Java的XML解析

XML：（eXtensible Markup Language）

可扩展标记语言

是一种数据格式，用于存储和传输数据

声明一个xml文件

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

　　

文档类型定义

<!DOCTYPE note SYSTEM “book.dtd”>

　　

only：有且只有一个跟节点

一个例子

<?xml version="1.0" encoding="ISO-8859-1"?>
<note>
<to>George</to>
<from>John</from>
<heading>Reminder</heading>
<body>Don't forget the meeting!</body>
</note>

　　

特殊字符

在 XML 中，有 5 个预定义的实体引用：

格式验证

浏览器打开不报错，就ok

Java的XML解析的3个方法：

1.DOM（Document Object Model）

文档对象模型

xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="test">
	<select id="findUserById" parameterType="int" resultType="com.lucas.javase.mybatis.introduction.po.User" >
		SELECT * FROM user WHERE id = #{id}
	</select>
	<select id="findUserListByName" parameterType="string" resultType="com.lucas.javase.mybatis.introduction.po.User">
		SELECT * FROM user WHERE username LIKE '%${value}%'
	</select>
	<insert id="insertUser" parameterType="com.lucas.javase.mybatis.introduction.po.User" useGeneratedKeys="true">
		INSERT INTO user (username,sex,birthday,address) VALUES (#{username},#{sex},#{birthday},#{address})
	</insert>
</mapper>

Dom.java

static String uri="UserMapper.xml";
public static void dom() throws ParserConfigurationException, SAXException, IOException{
		//DocumentBuilderFactory是抽象类，不能实例化new
		DocumentBuilderFactory instance = DocumentBuilderFactory.newInstance();
		DocumentBuilder builder = instance.newDocumentBuilder();
		
		Document document = builder.parse(uri);
		print(document,0);
	}

private static void print(Node document, int i) {
		for (int j = 0; j < i; j++) {
			System.out.print(" ");
		}
		switch (document.getNodeType()) {
			case Node.DOCUMENT_NODE:
				System.out.println("DOCUMENT_NODE: "+document.getNodeName());
				break;
			case Node.ELEMENT_NODE:
				System.out.println("ELEMENT_NODE: "+document.getNodeName());
				break;
			case Node.TEXT_NODE:
				System.out.println("TEXT_NODE: "+document.getNodeName()+"="+document.getNodeValue());
				break;
			case Node.ATTRIBUTE_NODE:
				System.out.println("ATTRIBUTE_NODE: "+document.getNodeName()+"="+document.getNodeValue());
				break;
			case Node.CDATA_SECTION_NODE:
				System.out.println("CDATA_SECTION_NODE: "+document.getNodeName()+"="+document.getNodeValue());
				break;
			case Node.COMMENT_NODE:
				System.out.println("COMMENT_NODE: "+document.getNodeName()+"="+document.getNodeValue());
				break;
			default:
				System.out.println("NODETYPE:"+document.getNodeType()+",NODEVALUE:"+document.getNodeValue());
				break;
		}
		for (Node child = document.getFirstChild(); child !=null; child=child.getNextSibling()) {
			print(child,i+1);
		}
	}

　　

输出

DOCUMENT_NODE: #document
 NODETYPE:10,NODEVALUE:null
 ELEMENT_NODE: mapper
  TEXT_NODE: #text=
	
  ELEMENT_NODE: select
   TEXT_NODE: #text=
		SELECT * FROM user WHERE id = #{id}
	
  TEXT_NODE: #text=
	
  ELEMENT_NODE: select
   TEXT_NODE: #text=
		SELECT * FROM user WHERE username LIKE '%${value}%'
	
  TEXT_NODE: #text=
	
  ELEMENT_NODE: insert
   TEXT_NODE: #text=
		INSERT INTO user (username,sex,birthday,address) VALUES (#{username},#{sex},#{birthday},#{address})
	
  TEXT_NODE: #text=

缺点是：一次性加载整个dom，占用内存大，速度慢　　

2、SAX（Simple API for XML）

XML的简单接口

Sax.java

public static void sax() throws ParserConfigurationException, SAXException, IOException{
		//SAXParserFactory也是抽象类
		SAXParserFactory instance = SAXParserFactory.newInstance();
		SAXParser saxParser = instance.newSAXParser();
		saxParser.parse(uri, new SaxHandler());
	}

　　

