使用dom解析xml文档

声明：本文是观看传智播客方立勋视频的学习过程，非常详细，做一点总结。

一：在解析xml文档对象以前，需要获得文档对象。这部分是模版代码

    //1：创建工厂，使应用程序能够从 XML 文档获取生成 DOM 对象树的解析器  
    DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();        
    //2：得到dom解析器  
    DocumentBuilder builder = factory.newDocumentBuilder();  
    //3：解析xml文档，得到代表文档的document  
    Document doc = builder.parse("src/Book.xml");  

 其中很多对文档操作后，需要更新文档的部分也是模版代码。

    //把跟新后的内存写会到文档  
            TransformerFactory tffactory = TransformerFactory.newInstance();  
            Transformer tf = tffactory.newTransformer();  
            tf.transform(new DOMSource(doc),new StreamResult(new FileOutputStream("src/Book.xml")));  

 当然这些代码应该放在一个工具类，但是也懒得做了，下面的代码显得臃肿了一些。

二：获得了文档对象以后，就是对文档的CRUD过程。
先说一句十分重要的话：XML文档中的类容会有对应的对象 ：标签ELEMENT对象，文本变为Text对象，还有属性Attri对象。但不管是什么对象，都是Node的子类，所以在开发中可以把获取到的任意节点都当做Node看待。合适的转换很重要。

文档添加：

a:添加节点

    //添加节点  
    @Test  
    public void add() throws Exception{  
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();  
        DocumentBuilder builder = factory.newDocumentBuilder();  
        Document doc = builder.parse("src/Book.xml");  
          
        //创建节点  
        Element price = doc.createElement("售价");  
        price.setTextContent("59.00");  
          
        //把创建的节点挂到第一本书上  
          
        Element book = (Element) doc.getElementsByTagName("书").item(0);  
        book.appendChild(price);  
          
        //把跟新后的内存写回到文档  
        TransformerFactory tffactory = TransformerFactory.newInstance();  
        Transformer tf = tffactory.newTransformer();  
        tf.transform(new DOMSource(doc),new StreamResult(new FileOutputStream("src/Book.xml")));  
          
    }  

 

这里面注意的是添加节点以后，要将更新后的内存写回到文档

b:将节点添加到指定的位置上

    //向文档中指定位置添加节点  
        @Test  
        public void add2() throws Exception{  
            DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();  
            DocumentBuilder builder = factory.newDocumentBuilder();  
            Document doc = builder.parse("src/Book.xml");  
              
            //创建节点  
            Element price = doc.createElement("售价");  
            price.setTextContent("59.00");  
            //得到参考节点  
            Element refnode = (Element) doc.getElementsByTagName("售价").item(0);  
              
            //得到要挂仔的节点  
            Element book = (Element) doc.getElementsByTagName("书").item(0);  
            //插入  
            book.insertBefore(price, refnode);  
              
            //把跟新后的内存写会到文档  
            TransformerFactory tffactory = TransformerFactory.newInstance();  
            Transformer tf = tffactory.newTransformer();  
            tf.transform(new DOMSource(doc),new StreamResult(new FileOutputStream("src/Book.xml")));  
              
        }  

 

c：添加属性

[java] view plaincopy

    //向文档中添加属性  
    @Test  
    public void addAttribute() throws Exception{  
          
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();  
        DocumentBuilder builder = factory.newDocumentBuilder();  
        Document doc = builder.parse("src/Book.xml");  
          
        Element element = (Element) doc.getElementsByTagName("书名").item(0);  
        element.setAttribute("name", "xxxx");  
          
        //把跟新后的内存写会到文档  
        TransformerFactory tffactory = TransformerFactory.newInstance();  
        Transformer tf = tffactory.newTransformer();  
        tf.transform(new DOMSource(doc),new StreamResult(new FileOutputStream("src/Book.xml")));          
    }  

 

读取文档：

a：得到指定标签的内容

    @Test  
    public void Read1() throws Exception{  
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();  
        DocumentBuilder builder = factory.newDocumentBuilder();  
        Document doc = builder.parse("src/Book.xml");  
          
