EJB Interview Questions and Answers for 5 years experience

1. What is EJB?

   • Answer: Enterprise Java Beans (EJB) is a server-side component architecture for modularizing business logic in Java EE applications. It simplifies development by providing a framework for managing transactions, security, concurrency, and persistence.

2. What are the different types of EJBs?

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

3. Explain Stateful Session Beans.

   • Answer: Stateful Session Beans maintain conversational state across multiple client invocations. Each instance serves a single client, preserving data between method calls. They are useful for applications requiring session management, like shopping carts.

4. Explain Stateless Session Beans.

   • Answer: Stateless Session Beans don't maintain conversational state. Each method call is treated independently. They are ideal for operations that don't require remembering previous interactions, improving scalability and concurrency.

5. Explain Singleton Session Beans.

   • Answer: Singleton Session Beans ensure only one instance exists across the application's lifetime. They're suitable for managing shared resources or providing global access to data.

6. What are Message-Driven Beans (MDBs)?

   • Answer: MDBs are asynchronous components that process messages from JMS queues or topics. They are excellent for handling events and decoupling components in a loosely coupled architecture.

7. What is the role of the EJB container?

   • Answer: The EJB container manages the lifecycle of EJBs, handles transactions, security, concurrency, and provides services like dependency injection and resource pooling.

8. Explain EJB deployment descriptors.

   • Answer: Deployment descriptors (ejb-jar.xml) are XML files that contain metadata about EJBs, including their names, interfaces, transaction attributes, and security roles. They provide configuration information to the EJB container.

9. What are EJB transactions?

   • Answer: EJB transactions ensure data consistency by grouping multiple operations into a single unit of work. If any operation fails, the entire transaction is rolled back, maintaining data integrity.

10. Explain different transaction attributes in EJB.

    • Answer: Attributes like Required, RequiresNew, Mandatory, Supports, NotSupported, and Never control how EJB methods participate in transactions. They determine whether a new transaction is started, an existing one is used, or transactions are avoided altogether.

11. How do you handle concurrency in EJBs?

    • Answer: The EJB container manages concurrency using techniques like thread pooling and synchronization. Stateless session beans are inherently thread-safe, while stateful beans require careful management of concurrency issues.

12. What is the difference between local and remote interfaces in EJB?

    • Answer: Local interfaces are used for accessing EJBs within the same JVM, offering better performance. Remote interfaces allow access from different JVMs via RMI or other remoting technologies.

13. Explain EJB security.

    • Answer: EJB security involves controlling access to EJB methods using roles and permissions. The EJB container enforces security policies defined in deployment descriptors or programmatically.

14. What are interceptors in EJB?

    • Answer: Interceptors are components that can intercept method calls on EJBs, allowing for cross-cutting concerns like logging, auditing, or security to be implemented without modifying the EJB's core logic.

15. What are timers in EJB?

    • Answer: EJB timers allow scheduling the execution of EJB methods at specific times or intervals. They're useful for tasks like batch processing or scheduled reminders.

16. How do you manage persistence in EJBs?

    • Answer: While Entity Beans were previously used, JPA (Java Persistence API) is now the standard for managing persistence in EJB applications. JPA provides an object-relational mapping (ORM) framework for mapping Java objects to database tables.

17. Explain dependency injection in EJB.

    • Answer: Dependency Injection (DI) is a design pattern where dependencies are provided to EJBs instead of the EJBs creating them. This improves modularity, testability, and maintainability.

18. What are the advantages of using EJB?

    • Answer: Advantages include simplified development, platform independence, scalability, security, transaction management, and support for various enterprise features.

19. What are the disadvantages of using EJB?

    • Answer: Disadvantages can include complexity for simple applications, potential performance overhead, and a steeper learning curve compared to simpler frameworks.

20. Describe your experience with different EJB versions.

    • Answer: (This answer needs to be tailored to your actual experience. Mention specific versions like EJB 2.x, 3.x, etc., and highlight relevant projects and technologies used.)

21. How have you used EJB in a real-world project? Describe the architecture and challenges faced.

    • Answer: (This answer should detail a specific project, its architecture using EJBs, and any challenges encountered and how they were overcome. Be specific about the EJB types used and their roles within the application.)

22. How would you design a system using EJB to handle high concurrency?

    • Answer: (Describe your approach, focusing on stateless session beans, appropriate transaction management, connection pooling, and caching strategies to optimize performance under heavy load.)

23. Explain your understanding of the EJB lifecycle.

    • Answer: (Detail the stages – creation, passivation, activation, removal – and how the container manages them for different EJB types.)

24. How do you handle exceptions in EJBs?

    • Answer: (Explain the use of try-catch blocks, custom exception classes, and proper logging to handle both application and system exceptions. Describe strategies for rolling back transactions when exceptions occur.)

25. Compare and contrast EJB with other technologies like Spring.

    • Answer: (Compare and contrast features, advantages, and disadvantages of EJB and Spring, noting differences in dependency injection mechanisms, transaction management, and overall architectural styles.)

26. How do you test EJBs?

    • Answer: (Explain the use of mocking frameworks, unit testing, integration testing, and container testing to verify the functionality of EJBs.)

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

    • Answer: (List best practices like using stateless beans for scalability, proper transaction management, efficient resource usage, logging, and adherence to coding standards.)

28. How do you debug EJB applications?

    • Answer: (Describe the debugging techniques, including remote debugging, logging, and using debugging tools specific to your application server.)

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

    • Answer: (List common performance tuning techniques, like connection pooling, caching, efficient query design, and optimizing database access.)

30. Explain your understanding of Java EE architecture.

    • Answer: (Explain your understanding of the Java EE architecture, including the role of the application server, web container, EJB container, and other components.)

31. How familiar are you with different application servers that support EJB?

    • Answer: (List various application servers like WildFly, GlassFish, JBoss EAP, WebLogic, WebSphere, and describe your experience with them.)

32. What are the differences between EJB 2.x and EJB 3.x?

    • Answer: (Detail the key differences, such as annotation-based configuration, simplified deployment, removal of entity beans in favor of JPA, and improvements in dependency injection.)

33. Explain how you would handle a scenario where an EJB method takes a long time to execute.

    • Answer: (Describe strategies to handle long-running tasks like using asynchronous processing with MDBs, background threads, or message queues to avoid blocking the main application thread.)

34. How would you design an EJB application to be highly available and fault-tolerant?

    • Answer: (Describe techniques like clustering, load balancing, failover mechanisms, and using application server features to ensure high availability and fault tolerance.)

35. What are some security considerations when designing EJB applications?

    • Answer: (Discuss security best practices, such as authentication, authorization, secure coding practices, input validation, and protection against common vulnerabilities.)

36. Explain your experience with using different design patterns in EJB development.

    • Answer: (Discuss design patterns you've used, like Singleton, Factory, DAO, and others relevant to EJB development, and explain how they helped in your projects.)

37. How do you monitor the performance of EJB applications?

    • Answer: (Describe how you'd monitor EJB applications, including using application server monitoring tools, logging, performance counters, and profiling tools.)

38. Describe a challenging situation you faced while working with EJB and how you resolved it.

    • Answer: (Describe a real-world challenge, explain your approach to troubleshooting and solving the problem, and highlight the lessons learned.)

39. What are your preferred tools and technologies for developing and deploying EJB applications?

    • Answer: (List your favorite IDEs, build tools, application servers, and deployment tools.)

40. How do you keep your EJB skills up-to-date?

    • Answer: (Describe your methods for continuous learning, like attending conferences, reading articles, taking online courses, and participating in online communities.)

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