JAXB HashMap unmappable

Question

I want to convert a HashMap in a POJO class to XML. I tried using the XmlAdapter but it results in only the key and value pairs of the HashMap being the attributes of the XML Elements. I need the Key to be the Element itself and the value of the HashMap to be the value of the element. For instance, I need the following XML:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<cart>
<supervisor_id>555</supervisor_id>
<payments>
    <payment sequence="1">
        <amount>123.45</amount>
        <billing_method>12345</billing_method>
        <form>card</form>
        <delivery_mode>Q</delivery_mode>
    </payment>
<payment sequence="2">
        <amount>123.45</amount>
        <person_id>2333</person_id>
        <form>cash</form>
        <delivery_mode>Q</delivery_mode>
    </payment>
</payments>
</cart>

I created the following classes: MyMapType holds a list of MyMapEntryType class which has two fields namely Key and Value. How do I change the Key element to be @XmlElement and assign the value field to the Key field?

---

Here are my source files.

MyMapType.java

import java.util.ArrayList;
import java.util.List;

public class MyMapType {

    private List<MyMapEntryType> entry = new ArrayList<MyMapEntryType>();

    public List<MyMapEntryType> getEntry() {
        return entry;
    }

    public void setEntry(List<MyMapEntryType> entry) {
        this.entry = entry;
    }

}

MyMapEntryType.java

import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlValue;

@XmlAccessorType(XmlAccessType.FIELD)
public class MyMapEntryType {

@XmlAttribute
private String key;
@XmlValue
private String value;
public String getKey() {
    return key;
}
public void setKey(String key) {
    this.key = key;
}
public String getValue() {
    return value;
}
public void setValue(String value) {
    this.value = value;
}
}

Please also find the adapter class:

MyMapAdapter.java

import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;
import javax.xml.bind.annotation.adapters.XmlAdapter;

public class MyMapAdapter extends XmlAdapter<MyMapType, Map<String, String>> {

    @Override
   public MyMapType marshal(Map<String, String> map) throws Exception {

        MyMapType myMapType = new MyMapType();

      for(Entry<String, String> entry : map.entrySet()) {
         MyMapEntryType myMapEntryType = new MyMapEntryType();
         myMapEntryType.setKey(entry.getKey());
         myMapEntryType.setValue(entry.getValue());
         myMapType.getEntry().add(myMapEntryType);
      }
      return myMapType;
   }

   @Override
   public Map<String, String> unmarshal(MyMapType map) throws Exception {
      HashMap<String, String> hashMap = new HashMap<String, String>();
      for(MyMapEntryType myEntryType : map.getEntry()) {
         hashMap.put(myEntryType.getKey(), myEntryType.getValue());
      }
      return hashMap;
   }
 }

This is the class which has the HashMap field:

XmlElementMap.java

@XmlAccessorType(XmlAccessType.FIELD)
public class XmlElementMap {

@XmlAttribute(name="sequence")
private int sequence;

@XmlJavaTypeAdapter(MyMapAdapter.class)
private Map<String, String> map = new HashMap<String, String>();

public int getSequence() {
    return sequence;
}

public void setSequence(int sequence) {
    this.sequence = sequence;
}

public Map<String, String> getMap() {
    return map;
}

public void setMap(Map<String, String> map) {
    this.map = map;
}


}

Please advise on how to achieve this.

Regards,
-Anand

Currently it produces the following output:

Answer 1

I have the same requirement "I need the Key to be the Element itself and the value of the HashMap to be the value of the element".

I didn't use customized adapter, but implemented it by converting the HashMap entries dynamically to a list of JAXBElement objects, and then annotated the list with @XmlAnyElement.

@XmlRootElement(name="root")
public class MyMapType {

    @XmlAnyElement
    public List<JAXBElement> entries = new ArrayList<JAXBElement>();

    public MyMapType() {    // JAXB required    
    }

    public MyMapType(Map<String, String> map) {
        for (Map.Entry<String, String> entry : map.entrySet()) {
            entries.add(new JAXBElement(new QName(entry.getKey()), 
                    String.class, entry.getValue()));
        }
    }

    public static void main(String[] args) throws Exception {
        JAXBContext context = JAXBContext.newInstance(MyMapType.class);
        Marshaller marshaller = context.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);

        Map<String, String> map = new LinkedHashMap<String, String>();
        map.put("key1", "value1");
        map.put("key2", "value2");
        MyMapType mt = new MyMapType(map);

        marshaller.marshal(mt, System.out); 
    }
}

The output is,

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<root>
    <key1>value1</key1>
    <key2>value2</key2>
</root>

Answer 2

Note: a marshal/unmarshal example for Map instance can be found here: Dynamic tag names with JAXB.