SaxHandler.java

public class SaxHandler extends DefaultHandler{

	void print(Object...objects){
		for (Object object : objects) {
			System.out.print(object);
			System.out.print(" ");
		}
	}
	@Override
	public void startDocument() throws SAXException {
		System.out.println("startDocument");
	}

	@Override
	public void endDocument() throws SAXException {
		System.out.println("endDocument");
	}

	@Override
	public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
		System.out.println("startElement "+localName+" "+qName);
	}

	@Override
	public void endElement(String uri, String localName, String qName) throws SAXException {
		System.out.println("endElement "+localName+" "+qName);
	}

	@Override
	public void characters(char[] ch, int start, int length) throws SAXException {
		System.out.println("characters "+new String(ch,start,length));
	}

	@Override
	public void error(SAXParseException e) throws SAXException {
		print("error:",e);
	}
	
}

　　

输出

startDocument
startElement  mapper
startElement  select
characters 
		SELECT * FROM user WHERE id = #{id}
	
endElement  select
startElement  select
characters 
		SELECT * FROM user WHERE username LIKE '%${value}%'
	
endElement  select
startElement  insert
characters 
		INSERT INTO user (username,sex,birthday,address) VALUES (#{username},#{sex},#{birthday},#{address})
	
endElement  insert
endElement  mapper
endDocument

　　

流式读取dom，占用内存小，速度快，基于事件，使用事件回调处理dom

 3、Jackson

这个一个开源XML工具

引入依赖包，maven的pom.xml

<dependency>
	  <groupId>com.fasterxml.jackson.dataformat</groupId>
	  <artifactId>jackson-dataformat-xml</artifactId>
	  <version>2.9.0</version>
	</dependency>
	<dependency>
	  <groupId>com.fasterxml.woodstox</groupId>
	  <artifactId>woodstox-core</artifactId>
	  <version>5.1.0</version>
	</dependency>

　　

 需要序列化的类

User.java

public class User {
	private int id;
	private String username;
	private String sex;
	private String birthday;
	private String address;
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getUsername() {
		return username;
	}
	public void setUsername(String username) {
		this.username = username;
	}
	public String getSex() {
		return sex;
	}
	public void setSex(String sex) {
		this.sex = sex;
	}
	public String getBirthday() {
		return birthday;
	}
	public void setBirthday(String birthday) {
		this.birthday = birthday;
	}
	public String getAddress() {
		return address;
	}
	public void setAddress(String address) {
		this.address = address;
	}
	@Override
	public String toString() {
		return "User [id=" + id + ", username=" + username + ", sex=" + sex + ", birthday=" + birthday + ", address="
				+ address + "]";
	}
	public User() {
	}
	public User(int id, String username, String sex, String birthday, String address) {
		super();
		this.id = id;
		this.username = username;
		this.sex = sex;
		this.birthday = birthday;
		this.address = address;
	}
}

　　

Jackson.java
public class Jackson {

	public static void main(String[] args) {
		try {
			//jacksonBean2XML();
			jacksonXML2Bean();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	
	/**
	 * POJO 转为XML
	 * 
	 * @throws JsonProcessingException
	 */
	public static void jacksonBean2XML() throws JsonProcessingException{
//		JacksonXmlModule module = new JacksonXmlModule();
//		module.setDefaultUseWrapper(false);
		
		XmlMapper xmlMapper = new XmlMapper();
		xmlMapper.setDefaultUseWrapper(false);
		User user=new User(1,"lucas","nan","2019-10-01","上海");
		String xml=xmlMapper.writeValueAsString(user);
		System.out.println(xml);
	}
	
	public static void jacksonXML2Bean() throws JsonParseException, JsonMappingException, IOException{
//		JacksonXmlModule module = new JacksonXmlModule();
//		module.setDefaultUseWrapper(false);
		XmlMapper xmlMapper = new XmlMapper();
		xmlMapper.setDefaultUseWrapper(false);
		//自动忽略无法对应pojo的字段
		xmlMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
		User user=xmlMapper.readValue("<User><id>1</id><username>lucas</username><sex>nan</sex><birthday>2019-10-01</birthday><address>上海</address></User>", User.class);
		System.out.println(user);
	}
	

}

　　

使用第三方的工具，更加方便，面向对象开发。

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原文地址：https://www.cnblogs.com/1906859953Lucas/p/10751339.html