EJB Interview Questions and Answers for 7 years experience

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EJB Interview Questions and Answers (7 Years Experience)

  1. What is EJB? Explain its purpose and benefits.

    • Answer: Enterprise JavaBeans (EJB) is a server-side component architecture for building distributed, transactional, and secure Java applications. Its purpose is to simplify the development of enterprise-level applications by providing a framework for managing complex tasks like transactions, security, concurrency, and persistence. Benefits include improved code reusability, simplified development, scalability, and enhanced security through container-managed services.

  2. Explain the different types of EJBs.

    • Answer: There are three main types of EJBs: Session Beans (Stateful, Stateless, Singleton), Message-Driven Beans (MDBs), and Entity Beans (now largely replaced by JPA).

  3. What is a Stateful Session Bean? When would you use one?

    • Answer: A Stateful Session Bean maintains conversational state for a client across multiple method calls. Use it when you need to preserve data specific to a client's interaction throughout a session, such as a shopping cart or a user's login information.

  4. What is a Stateless Session Bean? When would you use one?

    • Answer: A Stateless Session Bean doesn't maintain client-specific state between method invocations. Use it for operations that don't require session context, such as calculating values or accessing shared data.

  5. What is a Singleton Session Bean? Explain its lifecycle.

    • Answer: A Singleton Session Bean ensures only one instance exists throughout the application's lifecycle. Its lifecycle is managed by the container; it's created when the application starts and destroyed when it shuts down.

  6. What is a Message-Driven Bean (MDB)? How does it work?

    • Answer: An MDB is an asynchronous component that receives messages from a JMS (Java Message Service) queue or topic. It's event-driven; when a message arrives, the container invokes the MDB's `onMessage()` method to process it.

  7. Explain the difference between container-managed persistence (CMP) and bean-managed persistence (BMP).

    • Answer: CMP (largely deprecated) had the EJB container handle persistence logic. BMP required the bean to handle its own persistence (using JDBC, for example). JPA has largely replaced both.

  8. What is the role of the EJB container?

    • Answer: The EJB container provides services to EJBs, including transaction management, security, concurrency control, persistence, lifecycle management, and resource pooling.

  9. Explain the concept of transactions in EJB.

    • Answer: Transactions ensure data consistency. EJBs can use container-managed transactions (CMT), where the container manages transaction boundaries, or bean-managed transactions (BMT), where the bean explicitly controls transactions using JTA (Java Transaction API).

  10. Describe different transaction attributes in EJB.

    • Answer: Common transaction attributes include Required, RequiresNew, Mandatory, NotSupported, Supports, Never. These dictate how the transaction of a method call relates to existing transactions.

  11. How does security work in EJB?

    • Answer: EJB security is typically handled through declarative security (using annotations or deployment descriptors) or programmatic security (using JAAS). The container enforces security policies, such as authentication and authorization.

  12. What is dependency injection in the context of EJB?

    • Answer: Dependency Injection allows EJBs to obtain dependencies (other beans, resources) without explicitly creating them. This improves loose coupling and testability. It's often facilitated using annotations like `@Inject`.

  13. Explain the difference between local and remote interfaces in EJB.

    • Answer: Local interfaces are used for in-JVM communication, offering better performance. Remote interfaces are used for inter-JVM communication, requiring serialization and network calls.

  14. How do you handle exceptions in EJB?

    • Answer: Exceptions are handled using standard Java exception handling mechanisms (try-catch blocks). Application-specific exceptions can be thrown and caught, and the container can also manage exceptions related to transactions and security.

  15. What are deployment descriptors in EJB?

    • Answer: Deployment descriptors (ejb-jar.xml) contain metadata about the EJBs, including their interfaces, transaction attributes, security roles, and other deployment-specific configurations.

  16. How do you manage concurrency in EJBs?

    • Answer: The EJB container provides concurrency management features, including thread pooling and synchronization mechanisms. Stateless session beans are inherently thread-safe, while stateful beans might require explicit synchronization or concurrency control strategies.

