Top 40+ Spring Boot Interview Questions and Answers [2025]

Fresher-Level Spring Boot Interview Questions

The fresher-level questions focus on Spring Boot's core concepts, making them ideal for those new to the framework or anyone wanting to revisit the basics.

These Spring Boot interview questions cover key topics like Spring Boot key features, the role of the @SpringBootApplication annotation, configuration, and more. Mastering these fundamentals is key to understanding how Spring Boot operates.

1. What Is Spring Boot?

This is one of the most commonly asked questions in Spring Boot interview questions. Spring Boot is one of the Java frameworks designed to create production-quality, stand-alone Spring-based applications. It's widely used for building microservices and RESTful web services, making it a top choice for Java development. Spring Boot was created to simplify the setup process by eliminating the need for manual configuration, allowing developers to focus on building their applications.

2. Explain the Key Features of Spring Boot

Spring Boot has its own specific features that distinguish it from its umbrella framework, Spring. It offers several capabilities to speed up and simplify the setup and configuration process.

Here are a few of Spring Boot's main attributes:

• Auto-Configuration: Using the dependencies you've supplied, this feature automatically configures your Spring application. It can also be listed while creating a project using one of the auto-initializers.
• Embedded Servers: Provides WAR file deployment without the requirement for embedded servers like Tomcat, Jetty, or Undertow.
• Embedded In-Memory Database: This provides an H2 database for small-scale projects that use an in-memory mechanism.
• Production-Ready: Offers features like health checks, metrics, and externalized configurations that are ready for production.
• Minimal Configuration: By utilizing convention over configuration concepts, this approach lessens the requirement for complex XML configuration.

3. What Is the Difference Between Spring and Spring Boot?

Spring Boot is one of the sub-frameworks within Spring that is specifically used for creating RESTful applications that provide multiple embedded and monitoring components that further reduce the complexity of the application. This improves the durability of the application and makes it more secure.

Understanding these differences is essential, as they are commonly asked in Spring Boot interview questions and help you grasp the framework's core benefits and real-world applications.

4. Explain the Use of @PathVariable and @RequestParam in Spring Boot

@PathVariable helps extract values from the URI path in Spring Boot, whereas @RequestParam is used to extract query parameters from the URL. Understanding these differences is crucial for developers, as they are commonly asked in Spring Boot interview questions when mapping client requests to controller methods in Spring Boot applications.

5. How Does Spring Boot Handle Dependency Management?

Spring Boot uses a utility called Spring Boot Starter to simplify dependency management. These starters are collections of useful dependency descriptors that you can include in your application. For example, to use Spring Data JPA, simply add the Spring Boot-starter-data-jpa dependency, and it will automatically include all the required dependencies.

Additionally, Maven or Gradle manages these dependencies, and Spring Boot ensures compatibility by maintaining the versions of supported dependencies. This helps eliminate version conflicts and reduces the need for manual version management. Understanding how Spring Boot handles dependencies is a key topic and often appears in most interview questions.

6. Explain the Use of @RestController in Spring Boot

In simple terms, @RestController is used when you want to build a web service that sends data directly to a client, like a web browser or an app. This annotation combines two things: it marks the class as one that will handle web requests, and it tells Spring to return data from methods in this class directly to the client.

The data is automatically converted into formats like JSON or XML, making it easier to develop APIs without manually handling data conversion. Since @RestController is essential for building APIs, it is a common topic to appear in most of the Spring Boot interview questions.

7. What Is application.properties or application.yml in Spring Boot?

In Spring Boot, the application.properties or application.yml file is used for configuring the application. These files allow you to set various properties and settings, such as server port, database connection details, and custom application settings. By placing this configuration in a centralized file, you can easily manage and change them without modifying the code.

The application.yml file uses YAML format, which is more readable for nested configurations, while application.properties is a simple key-value pair format.

Example of application.properties:

# Server configuration
server.port=8080

# Database configuration
spring.datasource.url=jdbc:mysql://localhost:3306/mydatabase
spring.datasource.username=root
spring.datasource.password=password

# JPA (Java Persistence API) settings
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true

Both files serve the same purpose and are loaded by Spring Boot at runtime to configure the application’s behavior. Since configuration management is a crucial topic in Spring Boot, having an understanding of these files for a developer is essential, making it the most frequent question to appear in most of the Spring Boot interview questions.

8. How Do You Configure a Database in Spring Boot?

Spring Boot streamlines database integration through automated configuration and libraries. Here is a quick guide to the key concepts:

• Dependencies: Add Spring Boot-starter-data-jpa dependency (try to use the latest version) to include JPA support and a database driver, such as MySQL’s connector.
• Data Source Configuration: Define connection details (URL, username, password) in application.properties or application.yml. Spring Boot sets up a connection pool automatically.
• JPA (Java Persistence API): JPA simplifies database interactions by allowing you to use Java objects to manage database tables. Entities represent tables, and repositories handle CRUD operations.
• Entity Classes: Annotate classes with @Entity to map them to database tables. Fields in these classes correspond to table columns.
• Repositories: Define interfaces extending JPA Repository to perform database operations with minimal code. Custom queries can be added as needed.
• Configuration Properties: Set properties like spring.datasource.url and spring.jpa.hibernate.ddl-auto in your configuration file to control database connection and schema management.
• Schema Management: Use spring.jpa.hibernate.ddl-auto to manage schema updates, with options like update or create.
• Transaction Management: Manage transactions with the @Transactional annotation to ensure data consistency.

Example: Add this to either your pom.xml or your build.gradle:

Maven:

    <groupId>org.springframework.boot</groupId>
    <artifactId>Spring Boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
</dependency>

Gradle:

implementation 'org.springframework.boot:Spring Boot-starter-data-jpa'
implementation 'mysql:mysql-connector-java'

Configure the following database connectivity properties in your application.properties:

spring.datasource.url=jdbc:mysql://localhost:3306/yourdbname
spring.datasource.username=yourusername
spring.datasource.password=yourpassword
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true

Since database configuration is a critical aspect of Spring Boot development, it frequently appears in Spring Boot interview questions, making it essential for candidates to understand.

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9. What Is Spring Boot Actuator?

Spring Boot Actuator is a rich collection of features that contain a set of tools that offer insights into a Spring Boot application's internal workings. It becomes simpler for developers to watch activity, identify problems, and make sure the application is operating as intended by assisting with monitoring and managing their applications in production using the features of the Actuator.

Purpose of Spring Boot Actuator

The main purpose of Actuator is to give you a detailed view of your application’s health, metrics, and environment without requiring you to manually implement these features. It automatically exposes various endpoints that provide valuable information and operational control over your application.

Key Features of Spring Boot Actuator:

• Health Checks: One of the most critical features is the health check endpoint, which reports the status of the application and its dependencies. For instance, it can check if your database connection is up and running or if any critical component is failing.
• Metrics: Actuator provides detailed metrics about your application, such as memory usage, CPU usage, HTTP request statistics, and garbage collection details. This data is crucial for understanding the performance and resource consumption of your application.
• Environment and Configuration: You can view the current state of your application’s environment, including configuration properties, system properties, environment variables, and more. This helps in troubleshooting configuration issues.
• Logging: The actuator allows you to manage and monitor the application’s logging levels at runtime, allowing you to change them without restarting the application.
• Tracing: It provides traces of HTTP requests and other activities within the application, which is useful for debugging and analyzing the flow of requests through the system.

