The Top Enterprise JavaBeans (EJB) Interview Questions for 2023

Enterprise JavaBeans (EJB) is a critical framework for building robust enterprise applications in Java. As one of the core technologies in the Java Enterprise Edition platform, mastery of EJB is a must for any serious Java developer.

In this comprehensive guide, we provide the top EJB interview questions that employers frequently ask Java candidates. Whether you’re prepping for an upcoming interview or looking to brush up on your EJB knowledge, this article has all the key questions and detailed answers you need to demonstrate your expertise.

What is EJB?

EJB stands for Enterprise JavaBeans. It is a server-side component architecture that provides an abstraction layer for building distributed, transactional, secure and portable applications using Java.

Key highlights:

• Managed by EJB containers which handle low-level system services
• Simplifies development by focusing on business logic
• Supports distributed applications and databases
• Provides declarative transaction management
• Enables rapid application development

What are the different types of EJB components?

There are 3 main types of EJB components:

• Session beans – Manage business logic and workflow. Further divided into:
  • Stateless – Does not maintain state between client calls
  • Stateful – Maintains state across method calls for a client
  • Singleton – Single shared instance across clients
• Message-driven beans – React asynchronously to messages from Java Message Service (JMS)
• Entity beans – Represent data from a database

What are the benefits of EJB?

Key benefits of using EJB:

• Rapid application development through configuration over code
• Simplified development by handling low-level details
• Support for distributed applications and databases
• Declarative transaction management
• Integration with other Java EE technologies
• Vendor portability across application servers
• Built-in pooling and caching
• Scalability through container-managed instances

Explain the EJB architecture.

The EJB architecture consists of the following components

• Enterprise Beans – Business logic components running in the EJB container
• Home interface – Defines create, remove, finder methods
• Remote interface – Defines business logic methods
• EJB container – Manages EJB instances, transactions, security, etc
• EJB server – Hosts the EJB container and provides services like threading, caching, etc
• Client – Invokes methods on the enterprise beans

What is the EJB container and what does it provide?

The EJB container hosts enterprise beans and handles all system-level services like:

• Lifecycle management – Bean instantiation, pooling, destruction
• Transaction management – Handles distributed ACID transactions
• Concurrency control – Synchronization and locking
• Persistence – Integration with database and ORM tools
• Security – Declarative security with role-based access
• Support services – Caching, pooling, messaging, remoting

This allows developers to just focus on the business logic in enterprise beans.

What is the difference between Stateless and Stateful session beans?

Stateless beans are preferred for scalability while stateful beans are useful for persistent workflows.

How does EJB handle transactions?

EJB provides declarative transaction management via annotations like @TransactionAttribute. The possible values are:

• REQUIRED – Default. Container starts a transaction
• REQUIRES_NEW – Suspends current and starts new transaction
• MANDATORY – Throws exception if no transaction exists
• NOT_SUPPORTED – Suspends any current transaction
• NEVER – Throws exception if transaction exists
• SUPPORTS – Runs with or without a transaction

The EJB container handles Beginning and commit/rollback based on this configuration.

What is dependency injection and how is it used in EJB?

Dependency injection (DI) allows the container to supply dependencies to a bean automatically. This removes the need for lookup code.

The @EJB annotation can be used to inject references to other beans. The container handles this wiring, so beans don’t need to lookup dependencies manually.

How does EJB 3 simplify development compared to EJB 2?

EJB 3 introduced annotations to reduce configuration code. Key improvements:

• POJO-based – No need for home & remote interfaces
• Annotations – Simpler compared to XML deployment descriptors
• Dependency injection – Automated dependency management
• Interceptors – Modular logic insertion
• Default values – Reduced XML configuration
• JPA – Simpler data persistence

Overall EJB 3 aims to simplify enterprise development using convention over configuration.

What are the steps in an EJB client calling a session bean method?

1. Obtain home object reference from JNDI
2. Create EJB instance through home object
3. Obtain remote reference from instance
4. Invoke business method on remote reference
5. Container delegates call to bean instance
6. Bean performs logic and returns value

The container manages pooling, transactions, security and other services during this process.

How are EJBs made secure?

EJBs use declarative security through deployment descriptors. Security roles are defined and mapped to users/groups. The @RolesAllowed annotation is used to define access to bean methods.

At runtime, the container handles authorization by checking the user has the required role before allowing access to bean methods.

What is the benefit of interceptors in EJB 3?

Interceptors allow common logic like logging, auditing and monitoring to be inserted modularly into beans. They are invoked transparently by the container when a bean method is called.

This avoids code duplication across beans for cross-cutting concerns. Interceptors improve maintainability and reusability.

How are EJBs scoped?

Beans can be scoped at different levels:

• Application scoped – Shared by all components in app
• Module scoped – Shared by components within the same module
• Instance scoped – Unique to each bean instance

Scopes control how widely an enterprise bean can be accessed within the application.

Explain Bean Managed Persistence vs Container Managed Persistence

Bean Managed Persistence (BMP):

• Developer handles SQL, JDBC code
• Allows complex queries across multiple tables
• Tight coupling to RDBMS

Container Managed Persistence (CMP):

• Container handles SQL transparently
• Developer works with persistent domain objects
• Usually involves ORM framework like Hibernate
• Loose coupling, easily portable

CMP is simpler but BMP offers fine-grained control over data access.

What is pooling in EJB and how does it help?

Pooling creates a pool of reusable bean instances to serve client requests. This avoids creating a new instance per request which is expensive.

Pooling improves performance and scalability. Stateless session beans are commonly pooled since they hold no conversational state.

How does EJB support asynchronous processing?

Message-driven beans allow asynchronous processing by reacting to messages from messaging systems like JMS. The steps are:

1. Client sends JMS message to destination
2. MDB instance listens on destination
3. Container calls MDB as messages arrive
4. MDB processes message & returns

This allows time-consuming processing to be done asynchronously without tying up clients.

What are some best practices in EJB development?

Some best practices include:

• Prefer stateless beans for scaling and simplicity
• Use separate beans for unrelated business methods
• Validate arguments and throw exceptions early
• Avoid large methods, break into smaller chunks
• Minimize lookups by caching frequently used resources
• Use CMT for transactions instead of BMT
• Monitor performance and optimize bottlenecks

Proper encapsulation, loose coupling and scale out design are key to developing robust EJBs.

EJB is a critical skill for Java EE developers. Mastering common EJB interview questions like these will help you stand out from other candidates and land your dream job.

This list covers the fundamental concepts like architecture, key components, transactions, security and design patterns. Studying the detailed answers will give you deep knowledge of EJB and its practical use in building enterprise Java applications.