Understanding Static and Dynamic Entities

There are two high-level ways to use EclipseLink JAXB: using pre-existing Java classes (Using Static MOXy), or using EclipseLink-generated in-memory Java classes (Using Dynamic MOXy).

Using Static MOXy

The most common way to use EclipseLink JAXB is with existing Java classes, mapped to XML using Java annotations and/or EclipseLink OXM metadata. These classes might be ones that you have written yourself, or they could be generated from an XML Schema using the XJC compiler tool.

Using this approach, you will be dealing with your actual domain objects when converting to and from XML. Example 9-1 shows a simple Java class that can be used with JAXB.

Example 9-1 Sample Java Class

import jakarta.xml.bind.annotation.XmlAttribute;
import jakarta.xml.bind.annotation.XmlRootElement;
 
@XmlRootElement
public class Customer {
   @XmlAttribute
   private long id;
 
   private String name;
 
   // ...
   // get() and set() methods
   // ...
}

Note:

When using static classes with JAXB, you can take advantage of JAXB's defaulting behavior and only annotate things which differ from the default. For example, all fields on a Java class will default to being mapped to an XML element, so no annotation is needed on the name field. We want the id field, however, to map to an XML attribute, so have annotated it as such.

Example 9-2 demonstrates how to unmarshal, modify, and marshal an object using static JAXB:

Example 9-2 Marshalling and Unmarshalling Example

JAXBContext jaxbContext = JAXBContext.newInstance(Customer.class, Address.class);
Customer customer = (Customer) jaxbContext.createUnmarshaller().unmarshal(instanceDoc);
 
Address address = new Address();
address.setStreet("1001 Fleet St.");
 
customer.setAddress(address);
 
jaxbContext.createMarshaller().marshal(customer, System.out);

Using Dynamic MOXy

With EclipseLink Dynamic MOXy, you can bootstrap a JAXBContext from a variety of metadata sources and use existing JAXB APIs to marshal and unmarshal data…without having compiled Java class files on the classpath. This allows you to alter the metadata as needed, without having to update and recompile the previously-generated Java source code.

You should consider using Dynamic MOXy when:

You want EclipseLink to generate mappings from an XML schema (XSD).
You do not want to deal with concrete Java domain classes.

Using Dynamic Entities

Instead of using actual Java classes (such as Customer.class or Address.class), Dynamic MOXy uses a simple get(propertyName)/set(propertyName, propertyValue) API to manipulate data. EclipseLink generates (in memory) a DynamicType associated with each DynamicEntity.

Note:

DynamicTypes are similar to Java classes; whereas DynamicEntities can be thought of as instances of a DynamicType.

Example 9-3 demonstrates how to unmarshal, modify, and marshal an object using dynamic JAXB:

Example 9-3 Marshalling and Unmarshalling Example

DynamicJAXBContext dynamicJAXBContext = DynamicJAXBContextFactory.createContextFromXSD(xsdInputStream, null, myClassLoader, null);
DynamicEntity customer = (DynamicEntity) dynamicJAXBContext.createUnmarshaller().unmarshal(instanceDoc);
 
String lastName = customer.get("lastName");
List orders = customer.get("orders");
...
DynamicEntity address = dynamicJAXBContext.newDynamicEntity("mynamespace.Address");
address.set("street", "1001 Fleet St.");
 
customer.set("lastName", lastName + "Jr.");
customer.set("address", address);
 
dynamicJAXBContext.createMarshaller().marshal(customer, System.out);

Note:

XML names found in the metadata (complex type names, element names, attribute names) will be translated to Java identifiers according to the algorithms described in "Appendix D: Binding XML Names to Java Identifiers" of the Java Architecture for XML Binding (JAXB) 2.2 Specification (http://jcp.org/en/jsr/detail?id=222).

In Example 9-3, last-name in XML was translated to lastName for the Java object.