From dbe845dbdae316fe3627e0c7179a18a42e4abb47 Mon Sep 17 00:00:00 2001
From: joehni <joerg.schaible@gmx.de>
Date: Wed, 27 Sep 2023 01:54:54 +0200
Subject: [PATCH] Calculate list of child elements in DomReader only once.
 Closes #342.

---
 xstream-distribution/src/content/changes.html |  1 +
 .../xstream/io/xml/DomReader.java             | 24 +++++++++++++++++--
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/xstream-distribution/src/content/changes.html b/xstream-distribution/src/content/changes.html
index 1d49167aa..a8c4d62ec 100644
--- a/xstream-distribution/src/content/changes.html
+++ b/xstream-distribution/src/content/changes.html
@@ -113,6 +113,7 @@ <h2>Minor changes</h2>
 	<ul>
 		<li>GHPR:#331, GHI:#326: Fix handling of empty java.util.concurrent.atomic.AtomicReference (by Alex Blekhman of Atlassian).</li>
 		<li>GHPR:#334: Fix remaining buffer size calculation in QuickWriter (by Higuchi Yuta).</li>
+		<li>GHI:#342: Optimize internal handling of children in DomReader avoiding O(n²) access times for siblings (by Shiang-Yun Yang).</li>
 	</ul>
 
 	<h1 id="1.4.20">1.4.20</h1>
diff --git a/xstream/src/java/com/thoughtworks/xstream/io/xml/DomReader.java b/xstream/src/java/com/thoughtworks/xstream/io/xml/DomReader.java
index daff7e4d9..37a5fe9f4 100644
--- a/xstream/src/java/com/thoughtworks/xstream/io/xml/DomReader.java
+++ b/xstream/src/java/com/thoughtworks/xstream/io/xml/DomReader.java
@@ -1,12 +1,12 @@
 /*
  * Copyright (C) 2004, 2005, 2006 Joe Walnes.
- * Copyright (C) 2006, 2007, 2009, 2011, 2014, 2015 XStream Committers.
+ * Copyright (C) 2006, 2007, 2009, 2011, 2014, 2015, 2023 XStream Committers.
  * All rights reserved.
  *
  * The software in this package is published under the terms of the BSD
  * style license a copy of which has been included with this distribution in
  * the LICENSE.txt file.
- * 
+ *
  * Created on 07. March 2004 by Joe Walnes
  */
 package com.thoughtworks.xstream.io.xml;
@@ -21,6 +21,7 @@
 import org.w3c.dom.NodeList;
 import org.w3c.dom.Text;
 
+import com.thoughtworks.xstream.core.util.FastStack;
 import com.thoughtworks.xstream.io.naming.NameCoder;
 
 
@@ -29,6 +30,7 @@ public class DomReader extends AbstractDocumentReader {
     private Element currentElement;
     private final StringBuilder textBuffer;
     private List<Element> childElements;
+    private final FastStack<List<Element>> childrenStack;
 
     public DomReader(final Element rootElement) {
         this(rootElement, new XmlFriendlyNameCoder());
@@ -44,6 +46,8 @@ public DomReader(final Document document) {
     public DomReader(final Element rootElement, final NameCoder nameCoder) {
         super(rootElement, nameCoder);
         textBuffer = new StringBuilder();
+        childrenStack = new FastStack<>(16);
+        collectChildElements();
     }
 
     /**
@@ -130,6 +134,9 @@ protected int getChildCount() {
     @Override
     protected void reassignCurrentElement(final Object current) {
         currentElement = (Element)current;
+    }
+
+    private void collectChildElements() {
         final NodeList childNodes = currentElement.getChildNodes();
         childElements = new ArrayList<>();
         for (int i = 0; i < childNodes.getLength(); i++) {
@@ -140,6 +147,19 @@ protected void reassignCurrentElement(final Object current) {
         }
     }
 
+    @Override
+    public void moveDown() {
+        super.moveDown();
+        childrenStack.push(childElements);
+        collectChildElements();
+    }
+
+    @Override
+    public void moveUp() {
+        childElements = childrenStack.pop();
+        super.moveUp();
+    }
+
     @Override
     public String peekNextChild() {
         final NodeList childNodes = currentElement.getChildNodes();