Summary of "Can You Answer These EPAM Java Spring Boot Questions? | 3 Yrs Mock Interview"

Summary of the Video

“Can You Answer These EPAM Java Spring Boot Questions? | 3 Yrs Mock Interview”

This video features a mock interview session with Hmon, a senior Java developer with 3.5 years of experience in Java Spring Boot and microservices. The interviewer, Ali, asks a series of technical questions commonly encountered in Java Spring Boot interviews, focusing on practical problem-solving, core Java concepts, Spring Boot internals, microservices communication, and related technologies.

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Main Ideas, Concepts, and Lessons Conveyed

1. Introduction and Candidate Background

• Hmon has 3.5 years of relevant experience in Java Spring Boot and microservices.
• Currently working on an e-commerce application using microservices, Kafka, React, and MySQL.

2. Debugging and Error Handling in Spring Boot

• 500 Internal Server Error:
  • Use breakpoints and debug mode to trace errors (e.g., NullPointerException).
  • Check logs (logback XML) for error details.
• Scheduled Jobs Running Twice:
  • Could be due to multiple instances running the same job.
  • Duplicate cron jobs or misconfigured schedulers.
• Entity Updates Not Reflecting in DB:
  • Possible session closure or mismatch between entity fields and DB columns.

3. Performance Optimization

• Slow endpoints querying multiple tables:
  • Avoid SELECT *, fetch only required columns.
  • Use pagination to limit data fetched at once.

4. Interview Preparation Kit

• Four parts:
  • Complete interview material covering 99% of questions.
  • Real enterprise client projects (code + video).
  • Lifetime chat support for doubts.
  • Referral support to top agencies.

5. Microservices and DTO Sharing

• Use a multi-module project to share common DTOs across microservices by placing DTOs in a common package/module.

6. Java 8 Optional Usage

• Used to avoid NullPointerException when fetching entities by ID.
• Difference between Optional.of() (throws NPE if null) and Optional.ofNullable() (creates empty optional if null).

7. Java Concepts

• Comparator vs Comparable:
  • Comparable: single natural ordering, modifies the class itself.
  • Comparator: multiple custom orderings, external to the class.
• Making a Class Immutable:
  • Mark class as final.
  • Make fields private final.
  • Remove setters.
  • Use defensive copying for mutable fields like lists.
• Garbage Collection:
  • Works on mark-and-sweep algorithm.
  • Uses young and old generation heap spaces.
  • Stop-the-world event pauses app during GC.
• String Comparison:
  • Use .equals() for content equality, not == which compares references.
• Thread Safety:
  • Use Thread, Runnable, Callable.
  • Prefer ConcurrentHashMap over Collections.synchronizedMap due to finer-grained locking (bucket-wise vs whole map).

8. Functional Interface and Stream API

• Functional Interface: single abstract method interface, annotated with @FunctionalInterface.
• Stream API improves readability and performance by enabling functional-style operations like map, filter, and allows chaining with lambda expressions.

9. Spring Boot Internals

• Application startup begins with SpringApplication.run().
• Uses annotations: @SpringBootApplication (includes @EnableAutoConfiguration, @ComponentScan).
• IOC container scans components and creates beans.
• Component scan can be customized to scan specific packages.

10. Dependency Injection

• Field injection vs Constructor injection:
  • Constructor injection preferred for compile-time safety and no need for @Autowired in Spring 4+.
  • Field injection can lead to null pointer exceptions if dependencies are not injected properly.

11. Configuration Properties

• @Value injects individual property values.
• @ConfigurationProperties binds a group of properties into a POJO.

12. Global Exception Handling

• Use @RestControllerAdvice for centralized exception handling.
• Use try-catch in service layer for specific exception handling.

13. Validation Annotations

• @Valid and @Validated are used for request object validation (exact differences not fully clarified).

14. JSON Conversion in Spring Boot

• Uses Jackson API internally to convert JSON to Java objects and vice versa.
• Jackson dependency is included by default in Spring Boot.

15. Performance Tuning Techniques

• Remove unnecessary dependencies.
• Optimize queries (select only required fields, avoid unnecessary joins).
• Use pagination.
• Use lazy initialization (@Lazy) to defer bean loading until needed.

16. Custom Queries in Hibernate

• Use @Query annotation for HQL or native SQL queries.
• HQL uses entity class names; native queries use DB table/column names.

17. Entity Behavior

• If @Table annotation is missing, entity class name is used as table name in lowercase.
• Difference between save(), saveAll(), and flush() methods in Spring Data JPA explained.

18. Fetch Types in JPA

• FetchType.LAZY: loads related entities on demand (using proxies).
• FetchType.EAGER: loads related entities immediately.

19. Cascade Types

• CascadeType.ALL: all operations (save, update, delete) cascade to child entities.
• CascadeType.MERGE: cascades only merge operations.

20. Microservices Communication

• Four ways: RestTemplate (deprecated), RestClient, WebClient, and FeignClient.
• Synchronous communication waits for response; asynchronous does not.

21. CI/CD Pipelines

• Continuous Integration and Deployment using Jenkins, Maven, Docker, Kubernetes.
• Pipeline triggers on GitHub code changes, compiles code, runs tests, packages JAR, deploys to Kubernetes cluster.

22. Git Commands

• Basic commands: git init, git add, git status, git commit.
• git cherry-pick used to selectively merge commits from one branch to another.

23. Less Frequently Used Spring Boot Annotations

• Examples: @Async, @Cacheable, @CacheEvict, stereotype annotations like @ControllerAdvice, @Service, @Repository.

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Detailed Methodologies / Instructions Presented

Debugging 500 Internal Server Error

• Identify endpoint causing error.
• Set breakpoints and debug in IDE.
• Check logs (logback.xml).

Optimizing Slow Endpoints

• Avoid SELECT *.
• Fetch only required columns.
• Use pagination to limit data size.

Making a Class Immutable

• Mark class as final.
• Make fields private final.
• Remove setter methods.
• Defensive copy mutable fields (e.g., lists).

Sharing DTOs in Microservices

• Use a multi-module project.
• Place common DTOs in a shared module/package.

Global Exception Handling in Spring Boot

• Create a class annotated with @RestControllerAdvice.
• Define exception handler methods annotated with @ExceptionHandler.

Writing Custom Queries in Hibernate

• Use @Query annotation for HQL queries.
• Use nativeQuery=true for native SQL queries.

CI/CD Pipeline Workflow

• Trigger pipeline on Git commit.
• Jenkins fetches latest code.
• Maven compiles and runs tests.
• Package code into JAR.
• Deploy Docker image to Kubernetes cluster.

Using Git Cherry-Pick

• Selectively merge specific commits from feature branch into main branch without merging all commits.

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Speakers / Sources Featured

• Hmon: Senior Java Developer (candidate) with 3.5 years experience in Java Spring Boot and microservices.
• Ali: Interviewer conducting the mock interview and explaining the interview preparation kit.

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This summary captures the key technical topics, practical advice, and methodologies discussed in the mock interview, providing a comprehensive overview of the candidate’s responses and the interviewer’s guidance.

Category

Educational

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