使用JAXP对XML文档进行DOM解析

一、XML解析方式分为两种：dom和sax

dom：（Document Object Model,即文档对象模型）是W3C组织推荐的解析XML的一种方式。
sax：（Simple API for XML)不是官方标准，但它是XML社区事实上的标准，几乎所有的XML解析器都支持它。

dom和sax解析方法的区别：

dom：对文档CRUD（增删改查）比较方便，缺点：占用内存比较大（将xml文件全部读入内存）。
sax：占用内存较少，解析速度快（从上往下读一行解析一行）。缺点：只适合读取，不适合CRUD。

XML解析开发包：Jaxp（sun）、Jdom、dom4j

今天学习Jaxp：

二、使用JAXP对XML文档进行DOM解析：

private static String filename="src/exam.xml"; public static Document getDocument() throws Exception{//1创建工厂DocumentBuilderFactory factory=DocumentBuilderFactory.newInstance();//2得到dom解析器对象DocumentBuilder builder=factory.newDocumentBuilder();//3解析xml文档，得到代表文档的documentreturn builder.parse(filename);}

更加形象的描述为下图：

增，删，改需要将更新后的内容在写到xml中

public static void writeXml(Document document) throws TransformerException{TransformerFactory factory=TransformerFactory.newInstance();Transformer tf=factory.newTransformer();//transform(Source xmlSource, Result outputTarget)tf.transform(new DOMSource(document), new StreamResult(filename) );}

三、实战演练：

books.xml

<?xml version="1.0" encoding="UTF-8" standalone="no"?><书架><书><书名 name="xxx">影响力</书名><作者>罗伯特.西奥迪尼</作者><售价>90</售价></书><书><书名>JavaScript</书名><作者>JS</作者><售价>45</售价></书>
</书架>

读取XML文件，JUnit测试：

@Testpublic  void read() throws ParserConfigurationException, SAXException, IOException {DocumentBuilderFactory factory=DocumentBuilderFactory.newInstance();DocumentBuilder builder=factory.newDocumentBuilder();Document document=builder.parse("src/books.xml");NodeList list= document.getElementsByTagName("书名");Node node= list.item(0);String content=node.getTextContent();System.out.println(content);}

递归遍历XML文件中的所有节点

    @Testpublic  void read1() throws ParserConfigurationException, SAXException, IOException {DocumentBuilderFactory factory=DocumentBuilderFactory.newInstance();DocumentBuilder builder=factory.newDocumentBuilder();Document document=builder.parse("src/books.xml");Node root=document.getElementsByTagName("书架").item(0);list(root);        }/** 递归遍历XML文件中的所有节点* */public  void list(Node node){if(node instanceof Element){System.out.println(node.getNodeName());}NodeList childs= node.getChildNodes();for(int i=0;i<childs.getLength();i++){Node child=childs.item(i);list(child);}}

添加节点到XML文件中：

    @Testpublic  void add() throws ParserConfigurationException, SAXException, IOException, TransformerException{DocumentBuilderFactory factory=DocumentBuilderFactory.newInstance();DocumentBuilder builder=factory.newDocumentBuilder();Document document=builder.parse("src/books.xml");Element price=document.createElement("售价");//创建节点//把创建的节点添加到第一本书price.setTextContent("90");Element book=(Element) document.getElementsByTagName("书").item(0);book.appendChild(price);//把更新后的文档TransformerFactory tfactory=TransformerFactory.newInstance();Transformer tf=tfactory.newTransformer();tf.transform(new DOMSource(document), new StreamResult("src/books.xml"));}

为标签添加属性：

    @Testpublic  void addAttr() throws ParserConfigurationException, SAXException, IOException, TransformerException{DocumentBuilderFactory factory=DocumentBuilderFactory.newInstance();DocumentBuilder builder=factory.newDocumentBuilder();Document document=builder.parse("src/books.xml");Element bookname=(Element) document.getElementsByTagName("书名").item(0);bookname.setAttribute("name", "xxx");//把更新后的文档TransformerFactory tfactory=TransformerFactory.newInstance();Transformer tf=tfactory.newTransformer();tf.transform(new DOMSource(document), new StreamResult("src/books.xml"));}

删除操作：

@Testpublic  void delete() throws ParserConfigurationException, SAXException, IOException, TransformerException{DocumentBuilderFactory factory=DocumentBuilderFactory.newInstance();DocumentBuilder builder=factory.newDocumentBuilder();Document document=builder.parse("src/books.xml");Element bookname=(Element) document.getElementsByTagName("售价").item(0);//把更新后的文档Element e=(Element) document.getElementsByTagName("书").item(0);e.removeChild(bookname);TransformerFactory tfactory=TransformerFactory.newInstance();Transformer tf=tfactory.newTransformer();tf.transform(new DOMSource(document), new StreamResult("src/books.xml"));}