Convert recursive XML to POJO and back

Question

I've XML like this:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Trees>
    <Tree Id="1" Name="FirstTree" Type="Main Tree">
        <Description>Main Tree</Description>
        <Versions >
            <Version Id="20592" RootNodeId="117341" CreateDate="2018-01-17 17:01:38 Europe/Moscow" Status="EDIT" Label="TestTree">
                <Switch Id="117341" DisplayName="root structure"/>
                <Switch Id="117342" DisplayName="root structure">
                    <ScalarCase Id="40808"/>
                    <Switch Id="117343" DisplayName="root structure">
                        <ScalarCase Id="40809"/>
                         <Switch Id="117344" DisplayName="root structure">
                            <ScalarCase Id="40810"/>
                            <Leaf Id="117345"/> 
                            <Condition Id="117346">
                                <Leaf Id="117347"/>
                            </Condition>
                        </Switch>
                    </Switch>
                </Switch>
            </<Version>
        </Versions>
    </Tree>
</Trees>

How could my POJO look like the structure of this XML? It's unclear what the POJO should do to describe the Version object. I have the abstract class Nodeand created 3 inheritors: Switch, Leaf and Condition.

How can I make the recursive nesting of such objects to convert XML into an object and back?

Answer 1

Assuming that you have created the POJOs that mirror your xml, starting from:

@XmlAccessorType(XmlAccessType.FIELD)
@XmlRootElement(name="Trees")
public class Trees {
    private Tree Tree;
    // getters and setters
}

to Switch class (and the rest I will not write here):

@XmlAccessorType(XmlAccessType.FIELD)
public class Switch {
    private Condition Condition;
    private ScalarCase ScalarCase;
    private String Id;
    private String DisplayName;
    private Leaf Leaf;
    @XmlElement(name="Switch")
    private Switch aSwitch;
    // getters and setters
}

All your POJOs to have the proper annotations, etc.

Then trying to read the xml into POJO, seems to work:

   public static void main(String[] args) {

        try {
            File file = new File("trees.xml");
            JAXBContext jaxbContext = JAXBContext.newInstance(Trees.class);
            Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller();

            Trees trees = (Trees) jaxbUnmarshaller.unmarshal(file);
            System.out.println(trees);

         } catch (JAXBException e) {
            e.printStackTrace();
        }

    }

Edit: To reply to the comment in the answer section as well.

When a class contains a field with itself as a type, it essentially creates a LinkedList so you can have any depth you want (within the memory limits).