Using xpath to parse xml in Java

xpath is a language for finding information in xml documents. xpath is used to navigate through elements and attributes in XML documents. Its return value may be nodes, node collections, text, and a mixture of nodes and text, etc.
Before studying this document, you should have a certain understanding of XML nodes, elements, attributes, text, processing instructions, comments, root nodes, namespaces and node relationships, as well as xpath.
XML learning address: http://www.runoob.com/xml/xml-tutorial.html
xpath basic syntax learning address: http://www.runoob.com/xpath/xpath-tutorial.html
xpath official documentation : https://yunpan.cn/cvc4tEIGy5EvS Access password 9d16
This article mainly introduces: using xpath operation to operate xml in Java.
1) First, how to use xpath technology in dom4j
Import the jar package supported by xPath. jaxen-1.1-beta-6.jar (first import the dom4j package, dom4j download address: http://www.dom4j.org/dom4j-1.6.1/).

As shown in the figure after importing the package:

If you don’t know how to import the package, please refer to my previous blog: Summary of Java Obtaining XML Nodes and Reading XML Documents Node
2) There are two main points for using the xpath method in Java:
List selectNodes("xpath expression"); Query multiple node objects
Node selectSingleNode("xpath expression"); Query a node object
Below Just use examples to illustrate how to use it.

1. How to use selectNodes:

package com.vastsum.demo;

import java.io.File;
import java.io.FileOutputStream;
import java.util.List;

import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.Node;
import org.dom4j.io.OutputFormat;
import org.dom4j.io.SAXReader;
import org.dom4j.io.XMLWriter;

/**
 * 
 * @author shutu008
 *selectNode的使用方法
 */
public class xpathDemo {

    public static void main(String[] args) throws Exception {

    Document doc = new SAXReader().read(new File("./src/contact.xml"));
        
        /**
         * @param xpath 表示xpath语法变量
         */
    String xpath="";
        
        /**
         * 1.      /      绝对路径      表示从xml的根位置开始或子元素（一个层次结构）
         */
        xpath = "/contactList";
        xpath = "/contactList/contact";
        
        /**
         * 2. //     相对路径       表示不分任何层次结构的选择元素。
         */
        xpath = "//contact/name";
        xpath = "//name";
        
        /**
         * 3. *      通配符         表示匹配所有元素
         */
        xpath = "/contactList/*"; //根标签contactList下的所有子标签
        xpath = "/contactList//*";//根标签contactList下的所有标签（不分层次结构）
        
        /**
         * 4. []      条件           表示选择什么条件下的元素
         */
        //带有id属性的contact标签
        xpath = "//contact[@id]";
        //第二个的contact标签
        xpath = "//contact[2]";
        //选择最后一个contact标签
        xpath = "//contact[last()]";
        
        /**
         * 5. @     属性            表示选择属性节点
         */
        xpath = "//@id"; //选择id属性节点对象，返回的是Attribute对象
        xpath = "//contact[not(@id)]";//选择不包含id属性的contact标签节点
        xpath = "//contact[@id='002']";//选择id属性值为002的contact标签
        xpath = "//contact[@id='001' and @name='eric']";//选择id属性值为001，且name属性为eric的contact标签
        
        /**
         *6.  text()   表示选择文本内容
         */
        //选择name标签下的文本内容，返回Text对象
        xpath = "//name/text()";
        xpath = "//contact/name[text()='张三']";//选择姓名为张三的name标签
        
        
        List<Node> list = doc.selectNodes(xpath);
        for (Node node : list) {
            System.out.println(node);
        }
    
        //写出xml文件
        //输出位置
        FileOutputStream out = new FileOutputStream("d:/contact.xml");
        
        //指定格式
        OutputFormat format = OutputFormat.createPrettyPrint();
        format.setEncoding("utf-8");
        XMLWriter writer = new XMLWriter(out,format);
        
        //写出内容
        writer.write(doc);
        
        //关闭资源
        writer.close();
        
    }
    

}

2. How to use selectSingleNode

package com.vastsum.demo;

import java.io.File;
import java.util.Iterator;

import org.dom4j.Attribute;
import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;

/**
 * 
 * @author shutu008
 *selectSingleNode的使用
 */
 public class xpathDemo1{
     public static void main(String[] args) throws Exception{
         //读取XML文件，获得document对象
        SAXReader saxReader = new SAXReader();    
        Document doc = saxReader.read(new File("./src/contact.xml"));
        
        //使用xpath获取某个节点
        String xpath = "";
        
        //对contact元素 id="001"的节点，操作
        xpath = "//contact[@id = '001']";
        Element contactElem =    (Element)doc.selectSingleNode(xpath);
        
        //设置这个节点的属性值
        contactElem.addAttribute("name", "001");
        
        //输出这个节点的所有属性值
        for(Iterator it = contactElem.attributeIterator();it.hasNext();){
        Attribute conAttr = (Attribute)it.next();
        String conTxt = conAttr.getValue();
        String conAttrName = conAttr.getName();
        System.out.println(conAttrName+" = "+conTxt);
        }
        
     }
 }