60+ Mostly Asked Spring Boot Interview Questions for 3+ Yrs

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Here is a list of 60+ Spring Boot interview questions for candidates with 3+ years of experience:

1. What is Spring Boot?

Ans: Spring Boot is an open-source Java framework built on top of the Spring Framework. It helps developers to create easily production-ready, stand-alone, and microservice-based applications with less effort. It provides a various dependency that helps to integrated desired library in the project very easily by just adding in the POM.xml file.

2. Explain the advantages of using Spring Boot.

Ans:

Advantages of Spring Boot

  • Rapid Development: Spring Boot reduces the need for writing a lot of boilerplate code. It allowing developers to focus on business logic rather than dependency configuration.
  • Microservices: Spring boot is the well-suited and popular java framework for building microservices applications. It is possible because of its modular and self-contained nature.
  • Auto-Configuration: It automatically configures application components based on dependencies present in the classpath.
  • Embedded Servers: Spring Boot comes with embedded servers like Tomcat, Jetty, and Undertow, making deployment easier. We need only pom.xml file configurations.
  • Production-Ready: Built-in features like health checks, metrics, and security make applications ready for production deployment.
  • Easy Testing: Spring Boot supports various testing frameworks, making unit and integration testing simpler.

3. What are the Different ways to create a Spring Boot application?

Ans:

Different Ways to Create a Spring Boot Application

  • Using Spring Initializr: You can use the Spring Initializr web tool to generate a Spring Boot project with the required dependencies. Web tool link is https://start.spring.io/
  • Using Spring Boot CLI: The Spring Boot CLI stands for command line interface, that allows you to quickly create Spring Boot applications using the command line.
  • Using IDEs: With the help of IDEs (Integrated Development Environments) like Eclipse, IntelliJ IDEA, and Visual Studio Code you can also create spring boot applications. You need plugins to create Spring Boot projects.
  • Manually: You can manually set up a Spring Boot project by adding the required dependencies and configurations.

4. How does Spring Boot Simplify the Configuration Process?

Ans: Spring Boot simplifies the configuration process in many ways for the developer. It makes setup and configuration process easier for developers. Some key features that simplify the configuration process are Auto-Configuration, Starter Dependencies, Default Configuration, Property Binding, Profile Management, Embedded Servers, Production-Ready Actuators, Command-Line Interface (CLI) etc.

5. What is the purpose of the @SpringBootApplication annotation?

Ans: @SpringBootApplication annotation is used to mark the main class of a Spring Boot application. It is basically a starting point of the spring boot applications. It combines three annotations: @SpringBootConfiguration, @EnableAutoConfiguration, and @ComponentScan.

6. Explain the auto-configuration feature in Spring Boot.

Ans: Spring Boot’s auto-configuration automatically configures Spring beans based on the libraries and dependencies detected on the classpath. It eliminates the need for manual bean configuration, making the application setup more convenient and faster.

7. How can you customize the default behavior of Spring Boot?

Spring Boot default behavior can be customized by the providing your own configuration classes, properties, and beans. Or we can also customized by overriding auto-configured beans or properties, as per our specific needs of the application.

8. What is Spring Boot Actuator?

Spring Boot Actuator is a set of monitoring tool provided by the spring boot. It helps in production to monitor the spring boot application health. It helps to monitor and manage applications by exposing various endpoints, such as health, metrics, info, and more.

9. How do you enable Actuator endpoints in a Spring Boot application?

Actuator endpoints can be enabled by adding the spring-boot-starter-actuator dependency to your project’s pom.xml file. The endpoints are enabled by default, but you can configure which ones to expose and their properties.

10. What are some commonly used Actuator endpoints?

/actuator/health: Provides information about the health of the application.

/actuator/metrics: Exposes application metrics.

/actuator/info: Displays custom application information.

/actuator/env: Shows properties from the application’s environment.

11. How can you secure Actuator endpoints in Spring Boot?

Actuator endpoints are sensitive by default. If not secure, any one can access it. So for that reason they require appropriate security configuration. You can secure them by configuring authentication and authorization settings in the application’s configuration files.

12. What is the purpose of the @RestController annotation?

In Spring Boot Framework, @RestController annotation is used to indicate that a class is a specialized version of the @Controller class. It is used in building RESTful web services. It combines @Controller and @ResponseBody, indicating that the methods in the class return the response body directly. List of the @RestController annotations purpose are Creating REST Endpoints, Response Serialization, No Need for @ResponseBody etc.

