Top 100 spring questions and answers, crack any java spring interview

1. What is Spring Framework?

Definition:
Spring is an open-source, lightweight Java framework designed to simplify enterprise application development. It promotes loose coupling through Dependency Injection (DI) and provides comprehensive infrastructure support for developing Java applications.

Features:

• Dependency Injection
• Aspect-Oriented Programming (AOP)
• Declarative transaction management
• MVC Web Framework
• Integration with frameworks like JPA, Hibernate

2. What is Inversion of Control (IoC)?

Definition:
IoC is a design principle where the control of object creation and dependency resolution is shifted from the application code to a container (like Spring).

Example:

@Component
public class Vehicle {
    public void start() {
        System.out.println("Vehicle started");
    }
}

@Component
public class Driver {
    @Autowired
    private Vehicle vehicle;

    public void drive() {
        vehicle.start();
    }
}

In this example, Spring injects the Vehicle object into the Driver object, not manually.

3. What is Dependency Injection (DI)?

Definition:
DI is the process of providing an object’s dependencies externally rather than creating them inside the class.

Types:

• Constructor Injection
• Setter Injection
• Field Injection (not recommended for testing)

Example (Constructor Injection):

@Component
public class Engine {
    public void run() {
        System.out.println("Engine running...");
    }
}

@Component
public class Car {
    private final Engine engine;

    @Autowired
    public Car(Engine engine) {
        this.engine = engine;
    }

    public void move() {
        engine.run();
    }
}

4. Constructor vs Setter Injection

• Constructor: Immutable, best for required dependencies.
• Setter: Flexible, good for optional dependencies.

Constructor Example:

@Autowired
public Car(Engine engine) {
    this.engine = engine;
}

Setter Example:

@Autowired
public void setEngine(Engine engine) {
    this.engine = engine;
}

5. Field Injection vs Setter Injection

• Field: Easy to write, but hard to test.
• Setter: More testable, supports optional injection.

Field Injection (Not ideal):

@Autowired
private Engine engine;

6. Difference Between @Component, @Service, @Repository, @Controller

All these annotations register a class as a Spring Bean.

• @Component: Generic stereotype.
• @Service: Marks a service layer class.
• @Repository: DAO layer, enables exception translation.
• @Controller: Used in MVC for handling HTTP requests.

Example:

@Service
public class UserService {
    public String getUser() {
        return "Ved";
    }
}

7. What is @Autowired?

Definition:
Used to automatically wire dependencies by type (and optionally by name).

Example:

@Component
public class Bike {
    @Autowired
    private Engine engine;
}

Options:

• @Autowired(required=false)
• Used with @Qualifier for multiple beans.

8. What is @Qualifier?

Definition:
Used to resolve ambiguity when multiple beans of the same type exist.

Example:

@Component("dieselEngine")
public class DieselEngine implements Engine {}

@Component("petrolEngine")
public class PetrolEngine implements Engine {}

@Component
public class Car {
    @Autowired
    @Qualifier("petrolEngine")
    private Engine engine;
}

. What are Bean Scopes in Spring?

Definition:
A bean’s scope defines the lifecycle and visibility of the bean in the Spring container.

Types:

• singleton: Default. One shared instance.
• prototype: New instance per injection.
• Web scopes: request, session, application

Example:

@Component
@Scope("prototype")
public class Toy {
    public Toy() {
        System.out.println("New Toy created");
    }
}

10. What is Lazy Initialization?

Definition:
Delays the creation of a bean until it’s first used.

Example:

@Component
@Lazy
public class HeavyComponent {
    public HeavyComponent() {
        System.out.println("HeavyComponent initialized");
    }
}

Without @Lazy, this would be instantiated at startup.

11. What is the lifecycle of a Spring Bean?

1. Bean instantiation
2. Property population
3. setBeanName(), setBeanFactory(), setApplicationContext() (Aware interfaces)
4. @PostConstruct or afterPropertiesSet() (init phase)
5. Bean ready for use
6. @PreDestroy or destroy() (destroy phase)

Example:

@Component
public class MyBean implements InitializingBean, DisposableBean {
    @PostConstruct
    public void init() {
        System.out.println("PostConstruct");
    }

    @PreDestroy
    public void cleanup() {
        System.out.println("PreDestroy");
    }

    @Override
    public void afterPropertiesSet() {
        System.out.println("InitializingBean logic");
    }

    @Override
    public void destroy() {
        System.out.println("DisposableBean logic");
    }
}

12. What is the difference between ApplicationContext and BeanFactory?

• BeanFactory: Basic container, lazy loading.
• ApplicationContext: Advanced container, supports:
  • Event propagation
  • AOP
  • Internationalization
  • Eager loading

13. What is the use of @PostConstruct and @PreDestroy?

• @PostConstruct: Executes after dependency injection is done.
• @PreDestroy: Executes before the bean is removed from the container.

