Lesson 1

In the last module, we explored the world of distributed objects and looked at how components can be managed and combined to create flexible applications. Enterprise JavaBeans (EJB) in Java EE 8 provides a robust framework for building scalable, transactional, and distributed applications in Java. EJB architecture facilitates the development and deployment of enterprise-level applications by leveraging the concept of distributed objects.
EJB Architecture and Distributed Objects in Java EE 8

1. Component-Based Architecture:
   • EJBs are modular components that encapsulate business logic.
   • These components can be deployed in a distributed environment, allowing them to interact with clients and other EJBs across different machines in a network.
2. RMI and Remote Method Invocation:
   • EJB relies on Java Remote Method Invocation (RMI) to support distributed objects.
   • Clients can invoke methods on EJBs deployed on remote servers as if they were local objects. This is achieved using the @Remote annotation for EJBs, which exposes the EJB's interface for remote access.
3. Container-Managed Environment:
   • The EJB container manages the lifecycle, security, transactions, and remote communication of EJBs.
   • The container abstracts the complexity of remote communication, allowing developers to focus on business logic instead of underlying networking code.
4. Session Beans for Distributed Interactions:
   • Session beans (Stateless, Stateful, Singleton) are used to implement distributed objects.
   • Stateless Beans: Provide stateless services that can be accessed by multiple clients simultaneously, ideal for distributed and scalable applications.
   • Stateful Beans: Maintain client-specific state across multiple method calls, suitable for use cases where session data is important.
   • Singleton Beans: Shared among all clients, often used for caching and configuration data in distributed systems.
5. Interoperability with Protocols:
   • EJBs support interoperability through various protocols like CORBA and RMI-IIOP (Internet Inter-ORB Protocol).
   • This allows EJBs to communicate with components and services in other programming languages or platforms, enhancing their distributed nature.
6. Transactions and Distributed Systems:
   • EJBs integrate seamlessly with Java Transaction API (JTA) to manage distributed transactions across multiple resources.
   • This ensures data consistency and reliability in distributed environments.
7. Security:
   • EJBs leverage Java EE's security framework to ensure secure communication and access control in distributed applications.
   • Security roles and policies can be defined declaratively or programmatically.
8. Load Balancing and Failover:
   • The EJB architecture supports clustering, enabling load balancing and failover capabilities.
   • Distributed objects (EJBs) can operate in a cluster, ensuring high availability and scalability.

Advantages of EJB in Distributed Environments

• Simplifies the development of distributed applications by abstracting complexities.
• Provides built-in support for transactions, security, and lifecycle management.
• Scales easily with increased demand through clustering and load balancing.
• Ensures reliable communication with support for distributed transactions and error handling.

In summary, EJB architecture is tightly integrated with the concept of distributed objects in Java EE 8. It abstracts the complexities of distributed systems, enabling developers to focus on implementing business logic while relying on the platform for transaction management, remote communication, and scalability.

In this module, we look at Enterprise JavaBeans and how the EJB architecture relates to that of distributed objects in general. Enterprise JavaBeans are also known as EJBs and, for simplicity, I will refer to them as a bean or beans.
A "bean instance" or "bean object" indicates an actual instance of a bean.

• Exploring EJB architecture
  The first lesson will remove any myths or confusion regarding Java's notion of JavaBeans versus Enterprise JavaBeans.
  I will then explain how the EJB architecture fits the Object Monitor (OM) model and describe in detail the contract that the bean has, and the one that the client has, with the container. We will explore the plumbing (system services) that the EJB server container combination provides to, and on behalf, of the bean.

In the next few lessons, we will look at the three types of EJBs:stateful session beans, stateless session beans, and entity beans.

We will look at how you can declaratively specify the deployment parameters for a bean in a deployment descriptor and package the beans in jar files for ease of handling.

1. Deployment descriptor: Information that describes both the structure of an Enterprise Java Bean, and the information required by it at runtime.
2. Jar file: A file created with the Java jar program which is similar to tar on the Unix platform.

In the next lesson, the difference between Enterprise JavaBeans and JavaBeans will be discussed.