The actuator automatically exposes several endpoints, each providing different types of information or control over the application:

• /actuator/health: Shows the health status of the application.
• /actuator/metrics: Displays various metrics like JVM memory usage, CPU usage, etc.
• /actuator/env: Exposes the current environment properties.
• /actuator/loggers: Allows you to view and modify the logging levels.
• /actuator/info: Provides general information about the application, like build version, description, etc.

Since Actuator plays a crucial role in application observability, these endpoints can be secured, and you can choose which ones to expose based on your needs. They are useful in both development and production environments. It is often discussed in Spring Boot interview questions, making it important for developers to understand how to configure and use it effectively.

10. What Is @SpringBootTest Used for?

The @SpringBootTest annotation in Spring Boot is used for integration testing by loading the entire application context, similar to how the application runs in production. It ensures that all components, such as the service layer, repository layer, and controller, work together correctly. Understanding the @SpringBootTest usage is crucial for developers, and it is often highlighted in Spring Boot interview questions,

When to use it:

Imagine you are working on a Spring Boot application and want to ensure that your service layer and repository layer function correctly. You wouldn’t typically use it for simple unit tests, as it would be excessive for testing a single method. However, for integration tests—where different parts of your application interact—it is ideal. It’s like saying, “Okay, let’s fire up the whole application and see how these pieces work together.”

11. What Is a Microservice, and How Does Spring Boot Support Microservices?

A microservice is a small, independent service that performs a specific function within a large application. This architecture makes it easier to define and maintain each service, and it can be developed and managed independently.

This concept is frequently asked in most Spring Boot interview questions, as developers must understand microservice architecture. Spring Boot is a framework that simplifies the creation of microservices in Java.

It offers several features to support microservices:

• Easy Setup: Reduces the need for extensive configuration, making it quicker to get started.
• Embedded Servers: Includes servers like Tomcat, so you don’t need to set up an external server.
• RESTful APIs: Makes it straightforward to create RESTful APIs for communication between services.
• Service Discovery: With Spring Cloud, Spring Boot supports service discovery, allowing services to find each other.
• Load Balancing: Spring Cloud also provides tools for load balancing to distribute requests evenly.
• Configuration Management: Spring Cloud Config helps manage configurations across services.
• Monitoring: Spring Boot includes tools for monitoring and tracking the health of services.

12. Explain the Concept of Embedded Servers in Spring Boot

Spring Boot is a stand-alone framework that comes with an embedded server, eliminating the need to install and configure any external server. This reduces complexity by allowing you to avoid deploying your application to an external server, as the server is packaged within the application itself. This makes the deployment and management process easier.

Here are some key points about embedded servers in Spring Boot:

• Default Server: Spring Boot uses Tomcat as the default embedded server. However, you can choose to use Jetty or Undertow if preferred.
• Configuration: You can configure the embedded server through properties files or programmatically. One major configuration might include changing the default port from 8080 to another port (in case another application uses 8080), which can be done by setting the server.port property in your application.properties file. Other server-related properties can also be configured in this file.
• Self-Contained: Since the server is embedded, your application is self-contained. This simplifies deployment because you don't need to install and configure a separate server.
• Flexibility: You can easily switch between different embedded servers by including the appropriate dependencies in your project.

The Spring Boot interview questions discussed above are essential for any fresher, as they establish a foundational understanding of key concepts and practices in Spring Boot development. Grasping these fundamentals is crucial for building a solid skill set and excelling in interviews.

As you progress, you will encounter intermediate-level Spring Boot interview questions that will enhance your knowledge and expertise. This progression will enable you to tackle more complex topics and scenarios, helping you advance your skills in Spring Boot development.

Intermediate-Level Spring Boot Interview Questions

The intermediate-level Spring Boot interview questions delve deeper into Spring Boot's fundamental features, testing your understanding of topics such as dependency injection, RESTful services, security, and data management. These questions are designed for developers with some hands-on experience and aim to evaluate your practical understanding and ability to apply these principles in real-world scenarios.

13. How Do You Write Unit Tests in Spring Boot?

In Spring Boot, writing unit tests is a must to make sure all the parts of your program function as intended. Unit tests concentrate on testing distinct components of your program separately, which aids in the early detection of defects and acts as a safety precaution while reworking code.

This is how you go about it:

• Setting Up the Testing Environment: Spring Boot simplifies testing by providing various annotations and utilities. To get started, ensure that your project includes dependencies for testing, such as JUnit (the default testing framework in Spring Boot) and possibly Mockito (for mocking dependencies).

It sets up a test context that mimics the real application context but isolates it from the components you want to test. This makes it easier to test Spring-managed beans without having to load the entire application.

• Using Annotations to Simplify Testing: Spring Boot provides several annotations that make writing unit tests easier:
• @Test: Marks a method as a test method.
• @SpringBootTest: Often used for integration tests but not typically for unit tests, as it loads the full application context.
• @MockBean and @Autowired: These are used to mock dependencies and inject them into your test class.

However, for unit tests, you will usually rely more on @Mock (from Mockito) and @InjectMocks to create and inject mock dependencies, keeping the test focused on the unit of code you’re testing.

• Mocking Dependencies: Mocking is a technique for creating a fake version of a dependency that returns controlled responses. It allows you to isolate the unit of code you’re testing and avoid relying on external systems like databases or APIs.

For example, if you’re testing a service that depends on a repository, you would mock the repository so that it returns predefined data instead of hitting a real database. This ensures that your test remains fast and reliable.

Consider the following example: Let's assume we need to test the following method within the class DiscountService:

public class DiscountService {
    public double calculateDiscount(String membershipLevel, double purchaseAmount) {
        switch (membershipLevel.toLowerCase()) {
            case "gold":
                return purchaseAmount * 0.20;  // 20% discount
            case "silver":
                return purchaseAmount * 0.10;  // 10% discount
            case "bronze":
                return purchaseAmount * 0.05;  // 5% discount
            default:
                return 0.0;  // No discount
        }
    }
}

The DiscountServiceTest.java would look something similar to:

import static org.junit.jupiter.api.Assertions.assertEquals;
import org.junit.jupiter.api.Test;

public class DiscountServiceTest {

    private final DiscountService discountService = new DiscountService();

    @Test
    public void testGoldMemberDiscount() {
        double discount = discountService.calculateDiscount("gold", 100.0);
        assertEquals(20.0, discount, "Gold members should get a 20% discount");
    }

    @Test
    public void testSilverMemberDiscount() {
        double discount = discountService.calculateDiscount("silver", 100.0);
        assertEquals(10.0, discount, "Silver members should get a 10% discount");
    }

    @Test
    public void testBronzeMemberDiscount() {
        double discount = discountService.calculateDiscount("bronze", 100.0);
        assertEquals(5.0, discount, "Bronze members should get a 5% discount");
    }

    @Test
    public void testNoDiscountForOtherLevels() {
        double discount = discountService.calculateDiscount("platinum", 100.0);
        assertEquals(0.0, discount, "Non-standard membership levels should get no discount");
    }
}

Writing clean, effective unit tests is essential for maintaining high code quality, and this is often a key point highlighted in Spring Boot interviews for development roles.

