Moving On: Migrating from EJB 2.1 to EJB 3.0 : Page 2

Migrating Session Beans
The example EJB 2.1 session bean class, called BookCatalogBean, specifies an ejbCreate method, a business method called getTitle(), and the callback methods shown below:

   // BookCatalogBean.java
   import javax.ejb.SessionBean;
   import javax.ejb.SessionContext;
   
   public class BookCatalogBean implements SessionBean 
   {
      private SessionContext ctx;
      public String getEdition(String title)
      {
         if(title.equals("Java & XML"))
            return new String("2nd edition");
         if(title.equals("Java and XSLT"))
            return new String("1st edition");
      }
      public void ejbCreate(){}
      public void ejbRemove() {}
      public void ejbActivate() {}
      public void ejbPassivate() {}
      public void setSessionContext(SessionContext ctx) 
        {this.ctx=ctx;}
   }

If you don't specify an interface (local or remote) in the bean class, the EJB server automatically generates a local business interface by default.

In EJB 3.0 session beans, you use metadata annotations to specify the bean type— Stateful or Stateless—with the annotations @Stateful and @Stateless respectively. You replace component and home interfaces in a session bean with a business interface. The business interface is a POJI and you can specify it as either local or remote using the annotations @Local and @Remote. A session bean may implement both local and remote interfaces.

If you don't specify an interface (local or remote) in the bean class, the EJB server automatically generates a local business interface by default. You may also specify the interface class in the @Local and @Remote annotations.

The EJB 3.0 session bean shown below is a POJO named BookCatalogBean.java that is a migrated version of the EJB 2.1 stateless session bean shown earlier. Note that it uses the @Stateless annotation, implements a local business interface, and specifies the local interface class name in the @Local annotation.

   // BookCatalogBean.java EJB 3.0 Session Bean
   @Stateless
   @Local ({BookCatalogLocal.java})
   public class BookCatalogBean implements 
      BookCatalogLocal
   {
      public String getEdition(String title)
      {
         if(title.equals("Java & XML"))
            return new String("2nd edition");
         if(title.equals("Java and XSLT"))
            return new String("1st edition");
      }
   }

Also note that the preceding EJB 3.0 bean class replaces the component and home interfaces of the EJB 2.1 version with a local business interface (POJI), annotated with the @Local annotation.

Migrating EJB Session Bean Clients
A client for an EJB 2.1 session bean obtains a session bean object using a JNDI name. The client shown below obtains a local home object using the JNDI name BookCatalogLocalHome, and then calls the create() method. Subsequently, the client outputs the edition value for a specified title with the getEdition(String) business method.

   import javax.naming.InitialContext;
   public class BookCatalogClient
   {
   
      public static void main(String[] argv)
      {
         try{
            InitialContext ctx=new InitialContext();
            Object objref=ctx.lookup(
               "BookCatalogLocalHome");
            BookCatalogLocalHome catalogLocalHome = 
               (BookCatalogLocalHome)objref;
            BookCatalogLocal catalogLocal = 
               (BookCatalogLocal) catalogLocalHome.
               create();
            String title="Java and XML";
            String edition = 
               catalogLocal.getEdition(title);
            System.out.println("Edition for Title: "
               + title + " " + edition);
   
         }
         catch(Exception e){}
      }

}

In EJB 3.0 you obtain a reference to a session bean object via dependency injection, which you implement with the @Inject annotation, the @Resource annotation, or the @EJB annotation. The EJB 3.0 session bean client class shown below injects the BookCatalogBean class with the @Inject annotation. It still obtains the edition value for a title using the getEdition(String) business method.

   public class BookCatalogClient
   {
      @Inject BookCatalogBean;
      BookCatalogBean catalogBean;
   
      String title="Java and XML";
      String edition=catalogBean.getEdition(edition);
      System.out.println("Edition for Title: "
         + title + " " + edition);
   }

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