如何使用Java将换行符添加到XML文件中？

String xmlString = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n" +
        "<root>\n" +
        "  <element1>value1</element1>\n" +
        "  <element2>value2</element2>\n" +
        "</root>";

String xmlString = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>" + System.lineSeparator() +
        "<root>" + System.lineSeparator() +
        "  <element1>value1</element1>" + System.lineSeparator() +
        "  <element2>value2</element2>" + System.lineSeparator() +
        "</root>";

StringBuilder xmlBuilder = new StringBuilder();
xmlBuilder.append("<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n");
xmlBuilder.append("<root>\n");
xmlBuilder.append("  <element1>value1</element1>\n");
xmlBuilder.append("  <element2>value2</element2>\n");
xmlBuilder.append("</root>");
String xmlString = xmlBuilder.toString();

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
import java.io.StringWriter;

public class XmlExample {
    public static void main(String[] args) {
        Root root = new Root();
        root.setElement1("value1");
        root.setElement2("value2");

        try {
            JAXBContext jaxbContext = JAXBContext.newInstance(Root.class);
            Marshaller marshaller = jaxbContext.createMarshaller();
            marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);

            StringWriter sw = new StringWriter();
            marshaller.marshal(root, sw);
            String xmlString = sw.toString();
            System.out.println(xmlString);
        } catch (JAXBException e) {
            e.printStackTrace();
        }
    }
}