14. How Do You Create a Simple RESTful Web Service With Spring Boot?

Creating a simple RESTful web service with Spring Boot is straightforward. Here’s a step-by-step guide:

• Set Up Your Project:
• Go to Spring Initializr.
• Select Maven Project, Java, and the latest version of Spring Boot.
• Add the Spring Web dependency.
• Click Generate to download the project, then unzip it.
• Create a Resource Representation Class:
• In your project, create a new package (e.g., com.example.demo).
• Inside this package, create a class named Greeting.java:

public class Greeting {
    private final long id;
    private final String content;

    public Greeting(long id, String content) {
        this.id = id;
        this.content = content;
    }

    public long getId() {
        return id;
    }

    public String getContent() {
        return content;
    }
}

• Create a Controller:
• In the same package, create a class named GreetingController.java:

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

import java.util.concurrent.atomic.AtomicLong;

@RestController
public class GreetingController {
    private static final String template = "Hello, %s!";
    private final AtomicLong counter = new AtomicLong();

    @GetMapping("/greeting")
    public Greeting greeting(@RequestParam(value = "name", defaultValue = "World") String name) {
        return new Greeting(counter.incrementAndGet(), String.format(template, name));
    }
}

• Run Your Application:
• Open the main application class (DemoApplication.java) and run it. Spring Boot will start an embedded server (Tomcat by default).
• Your RESTful web service will be available at http://localhost:8080/greeting .
• Test Your Service:
• Open a web browser or a tool like Postman.
• Navigate to http://localhost:8080/greeting to see the default greeting.
• Add a query parameter to customize the greeting, e.g., http://localhost:8080/greeting?name=Use.

Creating a simple RESTful web service with Spring Boot is essential for developers, as it demonstrates the core concepts of building RESTful web services. It's also often asked in most Spring Boot interview questions.

15. What Is a Spring Boot Starter?

A Spring Boot starter is a convenient way to integrate a collection of useful dependencies into your application. It provides a curated set of interdependent dependencies, making it easier to build Spring-based projects.

Here are some key points about Spring Boot starters:

• Convenience: You don't need to list every single dependency. A starter dependency acts as a package of multiple dependencies grouped together. For example, Spring Boot-starter-web includes an embedded Tomcat server, Spring MVC, and Jackson for JSON handling. This reduces manual effort and simplifies your configuration.
• Consistency: Starters ensure that the dependency versions are compatible with each other and with the Spring Boot version you're using, reducing potential conflicts.
• Reduced Configuration: By using a starter, you can avoid boilerplate configuration and focus on writing your application logic.

Here are some of the widely used Spring Boot starters:

• Spring Boot-starter-web: Facilitates the development of web applications, including RESTful services.
• Spring Boot-starter-data-jpa: Integrates Spring Data JPA and Hibernate for working with databases. Provides functions to perform CRUD operations while dealing with your DB.
• Spring Boot-starter-security: Adds security features to your application.
• Spring Boot-starter-test: Provides testing tools like JUnit, Hamcrest, and Mockito for testing Spring Boot applications.

To use a starter dependency in your project, you need to include it in your pom.xml (for Maven) or build.gradle (for Gradle).

Maven, add the following to your pom.xml:

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

Gradle, add the following to your build.gradle:

implementation 'org.springframework.boot:Spring Boot-starter-web'
OR
api('org.springframework.boot:Spring Boot-starter-web')

You must use the correct version of dependencies according to your project requirements, as version conflicts can cause issues in your codebase, especially depending on the version of Java you're using. This is a core concept in Spring Boot, as it simplifies dependency management and promotes best practices, and it is often covered in most Spring Boot interview questions.

16. What Is the Role of the @SpringBootApplication Annotation?

The @SpringBootApplication annotation is an important annotation in a Spring Boot application, which is used by the compiler to identify the main class in your project. During runtime, this annotation helps in jumping directly to the main class and executing it.

It combines the following three annotations into one:

• @SpringBootConfiguration: This annotation indicates that the class provides configuration for the Spring Boot application.
• @Configuration: This annotation is used to enable Spring Boot's autoconfiguration mechanism, which is used to configure your application based on the dependencies added.
• @ComponentScan: This annotation enables component scanning, which allows Spring to automatically discover and register beans in the package containing your application class and its sub-packages.

Here is a basic example:

package com.org.lambdaTest;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class Reservation {
    public static void main(String[] arguments) { // main class
        SpringApplication.run(Reservation.class, args); // this informs your spring application which class needs to run initially
    }
}

By using @SpringBootApplication, you simplify your configuration by combining three annotations into one, allowing you to use their default attributes. This setup initiates the Spring Boot application and automatically starts the necessary configuration, making it a core concept in Spring Boot, often highlighted in most Spring Boot interview questions.

17. What Is the Purpose of @Component, @Service, and @Repository Annotations?

In Spring, the @Component, @Service, and @Repository annotations are used to define classes that Spring should manage as beans. These annotations are commonly highlighted in most of the Spring Boot interview questions because each one has a specific purpose, though they all serve the general role of marking classes for Spring to handle.

• @Component: The @Component annotation is like the basic building block in a Spring-based project. When you use @Component on a class, you’re informing Spring to recognize that class as something it needs to manage. It’s a generic annotation, so it’s perfect for classes that don’t necessarily fall into a specific category, like utility classes or general-purpose components.

When to Use It: You might use @Component when you’ve got a class that’s part of your application’s core functionality but doesn’t quite fit into the “service” or “repository” categories. For instance, if you have a class that handles some internal processing or utility functions, @Component is a good fit. A real-time example would be to use this annotation for any middle-ware processing.

• @Service: The @Service annotation is a bit more specific. It’s used for classes that contain your business logic. When you use @Service in a class, it’s a signal that this class is where important operations happen. It’s not just a generic component; it’s a key part of the service layer.

When to Use It: You’ll use @Service for classes that perform core operations, like processing data, handling transactions, or coordinating actions between different parts of your application.

• @Repository: The @Repository annotation is all about data access. It’s designed for classes that interact with your database or any data source. When you use @Repository, it provides some additional benefits, like automatic exception translation—meaning that database-specific errors get converted into something that Spring can manage more easily.

When to Use It: You’ll want to use @Repository in classes that deal directly with data—whether you’re retrieving it from a database, saving it, or updating it. If your class is focused on managing how data is accessed and stored, @Repository is the way to go.

18. How Do You Implement Security in a Spring Boot Application?

Implementing security in a Spring Boot application typically involves using Spring Security, a powerful and customizable authentication and access control framework. Here’s a general approach:

• Add Dependencies: Start by including Spring Security in your project. You can do this by adding the following dependency to your pom.xml (for Maven) or build.gradle (for Gradle):

Maven:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>Spring Boot-starter-security</artifactId>
</dependency>

Gradle:

implementation 'org.springframework.boot:Spring Boot-starter-security'

• Using Spring Security in Spring Boot: When you include Spring Security in a Spring Boot project, it automatically secures all HTTP endpoints. By default, it uses basic authentication, requiring a username and password to access the application. However, this is just the starting point, and you can customize the security settings to fit your specific needs.
• Configuring Security: To implement more sophisticated security, you would typically configure Spring Security using a Java class.

This configuration allows you to:

• Define which paths or endpoints are secured and which are open to all users.
• Set up custom login forms instead of the default one provided by Spring Security.
• Implement password encoding for storing passwords securely.
• Specify user roles and configure access rules based on these roles.
• User Details Service: For custom user authentication, Spring Security allows you to connect to a database or any other user store. By implementing a UserDetailsService, you can load user-specific data and manage user credentials in your preferred way, often from a database. This service can also handle different user roles and permissions.
• Advanced Security Features: Spring Security offers many advanced features:
• CSRF Protection: Helps prevent cross-site request forgery attacks.
• HTTPS/SSL: Enforces secure communication over HTTPS.
• OAuth2 Integration: Enables third-party authentication providers like Google or Facebook.

