Java——使用dom4j和xpath进行解析xml

1. Dom4j常用的用法

-解析XML文件,得到xml文件的document对象:

//注意：路径src前面没有使用/符号
String path = "src/main/resources/students.xml";
SAXReader reader = new SAXReader();
Document document = reader.read(path);

-获取根节点：

Element root = document.getRootElement();

-获取某节点的某个子节点（如果存在多个，只返回第一个）：

Element childNode = parentNode.element("childNodeName");

-获取某节点的所有子节点：

List<Element> elemList = parentNode.elements("childNodeName");

-获取某节点的对应元素节点，及获取/修改元素节点的属性值：

Attribute attribute = elem.Attribute("attributeName");

String attributeValue = attribute.getText();

attribute.setText("newValue");

-获取/修改某节点的属性值：

String nodeValue = element.getText();

element.setText(newValue);

-添加元素节点：

parent.addAttribute("attributeName", attributeValue);

-添加节点：

Element childNode = parent.addElement("nodeName");

-移除节点：

Element parentNode = elem.getParent();

parentNode.remove(elem);

-将document对象回写到xml文件中：

// 带缩进的风格
OutputFormat format = OutputFormat.createPrettyPrint();
// 压缩风格OutputFormat.createCompactFormat()
format.setEncoding("UTF-8");

XMLWriter xmlWriter = new XMLWriter(new FileOutputStream(path), format);
xmlWriter.write(document);
xmlWriter.close();

2. XPath简介

XPath使用路径表达式来选取xml文档中的节点（Node）或节点集。

因此，可以通过这种方式使用路径表达式一次性定位到节点，在查找某节点时使用XPath会更加方便。

3. XPath路径表达式语法

-如果路径以斜线/开头，那么该路径表示节点的绝对路径：

/root/A/B

-如果路径以双斜线//开头，则表示任意层次关系的节点：

//B/C  （/root/A/B/C、/root/B/C都会被选择）

-星号*表示路径下的所有节点：

/root/A/*

-通过中括号[]指定节点集中的指定位置的节点：（1表示第一个，last()表示最后一个）

/root/A/B[1] 

/root/A/B[last()]

-通过中括号[]指定带元素属性的节点：

/root/A/B[@id]

/root/A/B[@id=”attributeValue”]

4.  Dom4j结合XPath使用的常用方法

-通过Document的实例对象获取节点或节点集合

        -获取文档中的节点集合：

    List<Node> nodeList = document.selectNodes(xpath);

        -获取节点：

Node node = document.selectSingleNode(xpath);

-通过某节点获取子节点或子节点的集合：(如果xpath不以斜杠/开头，则表示相对于该节点的相对路径)：

//node.selectNodes(xpath)

//node.selectSingleNode(xpath)

-获取节点的值：

String nodeValue = node.getText();

-获取节点的元素节点的属性值:

String attributeValue = node.valuesOf("@attributeName");

5. 简单的案例

5.1  引入相关依赖

 

引入jar包：

dom4j-#.jar（dom4j），jaxen-#.jar（xpath）

或者，pom文件引入依赖：

<dependency>
    <groupId>dom4j</groupId>
    <artifactId>dom4j</artifactId>
    <version>1.6.1</version>
</dependency>
<dependency>
    <groupId>jaxen</groupId>
    <artifactId>jaxen</artifactId>
    <version>1.1.6</version>
</dependency>

5.2  xml文件：

<?xml version="1.0" encoding="UTF-8"?>

<students> 
  <student id="student001"> 
    <name>zhangsan</name>  
    <age>18</age> 
  </student> 
</students>

5.3 使用Dom4jUtils类封装了两个static方法：

Document getDocumentFromPath(String path)：通过xml文件路径获取document对象

void xmlWrite(String path, Document document)：将document对象回写到指定路径的xml文件中

package com.lin.utils;

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.UnsupportedEncodingException;

import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.io.OutputFormat;
import org.dom4j.io.SAXReader;
import org.dom4j.io.XMLWriter;

public class Dom4jUtils {

	public static Document getDocumentFromPath(String path) {
		SAXReader saxReader = new SAXReader();

		try {
			Document document = saxReader.read(path);

			return document;
		} catch (DocumentException e) {
			e.printStackTrace();
		}
		return null;
	}

	public static void xmlWrite(String path, Document document) {

		try {
			OutputFormat format = OutputFormat.createPrettyPrint();
			//OutputFormat.createCompactFormat()
			format.setEncoding("UTF-8");

			XMLWriter xmlWriter = new XMLWriter(new FileOutputStream(path), format);
			xmlWriter.write(document);
			xmlWriter.close();
		} catch (UnsupportedEncodingException e) {
			e.printStackTrace();
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

