EJB 3

Notes from https://www.sun.com/offers/details/java_ee6_javabeans.xml

• EJB allows 'interface-less' session beans.
• EJB's can now be packaged in WAR files. EAR's are not required
• Profiles
  • Web profile: Local Session Beans, CMT/MBT, Declarative Security, Interceptors
  • Full profile: Lite + Message-Driven Beans, Timer Servie, Async method calls, CMP/BMP Entity Beans
• Portable JNDI names:
  • Globally unique name:

    java:global[/<app-name>]/<module-name>/<ejb-name>

  • Unique name within same application:

    java:app/<module-name>/<ejb-name>

  • Unique name within defining module:

    java:module/<ejb-name>

  • Example:

    @Stateless
    public class HelloBean implements Hello {
        public String sayHello(String msg) {
            return "Hello, " + msg;
        }
    }

    If deployed as hello.jar, JNDI entries are:

    java:global/hello/HelloBean
    java:app/hello/HelloBean
    java:module/HelloBean

• Embeddable EJBContainer for testing or JSE use:

  EJBContainer c = EJBContainer.createEJBContainer();
  Bank bank = (Bank) c.getContext().lookup("java:global/bank/BankBean");
  // ...
  c.close();

• New Features
  • Singletongs
    • Allows shared state
    • Designed for concurrent access
    • Lots in common with stateless/stateful beans
    • Example:

      // EJB
      @Singleton
      // @Startup // optionally create this bean eagerly
      public class SharedBean {
        private SharedData shared;
        
        // Note we can do things during construction and teardown (optional)
        @PostConstruct
        private void init() {
          shared = ...;
        }
      
        @PreDestroy
        private void destroy() {
          ...
        }
      
        public int getXYZ();
          return shared.xyz;
        }
      
        
      } 
      
      // Client
      @Stateless
      public class FooBean {
        // Inject reference to Singleton bean 
        @EJB
        private SharedBean shared
      
        public void foo() {
          int xyz = shared.getXYZ();
          ...
        }
      }

  • Concurrecy options: Single threaded (default), Container Managed (via method-level locking metadata), Bean Managed (all concurrent invocation can access bean instance)
• Improvements to EJB timer service.
  • richer calendar-base way to express timer expressions (like cron, but better)
  • Automatic Timer Creation:

    @Stateless
    public class BankBean {
    
      @PersistenceContext EntityManager accountDB;
      @Resource javax.mail.Session mailSession;
      
      // Callback the last day of each month at 8 a.m.
      @Schedule(hour="8", dayOfMonth="Last")
      void sendMonthlyBankStatements() {
         ...
      }
    }

• Asynchrounouse Session Bean Invocations
  • Fire and Forget or async results via Future<V>
  • Available for Stateful, Stateless and Singleton beans
  • Example of Fire and Forget:

    @Stateless public class DocBean {
      
      @PersistenceContext EntityManager resultsDB;
      @EJB DocBean myself;
    
      public void processDocument(Document doc) {
        myself.doAnalysisA(document);
        myself.doAnalysisB(document);
      }
    
      @Asynchronous public void doAnalysisA(Document d) { //... }
      @Asynchronous public void doAnalysisB(Document d) { //... }
    }

  • Example of Future:

    @EJB Processor proc;
    Task task = new Task(...);
    Future<int> computeTask = processor.compute(task);
    ...
    int result = computeTask.get();
    
    // EJB
    @Stateless
    public class ProcessorBean implements Processor {
      @PersistenceContext EntityManager db;
    
      @Asynchronous
      public Future<int> compute(Task t) {
        // perform computation
        int result = ...;
        return new javax.ejb.AsynchResult<int>(result);
      }
    }