ABSTRACT EJBs
Creating EJB beans by hand is a laborious task. But using a code 
generator to do the job often robs the developer of much-needed power.

There are two major types of EJB beans, Entity beans and Session beans. 
Both are created by implementing an interface. Each interface requires 
half a dozen methods, which can be tiresome when none of the methods 
require any actual code.

This is a perfect situation for an abstract class. The abstract class 
provides default implementations, leaving the developer to override 
them on the rare occasions.

The code for AbstractEntityBean is:

package com.generationjava.ejb; 
 
import javax.ejb.EntityBean; 
import javax.ejb.EntityContext; 
import java.rmi.RemoteException; 
 
public abstract class AbstractEntityBean implements EntityBean { 
 
    private EntityContext context; 
 
    public void ejbActivate() throws RemoteException { 
    } 
     
    public void ejbLoad() throws RemoteException { 
    } 
     
    public void ejbPassivate() throws RemoteException { 
    } 
     
    public void ejbRemove() throws RemoteException { 
    } 
     
    public void ejbStore() throws RemoteException { 
    } 
     
    public void setEntityContext(EntityContext e) throws 
RemoteException { 
        this.context = e; 
    } 
     
    public void unsetEntityContext() throws RemoteException { 
        this.context = null; 
    } 
 
    public EntityContext getEntityContext() throws RemoteException { 
        return this.context; 
    } 
     
}

The void methods are implemented by doing nothing, while the 
entityContext property is dealt with through a private EntityContext 
attribute.

The AbstractSessionBean looks much the same:

package com.generationjava.ejb; 
 
import javax.ejb.SessionBean; 
import javax.ejb.SessionContext; 
import java.rmi.RemoteException; 
 
public abstract class AbstractSessionBean implements SessionBean { 
 
    private SessionContext context; 
 
    public void ejbActivate() throws RemoteException { 
    } 
     
    public void ejbPassivate() throws RemoteException { 
    } 
     
    public void ejbRemove() throws RemoteException { 
    } 
     
    public void setSessionContext(SessionContext e) throws 
RemoteException { 
        this.context = e; 
    } 
     
    public SessionContext getSessionContext() throws RemoteException { 
        return this.context; 
    } 
     
}

Again, the void methods are dealt with by ignoring them, while a 
private SessionContext is added to deal with the sessionContext 
property.

By having an abstract set of classes, the effort required to develop a 
new EJB bean decreases. Occasionally a different implementation of a 
method is required, or the bean may extend another class. But in the 
majority of cases an abstract bean will save a developer much effort.

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