}

5.4  对xml文件进行解析，增加删除遍历操作（不使用XPath）

package com.lin.service;

import java.util.ArrayList;
import java.util.List;

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

import com.lin.pojo.Student;
import com.lin.utils.Dom4jUtils;

public class StuService {
	
	//注意：路径src前面没有使用/符号
	public static final String PATH = "src/main/resources/students.xml";
	
	public static List<Student> getAllStudent(){
		List<Student> list = new ArrayList<Student>();
		Document document = Dom4jUtils.getDocumentFromPath(PATH);
		Element root = document.getRootElement();
		List<Element> elemList = root.elements("student");
		for (Element elem : elemList) {
			Attribute id =  elem.attribute("id");
			
			String idv = id.getText();
			Element name = elem.element("name");
			String namev = name.getText();
			Element age = elem.element("age");
			String agev = age.getText();
			//System.out.println(idv+"-"+namev+"-"+agev);
			Student stu = new Student();
			stu.setId(idv);
			stu.setName(namev);
			stu.setAge(Integer.parseInt(agev));
			list.add(stu);		
		}
		return list;
	}
	
	public static void addStudent(Student stu) {
		Document document = Dom4jUtils.getDocumentFromPath(PATH);
		Element root = document.getRootElement();
		Element student = root.addElement("student");
		student.addAttribute("id", stu.getId());
		
		Element name = student.addElement("name");
		name.setText(stu.getName());
		Element age = student.addElement("age");
		age.setText(String.valueOf(stu.getAge()));
		//回写xml
		Dom4jUtils.xmlWrite(PATH, document);
	}
	
	public static Student deleteStudent(String idv) {
		Student stu = null;
		Document document = Dom4jUtils.getDocumentFromPath(PATH);
		Element root = document.getRootElement();
		List<Element> elemList= root.elements("student");
		for (Element elem : elemList) {
			Attribute idAttr = elem.attribute("id");
			String id = idAttr.getText();
			if(id.equals(idv)) {
				Element name = elem.element("name");
				String namev = name.getText();
				Element age = elem.element("age");
				int agev = Integer.parseInt(age.getText());
				stu = new Student();
				stu.setId(idv);
				stu.setName(namev);
				stu.setAge(agev);
				elem.getParent().remove(elem);
			}
		}
		Dom4jUtils.xmlWrite(PATH, document);
		return stu;
	}

}

5.5  对StuService中的查询/删除方法进行修改

（需要查找某节点的方法都可以进行xpath方式的修改）

package com.lin.service;

import java.util.ArrayList;
import java.util.List;

import org.dom4j.Attribute;
import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.Node;

import com.lin.pojo.Student;
import com.lin.utils.Dom4jUtils;

public class StudentService {
public static final String PATH = "src/main/resources/students.xml";
	
	public static List<Student> getAllStudent(){
		List<Student> list = new ArrayList<Student>();
		Document document = Dom4jUtils.getDocumentFromPath(PATH);
		List<Node> nodeList = document.selectNodes("//student");
		
		for (Node node : nodeList) {
			String idv = node.valueOf("@id");
			Node name = node.selectSingleNode("name");
			String namev = name.getText();
			Node age = node.selectSingleNode("age");
			int agev = Integer.valueOf(age.getText());
			System.out.println(idv+"-"+namev+"-"+agev);
			Student stu = new Student();
			stu.setId(idv);
			stu.setName(namev);
			stu.setAge(agev);
			list.add(stu);	
		}
		
		return list;
	} 
	
	//add方法没有使用Xpath的方式
	public static void addStudent(Student stu) {
		Document document = Dom4jUtils.getDocumentFromPath(PATH);
		Element root = document.getRootElement();
		Element student = root.addElement("student");
		student.addAttribute("id", stu.getId());		
		Element name = student.addElement("name");
		name.setText(stu.getName());
		Element age = student.addElement("age");
		age.setText(String.valueOf(stu.getAge()));
		//回写xml
		Dom4jUtils.xmlWrite(PATH, document);
	}
	
	public static Student deleteStudent(String idv) {
		Student stu = new Student();
		Document document = Dom4jUtils.getDocumentFromPath(PATH);
		Element root = document.getRootElement();
		String xpath = "//student[@id=\""+idv+"\"]";
		Node stuNode = document.selectSingleNode(xpath);
		String namev = stuNode.selectSingleNode("name").getText();
		int agev = Integer.valueOf(stuNode.selectSingleNode("age").getText());
		stu.setId(idv);
		stu.setName(namev);
		stu.setAge(agev);
		root.remove(stuNode);
		//回写xml
		Dom4jUtils.xmlWrite(PATH, document);
		return stu;
	}
}