13. Explain the difference between @Controller and @RestController in Spring Boot.

In Spring Boot, both @Controller and @RestController are used to handle HTTP requests and build web applications.

@Controller

  • The @Controller annotation is used to mark a class as a Spring MVC controller.
  • Controllers are responsible for handling incoming HTTP requests, processing them, and returning an appropriate response. They are commonly used to create dynamic web pages where the response might include HTML templates and view rendering.
  • Methods within a @Controller class are typically responsible for returning logical view names, which are resolved to actual view templates for rendering.

@RestController

  • The @RestController annotation is a specialized version of @Controller that is tailored for building RESTful web services.
  • Classes annotated with @RestController still handle incoming HTTP requests, but their primary focus is on returning data in various formats like JSON or XML, rather than rendering views.
  • Methods within a @RestController class automatically have the @ResponseBody annotation applied to them, meaning that the return values of these methods are directly serialized into the response body.

14. What is Spring Data JPA?

Spring Data JPA is a subproject of the Spring Framework. It provides a high-level abstraction over the Java Persistence API (JPA) standard for working with relational databases. It simplifies the process of interacting with databases and reduces the amount of boilerplate code required for common database operations like CRUD operations and querying databases.

15. How do you define database connections in Spring Boot?

Database connections in Spring Boot can be configure properties in the application.properties or application.yml file. Spring Boot provides auto-configuration for various databases, and you can also customize the configuration.

application.properties

# Database configuration
spring.datasource.url=jdbc:mysql://localhost:3306/mydb
spring.datasource.username=myuser
spring.datasource.password=mypassword
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver

application.yml

# Database configuration
spring:
  datasource:
    url: jdbc:mysql://localhost:3306/mydb
    username: myuser
    password: mypassword
    driver-class-name: com.mysql.cj.jdbc.Driver

16. Explain the use of Spring Boot Starter POMs.

Starter POMs are a set of convenient dependency descriptors that can be included in your project’s build configuration (like pom.xml) to automatically manage the dependencies required for specific functionalities, such as web, data, security, etc.

17. How can you handle exceptions in a Spring Boot application?

Exception handling is a critical aspect of building robust and user-friendly applications. In Spring Boot, there are several mechanisms to manage exceptions gracefully, ensuring that your application can recover from errors or provide meaningful feedback to the user.

Centralized Exception Handling with @ControllerAdvice

Spring Boot allows for centralized exception handling through the @ControllerAdvice annotation. This approach lets you create a global exception handler class that can catch exceptions thrown by any controller in your application, eliminating the need for repetitive error handling code within individual controllers.

Usage: Annotate a class with @ControllerAdvice and use @ExceptionHandler methods within it to handle different types of exceptions.

Custom Exception Classes with @ResponseStatus

For more control, you can define custom exception classes and annotate them with @ResponseStatus to indicate the HTTP status code when an exception is thrown.

18. What is the purpose of the @ComponentScan annotation?

@ComponentScan enables Spring to detect and register beans automatically. It scans the package and its sub-packages where it’s placed for classes annotated with @Component, @Service, @Repository, @Controller, etc., and registers them as beans in the Spring application context. This process eliminates the need for manual bean registration, facilitating rapid development and cleaner code.

Customization and Flexibility

  • Custom Scanning: Developers can customize the base package to scan by specifying the basePackages or basePackageClasses attribute of the @ComponentScan annotation. This is particularly useful when your components are located in packages outside of the main application package.
  • Filtering: @ComponentScan allows for the inclusion or exclusion of components through filters using includeFilters and excludeFilters attributes. This provides finer control over which components are registered.

19. Explain the Concept of Dependency Injection in Spring Boot.

Dependency Injection (DI) is a fundamental design pattern in Spring Boot, central to the framework’s Inversion of Control (IoC) principle. It’s a technique to achieve loose coupling between classes and their dependencies, making an application more modular, easier to test, and maintain.

Types of Dependency Injection in Spring Boot

Constructor Injection

Dependencies are provided through a class constructor.

@Component
public class MyService {

    private final MyRepository myRepository;

    @Autowired
    public MyService(MyRepository myRepository) {
        this.myRepository = myRepository;
    }
}

Setter Injection

Dependencies are provided through setter methods.

@Component
public class MyService {

    private MyRepository myRepository;

    @Autowired
    public void setMyRepository(MyRepository myRepository) {
        this.myRepository = myRepository;
    }
}

Field Injection

Dependencies are injected directly into the class fields.

