Add UseXmlReader Switch to ShardStringTable

benchmarks/NPOI.Benchmarks/LargeSSTBenchmark.cs

@@ -1,4 +1,5 @@
 using BenchmarkDotNet.Attributes;
+using NPOI.XSSF.Model;
 using NPOI.XSSF.UserModel;
 using System;
 using System.Collections.Generic;
@@ -46,8 +47,17 @@ public void XSSFWorkbookLargeSstOpenDispose()
     /// reduced in allocation compared to the old DOM path.
     /// </summary>
     [Benchmark]
-    public void XSSFWorkbookLargeSstLoadStrings()
+    public void XSSFWorkbookLargeSstLoadStringsViaXmlReader()
     {
+        SharedStringsTable.UseXmlReader = true;
+        using var workbook = new XSSFWorkbook(_largeFileWithSstPath, true);
+        // Force SST parse
+        _ = workbook.GetSharedStringSource().Count;
+    }
+    [Benchmark]
+    public void XSSFWorkbookLargeSstLoadStringsViaXmlDocument()
+    {
+        SharedStringsTable.UseXmlReader = false;
         using var workbook = new XSSFWorkbook(_largeFileWithSstPath, true);
         // Force SST parse
         _ = workbook.GetSharedStringSource().Count;

ooxml/XSSF/Model/SharedStringsTable.cs

@@ -176,7 +176,10 @@ private void EnsureLoaded()
                     {
                         try
                         {
-                            ReadFromStream(stream);
+                            if(UseXmlReader)
+                                ReadFromStreamViaXmlReader(stream);
+                            else
+                                ReadFromStreamViaXmlDocument(stream);
                         }
                         catch (XmlException e)
                         {
@@ -218,7 +221,24 @@ private void EnsureStmapBuilt()
         /// </summary>
         private const int TextReadBufferSize = 1024;
 
-        private void ReadFromStream(Stream stream)
+        internal static bool UseXmlReader { get; set; } = true;
+
+        public void ReadFromStreamViaXmlDocument(Stream is1)
+        {
+            try
+            {
+                XmlDocument xml = ConvertStreamToXml(is1);
+                _sstDoc = SstDocument.Parse(xml, NamespaceManager);
+                CT_Sst sst = _sstDoc.GetSst();
+                count = sst.count;
+                uniqueCount = sst.uniqueCount;
+            }
+            catch (XmlException e)
+            {
+                throw new IOException("unable to parse shared strings table", e);
+            }
+        }
+        private void ReadFromStreamViaXmlReader(Stream stream)
         {
             _sstDoc = new SstDocument();
             _sstDoc.AddNewSst();
@@ -509,24 +529,6 @@ private static CT_Color ParseColorAttributes(XmlReader reader)
             return color;
         }
 
-        /// <summary>
-        /// Read shared strings from a stream. Kept for backward compatibility; internally
-        /// delegates to the streaming parser.
-        /// </summary>
-        public void ReadFrom(Stream is1)
-        {
-            try
-            {
-                ReadFromStream(is1);
-                _loaded = true;
-                _stmapBuilt = false;
-            }
-            catch (XmlException e)
-            {
-                throw new IOException("unable to parse shared strings table", e);
-            }
-        }
-
         private static String GetKey(CT_Rst st)
         {
             return st.XmlText;