dom方式解析xml文档

public class DomDemo1 {    @Test //需求:把第一个user节点的name的值取出来   public void getDom() throws Exception {        //第一步，通过DocumentBuilderFactory类中的工厂方法等到一个dbf对象        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();        //第二步,通过dbf对象创建出一个DocumentBuilder对象        DocumentBuilder db = dbf.newDocumentBuilder();        //第三步,通过db对象创建出一个Document对象        Document dom = db.parse("./xml4/users.xml");// new File("./xml4/users.xml")        //System.out.println("dom:"+dom);        //然后进行dom操作        Node root= dom.getFirstChild();//根节点        //System.out.println("root:"+root);        System.out.println(root.getNodeName());        System.out.println(root.getFirstChild().getNodeName());        //上面一句的输出是：#text ----dom中把空白符也看成是一个Node，这种情况对我们的解析通常会造成很大的麻烦        //※※为解决上面的问题，我们以后解析时尽量不要用Node，而要用Element。因为Element是元素它不包含属性和文字内容(包括空白符),因此可避开空白符的干扰        Element eRoot = (Element)root;        NodeList list = eRoot.getElementsByTagName("user");        System.out.println("user元素的数量:"+list.getLength());        System.out.println("第1个user元素"+list.item(0));//通过item(index)来获取列表中的元素        System.out.println("第2个user元素"+list.item(1));        Node user1Node = list.item(0);        Element eUser1 = (Element)user1Node;//要把Node强转成Element，因为Element是子接口，里面有getElementBy*等方法，而Node没有(只能采用childNodes的方式，这种方式会受空白符的干扰)        NodeList listNames = eUser1.getElementsByTagName("name");        String nm = listNames.item(0).getNodeName();//name--标签名        String nmVal = listNames.item(0).getTextContent();//标签内部所包含的文本内容----innerText        System.out.println(nm+","+nmVal);        //bug::::直接通过dom对象获取其下节点---经测试,无法通过id来获取        Element ee = dom.getElementById("aa");        System.out.println("###: "+ee);//null   }    @Test //需求:把第二个user节点的age值取出来    public void getAge()throws Exception{        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();        DocumentBuilder db = dbf.newDocumentBuilder();        Document dom = db.parse("./xml4/users.xml");        Element root = (Element) dom.getFirstChild();        Element user2 =(Element) root.getElementsByTagName("user").item(1);        Element eAge =(Element) user2.getElementsByTagName("age").item(0);        String age = eAge.getTextContent();        System.out.println("age:"+age);    }    //用Java对xml文档进行CRUD---创建，遍历，更新，删除    //遍历    @Test    public void query() throws Exception{        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();        DocumentBuilder db = factory.newDocumentBuilder();        Document dom = db.parse( new File("./xml4/users.xml") );        Element root = (Element) dom.getFirstChild();        NodeList list = root.getElementsByTagName("user");        for(int i=0;i<list.getLength();i++){            Element user =(Element) list.item(i);            String id = user.getAttribute("id");            String name = user.getElementsByTagName("name").item(0).getTextContent();            String age = user.getElementsByTagName("age").item(0).getTextContent();            System.out.println("id:"+id+",name:"+name+",age:"+age);            System.out.println("-----------------------");        }    }    //更新---把最后一个user的年龄+10    @Test    public void update() throws Exception{        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();        DocumentBuilder db = factory.newDocumentBuilder();        Document dom = db.parse( new File("./xml4/users.xml") );        Element root = (Element) dom.getFirstChild();        //Element eUser = (Element) root.getLastChild();//注意bug：如果最后一个</user>和</users>标签之前有空白符(包括换行)，那么该句获得的节点是空白符        //System.out.println(root.getLastChild().getNodeName());//#text        NodeList list =  root.getElementsByTagName("user");        Element eUser = (Element) list.item(list.getLength()-1);        Element eAge = (Element) eUser.getElementsByTagName("age").item(0);        int age = Integer.parseInt(eAge.getTextContent().trim())+10;        eAge.setTextContent(""+age);        System.out.println(age);        //把内存中的当前dom对象存储到xml文件        TransformerFactory tf = TransformerFactory.newInstance();        Transformer trans = tf.newTransformer();        trans.transform(new DOMSource(dom), new StreamResult("./xml4/users.xml"));//把xml源 输出到 目标 ---如果目标存在则是更新，否则是创建    }    //创建 --需求：添加一个新的user    @Test    public void create() throws Exception{        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();        DocumentBuilder db = factory.newDocumentBuilder();        Document dom = db.parse( new File("./xml4/users.xml") );        Element root = (Element) dom.getFirstChild();        //创建一个新的user元素        Element eUserNew = dom.createElement("user");        eUserNew.setAttribute("id", "C001");        //创建name和age子元素        Element eName = dom.createElement("name");        eName.setTextContent("李四");        Element eAgeNew = dom.createElement("age");        eAgeNew.setTextContent("22");        //把所创建的元素组装成一棵子树,添加到整棵dom树上        eUserNew.appendChild(eName);        eUserNew.appendChild(eAgeNew);        root.appendChild(eUserNew);        //把内存中的当前dom对象存储到xml文件        TransformerFactory tf = TransformerFactory.newInstance();        Transformer trans = tf.newTransformer();        trans.transform(new DOMSource(dom), new StreamResult("./xml4/users.xml"));//把xml源 输出到 目标 ---如果目标存在则是更新，否则是创建    }    //删除---需求：删除最后一个元素    @Test    public void delete() throws Exception{        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();        DocumentBuilder db = factory.newDocumentBuilder();        Document dom = db.parse( new File("./xml4/users.xml") );        Element root = (Element) dom.getFirstChild();        //获取将要删除的元素        NodeList list = root.getElementsByTagName("user");        Element e = (Element) list.item( list.getLength()-1 );        e.getParentNode().removeChild(e);        //把内存中的当前dom对象存储到xml文件        TransformerFactory tf = TransformerFactory.newInstance();        Transformer trans = tf.newTransformer();        trans.transform(new DOMSource(dom), new StreamResult("./xml4/users.xml"));    }}