【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 est-xmlsrcdoc-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("	" + 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("	" + department.getNodeName());
                    //先获取节点属性集，再获取属性name的值
                    System.out.println("	" + 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("	" + "	" + employee.getNodeName());
                            System.out.print("	" + employee.getAttributes().getNamedItem("id").getNodeValue());
                            System.out.print("	" + employee.getAttributes().getNamedItem("name").getNodeValue());
                            System.out.println("	" + 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 est-xmlsrcdom-test.xml

　　doc-test.xml的内容：