14. How to make a bean singleton or prototype?

Use @Scope.

@Component
@Scope("prototype")
public class MyPrototypeBean {}

15. What is the role of @Configuration and @Bean?

• @Configuration: Marks a class with bean definitions.
• @Bean: Declares a bean method.

@Configuration
public class AppConfig {
    @Bean
    public Car car() {
        return new Car();
    }
}

16. How to inject values from a property file?

Use @Value and @PropertySource.

@Configuration
@PropertySource("classpath:app.properties")
public class AppConfig {
    @Value("${app.name}")
    private String appName;
}

17. What is the default bean scope in Spring?

• Singleton — one instance per container.

18. What is the difference between Singleton and Prototype scope?

Feature	Singleton	Prototype
Lifecycle	Managed fully	Only instantiation
Reuse	Yes	No
Garbage Col.	Done by Spring	Client responsibility

19. What are the different ways to configure Spring beans?

1. XML-based
2. Annotation-based
3. Java-based (@Configuration)

20. How to make a class aware of its Spring container?

Implement ApplicationContextAware or use @Autowired ApplicationContext.

21. What is AOP in Spring?

Definition: aspect oriented programmin
AOP allows separation of cross-cutting concerns (like logging, security, transactions) from business logic.

22. What are the key concepts of Spring AOP?

• Aspect: A class that contains advice.
• Join Point: A point during program execution (e.g., method call).
• Advice: Action taken (e.g., before method executes).
• Pointcut: Expression to match join points.
• Weaving: Linking aspects with other application types.

23. What are the types of advice in Spring AOP?

• @Before: Runs before method
• @After: Runs after method (regardless of outcome)
• @AfterReturning: Runs after successful method execution
• @AfterThrowing: Runs after an exception
• @Around: Controls method execution

Example:

@Aspect
@Component
public class LoggingAspect {
    @Before("execution(* com.example.service.*.*(..))")
    public void logBefore() {
        System.out.println("Before method execution");
    }
}

24. What is the difference between Spring AOP and AspectJ?

Feature	Spring AOP	AspectJ
Type	Proxy-based	Compile-time/weaving
Use Case	Simple AOP	Advanced AOP (e.g., fields)
Dependency	Spring only	Requires AspectJ tools

25. How to enable AOP in Spring?

Use @EnableAspectJAutoProxy.

@Configuration
@EnableAspectJAutoProxy
public class AppConfig {}

26. What is @Transactional annotation?

Marks methods/classes as transactional (rollback on failure, commit on success).

@Transactional
public void createUser(User user) {
    userRepository.save(user);
}

27. What is Transaction Propagation in Spring?

Defines how transactions relate to each other.

Type	Description
REQUIRED	Join existing or create new
REQUIRES_NEW	Always create new
SUPPORTS	Join if exists, else run non-transactional
MANDATORY	Must have existing transaction
NEVER	Must not run in a transaction

8. What is the default rollback behavior of @Transactional?

Rolls back on unchecked (RuntimeException) and Errors by default.

To rollback on checked exception:

@Transactional(rollbackFor = Exception.class)

29. What is the difference between @Transactional at class and method level?

• Class level: Applies to all methods.
• Method level: Overrides class-level for that method.

30. Can we have multiple transactions in a single service?

Yes. Use different methods with different @Transactional settings. But Spring proxy may not work for self-invocation (needs external call).

31. What is transaction isolation?

Defines how transaction integrity is visible to other transactions (e.g., READ_COMMITTED, SERIALIZABLE).

@Transactional(isolation = Isolation.READ_COMMITTED)

32. What is the default transaction isolation level in Spring?

• Typically READ_COMMITTED (depends on DB).

33. What is transaction timeout in Spring?

Timeout in seconds before rollback occurs.

@Transactional(timeout = 30)

34. What is the use of @EnableTransactionManagement?

Enables Spring’s annotation-driven transaction management.

