XML的两种解析方式
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JDK提供的XML解析方式分为两种:DOM方式和SAX方式
DOM:Document Object Model。需要读取整个XML文档,先需要在内存中构架代表整个DOM树的Document对象,可以进行随机访问. 需要考虑内存.适合增删改
SAX:Simple API for XML。采用事件驱动的方式解析XML文件,边读边对文档进行处理.适合读取
其他的xml解析包:Dom4J, PullParser(安卓)
Dom4J实现类似SAX方式, API类似DOM方式
DOM @JDK
public class DomTest { // 解析xml获取document对象 private Document getDocument() throws ParserConfigurationException, SAXException, IOException { // 1. 获得工厂 DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); // 2. 获得 builder对象 DocumentBuilder builder = factory.newDocumentBuilder(); // 3. 解析xml得带document对象 Document document = builder.parse("src/book.xml"); return document; } // 将内存中的document对象写回xml文件中 private void writeBack2Xml(Document document) throws TransformerFactoryConfigurationError, TransformerConfigurationException, TransformerException { TransformerFactory factory = TransformerFactory.newInstance(); Transformer transformer = factory.newTransformer(); transformer.transform(new DOMSource(document), new StreamResult("src/book.xml")); } // 读取节点文本 @Test public void testReadContent() throws Exception{ Document document = getDocument(); //根据标签名获得节点列表 NodeList nodeList = document.getElementsByTagName("书"); System.out.println("长度 : " + nodeList.getLength()); // 返回第一个节点 Node firstNode = nodeList.item(0); // 返回文本内容 String result = firstNode.getTextContent(); System.out.println(result); } // 读取节点的属性值 @Test public void testReadAttribute() throws Exception{ Document document = getDocument(); NodeList nodeList = document.getElementsByTagName("书"); // 确认本Node为元素节点后加强转 Node node = nodeList.item(0); if (node instanceof Element) { Element firstElement = (Element) node; String result = firstElement.getAttribute("出版社"); System.out.println(result); } } // 添加节点 @Test public void testAddPrice() throws Exception, SAXException, IOException{ Document document = getDocument(); Node firstNode = document.getElementsByTagName("书").item(0); Element newElement = document.createElement("售价"); newElement.setTextContent("79.00元"); firstNode.appendChild(newElement); writeBack2Xml(document); //写回 } // 删除节点 @Test public void testDelete() throws Exception, SAXException, IOException{ Document document = getDocument(); NodeList priceNodeList = document.getElementsByTagName("售价"); for (int i = 0; i < priceNodeList.getLength(); i++) { Node node = priceNodeList.item(i); if("39.00元".equals(node.getTextContent())){ // 从父节点删除子节点, 类似dom的api node.getParentNode().removeChild(node); } } writeBack2Xml(document); } // 打印所有元素节点的名称 @Test public void testPrintAllElementsName() throws Exception, SAXException, IOException{ Document document = getDocument(); // 递归打印 printAllElementsName(document); } public void printAllElementsName(Node node){ // 打印本节点 if(Node.ELEMENT_NODE==node.getNodeType()){ System.out.println(node.getNodeName()); } // 处理子节点 NodeList childNodes = node.getChildNodes(); for (int i = 0; i < childNodes.getLength(); i++) { //递归出口: 循环完成 Node item = childNodes.item(i); printAllElementsName(item); } } }
SAX @JDK
public class SaxTest { public static void main(String[] args) throws Exception, SAXException { SAXParserFactory factory = SAXParserFactory.newInstance(); SAXParser parser = factory.newSAXParser(); XMLReader reader = parser.getXMLReader(); reader.setContentHandler(new MyDefaultHandler()); reader.parse("src/book.xml"); } } class MyDefaultHandler extends DefaultHandler { // 作为被调用方, 流程不是这边控制, 所以定义状态位或计数器来标记流程进行的位置 private boolean isPrice = false; private int count =1; @Override public void startElement(String uri, String localName, String qName, // qName标签名 Attributes attributes) throws SAXException { if ("售价".equals(qName)) { isPrice = true; count++; } } @Override public void endElement(String uri, String localName, String qName) throws SAXException { if ("售价".equals(qName)) { isPrice = false; } } // 读到文本了 @Override public void characters(char[] ch, int start, int length) throws SAXException { if (isPrice&&count==3) { System.out.println("文本: " + new String(ch, start, length)); } } }
Dom4J
public class Dom4JTest { private Document getDocument() throws DocumentException { // 获得 代表 xml 文件的 document 对象 SAXReader reader = new SAXReader(); Document document = reader.read("src/book.xml"); return document; } private void wirteBack2Xml(Document document) throws UnsupportedEncodingException, FileNotFoundException, IOException { OutputFormat format = OutputFormat.createPrettyPrint(); format.setEncoding("UTF-8"); XMLWriter writer = new XMLWriter(new FileOutputStream("src/book.xml"), format); writer.write(document); writer.close(); } // 读取节点的文本内容 // 由于 dom4j采用sax方式去解析的xml文档, 所以dom4j不能直接获得深层次的某个节点, 需要一级级获得 @Test public void testReadContent() throws Exception{ Document document = getDocument(); Element rootElement = document.getRootElement(); Element firstLevelElement = rootElement.element("ele1"); Element secondLevelElement = firstLevelElement.element("ele2"); String value = secondLevelElement.getText(); System.out.println(value); } // 读取属性值 @Test public void testReadAttribute() throws Exception{ Document document = getDocument(); Element rootElement = document.getRootElement(); List<Element> list = rootElement.elements("书"); Element secondElement = list.get(1); Attribute attribute = secondElement.attribute("出版社"); String value = attribute.getValue(); System.out.println(value); } // 添加节点 @Test public void testAddPrice() throws Exception{ Document document = getDocument(); Element rootElement = document.getRootElement(); Element secondBookElement = (Element) rootElement.elements("书").get(1); // 创建新节点 secondBookElement.addElement("newEle").setText("this is new Element"); wirteBack2Xml(document); } // 删除节点 @Test public void testDeletePrice() throws Exception{ Document document = getDocument(); Element rootElement = document.getRootElement(); Element secondBookElement = (Element) rootElement.elements("书").get(1); Element targetBookPrice = (Element) secondBookElement.elements("售价").get(0); // 拿到父节点, 然后删除这个子节点 targetBookPrice.getParent().remove(targetBookPrice); wirteBack2Xml(document); } }
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