  17. Explain the concept of EJB timers.

    • Answer: EJB timers allow scheduling the execution of EJB methods at specific times or intervals. This is useful for background tasks, scheduled jobs, and event-driven processing.

  18. What are some best practices for developing EJB applications?

    • Answer: Use stateless beans whenever possible, follow design patterns (e.g., DAO), use CMT for transaction management, avoid excessive database access, design for scalability, properly handle exceptions, and perform thorough testing.

  19. How does EJB interact with other technologies like JMS?

    • Answer: EJBs can interact with JMS by using MDBs to asynchronously process messages from queues or topics. They can also use the JMS API directly within session beans to send and receive messages.

  20. Explain your experience with EJB 3.x and its improvements over previous versions.

    • Answer: (Requires a personalized answer based on actual experience. Mention aspects like simplified deployment, annotation-based configuration, POJO-style beans, and the reduced reliance on XML.)

  21. Describe a challenging EJB project you worked on and how you overcame the challenges.

    • Answer: (Requires a personalized answer based on actual experience. Focus on the problem, the approach taken, the solution, and the lessons learned.)

  22. How do you handle performance issues in EJB applications?

    • Answer: Techniques include profiling to identify bottlenecks, optimizing database queries, using connection pooling, caching frequently accessed data, using asynchronous processing (MDBs), and load balancing.

  23. What are some common EJB design patterns?

    • Answer: Data Access Object (DAO), Session Facade, Business Delegate, Service Locator, Intercepting Filter.

  24. How do you test EJBs?

    • Answer: Unit testing involves mocking dependencies and testing individual methods. Integration testing verifies the interaction between multiple EJBs. Use mocking frameworks (like Mockito or EasyMock) to isolate EJBs during testing.

  25. What are the differences between EJB and Spring?

    • Answer: Spring offers a lighter-weight alternative to EJB, providing dependency injection, AOP, and other features. EJB is more heavyweight, relying on a container for many services. Spring is more flexible and widely adopted, but EJB offers robust container-managed services.

  26. How would you choose between using EJB and other technologies for a new project?

    • Answer: Consider factors like project size, complexity, scalability requirements, existing infrastructure, team expertise, performance needs, and the need for strong container-managed services. For smaller projects, Spring might be a better choice, while EJB might be preferred for very large, complex enterprise systems.

  27. What is the role of an EJB timer service?

    • Answer: The EJB timer service allows scheduling the execution of EJB methods at specific times or intervals. This is useful for background tasks, scheduled jobs, and event-driven processing.

  28. Explain how to handle database connections in an EJB application.

    • Answer: Use JNDI (Java Naming and Directory Interface) to look up data sources provided by the application server. This abstracts away the connection details and allows for easier configuration and management. Use connection pooling to improve performance.

  29. Discuss your experience with different application servers that support EJB.

    • Answer: (Requires a personalized answer based on actual experience. Mention servers like JBoss, WildFly, GlassFish, WebLogic, WebSphere.)

  30. How do you ensure the scalability of an EJB application?

    • Answer: Strategies include using stateless session beans, optimizing database access, utilizing connection pooling, implementing caching, load balancing across multiple servers, and using asynchronous processing with MDBs.

  31. What are some common performance tuning techniques for EJB applications?

    • Answer: Profiling to identify bottlenecks, optimizing database queries, using connection pooling, caching frequently accessed data, using asynchronous processing (MDBs), and load balancing.

  32. Explain your understanding of the Java Persistence API (JPA) and its relationship with EJB.

    • Answer: JPA is a standard for object-relational mapping (ORM). It's widely used with EJBs to simplify persistence. JPA provides a standardized way to interact with databases, replacing the older CMP/BMP approaches. Entity beans are often implemented using JPA.