@Configuration
@EnableTransactionManagement
public class TxConfig {}

35. What is PlatformTransactionManager?

Interface that Spring uses to manage transactions across different platforms (JPA, JDBC, etc.).

36. What is the difference between programmatic and declarative transaction management?

Type	Description
Declarative	Uses @Transactional (recommended)
Programmatic	Manual transaction management using TransactionTemplate

37. How can AOP be used for logging?

Create an @Aspect class and log before/after method calls.

@Before("execution(* com.example.*.*(..))")
public void logBefore() {
    System.out.println("Method is about to execute");
}

38. What are the limitations of Spring AOP?

• Works only with public methods
• Based on proxies, cannot advise internal calls
• No field-level interception

39. What is JoinPoint and ProceedingJoinPoint?

• JoinPoint: Context info about method (before/after)
• ProceedingJoinPoint: Used in @Around advice to proceed with method execution

@Around("execution(* com.example.service.*.*(..))")
public Object log(ProceedingJoinPoint jp) throws Throwable {
    System.out.println("Before");
    Object result = jp.proceed();
    System.out.println("After");
    return result;
}

40. What is weaving in AOP?

Process of linking aspects with application types at runtime (Spring AOP) or compile time (AspectJ).

41. What is Spring MVC?

Spring MVC is a web framework that separates application logic into:

• Model: Business logic
• View: UI layer (JSP, Thymeleaf, etc.)
• Controller: Handles HTTP requests and binds models to views

42. What are key annotations in Spring MVC?

• @Controller
• @RestController
• @RequestMapping
• @GetMapping, @PostMapping, etc.
• @PathVariable, @RequestParam, @ModelAttribute
• @ResponseBody, @RequestBody

43. What is the difference between @Controller and @RestController?

Annotation	Purpose
@Controller	Returns views (HTML/JSP)
@RestController	Returns data (JSON/XML), auto applies @ResponseBody

44. How to handle HTTP GET and POST in Spring MVC?

@Controller
@RequestMapping("/users")
public class UserController {

    @GetMapping("/{id}")
    public String getUser(@PathVariable String id, Model model) {
        model.addAttribute("user", service.findUser(id));
        return "userDetails";
    }

    @PostMapping("/")
    public String saveUser(@ModelAttribute User user) {
        service.save(user);
        return "redirect:/users";
    }
}

45. What is @RequestParam vs @PathVariable?

• @RequestParam: Query param
• @PathVariable: Part of URL path

@GetMapping("/search")
public String search(@RequestParam String keyword) {}

@GetMapping("/user/{id}")
public String getById(@PathVariable String id) {}

46. What is the use of @ModelAttribute?

• Binds request params to a model object
• Also can pre-populate model attributes

@PostMapping("/register")
public String register(@ModelAttribute User user) {
    // fields auto-mapped from form
}

47. What is @RequestBody and @ResponseBody?

Used in REST APIs.

• @RequestBody: Binds JSON to Java object.
• @ResponseBody: Converts Java object to JSON.

@PostMapping("/save")
@ResponseBody
public User save(@RequestBody User user) {
    return userService.save(user);
}

48. How to validate form data in Spring MVC?

Use @Valid and BindingResult.

@PostMapping("/submit")
public String submit(@Valid @ModelAttribute User user, BindingResult result) {
    if (result.hasErrors()) return "formPage";
    return "success";
}

49. What is DispatcherServlet?

Front Controller in Spring MVC that:

• Receives all HTTP requests
• Delegates to controllers
• Resolves views

Defined in web.xml or Spring Boot auto-configured.

50. What is ViewResolver in Spring MVC?

Maps view names to actual view files (like JSPs or Thymeleaf templates).

@Bean
public InternalResourceViewResolver viewResolver() {
    InternalResourceViewResolver resolver = new InternalResourceViewResolver();
    resolver.setPrefix("/WEB-INF/views/");
    resolver.setSuffix(".jsp");
    return resolver;
}

51. What is HandlerMapping?

It maps requests to appropriate controller methods.

52. How to handle exceptions in Spring MVC?

• Use @ControllerAdvice and @ExceptionHandler.

@ControllerAdvice
public class GlobalExceptionHandler {

    @ExceptionHandler(UserNotFoundException.class)
    public String handleUserNotFound(Model model) {
        model.addAttribute("error", "User not found");
        return "errorPage";
    }
}

53. How does Spring MVC support file upload?

Using MultipartFile.

