jaxbComposition

Headline

Object-XML mapping with JAXB of the Java platform

Language:XML import and export is supported for a Java-based implementation by means of O/X mapping. The primary data model for companies is an XML schema. The schema compiler Technology:xjc of Technology:JAXB is used to generate Java classes from the schema. In this manner, operations on an XML representation of companies can be implemented in near-to-regular OO fashion while using a problem-specific object model. In different terms, one can carry out XML processing while essentially staying in the technological space of objectware. It is insightful to compare XML schema and schema-derived classes. The XML schema is defined in a manner that the resulting object model systematically leverages object composition and no class inheritance. In fact, the schema-derived classes are very similar to a regular OO design; see Contribution:javaComposition. It is important to note that the operations on companies are not implemented as instance methods since this would imply modification of schema-derived classes---unless advanced modularization mechanisms were leveraged. Instead, the operations are implemented as static methods in non-schema-derived classes.

Illustration

The data model is implemented as xml files (sampleCompany.xml) that conform to a schema (Company.xsd). For example departments:

 <xs:element name="department">
  <xs:complexType>
   <xs:sequence>
    <xs:element ref="name"/>
    <xs:element name="manager" type="employee"/>
    <xs:element ref="department" maxOccurs="unbounded" minOccurs="0"/>
    <xs:element name="employee"
        type="employee" maxOccurs="unbounded" minOccurs="0"/>
   </xs:sequence>
  </xs:complextype>
 </xs:element>

Actual Language:Java classes will be generated using Technology:xjc.

Feature:Open serialization is implemented using Technology:JAXB Un-/Marshaller:

    public static Company deserializeCompany(File input)
    throws JAXBException 
    {
        initializeJaxbContext();
        Unmarshaller unMarshaller = jaxbContext.createUnmarshaller();
        return (Company) unMarshaller.unmarshal(input);
    }

    public static void serializeCompany(File output, Company c)
    throws     JAXBException,
            FileNotFoundException,
            XMLStreamException 
    {
        initializeJaxbContext();
        OutputStream os = new FileOutputStream(output);
        Marshaller marshaller = jaxbContext.createMarshaller();
        XMLOutputFactory outputFactory = XMLOutputFactory.newInstance();
        XMLStreamWriter writer = outputFactory.createXMLStreamWriter(os);
        marshaller.marshal(c, writer); // TODO: need a stream writer that does indentation
    }

Feature:Total and Feature:Cut are implemented as static methods:

public class Total {

	public static double total(Company c) {
		double total = 0;
		for (Department d : c.getDepartment())
			total += total(d);
		return total;
	}

	public static double total(Department d) {
		double total = total(d.getManager());
		for (Department s : d.getDepartment())
			total += total(s);
		for (Employee e : d.getEmployee())
			total += total(e);
		return total;
	}

	public static double total(Employee e) {
		return e.getSalary();
	}

}

public class Cut {

	public static void cut(Company c) {
		for (Department d : c.getDepartment())
			cut(d);
	}

	public static void cut(Department d) {
		cut(d.getManager());
		for (Department s : d.getDepartment())
			cut(s);
		for (Employee e : d.getEmployee())
			cut(e);
	}

	public static void cut(Employee e) {
		e.setSalary(e.getSalary() / 2);
	}

}

Test cases are implemented for all Namespace:Features.

Relationships

For DOM-like implementations of in-memory XML processing see Contribution:dom, Contribution:jdom and Contribution:xom.

For a query-based implementation of in-memory XML processing see Contribution:xpathAPI.

For push-based XML processing see Contribution:sax.

For Object/XML mapping see Contribution:jaxbChoice (XSD with choice for different subunits), Contribution:jaxbComposition (XSD with object composition), Contribution:jaxbExtension (XSD with type extension) and Contribution:jaxbSubstitution (XSD with substitution groups).

Architecture

The contribution follows a standardized structure:

inputs contains input files for tests
src/main/java contains the following packages:
- org.softlang.company.features for implementations of Functional requirements.
src/test/java contains the following packages:
- org.softlang.company.tests for Technology:JUnit test cases for Namespace:Features.