xpath technology parses xml and cases simulate user login effects

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].

How to use xPath technology in dom4j

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)

                                                                                                                                                                                                                                                               

                                                                                                                                                  because Elements under what conditions Conditions Relationship (equivalent on &&)

TEXT () Text represents selection text content

## This case

##                                                                                                             ’ s ’ s ’                                                           ‐ ‐ ‐ ‐   ‐ ‐ ‐ ‐ ‐ ​ ​ ​ ​ ​ ​ ​   1 gt;

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");
		}
	}

}

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