19. How Does Spring Boot Autoconfiguration Work?

Imagine starting a new project with Spring Boot. While using Spring, you would need to manually declare all configurations, but with Spring Boot, instead of manually configuring each component, the heavy lifting for you.

Here's how it works:

• Class Path Scanning: When you start your application, Spring Boot looks at the libraries you’ve included. If it sees spring-webmvc, it knows you’re building a web app and sets up the necessary components for you.
• Conditional Configuration: Spring Boot uses conditions to decide what to configure. For example, it checks if certain classes are available before setting up related beans. This way, it only configures what you actually need.
• Configuration Properties: You can customize these default settings using properties files. Spring Boot binds these properties to Java objects, making it easy to tweak configurations without diving into the code.
• Meta-Annotations: The magic starts with annotations like @SpringBootApplication. This annotation tells Spring Boot to start the autoconfiguration process, setting up everything based on what’s in your classpath.
• Exclusions and Customization: If you don’t want certain configurations, you can exclude them. You can also define your own beans to override the defaults.

Example:

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

This approach to autoconfiguration in Spring Boot eliminates a lot of repetitive setups, allowing you to focus on building the functionality of your application. It's a concept that is frequently highlighted in most of the Spring Boot interview questions to understand Spring Boot's ease of use and configuration management.

20. What Are Custom Starters, and How Do You Create One?

Custom starters in Spring Boot are essentially pre-packaged sets of dependencies and configurations that simplify the setup for specific functionalities. They help developers avoid repetitive configuration tasks and quickly get started with their projects.

Here’s a step-by-step guide to creating your own custom starter:

• Create a New Project: Start by creating a new Maven or Gradle project. This project will contain your custom starter.
• Add Dependencies: Include the necessary dependencies for the functionality you want to provide. For example, if your starter is for a custom logging library, add that library as a dependency.
• Auto-Configuration Class: Create an auto-configuration class annotated with @Configuration and @ConditionalOnClass. This class will define the beans and configurations that your starter will provide.

@Configuration
@ConditionalOnClass(EmployeeUtil.class)
public class EmployeeServiceAutoConfiguration {
    @Bean
    public EmployeeServiceDepartment formatEmployeeServiceDepartment() {
        return new EmployeeServiceDepartment();
    }
}

• Properties Class: If your starter needs custom properties, create a properties class annotated with @ConfigurationProperties.

@ConfigurationProperties(prefix = "generic")
public class GenericProperties {
    private String propertyType;
    // getters and setters
}

• META-INF/spring.factories: Create a spring.factories file in the META-INF directory. This file will tell Spring Boot to load your auto-configuration class.

org.springframework.boot.autoconfigure.EnableAutoConfiguration=com.example.MyCustomAutoConfiguration

• Package and Publish: Package your project as a JAR file and publish it to a Maven repository. This way, other projects can include your starter as a dependency.

This process of creating custom starters is often highlighted in most of the Spring Boot interview questions as it helps streamline the application's configuration.

21. Explain the Internal Architecture of Spring Boot

Spring Boot is built on the Spring framework, which simplifies the development of new Spring applications. It follows a layered architecture, with each layer having a specific responsibility and communicating directly with adjacent layers.

Layers of Spring Boot

• Presentation Layer: This is the topmost layer that handles all the HTTP requests. It translates JSON parameters to objects, authenticates requests, and passes them to the business layer. Essentially, it deals with the user interface and user interaction.
• Business Layer: Sometimes called a service layer, this layer contains all the business logic. It processes the data received from the presentation layer and interacts with the persistence layer to fetch or save data. It also handles authorization and validation.
• Persistence Layer: This layer is responsible for interacting with the database. It translates business objects to database rows and vice versa. It contains repository classes that perform CRUD (Create, Read, Update, Delete) operations.
• Database Layer: The bottom layer where the actual database resides. It stores the data and handles database operations.

How It All Works Together

When you start a Spring Boot application, it begins with the main method, which invokes SpringApplication.run(). This method bootstraps the application, starting the Spring context and auto-configuring beans based on the dependencies you have included.

• Auto-Configuration: The auto-configuration feature within Spring Boot automatically configures your application based on the dependencies present in your classpath.
• Spring Context: The Spring context is the heart of any Spring application. It manages the lifecycle of beans and their dependencies. When the application starts, Spring Boot scans for classes annotated with @Configuration, @Component, @Service, etc., and creates objects for them.
• Dispatcher Servlet: For web applications, the Dispatcher Servlet is the front controller that handles all incoming HTTP requests. It routes the requests to the appropriate controllers based on the URL mappings.
• Controllers and Services: Controllers handle the incoming requests, process them using services, and return the appropriate responses. Services contain the business logic and interact with the repositories to fetch or save data.
• Repositories: Repositories are interfaces that provide CRUD operations for entities. They interact with the database layer to perform these operations.

The above internal architecture of Spring Boot ensures a smooth, streamlined application setup, focusing on simplicity and convention over configuration. This architecture is fundamental in Spring Boot, and it has often been highlighted in most of the Spring Boot interview questions as it helps in developing modern applications.

22. How Do You Optimize Performance in a Spring Boot Application?

Optimizing performance in a Spring Boot application can be quite rewarding. Several strategies can help your application run more efficiently.

Here are some practical tips:

• Use Lazy Initialization: By default, Spring Boot initializes all beans at startup. You can delay this process by using lazy initialization, which loads beans only when they are needed. This can significantly reduce startup time and memory usage.
• Minimize Auto-Configuration: Spring Boot’s auto-configuration is convenient but can sometimes include unnecessary configurations. You can exclude these in your application.properties or application.yml file to streamline your application.
• Profile-Specific Configuration: Use Spring profiles to load configurations selectively based on the environment (e.g., development, testing, production). This helps in optimizing resource usage for different environments.
• Reduce Dependencies: Only include the dependencies that your application truly needs. This not only reduces the size of your application but also minimizes potential conflicts and improves performance.
• Optimize Database Access: Use connection pooling to manage database connections efficiently. Tools like HikariCP can help manage connections better, reducing latency and improving throughput.
• Setup Caching: Caching has become one of the most crucial components of a large-scale application. Develop a caching system to cache frequently used data. There are multiple caching solutions available that are supported by Spring Boot, like Redis, Ehcache, and Hazelcast, which can drastically reduce the load on your database.
• Asynchronous Processing: For tasks that don’t need to be executed immediately or don't have any kind of dependency, they can be processed asynchronously. This can free up resources that get locked up by tasks currently being executed.
• Monitor and Profile: Use Spring Boot Actuator to monitor your application’s health and performance. Profiling tools like VisualVM or JProfiler can help identify bottlenecks and optimize resource usage.
• Garbage Collection Tuning: Adjust JVM garbage collection settings according to your application’s needs. This can help manage memory more efficiently and reduce pauses caused by garbage collection.
• Use the Latest Versions: Always try to use the latest stable versions of Spring Boot and Java. Newer versions often come with performance improvements and bug fixes.

23. What Are the Different Ways to Externalize Configuration in Spring Boot?

Spring Boot offers several ways to externalize configuration, making it easier to manage different environments.