  33. How do you manage transactions across multiple EJBs?

    • Answer: Use container-managed transactions (CMT). The container ensures that transactions span multiple EJB calls, providing atomicity and data consistency. Use appropriate transaction attributes to manage transaction boundaries.

  34. What tools or technologies have you used for debugging and monitoring EJB applications?

    • Answer: (Requires a personalized answer based on actual experience. Mention tools like debuggers within IDEs, application server logging and monitoring tools, and performance profilers.)

  35. Explain the concept of interceptors in EJB.

    • Answer: Interceptors allow you to intercept method calls on EJBs, adding cross-cutting concerns like logging, security, or auditing without modifying the bean's code directly.

  36. Describe your experience with using different types of JMS messaging (point-to-point vs. publish-subscribe).

    • Answer: (Requires a personalized answer based on actual experience. Describe scenarios where each type is appropriate.)

  37. How do you handle security within an EJB application, considering authentication and authorization?

    • Answer: Use container-managed security by defining security roles and assigning them to users or groups. Use annotations or deployment descriptors to specify security constraints on EJB methods. The container will handle authentication and authorization based on the defined rules.

  38. How do you manage the lifecycle of EJBs?

    • Answer: The EJB container manages the lifecycle of EJBs automatically. You can influence aspects of it (like passivation and activation for stateful beans) but the container handles creation, destruction, and pooling.

  39. What is the role of the ejb-jar.xml file?

    • Answer: It's the deployment descriptor for EJB modules, containing metadata about EJBs, including their interfaces, transaction attributes, security roles, and other deployment-specific configurations. Annotations largely replace it in modern EJB development.

  40. Explain the concept of passivation and activation in stateful session beans.

    • Answer: Passivation is when the container saves the state of a stateful bean to persistent storage to free resources. Activation is when the container restores the bean from storage when it's needed again. This is a memory management technique.

  41. How do you deal with resource leaks in EJB applications?

    • Answer: Use try-finally blocks or try-with-resources statements to ensure resources (database connections, file handles) are properly closed. Utilize connection pooling to manage database connections efficiently.

  42. What is your experience with using JTA (Java Transaction API) in EJB applications?

    • Answer: (Requires a personalized answer based on actual experience. Describe scenarios where JTA was used for distributed transactions.)

  43. Describe your experience with different approaches to dependency management in EJB applications.

    • Answer: (Requires a personalized answer based on actual experience. Mention approaches like JNDI lookup, dependency injection using annotations, and use of other tools like Maven or Gradle.)

  44. How do you handle logging and tracing in an EJB application?

    • Answer: Use a logging framework (like Log4j or SLF4j) to log information, errors, and debugging messages. Structure logging effectively for easy analysis and troubleshooting.

  45. Describe your experience with integrating EJB applications with other systems or services.

    • Answer: (Requires a personalized answer based on actual experience. Mention technologies like REST APIs, SOAP web services, and message queues.)

  46. How familiar are you with the concepts of microservices and how they relate to EJB?

    • Answer: While EJB can be used in a microservices architecture, it is often considered a heavyweight technology not ideal for the smaller, independent services characteristic of microservices. Lighter-weight frameworks are frequently preferred.

  47. How do you address concurrency issues in stateful session beans?

    • Answer: Use appropriate synchronization mechanisms (locks) to protect shared resources within the stateful bean. Consider the implications of passivation and activation on concurrent access.

  48. What are some common pitfalls to avoid when developing EJB applications?

    • Answer: Overusing stateful session beans, ignoring transaction management, inadequate error handling, inefficient database access, not considering scalability, and neglecting security.

  49. Explain your understanding of the different EJB deployment models.

    • Answer: Describe the different deployment options and when to choose each. (e.g., standalone application server, cloud deployment, containerization).

  50. How do you maintain code quality and follow best practices when developing EJB applications?

    • Answer: Utilize code reviews, static analysis tools, automated testing (unit, integration), adherence to design patterns, and following coding style guidelines.

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