Dom4j 實戰：XML 文件的建立、解析與更新完整指南

Dom4j 核心類介紹

• DocumentHelper：建立 Document 物件
• Element：代表 XML 元素，支援屬性、子元素操作
• SAXReader：基於 SAX 解析器，高效讀取 XML
• XMLWriter：將 Document 寫入檔案，支援格式化輸出

一、建立並寫入 XML

public static void writeXML(String filename) {
    try {
        Document document = DocumentHelper.createDocument();
        Element root = document.addElement("PortConfig");

        // 新增多個 Port 元素及屬性
        addPort(root, "portBloodpress", "COM12");
        addPort(root, "portWah", "COM14");
        addPort(root, "portBloodsugar", "COM16");
        addPort(root, "portBloodfat", "COM18");
        addPort(root, "portUric", "COM20");

        OutputFormat format = new OutputFormat(" ", true); // 縮排格式化
        XMLWriter writer = new XMLWriter(new FileWriter(new File(filename)), format);
        writer.write(document);
        writer.close();
    } catch (Exception e) { e.printStackTrace(); }
}

private static void addPort(Element root, String name, String number) {
    Element port = root.addElement("Port");
    port.addAttribute("Portname", name);
    port.addAttribute("Portnumber", number);
}

二、讀取並解析 XML

public static void readXML(String filename) {
    try {
        SAXReader reader = new SAXReader();
        Document document = reader.read(filename);
        Element root = document.getRootElement();

        for (Iterator it = root.elementIterator(); it.hasNext();) {
            Element port = it.next();
            String name = port.attributeValue("Portname");
            String value = port.attributeValue("Portnumber");
            // 根據名稱賦值給常數類（示例）
            switch (name) {
                case "portBloodpress": Constant.portBloodpress = value; break;
                case "portWah": Constant.portWah = value; break;
                case "portBloodsugar": Constant.portBloodsugar = value; break;
                case "portBloodfat": Constant.portBloodfat = value; break;
                case "portUric": Constant.portUric = value; break;
            }
        }
    } catch (Exception e) { e.printStackTrace(); }
}

三、更新 XML

public static void updateXML(String filename) {
    try {
        File file = new File(filename);
        SAXReader reader = new SAXReader();
        Document document = reader.read(file);
        Element root = document.getRootElement();

        for (Iterator it = root.elementIterator(); it.hasNext();) {
            Element port = it.next();
            String name = port.attributeValue("Portname");
            switch (name) {
                case "portBloodpress": port.setAttributeValue("Portnumber", Constant.portBloodpress); break;
                case "portWah": port.setAttributeValue("Portnumber", Constant.portWah); break;
                case "portBloodsugar": port.setAttributeValue("Portnumber", Constant.portBloodsugar); break;
                case "portBloodfat": port.setAttributeValue("Portnumber", Constant.portBloodfat); break;
                case "portUric": port.setAttributeValue("Portnumber", Constant.portUric); break;
            }
        }

        XMLWriter writer = new XMLWriter(new FileWriter(file));
        writer.write(document);
        writer.close();
    } catch (Exception e) { e.printStackTrace(); }
}

範例 XML 內容

<?xml version="1.0" encoding="UTF-8"?>
<PortConfig>
  <Port Portname="portBloodpress" Portnumber="COM126"/>
  <Port Portname="portWah" Portnumber="COM146"/>
  <Port Portname="portBloodsugar" Portnumber="COM166"/>
  <Port Portname="portBloodfat" Portnumber="COM186"/>
  <Port Portname="portUric" Portnumber="COM206"/>
</PortConfig>

關鍵點總結

1. 建立：DocumentHelper → Document → Element → Attribute
2. 解析：SAXReader → Document → RootElement → Iterator → attributeValue()
3. 更新：解析後用 setAttributeValue() 修改，再用 XMLWriter 寫回
4. 格式化輸出：OutputFormat(" ", true) 產生可讀性良好的縮排 XML