How would I marshal a List of Jaxb Elements without making a wrapper class?

Question

Short of actually making up a writer and appending each element onto the string. Is there a way to get the JAXB marshaller to marshall a list of objects where I can just give it the name of the top element?

I feel like I'm close with this

//http://blog.bdoughan.com/2012/07/jaxb-no-annotations-required.html
public <T> String jaxb(Collection<T> o, Class<T> clazz, String plural){
    try {
        ArrayList<T> al = new ArrayList<T>(o.size());
        al.addAll(o);
        JAXBContext jc = JAXBContext.newInstance(ArrayList.class);
        JAXBElement<ArrayList> amenity = new JAXBElement(new QName(plural), ArrayList.class, al);
        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        StringWriter writer = new StringWriter();
        marshaller.marshal(amenity, writer);
        return writer.toString();
    } catch (JAXBException e) {
        throw new RuntimeException(e);
    }
}

but the result is still coming back as an empty list

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<pluralName/>

Is there a way to do this without just manually pasting strings of xml together?

Update

With some help from Michael Glavassevich I've been able to do this with one caveat, the individual elements are <Item>s

//http://blog.bdoughan.com/2012/07/jaxb-no-annotations-required.html
@SuppressWarnings({ "unchecked", "rawtypes" })
public <T> String jaxb(Collection<T> elements, Class<T> elementClass, String plural){
    try {
        T[] array = (T[]) Array.newInstance(elementClass, elements.size());
        elements.toArray(array);
        JAXBContext jc = JAXBContext.newInstance(array.getClass());
        JAXBElement<T[]> topElement = new JAXBElement(new QName(plural), array.getClass(), array);
        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        StringWriter writer = new StringWriter();
        marshaller.marshal(topElement, writer);
        return writer.toString();
    } catch (JAXBException e) {
        throw new RuntimeException(e);
    }
}

The result then becomes

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Basketballs>
    <item>basketball one</item>
    <item>basketball two</item>
</Basketballs>

Michael Glavassevich · Accepted Answer · 2016-02-17T00:35:23.773

6

If you don't want to create a wrapper class you could convert the collection into an array, place that array in a JAXBElement and then marshal it.

For example:

public class JAXBArrayWriter {

    public static class Item {
        @XmlValue
        protected String value;

        public Item() {}

        public Item(String value) {
            this.value = value;
        }
    }

    public static void main (String [] args) throws Exception {
        List<Item> items = new ArrayList<Item>();
        items.add(new Item("one"));
        items.add(new Item("two"));
        JAXBContext jc = JAXBContext.newInstance(Item[].class);
        JAXBElement<Item[]> root = new JAXBElement<Item[]>(new QName("items"), 
                Item[].class, items.toArray(new Item[items.size()]));
        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        StringWriter writer = new StringWriter();
        marshaller.marshal(root, writer);
        System.out.println(writer.toString());
    }
}

which produces the following document:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<items>
    <item>one</item>
    <item>two</item>
</items>

edited Feb 17 '16 at 00:35

answered Feb 17 '16 at 00:26

Michael Glavassevich

1,030
5
7

This is step in the right direction, I'm having some trouble with one part though. Do you know how I would pass the class in to `JAXBContext.newInstance()` if I don't know the type? I apparently can't do `JAXBContext.newInstance(T[].class)` – mike Feb 17 '16 at 02:51
actually never mind that i figured it out. I do have another problem though. If I change the Item class name to something like Basketball in your demo. The individual elements still come out as ``. Any idea how to change this? – mike Feb 17 '16 at 03:22
1

Seems to be related to the mapping rules for multidimensional arrays, equivalent to a schema type with ``. At least at the spec level this isn't configurable. – Michael Glavassevich Feb 17 '16 at 12:40
What are the changes needed in above method to generate JSON instead of XML – Gaurav Sharma Sep 14 '17 at 12:41

jenjis · Answer 2 · 2016-02-16T23:36:11.290

Please try this:

First, create a list class:

