XML文档读取-DOM

DOM(Document Object Model)，“文档对象模型”早期是为了解决不用浏览器间数据兼容问题提出的解决方案，现在已经是W3C组织推荐的处理可扩展标志语言的标准编程接口。

W3C DOM 被分为 3 个不同的部分/级别（parts / levels）：

• 核心 DOM：用于任何结构化文档
• XML DOM：用于 XML 文档的标准模型
• HTML DOM：用于 HTML 文档的标准模型

XML DOM 是：

• 用于 XML 的标准对象模型
• 用于 XML 的标准编程接口
• 中立于平台和语言
• W3C 的标准

SUN公司的JAXP（Java API for XML Processing）提供了对dom的支持；

其解析步骤为：

• 创建 DOM 解析器的工厂
• 得到 DOM 解析器对象。

对整个XML文档进行操作

<?xml version="1.0" encoding="UTF-8"?>
<!-- <!DOCTYPE books SYSTEM "books.dtd"> -->
<books>
    <book>
        <author>joy</author>
        <title>java core</title>
        <price>100</price>
    </book>
    <book>
        <author>joy1</author>
        <title>Thinking in java</title>
        <price>100</price>
    </book>
    <book>
        <comment author="joy" id="S001" language="Chinese" price="20" title="Java"/>
        <comment author="joy" id="S002" language="Chinese" price="20" title="Thinking in Java"/>
    </book>
</books>

package com.sy;

import java.io.File;
import java.io.IOException;

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.TransformerFactoryConfigurationError;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;

public class first {
    private static void findElement() throws ParserConfigurationException,
            SAXException, IOException {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document doc = builder.parse(new File("books.xml"));
        NodeList list = doc.getElementsByTagName("title");
        Node node = list.item(1);
        System.out.println(node.getTextContent());
    }

    // 获取属性内容
    private static void getAttribute() throws ParserConfigurationException,
            SAXException, IOException {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document doc = builder.parse(new File("books.xml"));
        Element node = (Element) doc.getElementsByTagName("comment").item(1);
        System.out.println(node.getAttribute("title"));
    }

    // 使用递归遍历xml文档
    private static void loopNode() throws ParserConfigurationException,
            SAXException, IOException {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document doc = builder.parse(new File("books.xml"));
        loop(doc);
    }

    private static void loop(Node doc) {
        NodeList list = doc.getChildNodes();
        for (int i = 0; i < list.getLength(); i++) {
            Node node = list.item(i);
            System.out.println(node.getNodeName());
            loop(node);
        }

    }

    // 添加节点，内容，属性
    private static void createElement() throws ParserConfigurationException,
            SAXException, IOException, TransformerFactoryConfigurationError,
            TransformerConfigurationException, TransformerException {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document doc = builder.parse(new File("books.xml"));
        // 创建结点
        Element e = doc.createElement("language");
        // 添加内容
        e.setTextContent("Chinese");
        // 添加属性
        e.setAttribute("aa", "xxx");
        // 获取父节点，并append新创建的结点
        doc.getElementsByTagName("book").item(1).appendChild(e);
        // 使用Transformer将内存中更新过的xml文档写入实际的xml文档中
        TransformerFactory tfactory = TransformerFactory.newInstance();
        Transformer tf = tfactory.newTransformer();
        tf.transform(new DOMSource(doc),
                new StreamResult(new File("books.xml")));
    }

    // 注意：DOM的解析方式为将整个xml文档都加载入内存，因此对文档节点的添加、删除和修改操作都是只针对内存中的document对象，因此还需要使用Transformer类将修改真正写入到xml文件中！
    // 删除节点
    private static void deleteElement() throws ParserConfigurationException,
            SAXException, IOException, TransformerFactoryConfigurationError,
            TransformerConfigurationException, TransformerException {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document doc = builder.parse(new File("books.xml"));
        // 得到待删除的结点
        Element e = (Element) doc.getElementsByTagName("language").item(0);
        // 获取结点的父节点，然后删除该子结点
        e.getParentNode().removeChild(e);
        // 使用Transformer将内存中更新过的xml文档写入实际的xml文档中
        TransformerFactory tfactory = TransformerFactory.newInstance();
        Transformer tf = tfactory.newTransformer();
        tf.transform(new DOMSource(doc),
                new StreamResult(new File("books.xml")));
    }

    public static void main(String[] args) throws ParserConfigurationException,
            SAXException, IOException, TransformerConfigurationException,
            TransformerFactoryConfigurationError, TransformerException {
        // findElement();
        // getAttribute();
        // loopNode() ;
        // createElement();
        deleteElement();
    }

