JDOM不允许同一个节点同时被2个或多个文档相关联，要在第2个文档中使用原来老文档中的节点的话。首先需要使用detach()把这个节点分开来。

//读取文件：
StringReader sr = new StringReader(requestXml);
InputSource is = new InputSource(sr);
SAXBuilder builder = new SAXBuilder();
 Document doc = builder.build(is);

//输出元素:
Document newXmlDoc = new Document(newXmlRoot);
XMLOutputter output = new XMLOutputter();
String newXml = output.outputString(newXmlDoc);

//添加元素
root.addContent(new Element("jane"));

//获取元素：
Namespace soapenv = Namespace.getNamespace("soapenv",SOAP_URI);
Namespace put = Namespace. getNamespace("put",PUT_URI);
Element root = doc.getRootElement();
Element bodyElement = root.getChild( BODY,soapenv);
Element inbound = bodyElement.getChild("DisassembleJobcardFeedback",put).getChild( "DisassembleJobcardFeedbackInfo" );