package org.example;

import java.io.StringReader;
import java.io.StringWriter;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBElement;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;
import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlType;
import javax.xml.namespace.QName;
import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLStreamReader;

public class JAXBExample {

    @XmlRootElement
    @XmlType(propOrder = { "field" })
    @XmlAccessorType(XmlAccessType.FIELD)
    static class Xml1 {

        @XmlElement
        private String field;

        public String getField() {
            return field;
        }

        public void setField(String field) {
            this.field = field;
        }
    }

    @XmlRootElement
    @XmlType(propOrder = { "field" })
    @XmlAccessorType(XmlAccessType.FIELD)
    static class Xml2 {

        @XmlElement
        private String field;

        public String getField() {
            return field;
        }

        public void setField(String field) {
            this.field = field;
        }
    }

    public static void main(String[] args) throws Exception {
        Xml1 xml1 = new Xml1();
        xml1.setField("XML_1");

        Xml2 xml2 = new Xml2();
        xml2.setField("XML_2");

        JAXBContext context = JAXBContext.newInstance(Xml1.class, Xml2.class);

        try (StringWriter sw1 = new StringWriter(); StringWriter sw2 = new StringWriter()) {
            JAXBElement<Xml1> jaxbElement1 = new JAXBElement<>(new QName("abrakadabra"), Xml1.class, xml1);

            JAXBElement<Xml2> jaxbElement2 = new JAXBElement<>(new QName("avarakedavra"), Xml2.class, xml2);

            String xmlString1;
            String xmlString2;

            Marshaller m = context.createMarshaller();
            Unmarshaller u = context.createUnmarshaller();

            m.marshal(jaxbElement1, sw1);
            xmlString1 = sw1.toString();

            m.marshal(jaxbElement2, sw2);
            xmlString2 = sw2.toString();

            System.out.println(xmlString1);
            System.out.println(xmlString2);

            XMLInputFactory xif = XMLInputFactory.newFactory();
            XMLStreamReader xsr1 = xif.createXMLStreamReader(new StringReader(xmlString1));
            XMLStreamReader xsr2 = xif.createXMLStreamReader(new StringReader(xmlString2));

            xml2 = u.unmarshal(xsr1, Xml2.class).getValue();
            xml1 = u.unmarshal(xsr2, Xml1.class).getValue();

            System.out.println(xml1.getField());
            System.out.println(xml2.getField());
        } catch (Exception e) {
            e.printStackTrace(System.out);
        }
    }
}

<?xml version="1.0" encoding="UTF-8" standalone="yes"?><abrakadabra><field>XML_1</field></abrakadabra>
<?xml version="1.0" encoding="UTF-8" standalone="yes"?><avarakedavra><field>XML_2</field></avarakedavra>
XML_2
XML_1