}

代码解读

这个类内含七个函数（包括五个自定义功能函数，一个递归函数体，一个main函数）

五个功能函数：

JfindElement()：发现节点（输出特定节点的文本内容）

    private static void JfindElement() throws ParserConfigurationException,
            SAXException, IOException {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();// ????
        DocumentBuilder builder = factory.newDocumentBuilder();// ????
        Document doc = builder.parse(new File("./WebRoot/xml/t6.xml"));// 获取页面
        NodeList list = doc.getElementsByTagName("title");// 获取tittle节点
        System.out.println(list.getLength());// 输出title节点长度
        Node node = list.item(1);// 第二个节点
        System.out.println(node.getTextContent());// 输出第二个节点的文本信息
    }

getAttribute()：获得属性值（输出特定节点的属性值）

private static void getAttribute() throws ParserConfigurationException,
            SAXException, IOException {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document doc = builder.parse(new File("./WebRoot/xml/t6.xml"));
        Element node = (Element) doc.getElementsByTagName("comment").item(1);// 获取comment节点集合
        System.out.println(node.getAttribute("title"));// 输出node节点的tittle属性的值
    }

loop(Node doc)：递归主函数体

private static void loop(Node doc)// Document继承自Node，，，此处为向上转型
    {
        NodeList list = doc.getChildNodes();// 获取孩子节点的集合
        // 便利孩子节点集合
        // 输出每个节点的标签名
        // 递归调用，输出每一层的子节点
        for (int i = 0; i < list.getLength(); i++) {
            Node node = list.item(i);
            System.out.println(node.getNodeName());
            loop(node);
        }
    }

loopNode()递归输出所有节点

// 输出所有节点的节点名称
    private static void loopNode() throws ParserConfigurationException,
            SAXException, IOException {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document doc = builder.parse(new File("./WebRoot/xml/t6.xml"));
        loop(doc);// 函数调用输出doc所有子孙节点
    }

createElement()：

创建新节点

把新节点添加到父节点后面

更新文档(把修改后的xml文档同步到本地)

private static void createElement() throws ParserConfigurationException,
            SAXException, IOException, TransformerFactoryConfigurationError,
            TransformerConfigurationException, TransformerException {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document doc = builder.parse("./WebRoot/xml/t6.xml");
        // 创建结点
        Element e = doc.createElement("language");
        // 为新创建的节点添加内容
        e.setTextContent("Chinese");
        // 为新创建的节点添加属性
        e.setAttribute("aa", "xxx");
        // 为新创建的节点获取父节点，并append新创建的结点
        doc.getElementsByTagName("books").item(1).appendChild(e);
        // 使用Transformer将内存中更新过的xml文档写入实际的xml文档中
        TransformerFactory tfactory = TransformerFactory.newInstance();
        Transformer tf = tfactory.newTransformer();
        tf.transform(new DOMSource(doc), new StreamResult(new File(
                "./WebRoot/xml/t6.xml")));
    }

deleteElement()：删除节点

找到他的父节点

父节点删除要删除的节点

更新文档(把修改后的xml文档同步到本地)

private static void deleteElement() throws ParserConfigurationException,
            SAXException, IOException, TransformerFactoryConfigurationError,
            TransformerConfigurationException, TransformerException {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document doc = builder.parse(new File("./WebRoot/xml/t6.xml"));
        // 得到待删除的结点
        Element e = (Element) doc.getElementsByTagName("language").item(0);
        // 获取结点的父节点，然后删除该子结点
        e.getParentNode().removeChild(e);
        // 使用Transformer将内存中更新过的xml文档写入实际的xml文档中
        TransformerFactory tfactory = TransformerFactory.newInstance();
        Transformer tf = tfactory.newTransformer();
        tf.transform(new DOMSource(doc), new StreamResult(new File(
                "./WebRoot/xml/t6.xml")));
    }