of attributes will be used when writing a start element ???????????List<OpenXmlAttribute> attributes;
//这是我们为什么不会溢出的关键点, 使用XmlWriter写入磁盘 ???????????OpenXmlWriter writer; ?????????????WorksheetPart workSheetPart = document.WorkbookPart.AddNewPart<WorksheetPart>(); ???????????writer = OpenXmlWriter.Create(workSheetPart);
??????//使用OpenXML麻烦的地方就是我们要用SDK去拼接XML内容 ???????????writer.WriteStartElement(new Worksheet()); ???????????writer.WriteStartElement(new SheetViews()); //sheetViews ???????????writer.WriteStartElement(new SheetView() //sheetView ???????????{ ???????????????TabSelected = true, ???????????????WorkbookViewId = 0U ?//这里的下标是从0开始的 ???????????}); //这里是冻结列头，别问为什么是A2，我试了A1不行 ???????????Pane pane = new Pane() ???????????{ ???????????????State = new EnumValue<PaneStateValues>(PaneStateValues.Frozen), ???????????????VerticalSplit = new DoubleValue((double)1), ???????????????TopLeftCell = new StringValue("A2"), ???????????????ActivePane = new EnumValue<PaneValues>(PaneValues.BottomLeft) ???????????}; //对于一些文档本身的结构的描述，我们可以直接把准备属性设置正确，直接写入，因为描述实例很占用资源小，当然我们也可以把描述结点的子节点，子子节点都通过WriteStartElememt写入，不过很麻烦，容易出错 ???????????writer.WriteStartElement(pane); //Pane ???????????writer.WriteEndElement(); ??//Pane ???????????writer.WriteStartElement(new Selection() ???????????{ ???????????????Pane = new EnumValue<PaneValues>(PaneValues.BottomLeft) ???????????}); ???????????writer.WriteEndElement(); ??//Selection 关闭标签 ???????????writer.WriteEndElement(); //sheetView 关闭标签 ???????????writer.WriteEndElement(); //sheetViews 关闭标签 ???????????writer.WriteStartElement(new SheetData()); ???????????var rowIndex = 0; ???????????foreach (DataRow row in dt.Rows) ???????????{ ???????????????//build header ???????????????if (rowIndex == 0) ???????????????{ ???????????????????//create a new list of attributes ???????????????????attributes = new List<OpenXmlAttribute>(); ???????????????????// add the row index attribute to the list ???????????????????attributes.Add(new OpenXmlAttribute("r", null, (rowIndex + 1).ToString())); ???????????????????//header start ???????????????????writer.WriteStartElement(new Row(), attributes); ???????????????????foreach (DataColumn col in dt.Columns) ???????????????????{ ???????????????????????attributes = new List<OpenXmlAttribute>(); ???????????????????????//这里注意，在Excel在处理字符串的时候，会将所有的字符串保存到sharedStrings.xml, cell内写入在sharedString.XML的索引, 属性t(type)设置为s(str)//我们在导出excel的时候把sharedString.mxl考虑进来会加大复杂程度，所以将t设置为str, 一个不存在的type, excel会直接解析cell内的字串值 ???????????????????????attributes.Add(new OpenXmlAttribute("t", null, "str")); ???????????????????????//通过s指定style样式的下标 ???????????????????????attributes.Add(new OpenXmlAttribute("s", null, FORMAT_INDEX_HEADER.ToString()));
???????????????????????//能过r指定单元格位置，好像不是必需, 注意这里下标位置是从1开始的 ???????????????????????attributes.Add(new OpenXmlAttribute("r", "", string.Format("{0}{1}", GetColumnName(col.Ordinal + 1), rowIndex + 1))); ???????????????????????writer.WriteStartElement(new Cell(), attributes); ???????????????????????writer.WriteElement(new CellValue(col.ColumnName)); ???????????????????????writer.WriteEndElement(); ???????????????????} ???????????????????//header end ???????????????????writer.WriteEndElement(); ???????????????????rowIndex++; ???????????????} ???????????????//数据写入，我们通过xmlWriter不会触发异常//create a new list of attributes ???????????????attributes = new List<OpenXmlAttribute>(); ???????????????// add the row index attribute to the list ???????????????attributes.Add(new OpenXmlAttribute("r", null, (rowIndex + 1).ToString())); ???????????????//header start ???????????????writer.WriteStartElement(new Row(), attributes); ???????????????foreach (DataColumn col in dt.Columns) ???????????????{ ???????????????????attributes = new List<OpenXmlAttribute>(); ???????????????????switch (col.DataType.ToString()) ???????????????????{ ???????????????????????case "System.Int32": ???????????????????????????attributes.Add(new OpenXmlAttribute("s", null, FORMAT_INDEX_INT.ToString())); ???????????????????????????attributes.Add(new OpenXmlAttribute("t", null, "n")); //number ???????????????????????????break; ???????????????????????case "System.Double": ???????????????????????case "System.Decimal": ???????????????????????case "System.Float": ???????????????????????????attributes.Add(new OpenXmlAttribute("s", null, FORMAT_INDEX_DEC.ToString())); //header style ???????????????????????????attributes.Add(new OpenXmlAttribute("t", null, "n")); //number ???????????????????????????break; ???????????????????????default: ???????????????????????????attributes.Add(new OpenXmlAttribute("s", null, FORMAT_INDEX_STR.ToString())); //header style ???????????????????????????attributes.Add(new OpenXmlAttribute("t", null, "str")); //string ???????????????????????????break; ???????????????????