Here are some of the key steps:

• Properties Files: The most common method is to use application.properties or application.yml files. These files can be placed in different locations, such as inside your jar or in an external directory. You can also have profile-specific files, like application-dev.properties, for different environments.
• Environment Variables: Environment variables are used to override properties defined in your configuration files. This can be used for protecting sensitive data like passwords or for settings that change between environments.
• Command-Line Arguments: Another way to pass properties is to pass them through the command line while running your application. These can be new or existing properties. If the properties provided already exist, they will override the existing ones.
• @Value Annotation: The @Value annotation can be used in spring beans to provide simple properties.

@Value("${unit.property}")
private int id;

• @ConfigurationProperties: For more complex configurations, you can use the @ConfigurationProperties annotation to bind properties to a Java object. This is great for grouping related properties together.

@ConfigurationProperties(prefix = "id")
public class EmployeeProperties {
    private String description;
    // getters and setters
}

• Spring Environment Abstraction: You can access properties programmatically using Spring’s Environment abstraction. This is useful if you need to read properties dynamically.

@Autowired
private Environment env;

public void printUnitDescriptionProperty() {
    System.out.println(env.getProperty("unit.description"));
}

By following these key methods, you can significantly enhance the performance of your Spring Boot application, ensuring it runs efficiently and smoothly, even as it scales. This topic is often a central focus in many Spring Boot interview questions, as it demonstrates an understanding of optimizing applications for better performance.

24. How Do You Implement OAuth2 With Spring Boot?

OAuth2 is one of the most important Spring Boot components that is used to manage the flow between clients and one or more HTTP services.

Let's comply with the following steps to implement the same:

• Set Up Your Spring Boot Project: Create a new Spring Boot project. Spring Initializr can also be used to generate your project with the necessary dependencies or you can manually create it as well. Select Spring Web and Spring Security.
• Add Dependencies: In your pom.xml, add the following dependencies:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-oauth2-client</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-security</artifactId>
</dependency>

• Configure Application Properties: Next, configure your OAuth2 client in application.properties or application.yml. For example, if you’re using Google as your OAuth2 provider:

spring.security.oauth2.client.registration.google.client-id=your-client-id
spring.security.oauth2.client.registration.google.client-secret=your-client-secret
spring.security.oauth2.client.registration.google.scope=profile, email
spring.security.oauth2.client.provider.google.authorization-uri=https://accounts.google.com/o/oauth2/auth
spring.security.oauth2.client.provider.google.token-uri=https://oauth2.googleapis.com/token
spring.security.oauth2.client.provider.google.user-info-uri=https://www.googleapis.com/oauth2/v3/userinfo
spring.security.oauth2.client.provider.google.user-name-attribute=sub

• Create Security Configuration: Create a security configuration class to handle the OAuth2 login.

import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
import org.springframework.security.config.annotation.web.builders.HttpSecurity;
import org.springframework.context.annotation.Configuration;
import org.springframework.security.config.annotation.web.configuration.WebSecurityConfigurerAdapter;

@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {
    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
            .authorizeRequests()
                .antMatchers("/", "/login**").permitAll()
                .anyRequest().authenticated()
                .and()
            .oauth2Login();
    }
}

• Create a Controller: Create a simple controller to handle requests.

import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.security.oauth2.client.authentication.OAuth2AuthenticationToken;

@Controller
public class MainController {
    @GetMapping("/")
    public String index(Model model, OAuth2AuthenticationToken authentication) {
        if (authentication != null) {
            model.addAttribute("name", authentication.getPrincipal().getAttributes().get("username"));
        }
        return "index";
    }
}

• Create a Simple HTML Page: You'll have to create an HTML file (e.g., index.html, if not already present) to test your OAuth2 implementation.

<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
  <head>
      <title>Testing OAuth2 Login</title>
  </head>
  <body>
      <h1>Welcome to OAuth2 Testing component!</h1>
      <div th:if="${example}">
          <p>Hello, <span th:text="${example}"></span>!</p>
      </div>
      <div th:if="${example == null}">
          <a href="/oauth2/authorization/google">Login with Google</a>
      </div>
  </body>
</html>

This is a common topic in Spring Boot and has frequently appeared in Spring Boot interview questions. It's essential for developers to understand how to integrate OAuth2 with Spring Security for user authentication. By following these steps, your Spring Boot application will successfully integrate OAuth2 login, allowing users to authenticate via Google (or another provider if desired).

25. Explain the Process of Securing REST APIs With Spring Boot

One of the most important components to implement after you have implemented your application is security. You need to implement security to protect your application and data from unauthorized access. Following are the steps that can be followed to secure your REST APIs using Spring Security:

• Create a new Spring Boot Project, If not already created.
• Add Dependencies: In your pom.xml, add the following dependencies:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-security</artifactId>
</dependency>
<dependency>
    <groupId>io.jsonwebtoken</groupId>
    <artifactId>jjwt</artifactId>
    <version>0.9.1</version>
</dependency>

• Configure Security: Create a security configuration class to handle the security settings.

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.security.config.annotation.web.builders.HttpSecurity;
import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
import org.springframework.security.config.annotation.web.configuration.WebSecurityConfigurerAdapter;
import org.springframework.security.crypto.bcrypt.BCryptPasswordEncoder;
import org.springframework.security.crypto.password.PasswordEncoder;

@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {
    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
            .csrf().disable()
            .authorizeRequests()
                .antMatchers("/api/public/**").permitAll()
                .anyRequest().authenticated()
                .and()
            .httpBasic();
    }

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

• Create User Entity and Repository: Define a User entity and a repository to manage user data.

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String username;
    private String password;

    // Getters and setters
}

import org.springframework.data.jpa.repository.JpaRepository;

public interface UserRepository extends JpaRepository<User, Long> {
    User findByUsername(String username);
}

• Implement UserDetailsService: Create a service to load user-specific data.

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.security.core.userdetails.UserDetails;
import org.springframework.security.core.userdetails.UserDetailsService;
import org.springframework.security.core.userdetails.UsernameNotFoundException;
import org.springframework.stereotype.Service;

@Service
public class CustomUserDetailsService implements UserDetailsService {
    @Autowired
    private UserRepository userRepository;

    @Override
    public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
        User user = userRepository.findByUsername(username);
        if (user == null) {
            throw new UsernameNotFoundException("User not found");
        }
        return new org.springframework.security.core.userdetails.User(user.getUsername(), user.getPassword(), new ArrayList<>());
    }
}

• Secure Your Endpoints: Annotate your controller methods to secure them.

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/api")
public class ApiController {
    Address employeeAddress = new Address("Chennai");

    @GetMapping("/companyPolicy")
    public String getCompanyPolicy() {
        return "Following are the company's policy";
    }

    @GetMapping("/employeeAddress")
    public Address getEmployeeAddress() {
        System.out.println("Employee’s address is as follows: ");
        return employeeAddress;
    }
}

By following the above steps, you can easily secure your REST APIs in Spring Boot using Spring Security. This process is often highlighted in most of the Spring Boot interview questions as it helps ensure that unauthorized users cannot access your sensitive data. The integration of JWT or other forms of token-based authentication can further strengthen your API security.

26. How Do You Integrate Spring Boot With a Continuous Integration/Continuous Deployment (CI/CD) Pipeline?

One of the most important components to implement after you have implemented your application is security. You need to implement security to protect your application and data from unauthorized access. Following are the steps that can be followed to secure your REST APIs using Spring Security:

• Create a new Spring Boot Project, if not already created.
• Add Dependencies: In your pom.xml, add the following dependencies:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>Spring Boot-starter-security</artifactId>
</dependency>
<dependency>
    <groupId>io.jsonwebtoken</groupId>
    <artifactId>jjwt</artifactId>
    <version>0.9.1</version>
</dependency>

• Configure Security: Create a security configuration class to handle the security settings.