@Component
public class MyService {

    @Autowired
    private MyRepository myRepository;
}

Practical Example

Consider a service class in a Spring Boot application that requires a repository class to access the database. Instead of instantiating the repository class inside the service class, Spring Boot can inject this dependency through the constructor or a setter method annotated with @Autowired. This approach decouples the service class from the specific implementation of the repository, making the service class easier to test and maintain.

20. What is the Difference between @Autowired and @Inject annotations?

Feature@Autowired@Inject
SourceSpring FrameworkJava standard (JSR-330)
FlexibilityMore flexible with additional options like required=falseSimpler, without extra configuration options
UsagePredominantly used in Spring projects for seamless integration with Spring featuresCan be used in any Java project, promoting portability and adherence to standard
OptionsAllows specifying whether a dependency is required or notProvides straightforward dependency injection without additional options
CompatibilitySpecific to Spring, not natively supported outside Spring contextSupports use in various Java environments, encouraging use in diverse projects

This table summarizes the main differences, making it clear that @Autowired offers Spring-specific enhancements and flexibility, while @Inject adheres to Java standards and promotes broader compatibility.

21. How do you handle form submissions in Spring Boot?

Handling form submissions in Spring Boot involves creating a controller to process the form data, defining a model to bind form data, and setting up a view template to display the form.

Here’s a step-by-step guide:

1. Define a Model Class

First, define a model class that corresponds to the data you expect from the form. Spring uses this class to bind form data to objects.

public class User {
    private String name;
    private String email;
    // No-argument constructor
    public User() {
    }
    // Parameterized constructor
    public User(String name, String email) {
        this.name = name;
        this.email = email;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getEmail() {
        return email;
    }
    public void setEmail(String email) {
        this.email = email;
    }
}

2. Create a Controller

Create a controller with methods to show the form and to handle the form submission. Use @GetMapping to display the form and @PostMapping to process the form submission.

@Controller
public class UserController {

    @GetMapping("/register")
    public String showForm(Model model) {
        model.addAttribute("user", new User());
        return "register_form"; // Thymeleaf template
    }

    @PostMapping("/register")
    public String submitForm(@ModelAttribute("user") User user) { 
        System.out.println(user);
        return "register_success"; // Success template
    }
}

3. Create the Form in a View Template

Assuming you’re using Thymeleaf as your template engine, create an HTML form in the register_form.html file. Use Thymeleaf syntax to bind form fields to the model attributes.

<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
<head>
    <title>Register</title>
</head>
<body>
<form action="#" th:action="@{/register}" th:object="${user}" method="post">
    <label for="name">Name:</label>
    <input type="text" id="name" th:field="*{name}" />
    
    <label for="email">Email:</label>
    <input type="email" id="email" th:field="*{email}" />
    
    <button type="submit">Submit</button>
</form>
</body>
</html>

4. Process the Form Submission

In the submitForm method of your controller, you can process the form submission. Here, you might save the data to a database, send an email, or perform other business logic.

5. Create a Success Page

After the form is submitted, users can be redirected to a success page. Create a simple register_success.html to inform the user of the successful submission.

<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
<head>
    <title>Registration Successful</title>
</head>
<body>
    <h1>Registration Successful!</h1>
    <p>Thank you for registering with us.</p>
</body>
</html>

22. Explain the concept of Profiles in Spring Boot.

Profiles in Spring Boot are a powerful feature that allows developers to define sets of configuration and beans that are only active in certain environments. This means you can have different configurations for development, testing, production, etc., without needing to change your code.

What Are Profiles?

Imagine you’re a chef preparing to cook both a breakfast dish and a dinner dish. You wouldn’t use the same ingredients and cooking methods for both, right? Similarly, in software development, you might not want the same settings (like database connections or external service URLs) for development, testing, and production environments. Profiles in Spring Boot let you choose the right “ingredients” for each situation.

Example

Let’s say you have two profiles: dev for development and prod for production. Your dev profile might connect to a local database and use dummy data, while your prod profile connects to a real, live database. You can specify which profile to use when you start your application, and Spring Boot takes care of the rest, making sure the right configurations are applied.

Activating Profiles

You can activate profiles in several ways:

  • Setting an environment variable before starting your application.
  • Using a JVM system property when you run your application.
  • Specifying in your application.properties or application.yml file with the spring.profiles.active property.

