使用Dom4j在指定的节点下添加节点如何做 ？

[LLLDDDPPP]

<?xml version="1.0" encoding="UTF-8"?>
<ETLs><ETL><ETLId>1</ETLId><ETLName>ETL1</ETLName><ETLRecordSize>1000</ETLRecordSize><SourceDataSourceType>AdminRemoteDatabase</SourceDataSourceType><SourceId>0001</SourceId><SourceName>配置1</SourceName><SourceTable>users</SourceTable><SourceTableSQL>select usersId,usersName from user</SourceTableSQL><TargetDataSourceType>LocalDatabase</TargetDataSourceType><TargetId>0001</TargetId><TargetName>配置1</TargetName><TargetTable>user</TargetTable><TargetTableSQL>insert user (usersId,usersName)</TargetTableSQL><Sort>1</Sort><Columns><Column><ColumnId>1</ColumnId><SourceField>usersId</SourceField><SourceType>uniqueidentifier</SourceType><SourceLength>16</SourceLength><SourceNull>false</SourceNull><SourceDefault>NULL</SourceDefault><SourcePrecision/><SourceScale>0</SourceScale><TargetField>userId</TargetField><TargetType>varchar</TargetType><TargetLength>36</TargetLength><TargetNull>true</TargetNull><TargetDefault>NULL</TargetDefault><TargetPrecision/><TargetScale/></Column></Columns></ETL></ETLs>

我现在有以上的XML文件 ！我现在想要在ETLId=1的项下面添加一个Column节点项！ 这个如何做啊 ？ 各位大神 ！ 在线等 ~

[LLLDDDPPP]

Xml在这上面看的好像不是很清晰啊 ！！建议大家先拷贝出来用EditPlus看下 ！！ 在线等哈 ！

[LLLDDDPPP]

File file = new File(InfoPath.ADMINETL);
		SAXReader reader = new SAXReader();
		Document document = null;
		try {
			document = reader.read(file);
			document.setXMLEncoding("UTF-8");
			
			Element root = document.getRootElement(); // 获得根元素
			Element element = (Element) root.selectNodes("/ETLs/ETL[ETLId='1']/Columns").get(0);
			
			Element itemElement = DocumentHelper.createElement("Column");
			element.add(itemElement);
			
			Element sourceTypeElement = DocumentHelper.createElement("SourceType");
			sourceTypeElement.setText("ethan");
			itemElement.add(sourceTypeElement);
			
//			System.out.println(element.asXML());
			document.add(element);
		} catch (Exception e) {
			e.printStackTrace();
		}
		System.out.println(document.asXML());

我初步写出来一个，感觉没问题啊 ！ 可是报错呢 ！



org.dom4j.IllegalAddException: The node "org.dom4j.tree.DefaultElement@743399 [Element: <Columns attributes: []/>]" could not be added to the branch "file:///D:/Tools/Workspaces/successETL/WebRoot/WEB-INF/classes/config/xml/AdminETL.xml" because: Cannot add another element to this Document as it already has a root element of: ETLs
at org.dom4j.tree.AbstractDocument.checkAddElementAllowed(AbstractDocument.java:241)
at org.dom4j.tree.AbstractDocument.add(AbstractDocument.java:203)
at com.success.vo.Demo.main(Demo.java:33)

[cds27]

把document.add(element); 这句去掉就行了，这个句子一点用都没有。