Using EJB Bean References

How to create a bean reference in the deployment descriptor and look it up at runtime.

About this technique	Details
Category	Enterprise JavaBean Techniques
Description	You'll learn about: Specifying bean references in the deployment descriptor How the SBBankATM finds bean references
Related reading	See the part on developing Enterprise JavaBeans in the Programmer's Guide

Specifying bean references in the deployment descriptor   

To use the JAR Designer to add a bean reference to the deployment descriptor, you add the reference entry and specify its properties as shown here:

The information in the deployment descriptor includes the following:

Property value	Description
Name	This is the name that is used in the code that is doing the lookup. The EJB specification recomments that you preface this name with ejb/ At deployment time, the container maps this name to the appropriate EJB class
Referenced bean name	This is the name of the bean that you want to access as it is referred to within the EJB JAR. It is not bean's class name
Bean type	Can be entity or session
Home interface name	The fully qualified package name of the referenced bean's home interface
Remote interface name	The fully qualified package name of the referenced bean's remote interface

How the SBBankATM finds bean references   

The SBBankATMBean finds out about the entity beans that it manages in the initializeSessionBean() custom method. To get the bean references, the intializeSessionBean() method does the following:

• Instantiates an InitialContext.

• Gets the context for the internal bean-specific namespace.

• Does a lookup in the internal bean-specific namespace for the home for each of the entity beans that it will manage. It specifically gets the
  • EBAccountHome

  • EBCustomerHome

  • EBAccountTypeHome

  • EBAccountTransactionTypeHome

If it is not able to get find one of the bean references, the method throws an EJBException which is an unrecoverable error.

Here's the code that does a lookup for the EBCustomer bean and the EBAccount bean:

  try  
    { 
     m_initialContext = new javax.naming.InitialContext(); 
     Context contextEnv =  
       (Context) m_initialContext.lookup("java:comp/env");	 	 	  
     } 
  // The Environment name specified in the EJB jar must match the //name below. 
     Object objEntityBeanLookup = (Object)    contextEnv.lookup("/ejb/EBCustomer"); 
     m_EBCustomerHome = (EBCustomerHome)  
       PortableRemoteObject.narrow(objEntityBeanLookup,  
        com.examples.bankdemo.EBCustomerHome.class);	 	  
   
  // Then, get our EBAccountHome 
      objEntityBeanLookup = (Object) contextEnv.lookup("/ejb/EBAccount");	 	 	  
      m_EBAccountHome = (EBAccountHome) 
      PortableRemoteObject.narrow(objEntityBeanLookup,      com.examples.bankdemo.EBAccountHome.class); 
  } 
  catch (Exception e) 
  { 
       String sErrorMessage = e.toString(); 
  //This is an unrecoverable error, so throw an EJBException 
     throw new EJBException(sErrorMessage);} 
  }