34.3. Using Unbound Attributes

Overview

XML Schema has a mechanism that allows you to leave a place holder for an arbitrary attribute in a complex type definition. Using this mechanism, you can define a complex type that can have any attribute. For example, you can create a type that defines the elements <robot name="epsilon" />, <robot age="10000" />, or <robot type="weevil" /> without specifying the three attributes. This can be particularly useful when flexibility in your data is required.

Defining in XML Schema

Undeclared attributes are defined in XML Schema using the anyAttribute element. It can be used wherever an attribute element can be used. The anyAttribute element has no attributes, as shown in Example 34.7, “Complex Type with an Undeclared Attribute”.

Example 34.7. Complex Type with an Undeclared Attribute

<complexType name="arbitter">
  <sequence>
    <element name="name" type="xsd:string" />
    <element name="rate" type="xsd:float" />
  </sequence>
  <anyAttribute />
</complexType>
The defined type, arbitter, has two elements and can have one attribute of any type. The elements three elements shown in Example 34.8, “Examples of Elements Defined with a Wild Card Attribute” can all be generated from the complex type arbitter.

Example 34.8. Examples of Elements Defined with a Wild Card Attribute

<officer rank="12"><name>...</name><rate>...</rate></officer>
<lawyer type="divorce"><name>...</name><rate>...</rate></lawyer>
<judge><name>...</name><rate>...</rate></judge>

Mapping to Java

When a complex type containing an anyAttribute element is mapped to Java, the code generator adds a member called otherAttributes to the generated class. otherAttributes is of type java.util.Map<QName, String> and it has a getter method that returns a live instance of the map. Because the map returned from the getter is live, any modifications to the map are automatically applied. Example 34.9, “Class for a Complex Type with an Undeclared Attribute” shows the class generated for the complex type defined in Example 34.7, “Complex Type with an Undeclared Attribute”.

Example 34.9. Class for a Complex Type with an Undeclared Attribute

public class Arbitter {

    @XmlElement(required = true)
    protected String name;
    protected float rate;

    @XmlAnyAttribute
    private Map<QName, String> otherAttributes = new HashMap<QName, String>();

    public String getName() {
        return name;
    }

    public void setName(String value) {
        this.name = value;
    }

    public float getRate() {
        return rate;
    }

    public void setRate(float value) {
        this.rate = value;
    }

    public Map<QName, String> getOtherAttributes() {
        return otherAttributes;
    }

}

Working with undeclared attributes

The otherAttributes member of the generated class expects to be populated with a Map object. The map is keyed using QNames. Once you get the map , you can access any attributes set on the object and set new attributes on the object.
Example 34.10, “Working with Undeclared Attributes” shows sample code for working with undeclared attributes.

Example 34.10. Working with Undeclared Attributes

Arbitter judge = new Arbitter();
Map<QName, String> otherAtts = judge.getOtherAttributes(); 1

QName at1 = new QName("test.apache.org", "house"); 2
QName at2 = new QName("test.apache.org", "veteran");

otherAtts.put(at1, "Cape"); 3
otherAtts.put(at2, "false");

String vetStatus = otherAtts.get(at2); 4
1
Gets the map containing the undeclared attributes.
2
Creates QNames to work with the attributes.
3
Sets the values for the attributes into the map.
2
Retrieves the value for one of the attributes.