XML DOM简介

XML DOM 是用于获取、更改、添加或删除 XML 元素的标准。
XML 文档中的每个成分都是一个节点。

• DOM 是这样规定的：

整个文档是一个文档节点
每个 XML 标签是一个元素节点
包含在 XML 元素中的文本是文本节点
每一个 XML 属性是一个属性节点
注释属于注释节点

元素节点不包括文本，元素节点的文本是存储在文本节点中的。

XML 文档的 documentElement 属性是根节点。

在jdk中，Document接口继承自Node接口
Element接口也继承自Node接口

DOM方式读取XML文件

项目目录结构图：

config包下language.xml文件

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

<languages cat = "it">

    <lan id = "1">

        <name>java</name>

        <ide>Eclipse</ide>

    </lan>

    <lan id = "2">

        <name>swift</name>

        <ide>XCode</ide>

    </lan>

    <lan id = "3">

        <name>C#</name>

        <ide>Visual Studio</ide>

    </lan>

</languages>

ReadXML.java

import java.io.File;

import javax.xml.parsers.DocumentBuilder;

import javax.xml.parsers.DocumentBuilderFactory;

import org.w3c.dom.Document;

import org.w3c.dom.Element;

import org.w3c.dom.Node;

import org.w3c.dom.NodeList;

public class ReadXML {

    public static void main(String[] args) {

        try {

            DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

            DocumentBuilder builder = factory.newDocumentBuilder();

            Document document = builder.parse(new File("src/config/language.xml"));//解析文档

            Element root = document.getDocumentElement(); //获取根节点

            System.out.println("language=" + root.getAttribute("cat"));

            System.out.println("-------------");

            NodeList list = root.getElementsByTagName("lan");//获取根节点的标签名为“lan”的子节点

            for (int i = 0; i < list.getLength(); i ++) {

                Element lan =  (Element) list.item(i);  //遍历得到每个"lan"节点

                System.out.println(lan.getTagName()+ "=" + lan.getAttribute("id"));

                NodeList lanList = lan.getChildNodes();  //获取“lan”节点的子节点

                for (int j = 0; j < lanList.getLength(); j++) {

                    Node node = lanList.item(j);

                    if (node instanceof Element) {

                        System.out.println(node.getNodeName()+"="+node.getTextContent());

                    }

                }

                System.out.println("*****************");

            }

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

}

控制台输出如下：

language=it

-------------

lan=1

name=java

ide=Eclipse

*****************

lan=2

name=swift

ide=XCode

*****************

lan=3

name=C#

ide=Visual Studio

*****************

DOM方式创建XML文件

项目结构图如下：


CreateXML.java文件

import java.io.File;

import java.io.StringWriter;

import javax.xml.parsers.DocumentBuilder;

import javax.xml.parsers.DocumentBuilderFactory;

import javax.xml.parsers.ParserConfigurationException;

import javax.xml.transform.Transformer;

import javax.xml.transform.TransformerConfigurationException;

import javax.xml.transform.TransformerException;

import javax.xml.transform.TransformerFactory;

import javax.xml.transform.dom.DOMSource;

import javax.xml.transform.stream.StreamResult;

import org.w3c.dom.Document;

import org.w3c.dom.Element;

public class CreateXML {

    public static void main(String[] args) {

        try {

            DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

            DocumentBuilder builder = factory.newDocumentBuilder();

            Document document = builder.newDocument();

            Element languages = document.createElement("languages");

            languages.setAttribute("cat", "it");

            Element lan_1 = document.createElement("lan");

            lan_1.setAttribute("id", "1");

            Element name_1 = document.createElement("name");

            name_1.setTextContent("Java");

            Element ide_1 = document.createElement("ide");

            ide_1.setTextContent("Eclipse");

            lan_1.appendChild(name_1);

            lan_1.appendChild(ide_1);

            languages.appendChild(lan_1);

            document.appendChild(languages);

            //将构建好的xml输出

            TransformerFactory transformerFactory = TransformerFactory.newInstance();

            Transformer transformer = transformerFactory.newTransformer();

            //输出到控制台

            StringWriter writer = new StringWriter();

            transformer.transform(new DOMSource(document), new StreamResult(writer));

            System.out.println(writer.toString());

            //输出到文件

            transformer.transform(new DOMSource(document), new StreamResult(new File("language.xml")));

        } catch (ParserConfigurationException e) {

            e.printStackTrace();

        } catch (TransformerConfigurationException e) {

            e.printStackTrace();

        } catch (TransformerException e) {

            e.printStackTrace();

        }

    }

}

控制台输出如下：

<?xml version="1.0" encoding="UTF-8" standalone="no"?><languages cat="it"><lan id="1"><name>Java</name><ide>Eclipse</ide></lan></languages>

运行之后刷新项目目录，可看到已经产生language.xml文件：


language.xml文件：

<?xml version="1.0" encoding="UTF-8" standalone="no"?>

<languages cat="it">

    <lan id="1">

        <name>Java</name>

        <ide>Eclipse</ide>

    </lan>

</languages>