DOM parser parsing additions, deletions and changes study notes

import java.io.File;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.Result;
import javax.xml.transform.Source;
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;

public class Demo2 {
    //dom是否将空白字符当作一个有效的元素对待
    public static void main(String[] args) throws Exception{
        Document document = getDocument();
        Element rootElement = document.getDocumentElement();
        NodeList nodeList = rootElement.getChildNodes();
        System.out.println("共有" + nodeList.getLength()+"个直接元素");
    }
    @Test
    public void create() throws Exception{
        Document document = getDocument();
        Element newCarElement = document.createElement("汽车");
        newCarElement.setTextContent("我的汽车");
        Element rootElement = document.getDocumentElement();
        //rootElement.appendChild(newCarElement);
        rootElement.insertBefore(
                newCarElement,
                rootElement.getElementsByTagName("汽车").item(1));
        write2xml(document);
    }
    @Test
    public void update() throws Exception{
        Document document = getDocument();
        Element secondCarElement = (Element) document.getElementsByTagName("汽车").item(1);
        secondCarElement.getElementsByTagName("产地").item(0).setTextContent("深圳");
        secondCarElement.getElementsByTagName("车牌").item(0).getAttributes().getNamedItem("出产时间").setTextContent("2012年");
        write2xml(document);
    }
    @Test
    public void delete() throws Exception{
        Document document = getDocument();
        Element rootElement = document.getDocumentElement();
        Element secondCarElement = (Element) rootElement.getElementsByTagName("汽车").item(1);
        rootElement.removeChild(secondCarElement);
        write2xml(document);
    }
    private void write2xml(Document document)throws Exception {
        //将内存中的document对象写到外存的xml文件
        TransformerFactory tf = TransformerFactory.newInstance();
        Transformer transformer = tf.newTransformer();
        //源
        Source source = new DOMSource(document);
        //目
        Result result = new StreamResult(new File("src/xml/dom/car.xml"));
        transformer.transform(source,result);
    }
    private static Document getDocument() throws Exception {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        //设置dom解析器将空白字符过滤
        factory.setIgnoringElementContentWhitespace(true);
        DocumentBuilder domParser = factory.newDocumentBuilder();
        Document document = domParser.parse(new File("src/xml/dom/car.xml"));
        return document;
    }
}