23. How can you Implement Caching in a Spring Boot Application?

Implementing caching in a Spring Boot application is like giving your application a memory boost. It helps your application to remember things it has already done, so it doesn’t have to do them again. This can make your application faster, especially if it often does the same tasks.

Steps to implement Caching

Step1: Add Caching Dependencies

First, add Spring Boot’s caching starter to your pom.xml or build.gradle file. This step is like getting the tools you need.

If you’re using Maven, add this to your pom.xml:

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

For Gradle, add this line to your build.gradle:

implementation 'org.springframework.boot:spring-boot-starter-cache'

Step 2: Enable Caching

Next, turn on caching in your application. It’s like flipping a switch to activate caching. Add @EnableCaching annotation to one of your configuration classes, usually the main application class.

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

Step 3: Use Cache Annotations

Now, decide what data you want to cache. Use annotations to tell Spring Boot what to remember and when.

  • @Cacheable: Use this on methods to cache their results. The first time the method is called, its result is stored in cache. Later calls with the same arguments return the cached result.
  • @CachePut: Updates the cache with the result of the method it annotates every time the method is called.
  • @CacheEvict: Removes data from the cache. Useful for deleting outdated or unused data.

Step 4: Configure the Cache

Configure cache properties in your application.properties or application.yml. This step is like setting up rules for how the cache should work.

For example, to specify the cache names and other settings, add to your application.properties:

spring.cache.cache-names=books, authors
spring.cache.caffeine.spec=maximumSize=500,expireAfterAccess=600s

24. What is the purpose of the @Scheduled annotation?

The <strong>@Scheduled</strong> annotation in Spring Framework is used to define methods that should be executed at regular intervals or at specific times. It enables developers to easily schedule tasks without the need for manual timers or schedulers.

It Supports various ways to specify when the task should run, including fixed-rate, fixed-delay, and cron expressions, offering flexibility to address different scheduling needs.

  • Fixed-rate scheduling runs the specified task at a fixed interval every time the previous task completes.
  • Fixed-delay scheduling runs the task with a fixed delay between the completion of the last invocation and the start of the next.
  • Cron expression scheduling allows for more complex scheduling patterns, such as “every day at 6 pm”, or “every weekday at 8 am”.

To use <strong>@Scheduled</strong>, you need to enable scheduling in your Spring application, typically done with the @EnableScheduling annotation on one of your configuration classes. This tells Spring to look for @Scheduled annotations and process them accordingly.

Example of @Scheduled

import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;

@Component
public class ScheduledTasks {
    @Scheduled(fixedRate = 3000)
    public void reportCurrentTime() {
        System.out.println("Current time: " + System.currentTimeMillis());
    }
}

25. Explain the role of Spring Boot Starters in the Development Process.

Spring Boot Starters streamline the development process by pre-packaging sets of dependencies and auto-configuration logic needed for specific types of projects.

Some key points

  • Simplify Dependency Management: Starters bundle related dependencies together, so developers only need to include a single starter dependency for a specific functionality, such as web applications, data access, or security, instead of manually managing multiple related libraries.
  • Ensure Compatibility: They manage version compatibility of included libraries, reducing the risk of version conflicts and saving developers the hassle of version management.
  • Accelerate Project Setup: By providing a ready-to-use configuration, starters allow developers to quickly bootstrap new projects with less boilerplate code and configuration, enabling a focus on business logic from the get-go.
  • Promote Best Practices: Spring Boot starters are designed based on the best practices and recommendations for using the Spring framework, helping developers adhere to industry standards.

26. What is the purpose of the @EnableAutoConfiguration annotation?

The @EnableAutoConfiguration annotation in Spring Boot is designed to simplify the configuration process of your application. It automatically configures your Spring application based on the dependencies present on the classpath.

@EnableAutoConfiguration tells Spring Boot to start adding beans based on classpath settings, other beans, and various property settings. For instance, if Spring MVC is on the classpath, Spring Boot automatically sets up a web application context and configures a dispatcher servlet.

Typically, we won’t use @EnableAutoConfiguration directly; instead, we’ll use the @SpringBootApplication annotation, which is a convenience annotation that includes @EnableAutoConfiguration, @ComponentScan, and @Configuration.

27. How can you enable cross-origin requests in a Spring Boot application?

Enabling cross-origin requests in a Spring Boot application is essential for allowing web applications hosted on different domains to interact with your server. This can be achieved using Spring Security and the @CrossOrigin annotation or by global configuration.