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.security.config.annotation.web.builders.HttpSecurity;
import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
import org.springframework.security.config.annotation.web.configuration.WebSecurityConfigurerAdapter;
import org.springframework.security.crypto.bcrypt.BCryptPasswordEncoder;
import org.springframework.security.crypto.password.PasswordEncoder;

@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
            .csrf().disable()
            .authorizeRequests()
                .antMatchers("/api/public/**").permitAll()
                .anyRequest().authenticated()
                .and()
            .httpBasic();
    }

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

• Create User Entity and Repository: Define a User entity and a repository to manage user data:

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import org.springframework.data.jpa.repository.JpaRepository;


@Entity
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String username;
    private String password;

    // Getters and setters
}



public interface UserRepository extends JpaRepository<User, Long> {
    User findByUsername(String username);
}

• Implement UserDetailsService: Create a service to load user-specific data:

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.security.core.userdetails.UserDetails;
import org.springframework.security.core.userdetails.UserDetailsService;
import org.springframework.security.core.userdetails.UsernameNotFoundException;
import org.springframework.stereotype.Service;

@Service
public class CustomUserDetailsService implements UserDetailsService {

    @Autowired
    private UserRepository userRepository;

    @Override
    public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
        User user = userRepository.findByUsername(username);
        if (user == null) {
            throw new UsernameNotFoundException("User not found");
        }
        return new org.springframework.security.core.userdetails.User(user.getUsername(), user.getPassword(), new ArrayList<>());
    }
}

• Secure Your Endpoints: Annotate your controller methods to secure them:

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/employee")
public class EmployeeController {
    String employeePolicy = "This is the employeePolicy";
    Address address = new Address("New Delhi");
    @GetMapping("/employeePolicy")
    public String getEmployeePolicy() {
        return employeePolicy;
    }

    @GetMapping("/employeeAddress")
    public Address getEmployeeAddress() {
        System.out.println("This is a private endpoint:");
        return address;
    }
}

Setting up CI/CD integration with Spring Boot helps manage code, automate deployment pipelines, manage dependencies, and secure applications in CI/CD scenarios. It is one of the most important topics in Spring Boot and is often asked in most interview questions.

27. What Are the Best Practices for Writing Integration Tests in Spring Boot?

Once you are done with creating your application, your next step should be to implement tests that would test your application at a granular level and the entire application. Following are some of the standard practices that can be followed:

• Use @SpringBootTest Annotation: Use @SpringBootTest to load the complete application context. This annotation is essential for integration tests as it sets up the entire Spring application context, allowing you to test the interaction between different components.

Example:

@SpringBootTest
public class EmployeeIntegrationTest {
    @Autowired
    private EmployeeAddress getEmployeeAddress;

    @Test
    public void testEmployeeAddress() {
        // Test logic here
    }
}

• Mock External Dependencies: Integration tests should focus on the interaction between your components, not on external systems. Use tools like Mockito to mock external dependencies such as databases or web services.

Example:

@MockBean
private EmployeeRepository employeeRepository;

• Use In-Memory Databases: Spring Boot comes with embedded databases like H2. Try to make use of H2 DB for tests which don't require any external tools to be installed.

spring:
  datasource:
    url: jdbc:h2:mem:testdb
    driverClassName: org.h2.Driver
    username: sa
    password: password

• Test Configuration: Separate your test configuration from your production configuration to avoid unintended side effects.

Example:

@TestConfiguration
public class TestConfig {
    @Bean
    public EmployeeService getEmployeeAddress() {
        return new EmployeeAddressImpl();
    }
}

• Use @Transactional: Annotate your test classes with @Transactional to ensure that each test method runs in a transaction that is rolled back after the test completes. This keeps your tests isolated and repeatable.

Example:

@SpringBootTest
@Transactional
public class EmployeeDataInsertionTest {
    // Test methods
}

• Keep Tests Fast and Isolated: Fast tests encourage frequent execution, which helps catch issues early. Isolate tests to ensure they don’t depend on each other.

Note: Use profiles to separate test configurations from production configurations.

• Use @DirtiesContext Sparingly: @DirtiesContext can be used to indicate that the Spring context should be reset after a test. However, it can slow down your tests, so use it only when necessary.

Example:

@Test
@DirtiesContext
public void testDateConversion() {
    // Test logic
}

• Leverage MockMvc for Web Layer Testing: Use MockMvc to test your web layer without starting the server. This makes your tests faster and more focused.

Example:

@Autowired
private MockMvc mockMvc;

@Test
public void testGetCustomerDepartment() throws Exception {
    mockMvc.perform(get("/api/customer/department"))
           .andExpect(status().isOk())
           .andExpect(content().string("Human Resources"));
}

The following best practices can help ensure that your integration tests in Spring Boot are effective and maintainable. These practices are commonly asked in most of the Spring Boot interview questions, as they highlight essential testing strategies for building reliable applications.

Experienced-level Spring Boot Interview Questions

These experienced-level Spring Boot interview questions focus on advanced topics such as performance optimization, microservices architecture, security best practices, and testing strategies.

Here, questions are designed for developers with significant experience, enabling them to demonstrate their deep understanding and ability to solve complex challenges in Spring Boot applications.

27. How Do You Mock Dependencies in Spring Boot Tests?

Mocking dependencies in Spring Boot is the core topic, and it is often covered in most Spring Boot interview questions. It is a great way for developers to isolate the components being tested and ensure that tests are reliable and fast.

Here are some practical steps and tips to help you get started:

• Using @MockBean: @MockBean is used to add mock objects to the Spring application context. This is particularly useful in integration tests where you want to replace a real bean with a mock.

Example:

@SpringBootTest
public class MyServiceTest {
    @MockBean
    private MyRepository myRepository;

    @Autowired
    private MyService myService;

    @Test
    public void testServiceMethod() {
        // Define behavior for the mock
        when(myRepository.findById(1L)).thenReturn(Optional.of(new MyEntity()));

        // Call the service method
        MyEntity result = myService.findById(1L);

        // Verify the result
        assertNotNull(result);
    }
}

• Using @Mock and @InjectMocks: @Mock creates a mock instance of a dependency, while @InjectMocks injects these mocks into the class you’re testing.

Example:

@ExtendWith(MockitoExtension.class)
public class MyServiceTest {
    @Mock
    private MyRepository myRepository;

    @InjectMocks
    private MyService myService;

    @Test
    public void testServiceMethod() {
        // Define behavior for the mock
        when(myRepository.findById(1L)).thenReturn(Optional.of(new MyEntity()));

        // Call the service method
        MyEntity result = myService.findById(1L);

        // Verify the result
        assertNotNull(result);
    }
}

• Using @SpyBean: @SpyBean is used to create a spy of a Spring bean. This is useful when you want to partially mock a bean, allowing you to call real methods while still being able to stub or verify interactions.

Example:

@SpringBootTest
public class MyServiceTest {
    @SpyBean
    private MyService myService;

    @MockBean
    private MyRepository myRepository;

    @Test
    public void testServiceMethod() {
        // Define behavior for the mock
        when(myRepository.findById(1L)).thenReturn(Optional.of(new MyEntity()));

        // Call the service method
        MyEntity result = myService.findById(1L);

        // Verify the result
        assertNotNull(result);
        verify(myService).findById(1L);
    }
}

• Using Mockito in Plain Unit Tests: Sometimes, you might not need the full Spring context. In such cases, you can use Mockito directly in your unit tests.