} ???????????????????//add the cell reference attribute ???????????????????attributes.Add(new OpenXmlAttribute("r", null, string.Format("{0}{1}", GetColumnName(col.Ordinal + 1), rowIndex + 1))); ???????????????????writer.WriteStartElement(new Cell(), attributes); ???????????????????writer.WriteElement(new CellValue(row[col.Ordinal].ToString())); ???????????????????writer.WriteEndElement(); ???????????????} ???????????????//header end ???????????????writer.WriteEndElement(); ???????????????rowIndex++; ???????????} ???????????// End SheetData ???????????writer.WriteEndElement(); ???????????// End Worksheet ???????????writer.WriteEndElement(); ???????????writer.Close(); ???????????if (document.WorkbookPart.Workbook == null) ???????????{ ???????????????document.WorkbookPart.Workbook = new Workbook(); ???????????????document.WorkbookPart.Workbook.Append(new Sheets()); ???????????} ???????????//数据写入完成后，注册一个sheet引用到workbook.xml, 也就是在excel最下面的sheet name ???????????var sheet = new Sheet() ???????????{ ???????????????Name = !String.IsNullOrWhiteSpace(sheetName) ? sheetName : ("Sheet " + DateTime.Now.ToString("ms")), ???????????????SheetId = UInt32Value.FromUInt32((uint)m_sheetIndex++), ???????????????Id = document.WorkbookPart.GetIdOfPart(workSheetPart) ???????????}; ???????????document.WorkbookPart.Workbook.Sheets.Append(sheet);}//生成Style样式, 注意下标从0开始, 依次加1, 如果有跳过1直接设置3这样情况, 可能无法正常解析到样式private Stylesheet GenerateStylesheet() ???????{ ???????????Stylesheet styleSheet = null; ???????????Fonts fonts = new Fonts( ???????????????new Font( // Index 0 - default ???????????????????new FontSize() { Val = 11 } ???????????????), ???????????????new Font( // Index 1 - header ???????????????????new FontSize() { Val = 11 }, ???????????????????new Bold(), ???????????????????new Color() { Rgb = "FFFFFF" } ???????????????)); ???????????Fills fills = new Fills( ???????????????????new Fill(new PatternFill() { PatternType = PatternValues.None }), // Index 0 - default ???????????????????new Fill(new PatternFill() { PatternType = PatternValues.Gray125 }), // Index 1 - default ???????????????????new Fill(new PatternFill(new ForegroundColor { Rgb = new HexBinaryValue() { Value = "0070c0" } }) { PatternType = PatternValues.Solid }) ???????????????); ???????????Borders borders = new Borders( ???????????????????new Border(), // index 0 default ???????????????????new Border( // index 1 black border ???????????????????????new LeftBorder(new Color() { Auto = true }) { Style = BorderStyleValues.Thin }, ???????????????????????new RightBorder(new Color() { Auto = true }) { Style = BorderStyleValues.Thin }, ???????????????????????new TopBorder(new Color() { Auto = true }) { Style = BorderStyleValues.Thin }, ???????????????????????new BottomBorder(new Color() { Auto = true }) { Style = BorderStyleValues.Thin }, ???????????????????????new DiagonalBorder()) ???????????????); ???????????NumberingFormats numbers = new NumberingFormats( ???????????????new NumberingFormat() { NumberFormatId = 0, FormatCode = new StringValue("#,##0.00") }, ???????????????new NumberingFormat() { NumberFormatId = 1, FormatCode = new StringValue("0") } ???????????????); ???????????CellFormats cellFormats = new CellFormats( ???????????????????// default ???????????????????new CellFormat() { FormatId = FORMAT_INDEX_DEFUALT }, ???????????????????// body ?string ???????????????????new CellFormat { FormatId = FORMAT_INDEX_STR, FontId = 0, FillId = 0, BorderId = 1, ApplyBorder = true }, ???????????????????// body decimal ???????????????????new CellFormat { FormatId = FORMAT_INDEX_DEC, FontId = 0, FillId = 0, BorderId = 1, NumberFormatId = 0, ApplyBorder = true }, ???????????????????//header ???????????????????new CellFormat { FormatId = FORMAT_INDEX_HEADER, FontId = 1, FillId = 2, BorderId = 1, ApplyFill = true }, // header ???????????????????// body ?int ???????????????????new CellFormat { FormatId = FORMAT_INDEX_INT, FontId = 0, FillId = 0, BorderId = 1, NumberFormatId = 1, ApplyBorder = true } ???????????????); ???????????styleSheet = new Stylesheet(numbers, fonts, fills, borders, cellFormats); ???????????return styleSheet; ???????} private void WriteWorkbookStyle() ???????{ ???????????if (document != null) ???????????{ ???????????????WorkbookStylesPart stylePart = document.WorkbookPart.AddNewPart<WorkbookStylesPart>(); ???????????????var styleSheet = GenerateStylesheet(); ???????????????styleSheet.Save(stylePart); ???????????} ???????}设置样式，冻结首行，这些都可以简单完成，如果需要添加图表什么的，还是建议用NPOI, EPPlus等开源方案，有图表的excel不会太大。
对于Open XML的介绍就到这里了，有什么错误的地方，请指正。
.NET使用Office Open XML导出大量数据到 Excel
原文地址：https://www.cnblogs.com/rhino/p/8283219.html