umarshalling the XML, and transferring some new data to a new XML in JAVA

Question

I have a sample XML of the format as shown below:

<?xml version="1.0" encoding="UTF-8"?>
<Institutions>
    <Institution type = "School">
        <place>Munich</place>
        <Subjects>
            <Subject>English</Subject>
            <Subject>Deutsch</Subject>
        </Subjects> 
    </Institution>  
    <Institution type ="College">
        <place>Cologne</place>
        <Subjects>
            <Subject>Sports</Subject>
            <Subject>Gym</Subject>
        </Subjects> 
    </Institution>
    <Institution type= "University">
        <place>Hamburg</place>
        <Subjects>
            <Subject>MElectrical</Subject>
            <Subject>MComputers</Subject>
        </Subjects>
    </Institution>
</Institutions>

I have classes for Institutions and Institution as well

Institutions.java

import lombok.Data;
@XmlRootElement(name="Institutions")
@XmlAccessorType(XmlAccessType.FIELD)
@Data
public class Institutions {
    public List<Institution> Institution;   
}

Institution.java

@Data
@XmlAccessorType(XmlAccessType.FIELD)
public class Institution {

    @XmlAttribute(name = "type")
    private String type;
    
    @XmlElement(name = "place")
    private String place;
    
    @XmlElementWrapper(name="Subjects")   
    @XmlElement(name="Subject") 
    private List<String> subjects;
}

Now i have a main parser, whch takes care of the unmarshalling and marshalling. I want to add some more data to it, however this time, I want only the new added data in the newly produced XML.

For eg: I create a logic in the main

public static void main(String[] args) {
        // TODO Auto-generated method stub
        List<Institutions> entries = new ArrayList<Institutions>();
    
        
        try {
            
            File xmlFile = new File("sample.xml");
            JAXBContext jaxbContext;
            jaxbContext = JAXBContext.newInstance(Institutions.class);
            Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller();
            Institutions xmlentries = (Institutions) jaxbUnmarshaller.unmarshal(xmlFile);
            entries.add(xmlentries);
            List<Institution> institutionList = xmlentries.getInstitution();
            Institution newInstitution = null;
            for(Institution i : institutionList) {
                if(i.getType().equals("School")) {
                    newInstitution = new Institution();
                    newInstitution.setPlace("Augsburg"); //(1)
                    newInstitution.setType("School");
                    List<String> subjectList = new ArrayList<String>();
                    subjectList.add("Math");
                    subjectList.add("Science");
                    newInstitution.setSubjects(subjectList);
                    break;
                }               
            }
            if(newInstitution!=null) {
                institutionList.add(newInstitution);
            }
Marshaller marshaller = jaxbContext.createMarshaller();
            marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
            marshaller.marshal(xmlentries, new File("outputsample.xml"));//(2)
            
        }catch (JAXBException e) {
            e.printStackTrace();
        } catch (FactoryConfigurationError e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } 
    }

Here I add a new entry based on the location of the school.

(1) can the entry field here be made generic/ based on te condition given. I do not want to type the school name again. (2) produces the XML, but how do I make sure that I have only the latest addition?

The current outputsample.xml looks like this:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Institutions>
    <Institution type="School">
        <place>Munich</place>
        <Subjects>
            <Subject>English</Subject>
            <Subject>Deutsch</Subject>
        </Subjects>
    </Institution>
    <Institution type="College">
        <place>Cologne</place>
        <Subjects>
            <Subject>Sports</Subject>
            <Subject>Gym</Subject>
        </Subjects>
    </Institution>
    <Institution type="University">
        <place>Hamburg</place>
        <Subjects>
            <Subject>MElectrical</Subject>
            <Subject>MComputers</Subject>
        </Subjects>
    </Institution>
    <Institution>
        <place>Augsburg</place>
        <Subjects>
            <Subject>Math</Subject>
            <Subject>Science</Subject>
        </Subjects>
    </Institution>
</Institutions>

But, i want the outputsample.xml to look like this ( all the added mdificaaitons

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Institutions>
    <Institution>
        <place>Augsburg</place>
        <Subjects>
            <Subject>Math</Subject>
            <Subject>Science</Subject>
        </Subjects>
    </Institution>
</Institutions>

Any guidnce here ? How could this be achieved? Also the aftermarshall cannot be applied within the main program? I need to eliminate the previously mentioned contents and keep the recently added ones

Answer 1

This would produce the output that you are looking for:

public class Main {
    public static void main(String[] args) throws JAXBException, XMLStreamException {
        final InputStream inputStream = Main.class.getClassLoader().getResourceAsStream("sample.xml");
        final XMLStreamReader xmlStreamReader = XMLInputFactory.newInstance().createXMLStreamReader(inputStream);
        final Unmarshaller unmarshaller = JAXBContext.newInstance(Root.class).createUnmarshaller();
        final Root root = unmarshaller.unmarshal(xmlStreamReader, Root.class).getValue();
        System.out.println(root.toString());

        Marshaller marshaller = JAXBContext.newInstance(Root.class).createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FRAGMENT, Boolean.TRUE);
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE);
        marshaller.marshal(root, System.out);

        System.out.println();
        System.out.println(" ************************************** ");
        System.out.println();
        
        Institution newInstitution = new Institution();
        List<Institution> institutionList = root.getInstitution();
        for(Institution i : institutionList) {
            if(i.getType().equals("School")) {
                newInstitution = new Institution();
                newInstitution.setPlace("Augsburg"); //(1)
                newInstitution.setType("School");
                List<String> subjectList = new ArrayList<String>();
                subjectList.add("Math");
                subjectList.add("Science");
                newInstitution.setSubjects(subjectList);
                break;
            }
        }

        Marshaller newMarshaller = JAXBContext.newInstance(Institution.class).createMarshaller();
        newMarshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        QName qName = new QName("Institution");
        JAXBElement<Institution> newRoot = new JAXBElement<Institution>(qName, Institution.class, newInstitution);
        newMarshaller.marshal(newRoot, System.out);
    }
}

Output:

Root(Institution=[Institution(type=School, place=Munich, subjects=[English, Deutsch]), Institution(type=College, place=Cologne, subjects=[Sports, Gym]), Institution(type=University, place=Hamburg, subjects=[MElectrical, MComputers])])
<Institutions>
   <Institution type="School">
      <place>Munich</place>
      <Subjects>
         <Subject>English</Subject>
         <Subject>Deutsch</Subject>
      </Subjects>
   </Institution>
   <Institution type="College">
      <place>Cologne</place>
      <Subjects>
         <Subject>Sports</Subject>
         <Subject>Gym</Subject>
      </Subjects>
   </Institution>
   <Institution type="University">
      <place>Hamburg</place>
      <Subjects>
         <Subject>MElectrical</Subject>
         <Subject>MComputers</Subject>
      </Subjects>
   </Institution>
</Institutions>
 ************************************** 

<?xml version="1.0" encoding="UTF-8"?>
<Institution type="School">
   <place>Augsburg</place>
   <Subjects>
      <Subject>Math</Subject>
      <Subject>Science</Subject>
   </Subjects>
</Institution>