近期有个任务要求处理大XML文件，其中有个存了Base64的大节点（>90M，路径已知）。

这种任务只能上XmlReader，即使如此大节点的处理还是头疼了一阵……

最初查MSDN的时候，找到了ReadChars()，可以拿来对付大节点。

方法说明：

示例中提到使用方法是：

while(0 != reader.ReadChars(buffer, 0, 1)){    // Do something.    // Attribute values are not available at this point.}

这个处理规范格式的XML没有问题，比如这样的：

       
      
       Value
        
          
       
        Value
         
      
     

但是（没人喜欢这个词，然并卵……），遇到些格式诡异的XML就……

     
      
       Value
      
      
       
        Value
       
      
     

比如这个画风的，用示例代码去读第一个LeafNode的内容，估计会读出“ValueValue”来……

偏偏输入的XML就是这风格的……（*sigh*）

单步执行了一阵，发现这种情况下，XmlTextReader.Name会变化成下个节点的名称（XmlTextReader.LocalName亦如此），可以根据这个判断是否已经达到节点结尾。

改进版为：

string currentName = reader.LocalName;while(currentName == reader.LocalName && 0 != reader.ReadChars(buffer, 0, 1)){    // Do something.    // Attribute values are not available at this point.}

顺便贴上一个转写并对特定节点进行处理的代码：

List
     
       processNodePathList = new List
      
        {
   "/Root/Path/to/Target"};List
       
         bigNodePathList = new List
        
          { "/Root/Path/to/Big/Node" }; private static void ProcessBigXmlFile(string sourcePath, string targetPath, IList
         
           processNodePathList, IList
          
            bigNodePathList){ var processNodeNameList = processNodePathList.Select( processNodePath => processNodePath.Split(new[] { '/' }, StringSplitOptions.RemoveEmptyEntries)) .Select(nodePathParts => nodePathParts[nodePathParts.Length - 1]) .ToList(); var bigNodeNameList = bigNodePathList.Select( bigNodePath => bigNodePath.Split(new[] { '/' }, StringSplitOptions.RemoveEmptyEntries)) .Select(nodePathParts => nodePathParts[nodePathParts.Length - 1]) .ToList(); var sourceStream = new FileStream(sourcePath, FileMode.Open, FileAccess.Read); var reader = new XmlTextReader(sourceStream); var targetStream = new FileStream(targetPath, FileMode.Create, FileAccess.Write); var writer = new XmlTextWriter(targetStream, Encoding.UTF8); try { var pathStack = new Stack
           
            (); var readResult = reader.Read(); while (readResult) { int skipMode = 0; switch (reader.NodeType) { case XmlNodeType.Element: { pathStack.Push(reader.Name); writer.WriteStartElement(reader.LocalName); if (reader.HasAttributes) { while (reader.MoveToNextAttribute()) { writer.WriteAttributeString(reader.LocalName, reader.Value); } reader.MoveToElement(); } if (processNodeNameList.Contains(reader.LocalName)) { var index = processNodeNameList.IndexOf(reader.LocalName); if (CompareNodePath(pathStack, processNodePathList[index])) { // Replace node content writer.WriteFullEndElement(); skipMode = 1; } } else if (bigNodeNameList.Contains(reader.LocalName)) { var index = bigNodeNameList.IndexOf(reader.LocalName); if (CompareNodePath(pathStack, bigNodePathList[index])) { reader.MoveToContent(); var buffer = new char[1024]; int len; while (reader.LocalName == bigNodePathList[index] && (len = reader.ReadChars(buffer, 0, buffer.Length)) > 0) { writer.WriteRaw(buffer, 0, len); } writer.WriteFullEndElement(); skipMode = 2; } } if (reader.IsEmptyElement) { pathStack.Pop(); writer.WriteEndElement(); } break; } //case XmlNodeType.Attribute: //{ // newPackageWriter.WriteAttributeString(oldPackageReader.LocalName, oldPackageReader.Value); // break; //} case XmlNodeType.Text: { writer.WriteValue(reader.Value); break; } case XmlNodeType.CDATA: { writer.WriteCData(reader.Value); break; } //case XmlNodeType.EntityReference: //{ // newPackageWriter.WriteEntityRef(oldPackageReader.Name); // break; //} //case XmlNodeType.Entity: //{ // break; //} case XmlNodeType.ProcessingInstruction: { writer.WriteProcessingInstruction(reader.Name, reader.Value); break; } case XmlNodeType.Comment: { writer.WriteComment(reader.Value); break; } //case XmlNodeType.Document: //{ // break; //} case XmlNodeType.DocumentType: { writer.WriteRaw(string.Format("", reader.Name, reader.Value)); break; } //case XmlNodeType.DocumentFragment: //{ // break; //} //case XmlNodeType.Notation: //{ // break; //} case XmlNodeType.Whitespace: { writer.WriteWhitespace(reader.Value); break; } //case XmlNodeType.SignificantWhitespace: //{ // break; //} case XmlNodeType.EndElement: { pathStack.Pop(); writer.WriteFullEndElement(); break; } case XmlNodeType.XmlDeclaration: { writer.WriteStartDocument(); break; } } switch (skipMode) { case 1: { reader.Skip(); pathStack.Pop(); readResult = !reader.EOF; break; } case 2: { pathStack.Pop(); readResult = !reader.EOF; break; } default: { readResult = reader.Read(); break; } } } } finally { writer.Close(); targetStream.Close(); targetStream.Dispose(); reader.Close(); sourceStream.Close(); sourceStream.Dispose(); }}private static bool CompareNodePath(Stack
            
              currentNodePathStack, string compareNodePathString){ var currentArray = currentNodePathStack.Reverse().ToArray(); var compareArray = compareNodePathString.Split(new[] { '/' }, StringSplitOptions.RemoveEmptyEntries); if (compareArray.Length != currentArray.Length) { return false; } bool isDifferent = false; for (int i = 0; i < currentArray.Length; i++) { if (compareArray[i] != currentArray[i]) { isDifferent = true; break; } } return !isDifferent;}