DOM解析xml

DOM的全称是Document Object Model，即文档对象模型。在应用程序中，基于DOM的XML解析器将一个XML文档转换成一个对象模型的集合（通常称DOM树），应用程序正是通过对这个对象模型的操作，来实现对XML文档数据的操作。通过DOM接口，应用程序可以在任何时候访问XML文档中的任何一部分数据，因此，这种利用DOM接口的机制也被称作随机访问机制。

DOM树所提供的随机访问方式给应用程序的开发带来了很大的灵活性，它可以任意地控制整个XML文档中的内容。然而，由于DOM分析器把整个XML文档转化成DOM树放在了内存中，因此，当文档比较大或者结构比较复杂时，对内存的需求就比较高。而且，对于结构复杂的树的遍历也是一项耗时的操作。所以，DOM分析器对机器性能的要求比较高，实现效率不十分理想。不过，由于DOM分析器所采用的树结构的思想与XML文档的结构相吻合，同时鉴于随机访问所带来的方便，因此，DOM分析器还是有很广泛的使用价值的。

xml

<?xml version="1.0" encoding="UTF-8"?>
<exam>
	<student examid="222">
		<name>张三</name>
		<location>沈阳</location>
		<grade>89</grade>
	</student>

	<student idcard="333">
		<name>李四</name>

		<location>大连</location>
		<grade>110</grade>
	</student>

</exam>

　　

实例：

package com.bcrj.dom;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

public class Test1 {
    DocumentBuilderFactory dbf = null;
    DocumentBuilder db = null;
    private Document document = null;

    public Document getDocument() {
        return document;
    }

    public void setDocument(Document document) {
        this.document = document;
    }

    // 1、得到某个具体的节点内容,第一个student的location
    public String test1() {
        NodeList nl = document.getElementsByTagName("location");
        int index = 0;
        for (int i = 0; i < nl.getLength(); i++) {
            Node node = nl.item(i);
            String nodeName = node.getNodeName();
            if ("location".equals(nodeName)) {
                index++;
            }
            if (index == 1) {
                return node.getTextContent();
            }
        }
        return null;
    }

    // 2、遍历所有元素节点
    public void test2(Node node) {
        if (node instanceof Element) {
            System.out.println(node.getNodeName());
        }
        NodeList nl = node.getChildNodes();
        int len = nl.getLength();
        for (int i = 0; i < len; i++) {
            Node n = nl.item(i);
            test2(n);
        }
    }

    // 3、修改某个元素节点的主体内容,把第二个studnent的grade改为100
    public void test3() throws TransformerException {
        // 根元素
        int index = 0;
        Node n = document.getFirstChild();
        NodeList nl = n.getChildNodes();
        int len = nl.getLength();

        for (int i = 0; i < nl.getLength(); i++) {
            if (nl.item(i) instanceof Element) {
                index++;
                if (index == 2) {
                    NodeList nodelist = nl.item(i).getChildNodes();
                    for (int j = 0; j < nodelist.getLength(); j++) {
                        Node node = nodelist.item(j);
                        if (node instanceof Element) {
                            if (node.getNodeName().equals("grade")) {
                                node.setTextContent("110");
                            }
                        }
                    }
                }
            }
        }
        TransformerFactory facotry = TransformerFactory.newInstance();
        Transformer ts = facotry.newTransformer();
        ts.transform(new DOMSource(document), new StreamResult(
                "src/students.xml"));
    }

    // 4、向指定元素节点中增加子元素节点,第一student中增加子元素<age>23</age>
    public void test4() throws TransformerException {
        NodeList nl = document.getElementsByTagName("student");
        Element element = document.createElement("age");
        element.setTextContent("23");
        nl.item(0).appendChild(element);
        // 写入xml
        TransformerFactory facotry = TransformerFactory.newInstance();
        Transformer ts = facotry.newTransformer();
        ts.transform(new DOMSource(document), new StreamResult(
                "src/students.xml"));
    }

    // 5、向指定元素节点上增加同级元素节点,在第二个student的location后添加<age>23</age>
    public void test5() throws Exception {
        NodeList nl = document.getElementsByTagName("student");
        Element element = document.createElement("age");
        element.setTextContent("23");

