Problem: When using dom4j to query deep hierarchical structure nodes (labels, attributes, text), it is more troublesome! ! !
xpath is generated in this case-mainly used to quickly obtain the required [node object].
1) Import xPath supports jar package. jaxen-1.1-beta-6.jar
Node> selectNodes("xpath expression"); Query multiple node objects
Node selectSingleNode("xpath expression"); Query a node object
xPath syntax
# Starting from the root position of xml or a child element (a hierarchy)
Yes: Then it means that login is successful
没有: Then indicate the failure of login
## use as a database User.xml to store users The data code is as follows:import java.io.BufferedReader; import java.io.File; import java.io.InputStreamReader; import org.dom4j.Document; import org.dom4j.Element; import org.dom4j.io.SAXReader; /** * xpath案例: 模拟用户登录效果 * @author APPle * */ public class Demo3 { public static void main(String[] args)throws Exception{ //1.获取用户输入的用户名和密码 BufferedReader br = new BufferedReader(new InputStreamReader(System.in));//封装键盘录入,输入流 System.out.println("请输入用户名:"); String name = br.readLine(); System.out.println("请输入密码:"); String password = br.readLine(); //2.到“数据库”中查询是否有对应的用户 //对应的用户: 在user.xml文件中找到一个 //name属性值为‘用户输入’,且password属性值为‘用户输入’的user标签 Document doc = new SAXReader().read(new File("./src/user.xml")); Element userElem = (Element)doc.selectSingleNode("//user[@name='" +name +"' and @password='"+password+"']"); //在字符串中拼接变量的方法——先加一个双引号,再把光标移到双引号中间,写两个加号,再把光标移到加号中间写上变量。 //System.out.println(userElem.getName());//查看当前节点对象内容 if(userElem!=null){//说明在“数据库”里面找到了用户名和密码。 //登录成功 System.out.println("登录成功"); }else{ //登录失败 System.out.println("登录失败"); } } }