Object-JSON Mapping Concepts

EclipseLink MOXy supports the ability to convert objects to and from JSON (JavaScript Object Notation). This feature is useful when creating RESTful services; JAX-RS services can accept both XML and JSON messages.

EclipseLink supports all MOXy object-to-XML options when reading and writing JSON, including:

• EclipseLink's advanced and extended mapping features (in addition to the JAXB specification)

• Storing mappings in external bindings files

• Creating dynamic models with Dynamic JAXB

• Building extensible models that support multitenant applications

EclipseLink provides the following support for mapping JSON documents:

• JSON bindings that do not require compile time dependencies, in addition to those required for normal JAXB use. You can also write MOXy External Bindings files as JSON documents.

• Although XML has a single datatype, JSON differentiates between strings, numbers, and booleans. EclipseLink supports these datatypes automatically.

• JSON does not use attributes; anything mapped with a @XmlAttribute annotation will be marshalled as an element. By default, EclipseLink triggers both the attribute and element events, thereby allowing either the mapped attribute or element to handle the value.

• EclipseLink supports JSON documents without a root element. By default, if no @XmlRootElement annotation exists, the marshalled JSON document will not have a root element. With EclipseLink, you can override this behavior (that is, omit the root element from the JSON output).

• Because JSON does not use namespaces, all namespaces and prefixes are ignored by default when marshaling and unmarshaling. With EclipseLink, you can supply a Map of namespace-to-prefix (or an instance of NamespacePrefixMapper) to the marshaller and unmarshaller. The namespace prefix will appear in the marshalled document prepended to the element name.

• By default, when marshalling to JSON, EclipseLink marshals empty collections as [ ], EclipseLink allows you to override this behavior, so that empty collections are not marshalled at all.

• You can marshal and unmarshal root-level collections.

For more information on EclipseLink support for JSON documents, see "Using JSON Documents" in Developing JAXB Applications Using EclipseLink MOXy