Using @CrossOrigin Annotation

Method-Level Cross-Origin Configuration:

You can annotate individual controller methods with @CrossOrigin to enable cross-origin requests specifically for those endpoints.

@RestController
public class TestController {
    @CrossOrigin
    @GetMapping("/example")
    public String example() {
        return "Cross-Origin Requests";
    }
}

Controller-Level Cross-Origin Configuration:

Placing the @CrossOrigin annotation at the class level enables CORS for all handler methods within that controller.

@CrossOrigin
@RestController
public class TestController{
    // All endpoints in this controller are cross-origin enabled
}

28. Explain the concept of Spring Boot Actuator metrics.

Spring Boot Actuator is a powerful set of features designed to help you monitor and manage your Spring Boot applications. One of its key components is the ability to gather various metrics about your application’s runtime behavior and health.

29. What is the purpose of the @Transactional annotation?

Think of the @Transactional annotation in Spring like a safety net for your operations that involve changing data (like updating, inserting, or deleting information in a database).

Imagine you’re organizing a bookshelf, and you have a rule: if you add a new book, you must also make a note of it in your catalog. Both steps—adding the book and updating the catalog—need to happen together to keep everything in order. If you drop the book and it gets damaged, you wouldn’t add it to the catalog. Both actions are all or nothing.

Here’s how @Transactional works in this scenario:

  1. Start: When you start organizing (or when a method marked with @Transactional starts), you’re saying, “Let’s begin. If anything goes wrong, we’ll pretend this never happened.”
  2. Do the Work: You add the book to the shelf and update the catalog (or the method does its work, like updating data in a database).
  3. Finish Successfully: If all goes well (no dropped books), you finalize the catalog. This is like committing the transaction, making all changes permanent.
  4. Oops!: If you drop the book (or an error occurs), you don’t add it to the catalog and put everything back as it was. This is like rolling back the transaction, where no changes are saved.
@Transactional
public void updateUser(Long userId, String name, String email) {
    // Fetch user from the database
    User user = userRepository.findById(userId);
    // Update user's name 
    user.setName(name);
    // Update user's email
    user.setEmail(email); 
    userRepository.save(user);
}

By marking updateUser with @Transactional, you’re telling Spring: “Make sure either both the name and email are updated, or neither if something goes wrong. Keep it all in a neat package.”

30. How can you implement security in a Spring Boot application?

31. Explain the role of the Spring Boot DevTools.

Spring Boot DevTools is a set of tools designed to make the development process with Spring Boot faster and more efficient. DevTools monitors changes in your project files. When you save a change to any class or resource, it automatically restarts your application. This restart is faster than a cold start because DevTools uses two classloaders to keep the base application context cached.

Enabling Spring Boot DevTools

For Maven:

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-devtools</artifactId>
        <scope>runtime</scope>
        <optional>true</optional>
    </dependency>
</dependencies>

32. What is the purpose of the @RequestMapping annotation?

33. How can you enable HTTP compression in Spring Boot?

The @RequestMapping annotation in Spring Framework is used to map web requests to specific handler functions. It’s a central feature in Spring MVC (Model-View-Controller) and Spring WebFlux frameworks, enabling the creation of web applications.

@RequestMapping can be applied at the class or method level to specify which URL paths are handled by which controller methods.

While handling web requests, it’s crucial to differentiate between different types of HTTP operations (GET, POST, PUT, DELETE, etc.). @RequestMapping allows specifying the HTTP method a particular handler should respond to using its method attribute.

Example

@RequestMapping("/print")
public String printSpring() {
    return "Hello, Spring!";
}

34. Explain the concept of internationalization in Spring Boot.

Internationalization (i18n) in Spring Boot refers to the process of designing and developing applications that can be easily adapted to different languages and locales.

In Spring Boot, internationalization is typically implemented using message sources. A message source is a repository of messages, where each message corresponds to a text string in the application. These messages are stored in external properties files, one for each supported locale.

Example:

Suppose you have a message properties file named messages_en.properties with the following content:

message.language=Hello, {0}! This is english language.

In your Spring Boot application code, you can retrieve and interpolate this message as follows:

@Autowired
private MessageSource messageSource;

public String getMessage(String name, Locale locale) {
    return messageSource.getMessage("message.language", new Object[]{name}, locale);
}

35. What is Spring Boot Data REST?

Spring Boot Data REST is a powerful feature of the Spring Boot framework that simplifies the development of RESTful APIs for interacting with your data model. It allows you to expose your Spring Data repositories as RESTful endpoints with minimal configuration, enabling CRUD (Create, Read, Update, Delete) operations on your domain entities over HTTP.

