Using Extensible MOXy

In a multi-tenant architecture, a single application runs on a server serving multiple client organizations (tenants). Good multi-tenant applications allow per-tenant customizations. When these customizations are made to data, it can be difficult for the binding layer to handle them.

JAXB is designed to work with domain models that have real fields and properties. EclipseLink MOXy virtual properties provide a way to extend a class without modifying the source.

Using the @XmlVirtualAccessMethods Annotation

The @XmlVirtualAccessMethods annotation is used to specify that a class is extensible. An extensible class is required to have a get method that returns a value by property name, and a set method that stores a value by property name. The default names for these methods are get and set, and can be overridden with the @XmlVirtualAccessMethods annotation.

Since we will have multiple extensible classes in this example, we'll configure a base class for this behavior that extensible classes can extend. We will use the @XmlTransient annotation to prevent ExtensibleBase from being mapped as an inheritance relationship. The real properties represent the parts of the model that will be common to all tenants. The per-tenant extensions will be represented as virtual properties.

Example 8-16 Sample ExtensibleBase

package examples.virtual;
 
import java.util.HashMap;
import java.util.Map;
 
import javax.xml.bind.annotation.XmlTransient;
 
import org.eclipse.persistence.oxm.annotations.XmlVirtualAccessMethods;
 
@XmlTransient
@XmlVirtualAccessMethods(setMethod="put")
public class ExtensibleBase {
 
    private Map<String, Object> extensions = new HashMap<String, Object>();
 
    public <T> T get(String property) {
        return (T) extensions.get(property);
    }
 
    public void put(String property, Object value) {
        extensions.put(property, value);
    }
}

Example 8-17 Customer

The Customer class will be extensible since it inherits from a domain class that has been annotated with @XmlVirtualAccessMethods.

package examples.virtual;
 
import javax.xml.bind.annotation.XmlRootElement;
 
@XmlRootElement
public class Customer extends ExtensibleBase {
 
    private String firstName;
    private String lastName;
    private Address billingAddress;
 
    public String getFirstName() {
        return firstName;
    }
 
    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }
 
    public String getLastName() {
        return lastName;
    }
 
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }
 
    public Address getBillingAddress() {
        return billingAddress;
    }
 
    public void setBillingAddress(Address billingAddress) {
        this.billingAddress = billingAddress;
    }
 
}

Example 8-18 Address

It is not necessary to have every class in your model be extensible. In this example the Address class will not have any virtual properties.

package examples.virtual;
 
public class Address {
 
    private String street;
 
    public String getStreet() {
        return street;
    }
 
    public void setStreet(String street) {
        this.street = street;
    }
 
}

Example 8-19 PhoneNumber

Like Customer, PhoneNumber will be an extensible class.

package examples.virtual;
 
import javax.xml.bind.annotation.XmlValue;
 
public class PhoneNumber extends ExtensibleBase {
 
    private String number;
 
    @XmlValue
    public String getNumber() {
        return number;
    }
 
    public void setNumber(String number) {
        this.number = number;
    }
 
}

Creating Tenant 1

The first tenant is an online sporting goods store that requires the following extensions to the model:

Customer ID
Customer's middle name
Shipping address
A collection of contact phone numbers
Type of phone number (i.e. home, work, or cell)

The metadata for the virtual properties is supplied through MOXy's XML mapping file. Virtual properties are mapped in the same way as real properties. Some additional information is required including type (since this cannot be determined via reflection), and for collection properties a container type.

The virtual properties defined in Example 8-20 for Customer are: middleName, shippingAddress, and phoneNumbers. For PhoneNumber the virtual property is the type property.

Example 8-20 binding-tenant1.xml

<?xml version="1.0"?>
<xml-bindings
    xmlns="http://www.eclipse.org/eclipselink/xsds/persistence/oxm"
    package-name="examples.virtual">
    <java-types>
        <java-type name="Customer">
            <xml-type prop-order="firstName middleName lastName billingAddress shippingAddress phoneNumbers"/>
            <java-attributes>
                <xml-attribute
                    java-attribute="id"
                    type="java.lang.Integer"/>
                <xml-element
                    java-attribute="middleName"
                    type="java.lang.String"/>
                <xml-element
                    java-attribute="shippingAddress"
                    type="examples.virtual.Address"/>
                <xml-element
                    java-attribute="phoneNumbers"
                    name="phoneNumber"
                    type="examples.virtual.PhoneNumber"
                    container-type="java.util.List"/>
            </java-attributes>
        </java-type>
        <java-type name="PhoneNumber">
            <java-attributes>
                <xml-attribute
                    java-attribute="type"
                    type="java.lang.String"/>
            </java-attributes>
        </java-type>
    </java-types>
</xml-bindings>

