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EJB interview questions

  • what are Container-Managed Transactional attributes ? view answer
  • What's difference between httpsession and EJB session bean ? view answer
  • What are the Differences between EJB 3.0 and EJB 2.1? view answer
  • Q. what are Container-Managed Transactional arributes ? view answer
  • What is the default transaction attribute for an EJB? view answer
  • Difference between SessionBean remove() and EntityBean remove() method? view answer
  • Why do we have a remove method in both EJBHome and EJBObject? view answer
  • Is it possible to share an HttpSession between a JSP and EJB? What happens when I change a value in the HttpSession from inside an EJB? view answer
  • What is the difference between a ?Coarse Grained? Entity Bean and a ?Fine Grained? Entity Bean? view answer
  • What are the Interfaces need to create to implement Session Bean with Exmaple? view answer
  • What are the parameters must follow for Session Bean ? view answer
  • What are the callbacks method in Session Bean ? view answer
  • What are the ways for a client application to get an EJB object? view answer
  • What is handle and why it is used in EJB? view answer
  • What is an EJB Context? view answer
  • Implement Local and Remote Interfaces in EJB? view answer
  • How can I call one EJB from inside of another EJB? view answer
  • What is the difference between Message Driven Beans and Stateless Session beans? view answer
  • What happens if remove( ) is never invoked on a session bean? view answer
  • Can you control when passivation occurs? view answer
  • Can the primary key in the entity bean be a Java primitive type such as int? view answer
  • The EJB container implements the EJBHome and EJBObject classes. For every request from a unique client, does the container create a separate instance of the generated EJBHome and EJBObject classes? view answer
  • How can i maintain a user session between servlets and stateful session ejbs? view answer
  • What's difference between Servlet/JSP session and EJB session view answer
  • Is it possible to share an HttpSession between a JSP and EJB? What happens when I change a value in the HttpSession from inside an EJB? view answer
  • How to call any EJB from a servlet/JSP/Java Client? view answer
  • What are transaction isolation levels in EJB? view answer
  • What are transaction attributes? view answer
  • What is bean managed transaction? view answer
  • Can Entity Beans have no create() methods? view answer
  • What are the callback methods in Entity beans? view answer
  • What is the difference between Container-Managed Persistent (CMP) bean and Bean-Managed Persistent(BMP) ? view answer
  • What are the methods of Entity Bean? view answer
  • What is Entity Bean? view answer
  • What is Session Bean? view answer
  • What are the different kinds of enterprise beans? view answer

!!! EJB interview questions !!!

What are the callback methods in Entity beans?



The bean class defines create methods that match methods in the home interface and business methods that match methods in the remote interface. The bean class also implements a set of callback methods that allow the container to notify the bean of events in its life cycle. The callback methods are defined in the javax.ejb.EntityBean interface that is implemented by all entity beans.The EntityBean interface has the following definition. Notice that the bean class implements these methods.

public interface javax.ejb.EntityBean {
public void setEntityContext();
public void unsetEntityContext();
public void ejbLoad();
public void ejbStore();
public void ejbActivate();
public void ejbPassivate();
public void ejbRemove();
}

The setEntityContext() method provides the bean with an interface to the container called the EntityContext. The EntityContext interface contains methods for obtaining information about the context under which the bean is operating at any particular moment. The EntityContext interface is used to access security information about the caller; to determine the status of the current transaction or to force a transaction rollback; or to get a reference to the bean itself, its home, or its primary key. The EntityContext is set only once in the life of an entity bean instance, so its reference should be put into one of the bean instance's fields if it will be needed later.

The unsetEntityContext() method is used at the end of the bean's life cycle before the instance is evicted from memory to dereference the EntityContext and perform any last-minute clean-up.

The ejbLoad() and ejbStore() methods in CMP entities are invoked when the entity bean's state is being synchronized with the database. The ejbLoad() is invoked just after the container has refreshed the bean container-managed fields with its state from the database. The ejbStore() method is invoked just before the container is about to write the bean container-managed fields to the database. These methods are used to modify data as it's being synchronized. This is common when the data stored in the database is different than the data used in the bean fields.

The ejbPassivate() and ejbActivate() methods are invoked on the bean by the container just before the bean is passivated and just after the bean is activated, respectively. Passivation in entity beans means that the bean instance is disassociated with its remote reference so that the container can evict it from memory or reuse it. It's a resource conservation measure the container employs to reduce the number of instances in memory. A bean might be passivated if it hasn't been used for a while or as a normal operation performed by the container to maximize reuse of resources. Some containers will evict beans from memory, while others will reuse instances for other more active remote references. The ejbPassivate() and ejbActivate() methods provide the bean with a notification as to when it's about to be passivated (disassociated with the remote reference) or activated (associated with a remote reference).

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