如何在Java JDK 11中不借助额外库实现HashMap与XML互转？

可以实现，Java 11自带的javax.xml包提供了足够的API完成这个需求，以下是具体的实现方案：

1. HashMap 转 XML #

利用DOM API构建XML文档，再通过Transformer将文档转换为字符串，支持嵌套HashMap结构：

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import java.io.StringWriter;
import java.util.HashMap;
import java.util.Map;

public class HashMapToXml {
    public static String convert(HashMap<String, Object> hashMap, String rootName) throws Exception {
        // 初始化DOM文档
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document doc = builder.newDocument();

        // 创建根节点
        Element root = doc.createElement(rootName);
        doc.appendChild(root);

        // 遍历HashMap生成节点
        buildXmlNodes(doc, root, hashMap);

        // 格式化输出XML字符串
        TransformerFactory transformerFactory = TransformerFactory.newInstance();
        Transformer transformer = transformerFactory.newTransformer();
        transformer.setOutputProperty(OutputKeys.INDENT, "yes");
        transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "4");

        StringWriter writer = new StringWriter();
        transformer.transform(new DOMSource(doc), new StreamResult(writer));
        return writer.toString();
    }

    private static void buildXmlNodes(Document doc, Element parent, HashMap<String, Object> map) {
        for (Map.Entry<String, Object> entry : map.entrySet()) {
            Element node = doc.createElement(entry.getKey());
            Object value = entry.getValue();

            if (value instanceof HashMap) {
                // 处理嵌套HashMap
                buildXmlNodes(doc, node, (HashMap<String, Object>) value);
            } else {
                node.appendChild(doc.createTextNode(value.toString()));
            }
            parent.appendChild(node);
        }
    }

    public static void main(String[] args) throws Exception {
        HashMap<String, Object> data = new HashMap<>();
        data.put("id", "1001");
        data.put("username", "alice");

        HashMap<String, Object> contact = new HashMap<>();
        contact.put("email", "alice@example.com");
        contact.put("phone", "123456789");
        data.put("contact", contact);

        System.out.println(convert(data, "user"));
    }
}

2. XML 转 HashMap #

通过DocumentBuilder解析XML，递归遍历节点并将数据存入HashMap，支持嵌套结构：

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import java.io.ByteArrayInputStream;
import java.util.HashMap;

public class XmlToHashMap {
    public static HashMap<String, Object> convert(String xml) throws Exception {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document doc = builder.parse(new ByteArrayInputStream(xml.getBytes()));
        doc.getDocumentElement().normalize();

        HashMap<String, Object> result = new HashMap<>();
        parseXmlNode(doc.getDocumentElement(), result);
        return result;
    }

    private static void parseXmlNode(Node node, HashMap<String, Object> map) {
        if (node.getNodeType() != Node.ELEMENT_NODE) {
            return;
        }

        Element element = (Element) node;
        NodeList childNodes = element.getChildNodes();

        // 节点仅包含文本内容
        if (childNodes.getLength() == 1 && childNodes.item(0).getNodeType() == Node.TEXT_NODE) {
            map.put(element.getNodeName(), childNodes.item(0).getNodeValue().trim());
            return;
        }

        // 节点包含子元素，创建嵌套HashMap
        HashMap<String, Object> nestedMap = new HashMap<>();
        map.put(element.getNodeName(), nestedMap);

        for (int i = 0; i < childNodes.getLength(); i++) {
            parseXmlNode(childNodes.item(i), nestedMap);
        }
    }

    public static void main(String[] args) throws Exception {
        String xml = "<user>\n" +
                "    <id>1001</id>\n" +
                "    <username>alice</username>\n" +
                "    <contact>\n" +
                "        <email>alice@example.com</email>\n" +
                "        <phone>123456789</phone>\n" +
                "    </contact>\n" +
                "</user>";

        System.out.println(convert(xml));
    }
}

注意事项 #

• 模块化项目适配：如果使用Java模块系统，需要在module-info.java中添加requires java.xml;声明依赖
• 特殊字符处理：DOM API会自动处理XML文本中的特殊字符（如<、>、&），无需手动转义
• 重复节点扩展：若XML存在重复标签名，当前实现会覆盖值，可修改为将值存入List以支持多节点场景

内容的提问来源于stack exchange，提问作者Sathvik Bellary