1、新建XML文档：
Document doc = DocumentHelper.createDocument();
Element root = doc.addElement( "ocs");
root.addElement( "header");
Element body = root.addElement( "body");
Element fontnode = body.addElement( "font");
fontnode.addAttribute( "size", "9");
System. out.println(root.asXML());
2、打开现有XML文档（从字符串导入）：
Document doc = DocumentHelper.parseText(XMLStr);
Node node = doc.selectSingleNode( "ocs/body/font");
if (node instanceof Element)
{
Element pnode = (Element) node;
Attribute attr = pnode.attribute( "size");
System. out.println(attr.asXML());
}
Dom4j中内置了XPath，因此可以在selectSingleNode中象XPath那样访问路径字符串；
注意：需要引用jaxen-1.1.1.jar包，否则selectSingleNode会产生异常并返回Null;
3、打开现有文档（从文件导入）：
SAXReader saxReader = new SAXReader();
Document document = saxReader.read( XMLFile);
4、将Document写入到文件中:
try
{
XMLWriter output = new XMLWriter( new FileWriter( new File(XMLFile)));
output.write( doc);
output.close();
} catch (IOException e)
{
System. out.println(e.getMessage());
}