Example:

@ExtendWith(MockitoExtension.class)
public class MyServiceTest {
    @Mock
    private MyRepository myRepository;

    @InjectMocks
    private MyService myService;

    @Test
    public void testServiceMethod() {
        // Define behavior for the mock
        when(myRepository.findById(1L)).thenReturn(Optional.of(new MyEntity()));

        // Call the service method
        MyEntity result = myService.findById(1L);

        // Verify the result
        assertNotNull(result);
    }
}

28. How Do You Design and Deploy Spring Boot Microservices?

Effectively designing Spring Boot microservices is a crucial topic, and it is often highlighted in most interview questions. A well-structured microservices architecture ensures scalability, maintainability, and efficient communication.

Below are the steps on how to design and deploy a Spring Boot microservices :

• Define the Microservices: Break down your application into smaller, manageable services based on business capabilities. Each microservice should have a single responsibility.
• Choose Communication Strategies:
• RESTful APIs: Enable seamless communication between microservices.
• Message Queues: Use RabbitMQ or Kafka for asynchronous communication.
• Database Design:
• Database per Service: Each microservice should have its own database to ensure loose coupling.

Example: The user management service may use a relational database, while the product catalog service may use NoSQL.

• Configuration Management:
• Spring Cloud Config: Use Spring Cloud Config to manage configuration across all microservices.

Example:

spring:
  cloud:
    config:
      uri: http://config-server:8888

• Service Discovery:
• Eureka: Eureka can be used for discovering the services available to enable the microservices to look for other microservices and for inter-communication between microservices

Example:

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

• Load Balancing:
• Ribbon: Use Ribbon for client-side load balancing.

Example:

@LoadBalanced
@Bean
public RestTemplate restTemplate() {
    return new RestTemplate();
}

Deploying Spring Boot Microservices:

• Containerization:
• Docker: Containerize your microservices using Docker.

Example:

FROM openjdk:11-jre-slim
COPY target/my-service.jar my-service.jar
ENTRYPOINT ["java", "-jar", "my-service.jar"]

• Orchestration:
• Kubernetes: Kubernetes can be used to manage CRUD operations on your containers.

Example:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-service
spec:
  replicas: 3
  selector:
    matchLabels:
      app: my-service
  template:
    metadata:
      labels:
        app: my-service
    spec:
      containers:
      - name: my-service
        image: my-service:latest
        ports:
        - containerPort: 8080

• Monitoring:
• Prometheus and Grafana: Prometheus is one of the common tools usually used for monitoring. Grafana is a visualization tool with a UI that tracks your services and their status.
• CI/CD Pipeline:
• Jenkins/GitHub Actions: Set up a CI/CD pipeline to automate the build, test, and deployment process.

Example:

name: CI/CD Pipeline
on: [push]
jobs:
  build:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v2
    - name: Set up JDK 11
      uses: actions/setup-java@v1
      with:
        java-version: 11
    - name: Build with Maven
      run: mvn clean install
    - name: Build Docker image
      run: docker build -t my-service:latest .
    - name: Push Docker image
      run: docker push my-service:latest

29. What Is Spring Cloud, and How Does It Relate to Spring Boot?

Below is a short description of how Spring Cloud is related to Spring Boot:

• Spring Boot: It is a framework that helps you set up and run Spring applications with minimal configuration. It's like a toolbox that simplifies building a robust app.
• Spring Cloud: It is designed for building distributed systems and cloud-based applications, providing essential tools to address challenges like service discovery, centralized configuration, fault tolerance, and distributed tracing.

When deployed on cloud platforms like AWS, Azure, or Google Cloud, Spring Cloud enables seamless scaling, load balancing, and resilience, making it easier to manage and optimize microservices-based architectures.

As cloud-native applications scale, ensuring their reliability and performance across diverse environments becomes crucial. This is where the LambdaTest cloud-based testing platform enhances Spring Cloud applications by providing a scalable and efficient testing infrastructure.

By leveraging LambdaTest, teams can validate their Spring Cloud applications through both manual and automated Spring testing across 3000+ browser and OS combinations. This helps detect compatibility issues early, ensuring smooth operation in real-world distributed environments.

With LambdaTest, developers can:

• Optimize test execution with faster feedback loops, cutting down testing time significantly.
• Integrate with CI/CD tools like Jenkins, Bamboo, and Travis CI to maintain a seamless deployment pipeline.
• Ensure security and scalability, critical for microservices and cloud-based applications.

By integrating Spring Cloud with LambdaTest online testing cloud, teams can achieve faster releases, greater test coverage, and improved application resilience, making it an indispensable combination for modern cloud-native development. Understanding Spring Cloud is crucial for developers working with microservices and cloud-native applications, making it a common topic in Spring Boot interview questions.

30. Explain the Use of Eureka and Ribbon in Spring Boot Applications

Below is the use of Eureka and Ribbon in detail as understanding these concepts is essential as they frequently appear in Spring Boot interview questions, especially when discussing microservices and service discovery.

• Eureka: It is a service registry. You may think of it as a phone directory for your microservices. When a service is initiated, it gets registered with Eureka all by itself, which then makes it discoverable by other services. This is the reason why all the services are able to look up and communicate with other services without knowing their location.
• Ribbon: is a client-side load balancer. When a service wants to call another service, Ribbon helps distribute the load by choosing an available instance of the target service. It uses various algorithms, such as round-robin or response time-based strategies, to decide which instance to call.

How They Work Together

When you combine Eureka and Ribbon, you get a dynamic and resilient system. Here’s a simplified flow:

• Service Registration: A microservice registers itself with Eureka.
• Service Discovery: When another service needs to call this microservice, it asks Eureka for the list of available instances.
• Load Balancing: Ribbon takes this list and decides which instance to call, balancing the load across all available instances.

31. How Do You Handle Distributed Tracing in Spring Boot Microservices?

Distributed tracing is generally used for monitoring and troubleshooting in a microservices architecture.

Here’s how you can handle distributed tracing in Spring Boot microservices:

Key Components

• Spring Cloud Sleuth: This library is used for adding trace and span IDs to the logs. This makes it easier for the logs to be on the same wavelength as other services.
• Zipkin: This component uses a tracing technique to collect and visualize the data.

Steps to Implement Distributed Tracing

• Add Dependencies: Include the necessary dependencies in your pom.xml or build.gradle file:

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-sleuth</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-zipkin</artifactId>
</dependency>

• Configure Properties: Set up your application.properties or application.yml to configure
• Sleuth and Zipkin:

spring.zipkin.base-url=http://localhost:9411
spring.sleuth.sampler.probability=1.0

• Run Zipkin: You can run Zipkin using Docker:

docker run -d -p 9411:9411 openzipkin/zipkin

• Trace Requests: When your microservices handle a request, Sleuth will automatically add trace and span IDs to the logs. These IDs help you follow the request across different services.

Example Flow: Imagine you have three microservices: Service A, Service B, and Service C. A request starts at Service A, which calls Service B, and then Service B calls Service C. With distributed tracing:

• Service A logs the trace ID and span ID.
• Service B receives the trace ID from Service A and logs its own span ID.
• Service C continues the trace, adding its own span ID.
• Visualizing Traces: Once the traces are collected, you can visualize them in Zipkin’s UI. This helps you see the entire journey of a request, identify slow services, and troubleshoot issues effectively.