        NodeList  list = doc.getElementsByTagName("书名");  
        Node node = list.item(1);//从0开始  
        String content = node.getTextContent();  
        System.out.println(content);  
    }  

 b：遍历所有的标签，这里面使用的递归。

    @Test  
        public void Read2() throws Exception{  
            DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();  
            DocumentBuilder builder = factory.newDocumentBuilder();  
            Document doc = builder.parse("src/Book.xml");  
              
            //得到根节点  
            Node root = doc.getElementsByTagName("书架").item(0);  
            list(root);//递归打印  
        }  
          
        private void list(Node node) {  
            if(node instanceof Element){  
                System.out.println(node.getNodeName());  
            }  
            NodeList list = node.getChildNodes();  
            for(int i=0;i<list.getLength();i++){  
                Node child = list.item(i);  
                list(child);  
            }  
        }  

 c:得到指定标签的属性，这里面使用了Node--->Eelement的转换

    @Test  
    public void Read3() throws Exception{  
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();  
        DocumentBuilder builder = factory.newDocumentBuilder();  
        Document doc = builder.parse("src/Book.xml");  
          
        Element node = (Element) doc.getElementsByTagName("书名").item(0);  
        String value = node.getAttribute("name");  
        System.out.println(value);  
    }  

 3：删除:

@Test  
    public void delete() throws  Exception{  
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();  
        DocumentBuilder builder = factory.newDocumentBuilder();  
        Document doc = builder.parse("src/Book.xml");  
        //得到要删除的节点  
        Element e = (Element) doc.getElementsByTagName("售价").item(0);  
        //得到要删除节点的父节点  
        Element book = (Element) e.getParentNode();  
        //删除  
        book.removeChild(e);//或者e.getParentNode().removeChild(e);     
          
        //把跟新后的内存写会到文档  
        TransformerFactory tffactory = TransformerFactory.newInstance();  
        Transformer tf = tffactory.newTransformer();  
        tf.transform(new DOMSource(doc),new StreamResult(new FileOutputStream("src/Book.xml")));  
    } 

 4：更改

    @Test  
    public void update() throws  Exception{  
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();  
        DocumentBuilder builder = factory.newDocumentBuilder();  
        Document doc = builder.parse("src/Book.xml");  
        //得到要更新的节点  
        Element e = (Element) doc.getElementsByTagName("售价").item(0);  
          
        //把跟新后的内存写会到文档  
        TransformerFactory tffactory = TransformerFactory.newInstance();  
        Transformer tf = tffactory.newTransformer();  
        tf.transform(new DOMSource(doc),new StreamResult(new FileOutputStream("src/Book.xml")));  
              
    }  

 三：总结

通过上面的代码演示，可以感到到模版代码比较多。就是固定的获得文档，写回文档。

然后重要的亮点重复一下：

1：XML文档中的类容会有对应的对象：标签ELEMENT对象，文本变为Text对象，还有属性Attri对象。但不管是什么对象，都是Node的子类，所以在开发中可以把获取到的任意节点都当做Node看待。

2：递归遍历所有的标签。

 

实例

import java.io.IOException;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;

import org.junit.BeforeClass;
import org.junit.Test;
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;

/**
 * @author forlab
 * @version 2012-12-19
 */
public class Dom {

	@BeforeClass
	public static void setUpBeforeClass() throws Exception {
	}
	
	@Test
	public void readXml() throws ParserConfigurationException, SAXException, IOException{
		DocumentBuilderFactory db = DocumentBuilderFactory.newInstance();
		DocumentBuilder dbuilder = db.newDocumentBuilder();
		Document dom = dbuilder.parse("src/dom.xml");
		Node node = dom.getElementsByTagName("书架").item(0);
		list(node);
	}

	private void list(Node node) {
		if(node instanceof Element){
			System.out.println(node.getNodeName());
		}
		NodeList nodes = node.getChildNodes();
		for(int i=0;i<nodes.getLength();i++){
			Node child = nodes.item(i);
			list(child);
		}
	}
	
	@Test
	public void readXmlByAttrubuteName() throws ParserConfigurationException, SAXException, IOException{
		DocumentBuilderFactory db = DocumentBuilderFactory.newInstance();
		DocumentBuilder dbuilder = db.newDocumentBuilder();
		Document dom = dbuilder.parse("src/dom.xml");
		Element element = (Element) dom.getElementsByTagName("作者").item(0);
		System.out.println(element.getAttribute("name"));
	}
}