Beginning Java EE 6 with GlassFish 3, Second Edition

CHAPTER 7 ■ SESSION BEANS AND THE TIMER SERVICEListing 7-8. A Singleton Session Bean Not Allowing Concurrency@Singletonpublic class CacheEJB {private Map cache = new HashMap();@AccessTimeout(0)public void addToCache(Long id, Object object) {if (!cache.containsKey(id))cache.put(id, object);}public void removeFromCache(Long id) {if (cache.containsKey(id))cache.remove(id);}}public Object getFromCache(Long id) {if (cache.containsKey(id))return cache.get(id);elsereturn null;}Session Bean ModelSo far you’ve seen examples of code using the easiest programming model for session beans: anannotated POJO with no interface. But, depending on your needs, session beans can give you a muchricher model, allowing you to perform remote calls, dependency injection, or asynchronous calls.Interfaces and Bean ClassUntil now you’ve seen session beans composed only of a bean class. In fact, they can be richer and madeof the following elements:• Business interfaces: These interfaces contain the declaration of business methodsthat are visible to the client and implemented by the bean class. A session beancan have local interfaces, remote interfaces, or no interface at all (a no-interfaceview with local access only).• A bean class: The bean class contains the business method implementation andcan implement zero or several business interfaces. The session bean must beannotated with @Stateless, @Stateful, or @Singleton depending on its type.As shown in Figure 7-5, a client application can access a session bean by one of its interfaces (localor remote) or directly by invoking the bean class itself.214