xml 相关知识及xml解析（jaxp）

<?xml version="1.0" encoding="UTF-8" standalone="no"?><!--
xml 语言用于描绘数据之间的关系  可以用来保存有关系的数据，也可以作为软件配置文件。
cdata区，不会被解析引擎解析的区域
--><书架>
	<书 name="xxxx">					
	<书名 name="xxx"/>
	<作者>张</作者>
	<价格>34</价格>
	<售价>59.00元</售价></书>
	<书>
	<作者>a2</作者>
	<价格>book</价格>
	</书>
</书架>

xml 规范之一DTD，对于属性，和元素等的分类，详见w3c DTD教学。

xml文档可以使用xml-stylesheet指令，通知xml解析引擎，应用css文件显示xml

外联，
<?xml-stylesheet href="style.css"type="text/css"?>
内联：
<?xml-stylesheet href="#style"type="text/css"?>

Sax解析对内存需要较小，适合读取，不适合增删改查。读一行解析一行。

package test;

import java.io.FileOutputStream;

import javax.xml.parsers.DocumentBuilder;					//jaxp 开发包属于j2se开发包，所以不需要进行额外的导包
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;

import org.junit.Test;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;

import org.w3c.dom.Node;

public class Demo9 {

	//读取xml文档中的数据，Xml解析开发包：jaxp（sun），dom4j。下面的是jaxp方式
	@Test
	public void  read() throws Exception{
		DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
		DocumentBuilder builder = factory.newDocumentBuilder();
		Document document = builder.parse("src/catalog.xml");			//将xml进行解析获得一个document对象。
		
		NodeList list = document.getElementsByTagName("作者");
		Node node = list.item(1);		//1从第2个开始
		String context = node.getTextContent();
		System.out.println(context);
	}
	
	//
	@Test
	public void  read2() throws Exception{
		DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
		DocumentBuilder builder = factory.newDocumentBuilder();
		Document document = builder.parse("src/catalog.xml");
		
		Node root = document.getElementsByTagName("书架").item(0);
		list(root);
	}
	
	private void list(Node node){
		if(node instanceof Element){
		System.out.println(node.getNodeName());
		}
		NodeList list = node.getChildNodes();
		for(int i=1;i<list.getLength();i++){
			Node child = list.item(i);
			list(child);
		}
		
	}
	
	//
	@Test
	public void  read3() throws Exception{
		DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
		DocumentBuilder builder = factory.newDocumentBuilder();
		Document document = builder.parse("src/catalog.xml");
																				//node 作为父类，没有可以根据属性名称获得单一属性内容的方法
		Element root = (Element)document.getElementsByTagName("书架").item(0);//强转是因为知道可以（即知道所获得的数据可以被转为element）
		String value = root.getAttribute("name");
		System.out.println(value);
	}
	
	//增加节点到xml文档
	@Test
	public void  add() throws Exception{
		DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
		DocumentBuilder builder = factory.newDocumentBuilder();
		Document document = builder.parse("src/catalog.xml");
		
		//创建节点
		Element price = document.createElement("售价");
		price.setTextContent("59.00元");
		
		//把创建的节点挂在。。。
		Element book  = (Element)document.getElementsByTagName("书").item(0);
		book.appendChild(price);
		
		//把更新后的内存写回到xml文档
		TransformerFactory tffactory = TransformerFactory.newInstance();
		Transformer tf = tffactory.newTransformer();		//transform是一个接口，不能直接new。
		//transform 方法接受一个源和一个目的地，source 是一个接口，DOMsource是实现了该接口的类    result也是一个接口，StreamResualt是实现了该接口的类
		tf.transform(new DOMSource(document),new StreamResult(new FileOutputStream("src/catalog.xml")));
		//添加会默认添加到末尾。
	}
	
	//增加节点到xml文档指定位置
	@Test
	public void  add2() throws Exception{
		DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
		DocumentBuilder builder = factory.newDocumentBuilder();
		Document document = builder.parse("src/catalog.xml");
		
		//创建节点
		Element price = document.createElement("售价");
		price.setTextContent("59.00元");
		
		//得到参考节点
		Element refNode  = (Element)document.getElementsByTagName("书").item(0);
		
		//把创建的节点挂在。。。
		Element book  = (Element)document.getElementsByTagName("书").item(0);
		
		//把节点插在指定位置
		book.insertBefore(price,refNode);
		
		//把更新后的内存写回到xml文档
		TransformerFactory tffactory = TransformerFactory.newInstance();
		Transformer tf = tffactory.newTransformer();		
		tf.transform(new DOMSource(document),new StreamResult(new FileOutputStream("src/catalog.xml")));
		
	}
	
	//想xml文档上添加属性
	@Test
	public void  addAttr() throws Exception{
		
		DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
		DocumentBuilder builder = factory.newDocumentBuilder();
		Document document = builder.parse("src/catalog.xml");
		
		Element bookName = (Element)document.getElementsByTagName("书").item(0);
		bookName.setAttribute("name","xxxx");
		
		TransformerFactory tffactory = TransformerFactory.newInstance();
		Transformer tf = tffactory.newTransformer();		
		tf.transform(new DOMSource(document),new StreamResult(new FileOutputStream("src/catalog.xml")));
	}
	
	
	public void delete()  throws Exception {
		
		DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
		DocumentBuilder builder = factory.newDocumentBuilder();
		Document document = builder.parse("src/catalog.xml");
		
		Element e = (Element)document.getElementsByTagName("售价").item(0);
		//e.getParentNode().removeChild(e);
		Element book = (Element)document.getElementsByTagName("书").item(0);
		book.removeChild(e);
		
		TransformerFactory tffactory = TransformerFactory.newInstance();
		Transformer tf = tffactory.newTransformer();		
		tf.transform(new DOMSource(document),new StreamResult(new FileOutputStream("src/catalog.xml")));
	}
	
	public void update() throws Exception{
		DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
		DocumentBuilder builder = factory.newDocumentBuilder();
		Document document = builder.parse("src/catalog.xml");
		
		Element e = (Element)document.getElementsByTagName("售价").item(0);
		e.setTextContent("109元");
		
		TransformerFactory tffactory = TransformerFactory.newInstance();
		Transformer tf = tffactory.newTransformer();		
		tf.transform(new DOMSource(document),new StreamResult(new FileOutputStream("src/catalog.xml")));
	}
	
}

（编辑：李大同）

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