Java Queries

What are transactional attributes?

EJB transactions are a set of mechanisms and concepts, which insures the integrity and consistency of the database when multiple clients try to read/update the database simultaneously.

Transaction attributes are defined at different levels like EJB (or class), a method within a class or segment of a code withi

What are the implicit services provide by an EJB container?

Lifecycle Management: Individual enterprise beans do not need to explicitly manage process allocation,
thread management, object activation, or object destruction.

How does an EJB interact with its container and what are the call-back methods in entity beans?

EJB interacts with its container through the following mechanisms

Call-back Methods: Every EJB implements an interface (extends EnterpriseBean) which defines several
methods which alert the bean to various events in its lifecycle.

Can an EJB client invoke a method on a bean directly?

An EJB client should never access an EJB directly. Any access is done through the container. The container will intercept the client call and apply services like transaction, security etc prior to invoking the actual EJB. This relationship between the EJB and the container is like "don't call us, we will call you".

What are the different kinds of enterprise beans?

Session Bean: is a non-persistent object that implements some business logic running on the server. Session beans do not survive system shut down.

What are the benefits of Clustering and workload management?

1. It balances client processing requests, allowing incoming work requests to be distributed according to a configured Workload Management selection policy.

What is the difference between Message Driven Beans and Stateless Session beans?

In several ways, the dynamic creation and allocation of message-driven bean instances mimics the behavior of stateless session EJB instances, which exist only for the duration of a particular method call.

What are the basic classes required in the client for invoking an EJB?

The home and the remote interfaces, the implementation of the Naming Context Factory, the stubs and skeletons. In some App servers the stubs and the skeletons can be dynamically downloaded from the server

What is the new basic requirement for a CMP entity bean class in 2.0 from that of ejb 1.1?

must be abstract class. The container extends it and implements methods which are required for managing the relationships

How does a container-managed relationship work?

An entity bean accesses related entity beans by means of the accessor methods for its container-managed relationship fields, which are specified by the cmr-field elements of its abstract persistence schema defined in the deployment descriptor.