Example

Suppose you have a User entity managed by a Spring Data repository:

public interface UserRepository extends JpaRepository<User, Long> {
}

By simply adding the @RepositoryRestResource annotation to your repository interface, Spring Boot Data REST will automatically expose CRUD endpoints for your User entity at /users.

@RepositoryRestResource
public interface UserRepository extends JpaRepository<User, Long> {
}

36. How can you enable Swagger documentation in a Spring Boot application?

To enable Swagger documentation in a Spring Boot application, you can use the Swagger UI and Swagger annotations to generate interactive API documentation.

Add Swagger Dependencies

For Maven:

<dependency>
    <groupId>io.springfox</groupId>
    <artifactId>springfox-boot-starter</artifactId>
    <version>3.0.0</version>
</dependency>

For Gradle:

implementation 'io.springfox:springfox-boot-starter:3.0.0'

37. Explain the purpose of the @Value annotation in Spring Boot.

The @Value annotation in Spring Boot is used to inject values from external properties files, environment variables, or system properties into Spring components such as beans, fields, or method parameters. It allows developers to externalize configuration and avoid hardcoding values directly into the code, promoting better maintainability and flexibility.

Spring Boot encourages externalizing configuration to separate files (e.g., application.properties or application.yml) instead of embedding it directly into the code. The @Value annotation facilitates the injection of these externalized configuration values into Spring components.

Example

@Value("${app.name}")
private String appName;

In this example, the value of ${app.name} is injected into the appName field from the application.properties or application.yml file.

38. What is the purpose of the @ConfigurationProperties annotation?

The @ConfigurationProperties annotation in Spring Boot is used to bind external configuration properties directly to Java objects. It provides a convenient way to map properties from configuration files (e.g., application.properties or application.yml) to fields of a POJO (Plain Old Java Object), allowing for type-safe and structured access to configuration values.

Example

1). Define Configuration POJO:

@Component
@ConfigurationProperties(prefix = "app")
public class AppConfig {
    private String name;
    private int age; 
}

2). Bind Configuration Properties:

# application.yml
app:
  name: "MyApp"
  age: 1

3). Access Configuration Properties:

@Autowired
private AppConfig appConfig;

public void getValues() {
    String appName = appConfig.getName();
    int appAge = appConfig.getAge();
}

39. How can you perform unit testing in Spring Boot?

40. Explain the concept of application.properties in Spring Boot.

The application.properties file in Spring Boot plays a crucial role in externalizing configuration from the application code. It allows developers to define various settings and preferences for a Spring Boot application in a simple, key-value format. This approach enables easy management of application behavior without changing the code, making your application adaptable to different environments.

Spring Boot allows for defining environment-specific properties (e.g., application-dev.properties for development, application-prod.properties for production) that override the default configurations in application.properties when the corresponding profile is active.

Example

# Server configuration
server.port=8080

# Database configuration
spring.datasource.url=jdbc:mysql://localhost:3306/mydb
spring.datasource.username=dbusername
spring.datasource.password=dbpassword

41. What is the purpose of the Spring Boot Actuator health check?

The Spring Boot Actuator health check is a critical feature for monitoring and managing the health of a Spring Boot application. It provides a simple, yet comprehensive way to check the status of your application and its connected services.

Example

Accessing the health information typically involves making a GET request to the /actuator/health endpoint. The response includes the overall health status and details of each health indicator:

{
  "status": "UP",
  "components": {
    "db": {
      "status": "UP",
      "details": {
        "database": "MySQL",
        "validationQuery": "isValid()"
      }
    },
    "diskSpace": {
      "status": "UP",
      "details": {
        "total": 500000000,
        "free": 250000000,
        "threshold": 10000000
      }
    },
    // Other health indicators...
  }
}

42. How can you implement distributed logging in a Spring Boot microservice architecture?

43. Explain the concept of Spring Boot starters and parent POMs.

Spring Boot Starters:

Starters are a set of convenient dependency descriptors that you can include in your project to get a fully configured set of dependencies required for a specific feature or module. The primary goal of starters is to reduce the effort required to configure a Spring Boot application.

Examples:

  • spring-boot-starter-web: For building web applications using Spring MVC. Includes Tomcat as the default embedded container.
  • spring-boot-starter-data-jpa: For using Spring Data JPA with Hibernate.
  • spring-boot-starter-security: For adding Spring Security to an application.

