JAXB Problem List (2)

This blog is the second part of previous blog, and we will cover more detailed problem here.

Convert Elements to Map

A very handy and useful feature in JAXB is the adapter. You can take some xml types and change them into your specific Java class.
Here, we can change a xml element like following to a map:

<A>
  <B>1</B>
  <C>2</C>
  ...
</A>

public class MyAdapter extends XmlAdapter<MyAdapter.AdaptedMap, Map<String, Integer> {

  @XmlType(name = "A")
  public static class AdaptedMap {
    // represent the content in <A>...</A>
    @XmlAnyElement
    List<Element> elements = new ArrayList<>();
  }

  @Override
  public Map<String,Integer> unmarshal(AdaptedMap adaptedMap) throws Exception {
    HashMap<String,Integer> map = new HashMap<>();
    for (Element e : adaptedMap.elements) {          
      map.put(e.getTagName(),
          Integer.parseInt(e.getTextContent()));
    }
    return map;
  }

  ...
}

Map XML Enum to Java

Examples from doc of javax.xml.bind.annotation.XmlEnumValue:

@XmlEnum(String.class)
public enum Card { CLUBS, DIAMONDS, HEARTS, SPADES }

<!-- Example: XML Schema fragment -->
<xs:simpleType name="Card">
  <xs:restriction base="xs:string">
    <xs:enumeration value="CLUBS">
    <xs:enumeration value="DIAMONDS">
    <xs:enumeration value="HEARTS">
    <xs:enumeration value="SPADES">
</xs:simpleType>

Convert enum in your xml into the enum in Java class is relative easy, you can just mark your java class with @XmlEnum. If the name of you class and the type in xml, you may have to annotate your class with @XmlType to clarify it.

@XmlEnum
public enum A {
  a1, a2;
}

<xs:simpleType name="A" final="restriction">
    <xs:restriction base="xs:string">
        <xs:enumeration value="a1"/>
        <xs:enumeration value="a2"/>
    </xs:restriction>
</xs:simpleType>

NoSuchMethodError

java.lang.NoSuchMethodError: A.setXXX(I)V

In my case, JAXB will complain that my setter is not the default prototype. I sometimes use the builder setter template, which is convenient, but JAXB sometimes can recognize, sometimes can’t. It seems its bug, but I change builder pattern setter to default one fix the problem.

Adapter Is Not Applicable to xxx (primitive type)

I have an attribute which is similar to maxOccurs, which can be number or some strings represent some special cases, so I define it like following (If you don’t understand how this works, you may refer to my xsd tutorial):

<xs:element name="max" default="all">
    <xs:simpleType>
        <xs:union memberTypes="xs:int">
            <xs:simpleType>
                <xs:restriction base="xs:string">
                    <xs:enumeration value="all"/>
                </xs:restriction>
            </xs:simpleType>
        </xs:union>
    </xs:simpleType>
</xs:element>

And following is my adapter:

public class SelectNumAdapter extends XmlAdapter<String, Integer> {}

@XmlAttribute
@XmlJavaTypeAdapter(value = SelectNumAdapter.class)
private int max;

However, the type we returned and the type of max are not match, so the annotation checker will complain the mismatch.
Specifying the type makes code works:

@XmlAttribute
@XmlJavaTypeAdapter(type = int.class, value = SelectNumAdapter.class)
private int max;

Setter Not Called or Value Not Set

If you find your default value is not set, check the following possible problems:

• name of element/attribute is not match with class instance variable name
• lack annotation @XmlElement/XmlAttribute annotation or mark element with attribute or mark attribute with element
• wrong setter format: had better use default setter prototype, not to use builder type like following

// had better not use this type
public A setX() {
}
// instead, use default one
public void setX() {
}

• use="prohibited"
• if it is a collection, JAXB will call your setter only if your getter return null, i.e. you can’t init your collection with an empty one if you want your setter invoked.

Ref

• marsh long primitive

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