Beginning Java EE 6 with GlassFish 3, Second Edition

CHAPTER 15 ■ RESTFUL WEB SERVICESThe JAX-RS ModelFrom Listing 15-2, you can see that the REST service doesn’t implement any interface nor extend anyclass; the only mandatory annotation to turn a POJO into a REST service is @Path. JAX-RS relies onconfiguration by exception, so it has a set of annotations to configure the default behavior. Following arethe requirements to write a REST service:• The class must be annotated with @javax.ws.rs.Path.• To add EJB capabilities to a REST service, the class has to be annotated with@javax.ejb.Stateless.• The class must be defined as public, and it must not be final or abstract.• Root resource classes (classes with a @Path annotation) must have a default publicconstructor. Non-root resource classes do not require such a constructor.• The class must not define the finalize() method.JAX-RS is HTTP-centric by nature and has a set of clearly defined classes and annotations to dealwith HTTP and URIs. A resource can have several representations, so the API provides support for avariety of content types and uses JAXB to marshall and unmarshall XML and JSON representationsfrom/into objects. JAX-RS is also independent of the container, so resources can be deployed inGlassFish, of course, but also in a variety of servlet containers.How to Write a REST ServiceListing 15-2 shows how to write a very simple REST service. But most of the time you need to access adatabase, retrieve or store data in a transactional manner. You can have stateless session beansfunctionalities on REST services, by adding the @Stateless annotation allowing transactional access to apersistent layer (JPA entities), as shown in Listing 15-3.Listing 15-3. A Book Resource Creating and Retrieving Books from the Database@Path("books")@Stateless@Produces({"application/xml", "application/json"})@Consumes({"application/xml", "application/json"})public class BookResource {@Contextprivate UriInfo uriInfo;@PersistenceContext(unitName = "chapter15PU")private EntityManager em;464