SAXReader reader = new SAXReader();
try {
Document doc = reader.read(path);
Element ele = (Element)doc.selectSingleNode("//user[@username='" + username + "']");
if(ele == null) return null;中doc,ele到底指什么,'" + username + "'这里为什么既用单引号有用双引号,双引号是字符串了,为什么又搞个单引号,这不是变字符了吗?