@PostMapping("/upload")
public String upload(@RequestParam("file") MultipartFile file) {
    // save file logic
}

54. What is WebDataBinder?

Used to bind request parameters to model objects and register custom converters/validators.

55. What is @InitBinder?

Initializes WebDataBinder for a controller method.

@InitBinder
public void initBinder(WebDataBinder binder) {
    binder.registerCustomEditor(Date.class, new CustomDateEditor(...));
}

56. What is @SessionAttributes?

Stores model attributes in the HTTP session.

@SessionAttributes("user")
public class UserController {}

57. What is FlashAttribute?

Used to pass temporary attributes between redirects.

redirectAttributes.addFlashAttribute("message", "Saved successfully!");

58. How does Spring handle internationalization (i18n)?

Using ResourceBundleMessageSource and message.properties files.

@Bean
public MessageSource messageSource() {
    ResourceBundleMessageSource source = new ResourceBundleMessageSource();
    source.setBasename("messages");
    return source;
}

59. What is form backing bean?

Java object that backs an HTML form, typically bound using @ModelAttribute.

60. What are common return types in Spring MVC controller methods?

• String (view name)
• ModelAndView
• ResponseEntity
• void (for raw response)
• Domain object (auto converted in REST)

Spring Boot Intreview

61. What is Spring Boot?

Spring Boot is an opinionated framework built on Spring that helps developers create stand-alone, production-ready applications quickly with minimal configuration.

62. What are the key features of Spring Boot?

• Auto-configuration
• Embedded servers (Tomcat, Jetty)
• Starter dependencies
• Spring Boot CLI
• Production-ready metrics via Actuator

63. What are Spring Boot Starters?

A set of convenient dependency descriptors to reduce manual configuration.

Examples:

• spring-boot-starter-web
• spring-boot-starter-data-jpa
• spring-boot-starter-security

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-web</artifactId>
</dependency>

64. What is application.properties or application.yml?

Used for external configuration:

server.port=8081
spring.datasource.url=jdbc:mysql://localhost:3306/test

65. How to run a Spring Boot application?

mvn spring-boot:run

or

@SpringBootApplication
public class App {
    public static void main(String[] args) {
        SpringApplication.run(App.class, args);
    }
}

66. What is @SpringBootApplication?

It combines:

• @Configuration
• @EnableAutoConfiguration
• @ComponentScan

67. What is Spring Boot Actuator?

Provides production-ready endpoints like:

• /actuator/health
• /actuator/metrics
• /actuator/info

Enable in application.properties:

management.endpoints.web.exposure.include=*

68. What is the use of SpringApplication.run()?

It:

• Starts Spring context
• Triggers auto-configuration
• Starts embedded server

69. How to disable specific auto-configuration?

Use exclude in @SpringBootApplication:

@SpringBootApplication(exclude = DataSourceAutoConfiguration.class)

70. What are some common Spring Boot annotations?

• @SpringBootApplication
• @EnableAutoConfiguration
• @RestController
• @Value
• @Component, @Service, @Repository

Spring Security Intreview

71. What is Spring Security?

A powerful authentication and authorization framework for securing Spring-based applications.

72. What are the core features of Spring Security?

• Authentication
• Authorization
• Protection against CSRF, Session Fixation
• Password encoding
• Method-level security

73. How to secure a Spring Boot application with basic auth?

In application.properties:

spring.security.user.name=admin
spring.security.user.password=admin123

74. How to configure custom login in Spring Security?

@Override
protected void configure(HttpSecurity http) throws Exception {
    http
        .formLogin()
        .loginPage("/login")
        .permitAll()
        .and()
        .authorizeRequests()
        .anyRequest().authenticated();
}

75. What is the difference between Authentication and Authorization?

• Authentication: Verifying identity (e.g., username/password)
• Authorization: Verifying access rights (e.g., roles/permissions)

76. What is UserDetailsService?

An interface used to fetch user details for authentication.

@Service
public class MyUserDetailsService implements UserDetailsService {
    @Override
    public UserDetails loadUserByUsername(String username) {
        return new User("admin", "{noop}pass", List.of(new SimpleGrantedAuthority("ROLE_USER")));
    }
}

77. What is CSRF and how to handle it?

CSRF (Cross-Site Request Forgery) is an attack where a user is tricked into submitting unwanted actions.

Spring enables CSRF protection by default.

