jdom - 元素 "LevelRoot"无法添加为文档 : The Content already has an existing parent document 的根

Question

我在使用 JDOM2 时遇到了一些麻烦。我想序列化我的树，然后我去添加第一个根元素，它说它已经添加到文档中，但它是我将它添加到的新文档。
代码:

SceneGraphNode root = SceneGraphManager.root;
 
Element root_element = root.xmlData;
 
CJournal.Journal(XMLAdapter.class, "Serializing root element: " + root_element.getName());
 
Document doc = new Document();
 
doc.addContent(root_element);
 
CJournal.Journal(XMLAdapter.class, "Root element serialized ");
 
for (SceneGraphNode child: root.children)
{
    //save xml
    CJournal.Journal(XMLAdapter.class, "Serializing element: " + child.xmlData.getName());
    doc.addContent(child.xmlData);
    RecursiveSerialize(child, doc);

还有我的堆栈跟踪:

187 In Class::class GameMap.XMLAdapter Journal Entry:Serializing root element: LevelRoot
Exception in thread "Thread-8" org.jdom2.IllegalAddException: The element "LevelRoot" could not be added as the root of the document: The Content already has an existing parent document
    at org.jdom2.ContentList.checkPreConditions(ContentList.java:208)
    at org.jdom2.ContentList.add(ContentList.java:244)
    at org.jdom2.ContentList.add(ContentList.java:79)
    at java.base/java.util.AbstractList.add(Unknown Source)
    at org.jdom2.Document.addContent(Document.java:320)
    at GameMap.XMLAdapter.Serialize(XMLAdapter.java:238)
    at GameMap.CHotLoader.Serialize(CHotLoader.java:206)
    at GameMap.CHotLoader.loadNMap(CHotLoader.java:132)
    at GameMap.CHotLoader.loadMap(CHotLoader.java:115)
    at GameMap.CHotLoader.HotLoad(CHotLoader.java:84)
    at MainGame.Loop.run(Loop.java:29)

Answer 1

不应该是

root_element.addContent(child.xmlData);

像这样:

for (SceneGraphNode child: root.children)
{
    //save xml
    CJournal.Journal(XMLAdapter.class, "Serializing element: " + child.xmlData.getName());
    root_element.addContent(child.xmlData);
    RecursiveSerialize(child, doc);
}