Parent POM:

The Spring Boot parent POM (Project Object Model) is a special Maven project that provides dependency management and default configurations for your Spring Boot applications. By inheriting from the Spring Boot parent POM, your project can leverage the pre-defined setup provided by Spring Boot, including plugin configurations, resource filtering settings, and more.

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.3.1.RELEASE</version>
</parent>

44. What is the purpose of the @EnableCaching annotation?

The @EnableCaching annotation in Spring Framework is used to enable caching capabilities within a Spring application. It’s a declarative way to add cache support, optimizing performance by reducing the need to repeatedly compute or fetch data that has been previously retrieved.

You can use annotations like @Cacheable, @CachePut, and @CacheEvict on methods to control how their results are cached.

  • @Cacheable can be used to cache the method’s response.
  • @CachePut updates the cache with the method’s result.
  • @CacheEvict removes entries from the cache, either before or after the method execution.

45. How can you handle file uploads in Spring Boot?

46. Explain the use of the @Qualifier annotation in Spring Boot.

The @Qualifier annotation in Spring Boot is used to resolve ambiguities when more than one bean of the same type is available in the Spring container. It helps specify which bean should be injected into a class when there are multiple candidates.

Purpose:

  • Disambiguation: When multiple beans of the same type exist, @Qualifier helps to distinguish between them, allowing developers to specify which bean should be autowired.
  • Fine-grained Control: It provides more control over dependency injection, ensuring that the correct bean is wired where it’s needed.

Example:

Suppose you have two beans of the same type that are configured in your Spring application context.

@Configuration
public class AppConfig {

    @Bean
    public Vehicle car() {
        return new Car();
    }

    @Bean
    public Vehicle auto() {
        return new Auto();
    }
}

Inject with @Qualifier: When injecting a bean of type Vehicle, use the @Qualifier annotation to specify which bean should be injected.

@Component
public class VehicleService {

    private Vehicle vehicle;

    @Autowired
    public VehicleService(@Qualifier("car") Vehicle vehicle) {
        this.vehicle = vehicle;
    }
}

In this example, the VehicleService class requires a Vehicle bean. The @Qualifier annotation with the value "car" indicates that the car bean should be injected, resolving the ambiguity between car and auto.

47. What is the purpose of the @Transactional annotation in Spring Boot?

48. How can you handle asynchronous tasks in a Spring Boot application?

Handling asynchronous tasks in a Spring Boot application allows for non-blocking operations, where tasks can run in the background without holding up the main execution flow. This is particularly useful for operations that are time-consuming, such as sending emails, processing files, or making network calls.

Spring Boot simplifies the execution of asynchronous tasks using the @Async annotation and configuring an executor.

49. Explain the purpose of the @RestControllerAdvice annotation.

The @RestControllerAdvice annotation in Spring Boot is used to handle exceptions across the whole application in a global, catch-all type of way. It’s a specialization of @ControllerAdvice annotation that combines it with @ResponseBody to offer a convenient approach to exception handling with RESTful APIs.

Centralized Exception Handling:

  • Global Scope: It allows developers to define a global exception handling mechanism that applies to all controllers, making the code cleaner and more maintainable by avoiding repetitive local exception handlers.
  • Automatic Response Body Conversion: Since it’s tailored for RESTful services, @RestControllerAdvice ensures that exceptions are automatically converted to JSON or XML responses, adhering to the REST API’s response format.

Example

Annotate a class with @RestControllerAdvice to designate it as a global exception handler.

@RestControllerAdvice
public class GlobalExceptionHandler {

    @ExceptionHandler(ResourceNotFoundException.class)
    public ResponseEntity<Object> handleResourceNotFoundException(ResourceNotFoundException ex) {
        ErrorDetails errorDetails = new ErrorDetails(new Date(), ex.getMessage(), "Resource not found");
        return new ResponseEntity<>(errorDetails, HttpStatus.NOT_FOUND);
    } 
}

50. What is the role of Spring Boot Actuator in monitoring and managing a Spring Boot application?

51. How can you implement OAuth2 authentication in a Spring Boot application?

52. Explain the purpose of the @PathVariable annotation in Spring Boot.

The @PathVariable annotation in Spring Boot is used within Spring MVC or Spring WebFlux to bind a method parameter to a URI template variable. It’s a key feature for building RESTful web services, allowing dynamic values to be passed through URLs.

@PathVariable extracts values from the URI path itself. This is particularly useful for REST APIs where resource identifiers are part of the URL path.