To disable (not recommended):

http.csrf().disable();

78. What is the purpose of PasswordEncoder?

Used to hash passwords securely.

@Bean
public PasswordEncoder passwordEncoder() {
    return new BCryptPasswordEncoder();
}

79. What are method-level security annotations?

• @Secured("ROLE_ADMIN")
• @PreAuthorize("hasRole('ADMIN')")
• @PostAuthorize(...)

Enable with:

@EnableGlobalMethodSecurity(prePostEnabled = true, securedEnabled = true)

80. How to allow specific endpoints without authentication?

http.authorizeRequests()
    .antMatchers("/public/**").permitAll()
    .anyRequest().authenticated();

Spring Data JPA Interview

81. What is Spring Data JPA? Java Persistence API

A Spring project that simplifies JPA-based data access by reducing boilerplate code. It automatically implements repositories based on interfaces.

82. What is a Repository in Spring Data JPA?

A central interface for CRUD operations.

public interface UserRepository extends JpaRepository<User, Long> {
    List<User> findByName(String name);
}

83. Difference between CrudRepository, JpaRepository, PagingAndSortingRepository?

Interface	Features
CrudRepository	Basic CRUD operations
PagingAndSortingRepository	Adds pagination and sorting
JpaRepository	Includes all above + batch operations

CrudRepository -> PagingAndSortingRepository -> JpaRepository

84. What are derived query methods in Spring Data?

You can define queries based on method names.

List<User> findByEmail(String email);
List<User> findByAgeGreaterThan(int age);

85. How to write custom queries using @Query?

@Query("SELECT u FROM User u WHERE u.email = :email")
User getUserByEmail(@Param("email") String email);

86. What is @Modifying annotation?

Used with @Query for insert, update, delete operations.

@Modifying
@Query("DELETE FROM User u WHERE u.active = false")
void deleteInactiveUsers();

87. How to enable pagination in Spring Data?

Use Pageable and Page.

<User> findAll(Pageable pageable);

88. What is lazy vs eager loading in JPA?

• Lazy: Loads related data only when accessed.
• Eager: Loads all related data immediately.

@OneToMany(fetch = FetchType.LAZY) // or EAGER
private List<Order> orders;

89. How to handle transactions in Spring?

Use @Transactional on service methods.

@Transactional
public void updateUser(User user) {
    // rollback if exception occurs
}

90. What is EntityManager and when is it used?

JPA interface for interacting with persistence context.
Used when more control is needed over queries and transactions.

@PersistenceContext
private EntityManager em;

Spring Testing

91. How to test Spring components?

Use Spring TestContext framework with JUnit 5 or TestNG.

@SpringBootTest
class MyServiceTest {
    @Autowired MyService service;
}

92. What is @MockBean in Spring Boot tests?

Replaces a bean with a Mockito mock.

@MockBean
private UserRepository userRepo;

93. What is @DataJpaTest?

Used to test only JPA components.

@DataJpaTest
class RepoTest {
    @Autowired UserRepository repo;
}

94. What is @WebMvcTest?

Used to test only Spring MVC components like controllers.

Spring AOP

95. What is Spring AOP?

Aspect-Oriented Programming — separates cross-cutting concerns like logging, security.

Common annotations:

• @Aspect
• @Before, @After, @Around

@Aspect
@Component
public class LoggingAspect {
    @Before("execution(* com.example.service.*.*(..))")
    public void logBefore(JoinPoint jp) {
        System.out.println("Method called: " + jp.getSignature());
    }
}

96. What are Pointcut and Advice?

• Pointcut: Expression to match join points (methods)
• Advice: Code executed at matched point (before, after, etc.)

Spring Cloud & Microservices

97. What is Spring Cloud?

Set of tools for building microservices:

• Service Discovery (Eureka)
• Load Balancing (Ribbon)
• Config Server
• Circuit Breaker (Resilience4j, Hystrix)
• API Gateway (Zuul, Spring Cloud Gateway)

98. What is Spring Cloud Config Server?

Centralized configuration for all microservices.

99. What is Eureka Server?

Service Registry used for service discovery.

@EnableEurekaServer
@SpringBootApplication
public class EurekaApp {}

Clients register with:

@EnableEurekaClient

100. What are some best practices in Spring development?

• Use constructor injection
• Avoid field injection
• Use @Transactional on service layer
• Follow layered architecture
• Use profiles for environment configuration
• Use @ComponentScan wisely to avoid loading unnecessary beans