Beginning Java EE 6 with GlassFish 3, Second Edition

CHAPTER 1 ■ JAVA EE 6 AT A GLANCEJAX-RS specification. As shown in Listing 1-3, a RESTful web service is an annotated Java class thatresponds to HTTP actions. You will learn more about JAX-RS in Chapter 15.Listing 1-3. A RESTful Web Service@Path("books")public class BookResource {@PersistenceContext(unitName = "chapter01PU")private EntityManager em;}@GET@Produces({"application/xml", "application/json"})public List getAllBooks() {Query query = em.createNamedQuery("findAllBooks");List books = query.getResultList();return books;}The new version of the persistence API (JPA 2.0) is improved by adding collections of simple datatypes (String, Integer, etc.), pessimistic locking, a richer JPQL syntax, a brand-new Criteria API, andsupport for a caching API. JPA is discussed in Chapter 2 through Chapter 5.EJBs are easier to develop (with optional interfaces) and to package (in a war file), but they also havenew features, such as the possibility to use asynchronous calls or a richer timer service for schedulingtasks. There is also a new singleton session bean component. As shown in Listing 1-4, a singleannotation can turn a Java class into a container-managed singleton (one instance of the component perapplication). You will learn more about these new features in Chapter 6 through Chapter 9.Listing 1-4. A Singleton Session Bean@Singletonpublic class CacheEJB {private Map cache = new HashMap();public void addToCache(Long id, Object object) {if (!cache.containsKey(id))cache.put(id, object);}}public Object getFromCache(Long id) {if (cache.containsKey(id))return cache.get(id);elsereturn null;}17