【Java】XML解析之DOM

DOM介绍

　　DOM(Document Object Model)解析是官方提供的XML解析方式之一，使用时无需引入第三方包，代码编写简单，方便修改树结构，但是由于DOM解析时是将整个XML文件加载到内存中进行解析，因此当XML文件较大时，使用DOM解析效率会降低，而且可能造成内存溢出。

XML生成

　　代码如下：

　　

     public static void write() {  

         //文档构建工厂
         DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
         try {
             //文档构建器
             DocumentBuilder builder = dbf.newDocumentBuilder();
             //文档
             Document doc = builder.newDocument();
             //设置xml文件是否独立
             doc.setXmlStandalone(true);
             //设置xml文件版本,默认1.0
             doc.setXmlVersion("1.1");

             //创建根目录节点
             Element root = doc.createElement("conpany");
             //设置节点属性
             root.setAttribute("name", "hd");
             //添加根节点
             doc.appendChild(root);

             Element department = doc.createElement("department");
             department.setAttribute("name", "test");
             //设置节点文本
             department.setTextContent("123456");
             //添加到根节点
             root.appendChild(department);

             // 工厂类，用来获取转换对象
             TransformerFactory transFactory = TransformerFactory.newInstance();
             //转化对象
             Transformer transFormer = transFactory.newTransformer();
             // 设置文档自动换行
             transFormer.setOutputProperty(OutputKeys.INDENT, "yes");
             //设置编码方式，默认UTF-8
             //transFormer.setOutputProperty(OutputKeys.ENCODING, "GB2312");
             //文件源
             DOMSource domSource = new DOMSource(doc);

             File file = new File("src/doc-write.xml");
             if (file.exists()) {
                 file.delete();
             }
             file.createNewFile();
             //输出文件流
             FileOutputStream out = new FileOutputStream(file);

             //结果流
             StreamResult xmlResult = new StreamResult(out);
             //转化
             transFormer.transform(domSource, xmlResult);

             System.out.println("创建生成文件位置===========" + file.getAbsolutePath());
         } catch (Exception e) {
             e.printStackTrace();
         }
     }

　　输出：创建生成文件位置===========D:\workspace\test-xml\src\doc-write.xml

　　doc-write.xml的内容：

　　

XML解析

　　需要在src目录中，先存放一个test.xml文件

　　

 <?xml version="1.0" encoding="UTF-8"?>
 <conpany name="hd">
     <department name="department1">
         <employee name="employee1" id="1">123</employee>
     </department>
     <department name="department2">
         <employee name="employee2" id="2">321</employee>
         <employee name="employee3" id="3"></employee>
     </department>
     <department name="department3">
     </department>
 </conpany> 

　　新建一个TestDom的java类，里面写一个read方法，代码如下：

　　

     public static void read() {

         DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance();
         try {
             DocumentBuilder builder = builderFactory.newDocumentBuilder();
             //输入流
             InputStream is = TestDom.class.getClassLoader().getResourceAsStream("test.xml");
             //文档构建器解析，得到文档
             Document doc = builder.parse(is);

             //获取根目录，元素
             Element root = doc.getDocumentElement();
             if (root == null)     return;

             //获取元素名字
             System.out.print(root.getNodeName());
             //获取元素属性name的值
             System.out.println("\t" + root.getAttribute("name"));

             //获取根元素下的子节点，此方法获取节点（节点包括：标签间的文本，和空白部分）
             NodeList departmentNodes = root.getChildNodes();
             if (departmentNodes == null)     return;

             //遍历节点
             for (int i = 0; i < departmentNodes.getLength(); i++) {

                 Node department = departmentNodes.item(i);
                 if (department != null && department.getNodeType() == Node.ELEMENT_NODE) {//非空白文本标签

                     //获取节点名字
                     System.out.print("\t" + department.getNodeName());
                     //先获取节点属性集，再获取属性name的值
                     System.out.println("\t" + department.getAttributes().getNamedItem("name").getNodeValue());

                     //获取节点下面的所有子节点
                     NodeList employees = department.getChildNodes();
                     if (employees == null) continue;

                     for (int j = 0; j < employees.getLength(); j++) {

                         Node employee = employees.item(j);
                         if (employee != null && employee.getNodeType() == Node.ELEMENT_NODE) {

                             System.out.print("\t" + "\t" + employee.getNodeName());
                             System.out.print("\t" + employee.getAttributes().getNamedItem("id").getNodeValue());
                             System.out.print("\t" + employee.getAttributes().getNamedItem("name").getNodeValue());
                             System.out.println("\t" + employee.getTextContent().trim());

                         }
                     }
                 }
             }

         } catch (Exception e) {

             e.printStackTrace();
         }

     }

XML修改

　　新建一个TestDom的java类，里面写一个update方法，代码如下：

　　

     public static void update() {
         DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
         try {
             DocumentBuilder builder = dbf.newDocumentBuilder();
             InputStream is = TestDom.class.getClassLoader().getResourceAsStream("test.xml");
             Document doc = builder.parse(is);
             Element root = doc.getDocumentElement();
             if (root == null) return;

             // 修改属性
             root.setAttribute("name", "hd2");
             NodeList departmentNodes = root.getChildNodes();
             if (departmentNodes != null) {
                 for (int i = 0; i < departmentNodes.getLength() - 1; i++) {

                     Node department = departmentNodes.item(i);
                     if (department.getNodeType() == Node.ELEMENT_NODE) {
                         String departmentName = department.getAttributes().getNamedItem("name").getNodeValue();
                         if ("department3".equals(departmentName)) {

                             // 删除节点
                             root.removeChild(department);
                         } else if ("department2".equals(departmentName)) {

                             //新增节点
                             Element newChild = doc.createElement("employee");
                             newChild.setAttribute("name", "employee4");
                             newChild.setTextContent("44444");
                             department.appendChild(newChild);
                         }
                     }
                 }
             }

             TransformerFactory transFactory = TransformerFactory.newInstance();
             Transformer transFormer = transFactory.newTransformer();
             transFormer.setOutputProperty(OutputKeys.INDENT, "yes");
             DOMSource domSource = new DOMSource(doc);

             File file = new File("src/dom-test.xml");
             if (file.exists()) {
                 file.delete();
             }
             file.createNewFile();

             FileOutputStream out = new FileOutputStream(file);
             StreamResult xmlResult = new StreamResult(out);
             transFormer.transform(domSource, xmlResult);

             System.out.println("修改生成文件位置===========" + file.getAbsolutePath());
         } catch (Exception e) {
             e.printStackTrace();
         }
     }

 }

　　输出：修改生成文件位置===========D:\workspace\test-xml\src\dom-test.xml

　　doc-test.xml的内容：