Using XML Transformations

In many cases, you can use MOXy's @XmlTransformation annotation to give you considerably more control over the marshalling and unmarshalling of your objects. @XmlTransformation can be used to create a custom mapping where one or more XML nodes can be used to create the value for the Java attribute.

To handle the custom requirements at marshal (write) and unmarshall (read) time, @XmlTransformation uses instances of org.eclipse.persistence.mappings.transformers (such as AttributeTransformer and FieldTransformer), providing a non-intrusive solution that avoids the need for domain objects to implement any 'special' interfaces.

For example, if you wanted to map the following XML to objects and combine the values of DATE and TIME into a single java.util.Date object, you can use an @XmlTransformation:

<ELEM_B>
   <B_DATE>20100825</B_DATE>
   <B_TIME>153000</B_TIME>
   <NUM>123</NUM>
   <C_DATE>20100825</C_DATE>
   <C_TIME>154500</C_TIME>
</ELEM_B>

Note:

Ordinarily, you would use @XmlAdapter. However:

Although the DATE/TIME pairings are repeated throughout the document, the element name changes each time (such as B_DATE/B_TIME, C_DATE/C_TIME, and so on).
Because each pairing is missing a grouping element, you would need to adapt the entire ElemB class.

Because of these issues, MOXy's transformation mapping is much easier to implement:

Example 8-38 Mapping Example

 
package example;
 
import java.util.Date;
 
import javax.xml.bind.annotation.*;
import org.eclipse.persistence.oxm.annotations.*;
 
@XmlAccessorType(XmlAccessType.FIELD)
@XmlRootElement(name="ELEM_B")
public class ElemB {
 
    @XmlTransformation
    @XmlReadTransformer(transformerClass=DateAttributeTransformer.class)
    @XmlWriteTransformers({
        @XmlWriteTransformer(xmlPath="B_DATE/text()", transformerClass=DateFieldTransformer.class),
        @XmlWriteTransformer(xmlPath="B_TIME/text()", transformerClass=TimeFieldTransformer.class),
    })
    private Date bDate;
 
    @XmlElement(name="NUM")
    private int num;
 
    @XmlTransformation
    @XmlReadTransformer(transformerClass=DateAttributeTransformer.class)
    @XmlWriteTransformers({
        @XmlWriteTransformer(xmlPath="C_DATE/text()", transformerClass=DateFieldTransformer.class),
        @XmlWriteTransformer(xmlPath="C_TIME/text()", transformerClass=TimeFieldTransformer.class),
    })
    private Date cDate;
 
}

Using an AttributeTransformer

Use an AttributeTransformer to construct the Java attribute value:

Example 8-39 Sample AttributeTransfomer

package example;
 
import java.text.ParseException;
import java.text.SimpleDateFormat;
 
import org.eclipse.persistence.internal.helper.DatabaseField;
import org.eclipse.persistence.mappings.foundation.AbstractTransformationMapping;
import org.eclipse.persistence.mappings.transformers.AttributeTransformer;
import org.eclipse.persistence.sessions.Record;
import org.eclipse.persistence.sessions.Session;
 
public class DateAttributeTransformer implements AttributeTransformer {
 
    private AbstractTransformationMapping mapping;
    private SimpleDateFormat yyyyMMddHHmmss = new SimpleDateFormat("yyyyMMddHHmmss");
 
    public void initialize(AbstractTransformationMapping mapping) {
        this.mapping = mapping;
    }
 
    public Object buildAttributeValue(Record record, Object instance, Session session) {
        try {
            String dateString = null;
            String timeString = null;
 
            for (DatabaseField field : mapping.getFields()) {
                if (field.getName().contains("DATE")) {
                    dateString = (String) record.get(field);
                } else {
                    timeString = (String) record.get(field);
                }
            }
            return yyyyMMddHHmmss.parseObject(dateString + timeString);
        } catch(ParseException e) {
            throw new RuntimeException(e);
        }
    }
 
}

Using a FieldTransformer

Use a FieldTransformer to construct the XML field value from the Java object.

Each transformation mapping may have multiple write transformers. In this example, you will need two:

The first write transformer writes the year, month, and day in yyMMdd format:

Example 8-40 First Write Transformer

package example;
 
import java.text.SimpleDateFormat;
import java.util.Date;
 
import org.eclipse.persistence.mappings.foundation.AbstractTransformationMapping;
import org.eclipse.persistence.mappings.transformers.FieldTransformer;
import org.eclipse.persistence.sessions.Session;
 
public class DateFieldTransformer implements FieldTransformer {
 
    private AbstractTransformationMapping mapping;
    private SimpleDateFormat yyyyMMdd = new SimpleDateFormat("yyyyMMdd");
 
    public void initialize(AbstractTransformationMapping mapping) {
        this.mapping = mapping;
    }
 
    public Object buildFieldValue(Object instance, String xPath, Session session) {
        Date date = (Date) mapping.getAttributeValueFromObject(instance);
        return yyyyMMdd.format(date);
    }
 
}

The second write transformer writes out the hour, minutes, and seconds in HHmmss format.

Example 8-41 Second Write Transformer

package example;
 
import java.text.SimpleDateFormat;
import java.util.Date;
 
import org.eclipse.persistence.mappings.foundation.AbstractTransformationMapping;
import org.eclipse.persistence.mappings.transformers.FieldTransformer;
import org.eclipse.persistence.sessions.Session;
 
public class TimeFieldTransformer implements FieldTransformer {
 
    private AbstractTransformationMapping mapping;
    private SimpleDateFormat HHmmss = new SimpleDateFormat("HHmmss");
 
    public void initialize(AbstractTransformationMapping mapping) {
        this.mapping = mapping;
    }
 
    public Object buildFieldValue(Object instance, String xPath, Session session) {
        Date date = (Date) mapping.getAttributeValueFromObject(instance);
        return HHmmss.format(date);
    }
 
}