The get/set methods are used on the domain model to interact with the real properties and the accessors defined on the @XmlVirtualAccessMethods annotation are used to interact with the virtual properties. The normal JAXB mechanisms are used for marshal and unmarshall operations:

Customer customer = new Customer();
 
//Set Customer's real properties
customer.setFirstName("Jane");
customer.setLastName("Doe");
 
Address billingAddress = new Address();
billingAddress.setStreet("1 Billing Street");
customer.setBillingAddress(billingAddress);
 
//Set Customer's virtual 'middleName' property
customer.put("middleName", "Anne");
 
//Set Customer's virtual 'shippingAddress' property
Address shippingAddress = new Address();
shippingAddress.setStreet("2 Shipping Road");
customer.put("shippingAddress", shippingAddress);
 
List<PhoneNumber> phoneNumbers = new ArrayList<PhoneNumber>();
customer.put("phoneNumbers", phoneNumbers);
 
PhoneNumber workPhoneNumber = new PhoneNumber();
workPhoneNumber.setNumber("555-WORK");
//Set the PhoneNumber's virtual 'type' property
workPhoneNumber.put("type", "WORK");
phoneNumbers.add(workPhoneNumber);
 
PhoneNumber homePhoneNumber = new PhoneNumber();
homePhoneNumber.setNumber("555-HOME");
//Set the PhoneNumber's virtual 'type' property
homePhoneNumber.put("type", "HOME");
phoneNumbers.add(homePhoneNumber);
 
Map<String, Object> properties = new HashMap<String, Object>();
properties.put(JAXBContextProperties.OXM_METADATA_SOURCE, "examples/virtual/binding-tenant1.xml");
JAXBContext jc = JAXBContext.newInstance(new Class[] {Customer.class, Address.class}, properties);
 
Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
marshaller.marshal(customer, System.out);

Example 8-21 Output

<?xml version="1.0" encoding="UTF-8"?>
<customer>
   <firstName>Jane</firstName>
   <middleName>Anne</middleName>
   <lastName>Doe</lastName>
   <billingAddress>
      <street>1 Billing Street</street>
   </billingAddress>
   <shippingAddress>
      <street>2 Shipping Road</street>
   </shippingAddress>
   <phoneNumber type="WORK">555-WORK</phoneNumber>
   <phoneNumber type="HOME">555-HOME</phoneNumber>
</customer>

Creating Tenant 2

The second tenant is a streaming media provider that offers on-demand movies and music to it's subscribers. It requires a different set of extensions to the core model: a single contact phone number

For this tenant we will also leverage the mapping file to customize the mapping of the real properties, as shown in Example 8-22:

Example 8-22 binding-tenant2.xml

<?xml version="1.0"?>
<xml-bindings
    xmlns="http://www.eclipse.org/eclipselink/xsds/persistence/oxm"
    package-name="examples.virtual">
    <xml-schema namespace="urn:tenant1" element-form-default="QUALIFIED"/>
    <java-types>
        <java-type name="Customer">
            <xml-type prop-order="firstName lastName billingAddress phoneNumber"/>
            <java-attributes>
                <xml-attribute java-attribute="firstName"/>
                <xml-attribute java-attribute="lastName"/>
                <xml-element java-attribute="billingAddress" name="address"/>
                <xml-element
                    java-attribute="phoneNumber"
                    type="examples.virtual.PhoneNumber"/>
            </java-attributes>
        </java-type>
    </java-types>
</xml-bindings>

Customer customer = new Customer();
customer.setFirstName("Jane");
customer.setLastName("Doe");
 
Address billingAddress = new Address();
billingAddress.setStreet("1 Billing Street");
customer.setBillingAddress(billingAddress);
 
PhoneNumber phoneNumber = new PhoneNumber();
phoneNumber.setNumber("555-WORK");
customer.put("phoneNumber", phoneNumber);
 
Map<String, Object> properties = new HashMap<String, Object>();
properties.put(JAXBContextProperties.OXM_METADATA_SOURCE, "examples/virtual/binding-tenant2.xml");
JAXBContext jc = JAXBContext.newInstance(new Class[] {Customer.class, Address.class}, properties);
 
Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
marshaller.marshal(customer, System.out);

Example 8-23 Output

Note that even though both tenants share several real properties, the corresponding XML representation can be quite different due to virtual properties:

 
<?xml version="1.0" encoding="UTF-8"?>
<customer xmlns="urn:tenant1" firstName="Jane" lastName="Doe">
   <address>
      <street>1 Billing Street</street>
   </address>
   <phoneNumber>555-WORK</phoneNumber>
</customer>