CODEWITHSUNDEEP
javaxmljaxb
Tim Bellis
Tim Bellis

Reputation: 1657

JAXB: Getting empty values when serializing nested maps

I'm trying to use JAXB to serialize a class in XML.

@XmlRootElement
class Foo
{
   Hashtable<String, Hashtable<String, Integer>> table = new Hashtable<>();

   public Hashtable<String, Hashtable<String, Integer>> getTable() {
     return table;
   }

   public void setTable(Hashtable<String, Hashtable<String, Integer>> t) {
     table = t;
  }
}

However, this produces XML with empty values (I assure you that the values are actually present!)

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Foo>
    <table>
        <entry>
            <key>Test key</key>
            <value/>
        </entry>
    </table>
</Foo>

Is there a simple way to fix this? I don't really want to have to use @XmlJavaTypeAdapters unless I really have to.

Using a normal hashtable works fine: Hashtable<String, Integer>> table = new Hashtable<>();

Upvotes: 1

Views: 490

Answers (1)

Dawid Pytel
Dawid Pytel

Reputation: 2810

Sorry to disappoint you but currently there is no simple way to fix it. There is significant difference between outer and inner hashtable. Outer one is a property and is handled internally by com.sun.xml.bind.v2.runtime.property.SingleMapNodeProperty<BeanT, ValueT> class. This class does some magic to represent maps as key/value entries.

However, in case of inner Hashtable it is not "static" property, rather dynamic one. That's why it is handled by generic com.sun.xml.bind.v2.model.impl.RuntimeClassInfoImpl. This class does not find any JAXB properties in Hashtable (i.e. java bean properties - with both getter and setter). As a result you get empty value element.

Because of the same reason the following dynamic Hashtable property won't work either:

@XmlRootElement
@XmlSeeAlso(Hashtable.class)
public static class TypeWithHashtableAsObject {
    private Object property;

    public Object getProperty() {
        return property;
    }

    public void setProperty(Object property) {
        this.property = property;
    }

}

...
TypeWithHashtableAsObject foo = new TypeWithHashtableAsObject();
Hashtable<String, Integer> property = new Hashtable<>();
property.put("innerKey", 12);
foo.setProperty(property);
StringWriter writer = new StringWriter();
marshaller.marshal(foo, writer);
System.out.println(writer.toString());

Result:

<typeWithHashtableAsObject>
    <property xsi:type="hashtable" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"/>
</typeWithHashtableAsObject>

That is empty element.

In another answer you can find more examples how to marshal nested collections. Another solution would be to wrap Hashtable with another type. Like Table:

public class Table {
    private Hashtable<String, Integer> table = new Hashtable<>();

    public Table(Hashtable<String, Integer> table) {
        this.table = table;
    }

    public Table() {

    }

    public Hashtable<String, Integer> getTable() {
        return table;
    }

    public void setTable(Hashtable<String, Integer> table) {
        this.table = table;
    }

}

and change Foo.table type to Hashtable<String, Table>.

The result is more verbose than original one but IMHO quite consistent:

<foo>
   <table>
      <entry>
         <key>key1</key>
         <value>
            <table>
               <entry>
                  <key>innerKey</key>
                  <value>12</value>
               </entry>
            </table>
         </value>
      </entry>
   </table>
</foo>

Upvotes: 1

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