Extending JAXB - Representing Metadata as JSON

In previous posts I have described the XML mapping document and JSON-binding extensions in EclipseLink JAXB (MOXy).   Since MOXy has a JAXB model for its mapping document we were able to eat our own dog food, and now MOXy offers a JSON mapping document.

An external metadata representation is useful when:

• You cannot modify the domain model (it may come from a 3rd party).
• You do not want to introduce compile dependencies on JAXB APIs (if you are using a version of Java prior to Java SE 6).
• You want to apply multiple JAXB mappings to a domain model (you are limited to one representation with annotations).
• Your object model already contains so many annotations from other technologies that adding more would make the class unreadable.

Creating a RESTful Web Service - Part 2/5 (XML Metadata)

Java Persistence Architecture (JPA) is the Java EE standard for mapping POJOs to a relational database. In this example we will use JPA to interact with our database data we set up in part 1.  In the previous post we specified the mapping metadata as annotations.  This post will demonstrate how to specify the same metadata as XML.  One advantage of specifying the metadata as XML is that the domain objects will not have a dependency on the JPA APIs.  This is useful if we want to use the same domain classes on the client side.

• Part 1 - The Database
• Part 2 - Mapping the Database to JPA Entities 
• Annotations
• XML Metadata
• Part 3 - Mapping JPA entities to XML (using JAXB)
• Part 4 - The RESTful Service
• Part 5 - The Client

Binding to JSON & XML - Handling Null

In a previous post I demonstrated how EclipseLink MOXy can be leveraged to produce both XML and JSON representations of your domain model.  The same metadata is used for both representations and MOXy applies it to leverage the capabilities of the media type.  In this post I'll focus on how null is handled in each of these representations.

JAXB and Unmapped Properties

JAXB (JSR-222) is configuration by exception, meaning that there is a default mapping applied to domain objects.  This means that sometimes you need to explicitly exclude a field/property.  In this post I'll discuss how this can be done using @XmlTransient or @XmlAccessorType(XmlAccessType.NONE) and when each option is appropriate.