用java json 转 xml 加头

你可以使用Java中的Jackson库来将JSON转换为XML，并且使用Java中的DOM API来添加XML头。以下是一个示例代码：

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.databind.node.ObjectNode;
import org.w3c.dom.Document;
import org.w3c.dom.Element;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
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;

public class JsonToXmlConverter {

    public static void main(String[] args) throws Exception {
        String json = "{\"name\":\"John\",\"age\":30,\"city\":\"New York\"}";

        // Convert JSON to XML
        ObjectMapper objectMapper = new ObjectMapper();
        JsonNode jsonNode = objectMapper.readTree(json);
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document doc = builder.newDocument();
        Element root = doc.createElement("root");
        doc.appendChild(root);
        appendJsonNodeToXmlElement(jsonNode, root, doc);

        // Add XML header
        TransformerFactory transformerFactory = TransformerFactory.newInstance();
        Transformer transformer = transformerFactory.newTransformer();
        transformer.setOutputProperty("encoding", "UTF-8");
        transformer.setOutputProperty("indent", "yes");
        StringWriter sw = new StringWriter();
        transformer.transform(new DOMSource(doc), new StreamResult(sw));
        String xml = sw.toString();
        xml = "<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"yes\"?>\n" + xml;

        System.out.println(xml);
    }

    private static void appendJsonNodeToXmlElement(JsonNode jsonNode, Element element, Document doc) {
        if (jsonNode.isObject()) {
            ObjectNode objectNode = (ObjectNode) jsonNode;
            objectNode.fields().forEachRemaining(entry -> {
                String key = entry.getKey();
                JsonNode value = entry.getValue();
                Element childElement = doc.createElement(key);
                element.appendChild(childElement);
                appendJsonNodeToXmlElement(value, childElement, doc);
            });
        } else if (jsonNode.isArray()) {
            jsonNode.elements().forEachRemaining(childNode -> appendJsonNodeToXmlElement(childNode, element, doc));
        } else if (jsonNode.isValueNode()) {
            String value = jsonNode.asText();
            element.appendChild(doc.createTextNode(value));
        }
    }
}

这将输出以下XML：

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<root>
  <name>John</name>
  <age>30</age>
  <city>New York</city>
</root>