@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class AmenityList {
    @XmlElement(name = "amenity")
    List<Amenity> amenities = new ArrayList<Amenity>();

    public AmenityList() {}

    public void setList(List<Amenity> amenities) {
        this.amenities = amenities;
    }
}

then the Amenity class:

@XmlAccessorType(XmlAccessType.FIELD)
class Amenity {
    private String amenityName;
    private String amenityDate;

    public Amenity(String name, String date) {
        this.amenityName = name;
        this.amenityDate = date;
    }
}

set where needed your amenities in a list - maybe in a less redundant way :) - and assign it to an AmenityList:

AmenityList amenityList = new AmenityList();
List <Amenity> amenities = new ArrayList<Amenity>();
amenities.add(new Amenity("a_one", "today"));
amenities.add(new Amenity("a_two", "tomorrow"));
amenity.setList(amenities);

and finally, a toXml method:

public static String toXml(AmenityList amenityList) throws JAXBException {
    JAXBContext jaxbContext = JAXBContext.newInstance(AmenityList.class);
    Marshaller jaxbMarshaller = jaxbContext.createMarshaller();
    jaxbMarshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
    StringWriter sw = new StringWriter();
    jaxbMarshaller.marshal(amenityList, sw);
    return sw.toString()
}

obtaining, i.e. :

<amenityList>
    <amenity>
        <amenityName>a_one</amenityName>
        <amenityDate>today</amenityDate>
    </amenity>
    <amenity>
        <amenityName>a_two</amenityName>
        <amenityDate>tomorrow</amenityDate>
    </amenity>
</amenityList>

I don't know that the list of objects will be amenities, which is why I'm trying to to do it without a wrapper class. — mike, Feb 17 '16 at 01:30

score 0 · Answer 3 · answered Jun 15 '20 at 13:18

Try this.

POJO class:

@XmlRootElement(name = "classNameTAG")
@XmlAccessorType(XmlAccessType.FIELD)
public class ClassName {

    @XmlElementWrapper(name="listTAG")
    @XmlElement(name="itemTAG") 
    private List<ClassItem> items;
}

The marshall code:

public static void pojo2xml(ClassName classData, File outputFile) throws Exception {
    JAXBContext context;
    BufferedWriter writer = null;
    writer = new BufferedWriter(new FileWriter(outputFile));
    context = JAXBContext.newInstance(ClassName.class);
    Marshaller m = context.createMarshaller();
    m.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
    m.marshal(classData, writer);
    writer.close();
}

Xml result:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<classNameTAG>
    <listTAG>
        <itemTAG>data</itemTAG>
        <itemTAG>data</itemTAG>
    </listTAG>
</classNameTAG>

It works for me.

Gonen I · Answer 4 · 2018-05-17T12:26:51.310

The accepted solution with array works but causes each inner element to be named : < item >

The following solution taken from this link worked better for me:

Is it possible to programmatically configure JAXB?

public class Wrapper<T> {

private List<T> items = new ArrayList<T>();

@XmlAnyElement(lax=true)
public List<T> getItems() {
    return items;
}

}

//JAXBContext is thread safe and so create it in constructor or 
//setter or wherever:
... 
JAXBContext jc = JAXBContext.newInstance(Wrapper.class, clazz);
... 

public String marshal(List<T> things, Class clazz) {

  //configure JAXB and marshaller     
  Marshaller m = jc.createMarshaller();
  m.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);

  //Create wrapper based on generic list of objects
  Wrapper<T> wrapper = new Wrapper<T>(things);
  JAXBElement<Wrapper> wrapperJAXBElement = new JAXBElement<Wrapper>(new QName(clazz.getSimpleName().toLowerCase()+"s"), Wrapper.class, wrapper);

  StringWriter result = new StringWriter();
  //marshal!
  m.marshal(wrapperJAXBElement, result);

  return result.toString();

}

It does not require converting the list to an array, but does require 1 generic general purpose class.

How would I marshal a List of Jaxb Elements without making a wrapper class?

Update

4 Answers4