Example

When defining request mappings in a controller, you can specify parts of the URL path as variables using curly braces {}. The @PathVariable annotation is then used to map these variables to method parameters.

@GetMapping("/users/{userId}")
public ResponseEntity<User> getUserById(@PathVariable Long userId) {
    User user = userService.findById(userId);
    return ResponseEntity.ok(user);
}

In this example, {userId} in the URL path is mapped to the userId method parameter, making the actual value of userId in the request URL accessible within the method.

53. What is the purpose of the @Entity annotation in Spring Boot?

The @Entity annotation in Spring Boot, originating from the Java Persistence API (JPA), is used to indicate that a class is an entity in the domain model. An entity represents a table stored in a database, and each instance of the entity corresponds to a row in the table. The primary purpose of the @Entity annotation is to define the class as a JPA entity so that it can be mapped to a database table.

Example:

To use the @Entity annotation, simply annotate the class with @Entity and specify a primary key with @Id:

import javax.persistence.Entity;
import javax.persistence.Id;

@Entity
public class User {

    @Id
    private Long id;
    private String name; 
    // Getters and setters
}

In this example, the User class is mapped to a User table in the database, with id, and <code>name columns corresponding to the class’s fields.

54. How can you configure a connection pool in Spring Boot?

55. Explain the purpose of the @Async annotation in Spring Boot.

The @Async annotation in Spring Boot is used to indicate that a method should be executed asynchronously, meaning it will run on a separate thread, allowing the caller to continue processing without waiting for the method to complete. This is particularly useful for improving the performance of your application by performing long-running tasks in the background.

56. What is the purpose of the Spring Boot Actuator info endpoint?

57. How can you implement rate limiting in a Spring Boot application?

58. Explain the concept of Spring Boot Actuator tracing.

59. What is the purpose of the @ResponseStatus annotation in Spring Boot?

The @ResponseStatus annotation in Spring Boot is used to specify the HTTP status code to be returned by a web request handler method. It allows developers to easily indicate the outcome of an HTTP operation directly from the controller layer of the application.

Example

You can annotate controller methods with @ResponseStatus to indicate the HTTP status code that should be returned after the method execution.

@PostMapping("/items")
@ResponseStatus(HttpStatus.CREATED)
public Item addItem(@RequestBody Item item) {
    return itemService.save(item);
}

In this example, whenever the addItem method is called and successfully completes, the HTTP status 201 Created is returned.

60. How can you configure multiple data sources in a Spring Boot application?

Now, let’s move on to the interview clearing guide. Here are some tips to help you succeed in a Spring Boot interview:

  1. Review the Basics: Ensure you have a strong understanding of the fundamental concepts of Spring Boot, including dependency injection, annotations, and inversion of control.
  2. Hands-on Experience: Be prepared to discuss your experience working with Spring Boot. Showcase any relevant projects or assignments you have completed using the framework.
  3. Understand Spring Boot Features: Familiarize yourself with key Spring Boot features such as auto-configuration, Actuator, data access with Spring Data JPA, security, and caching. Be ready to explain how you have utilized these features in your projects.
  4. Demonstrate Problem-Solving Skills: Expect questions that require you to solve problems related to Spring Boot. Prepare yourself by practicing coding exercises and scenarios that involve troubleshooting and debugging.
  5. Dive into Documentation: Take the time to explore the official Spring Boot documentation. Understand the various configuration options, available annotations, and best practices recommended by the framework.
  6. Stay Up-to-Date: Keep yourself updated with the latest trends and advancements in Spring Boot. Stay informed about new releases, enhancements, and community-driven developments.
  7. Prepare for Common Interview Questions: Review commonly asked interview questions and practice your answers. This will help you articulate your thoughts effectively during the interview.
  8. Showcase your Practical Knowledge: Whenever possible, share examples from your previous projects where you have utilized Spring Boot effectively. Discuss the challenges you faced and how you overcame them.
  9. Be Confident and Professional: Approach the interview with confidence and maintain a professional demeanor throughout. Display your enthusiasm for Spring Boot and your eagerness to learn and grow as a developer.
  10. Ask Questions: At the end of the interview, don’t hesitate to ask questions about the company’s usage of Spring Boot, their development processes, or any other relevant topics. This demonstrates your interest in the role and your desire to understand the organization better.

Remember, preparation is key to success. By following these guidelines, you’ll be well-prepared to clear your Spring Boot interview with confidence. Good luck!