        NodeList nll = nl.item(1).getChildNodes();
        for (int i = 0; i < nll.getLength(); i++) {

            if ((nll.item(i) instanceof Element)
                    && "location".equals(nll.item(i).getNodeName())) {
                nll.item(i).getParentNode().insertBefore(element, nll.item(i));
            }
        }
        TransformerFactory facotry = TransformerFactory.newInstance();
        Transformer ts = facotry.newTransformer();
        ts.transform(new DOMSource(document), new StreamResult(
                "src/students.xml"));
    }

    // 6、删除指定元素节点，删除第二个student元素的age子元素
    public void test6() throws Exception {
        NodeList nl = document.getElementsByTagName("student");
        NodeList nll = nl.item(1).getChildNodes();
        for (int i = 0; i < nll.getLength(); i++) {
            if ((nll.item(i) instanceof Element)
                    && "age".equals(nll.item(i).getNodeName())) {
                //由父元素调用删除
                nll.item(i).getParentNode().removeChild(nll.item(i));
            }
        }

        TransformerFactory facotry = TransformerFactory.newInstance();
        Transformer ts = facotry.newTransformer();
        ts.transform(new DOMSource(document), new StreamResult(
                "src/students.xml"));
    }

    // 7、操作XML文件属性,打印第一学生的examid
    public void test7(){
        NodeList nl = document.getElementsByTagName("student");
        Element nll = (Element)nl.item(0);
        String examid = nll.getAttribute("examid");
        System.out.println(examid);
        
    }
    
    // 8、添加一个idcard属性给第二student
    public void test8() throws Exception{
        NodeList nl = document.getElementsByTagName("student");
        Element nll = (Element)nl.item(1);
        nll.setAttribute("idcard", "333");

        TransformerFactory facotry = TransformerFactory.newInstance();
        Transformer ts = facotry.newTransformer();
        ts.transform(new DOMSource(document), new StreamResult(
                "src/students.xml"));
    }
    
    //9.删除第一个student的idcard
    public void test9() throws Exception{
        NodeList nl = document.getElementsByTagName("student");
        Element nll = (Element)nl.item(0);
        nll.removeAttribute("idcard");
        
        TransformerFactory facotry = TransformerFactory.newInstance();
        Transformer ts = facotry.newTransformer();
        ts.transform(new DOMSource(document), new StreamResult(
                "src/students.xml"));
    }
    
    // Document 对象的一个新实例来生成一个 DOM 树
    public Document getDomParser() throws Exception {
        // DOM解析工厂
        dbf = DocumentBuilderFactory.newInstance();
        // DOM对象数解析器
        db = dbf.newDocumentBuilder();
        // 获取 DOM Document 对象的一个新实例来生成一个 DOM 树
        document = db.parse("src/students.xml");
        return document;
    }

}

单元测试

package com.bcrj.test;

import static org.junit.Assert.*;

import javax.xml.transform.TransformerException;

import org.junit.Assert;
import org.junit.Before;
import org.junit.BeforeClass;
import org.junit.Test;
import org.w3c.dom.Document;

import com.bcrj.dom.Test1;

public class Domtest {
    
    static Test1 test = null;
    
    @BeforeClass
    public static  void a(){
        test= new Test1();
    }
    
    @Before
    public void  setUp() throws Exception {
        test.getDomParser();
        
    }

//    @Test
//    public void testTest1() {
//        String str = test.test1();
//        Assert.assertEquals("沈阳", str);
//    }
    
//    @Test
//    public void testTest2(){
//        Document document = test.getDocument();
//        test.test2(document);
//    }
//    
//    @Test
//    public void testTest3() throws TransformerException {
//         test.test3();
//        //Assert.assertEquals("沈阳", str);
//    }
//    
//    @Test
//    public void testTest4() throws TransformerException {
//         test.test4();
//        //Assert.assertEquals("沈阳", str);
//    }
    
//    @Test
//    public void testTest4() throws Exception {
//         test.test5();
//        //Assert.assertEquals("沈阳", str);
//    }
    
    @Test
    public void testTest4() throws Exception {
         test.test9();
        //Assert.assertEquals("沈阳", str);
    }

}