Benefits:

• Improved Debugging: Quickly pinpoint where issues occur.
• Performance Monitoring: Identify slow services and optimize them.
• Better Insights: Understand the flow of requests across your microservices.

Understanding distributed tracing is a valuable topic in Spring Boot, and it’s often asked in most of the Spring Boot interview questions, as it helps explain how to diagnose latency issues and improve microservices performance.

32. What Are the Patterns for Inter-service Communication in Microservices?

Communication between services is an important part of microservice architecture. Here are some examples used to ensure efficient and reliable communication between services:

• Parallel Communication: Communication takes place between services, and one service waits for a response from the other. This is done via HTTP/REST or gRPC.
• HTTP/REST: Services communicate using standard HTTP methods (GET, POST, etc.). It's simple and widely supported.
• gRPC: A full-featured RPC framework that uses HTTP/2 for transport serialization protocols and provides features such as bi-directional streaming.
• Synchronous Communication: Synchronous communication allows collaboration without waiting for an immediate response. This is useful for disconnecting services and improving resiliency.
• Message Buyer: Tools like RabbitMQ, Kafka, or AWS SQS handle asynchronous messaging. Services send messages to a broker, which forwards them to the appropriate service.
• Event-based architecture: Services send events when something important happens. Other services subscribe to these events and respond accordingly. This model is implemented using message brokers.
• Publish-Subscribe: In the publish-subscribe model, services publish messages to a program, and multiple subscribers receive these messages. This is useful for reporting to multiple services.
• Example: The user registration service creates an event when a new user registers. Other services, such as email notification and analytics, subscribe to this event and perform their tasks.
• Request-response: The request-response model is a type of asynchronous communication in which a service sends a request and waits for a response.
• Example: A payment service requests user details from a user service and waits for a response before proceeding with the transaction.
• Circuit Breakers: The Circuit Breaker pattern helps prevent flow failures by blocking requests to a failed service. If the service fails, the circuit breaker opens, and requests will not be served until it is restored.
• Example: If the payment service crashes, it stops sending requests to it, so it doesn't crash again.
• Service Network: A service network provides a special architectural framework layer to facilitate service-to-service communication. It offers features such as load balancing, service discovery, and security.
• Example: Istio is a popular cloud service that provides traffic management, security, and discovery.

The choice of communication model depends on the specific needs of the application. Asynchronous communication is efficient but can lead to tight coupling and potential bottlenecks.

Synchronous communication, on the other hand, provides better isolation and flexibility but is more complex to implement. Inter-service communication is a crucial aspect of Spring Boot interview questions, as it determines how microservices interact while ensuring scalability and fault tolerance.

33. How Do You Create a Spring Boot Application?

The following procedures can be used to construct the Spring Boot application once the environment setup is complete:

Prereq:

• Java 8 - Before starting the project, make sure to install Java 8 or higher in your system. And set the path for JAVA_HOME in environment variables.
• Installing an Integrated Development Environment (IDE), such as Eclipse (recommended), IntelliJ, or VS Code. Sometimes, you don’t need to install Java separately when you install an IDE.

Once you are ready with the environment setup, you must follow the steps to create the Spring Boot application:

• Make a New Spring Boot Project:

Method-1:

• One way is to use Spring Initializr. Select the Spring Boot version, language (Java, Kotlin, or Groovy) and project type (Maven or Gradle).
• Select the dependencies you require, such as Spring Data JPA, Spring Web, etc.
• To download the project as a ZIP file, click "Generate." Extract it to the place of your choice.

Method-2:

• Another way is to create a project through your IDE.
• This method would be somewhat tedious, as it requires manually adding all the dependencies and non-conflicting versions.
• You’ll have to set up the config manually as well.
• Open Your IDE and import the project:
• The project can be imported as a Maven or Gradle project when you open your IDE.
• Make sure that the right JDK version is being used by your IDE.
• Establish the Main Application Class:
• Make a new class with a main method annotated with @SpringBootApplication in the src/main/java directory.

Example:

package com.org.lambdaTest;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class Reservation {
    public static void main(String[] arguments) { // main class
        SpringApplication.run(Reservation.class, args); // this informs your spring application which class needs to run initially
    }
} 

• Launch the Program:
• The main function in the Reservation class can be called to launch the program directly from your IDE
• Alternatively, you can run./gradlew bootRun (for Gradle) or./mvnw Spring Boot:run (for Maven) from the command line after finding the project directory.
• Create REST Endpoints:
• Create a new controller class in the src/main/java directory
• Add necessary endpoints

Example:

package com.org.lib.lambdaTest;
iimport org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController // informs the compiler that this is a controller
public class Employer {
    @GetMapping("/getAllEmployers") // informs the compiler of the uri
    public String hello() {
        return "Here is a list of all Emlpoyers";
    }
}

• Test Your Application:
• Your application is not 100% failsafe until you test it. You don’t want your application to have all kinds of issues when you go live.
• Open up any web browser and navigate to http://localhost:8080/ <name_of_your_controller> (Please note, port 8080 is the default port defined for the application. If you have any other services using this port, you can change/use an unused one).
• You should be able to see the text that you have defined in your controller, “Hello, Spring Boot!” in this case.
• If you do not see the expected results, you will need to debug or revisit the steps above.

This step-by-step approach above is a common topic in Spring Boot, and it is one of the most commonly asked Spring Boot interview questions, as the understanding of setting up and running a Spring Boot application efficiently.

34. How Do You Handle Transactions in Spring Boot?

Handling transactions in any application is the most crucial part that ensures data consistency and integrity, especially in applications that involve multiple database operations and confidential information.

Here’s a straightforward guide on how to manage transactions effectively:

• Using the @Transactional Annotation: The way transactions are managed is by using the @Transactional annotation in your project. The scope of the transaction can be either at the class level or method level.
• Dependencies: Inject all the required dependencies in your project by declaring them in either your pom.xml or build.gradle file:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>Spring Boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
    <scope>runtime</scope>
</dependency>

• Enable Transaction Management: Add the @EnableTransactionManagement annotation to your main class as shown below:

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

• Use @Transactional: Apply the @Transactional annotation to your service methods where you want to manage transactions:

@Service
public class UserService {

    @Autowired
    private UserRepository userRepository;

    @Transactional
    public void createUser(User user) {
        userRepository.save(user);
        // Additional operations can be added here
    }
}

Key Features of @Transactional:

• Propagation: Defines how transactions relate to each other. REQUIRED (default) would join another existing transaction; otherwise, create a new one.
• Isolation: Specifies the isolation level of the transaction, such as READ_COMMITTED or SERIALIZABLE.
• Duration: Specifies the maximum amount of time a transaction can run before automatically rolling back.
• Read-only: It is used for transactions that can only be read and not modified, thereby increasing the performance.
• Rollback Rule: By default, transactions are rolled back based on unchecked positions. You can customize this behavior by using rollbackFor and noRollbackFor.

Sample Example: Consider a service where you have user registration. The service stores information about users and sends them emails. If the user fails to save, the email should not be sent and vice versa. By using @Transactional, you can ensure that both operations are part of the same transaction:

@Service
public class RegisterService {

  @Autowired
  private UserService userService;

  @Autowired
  EmailService Private EmailService.

  @Transactions
  public void registerUser(User user) {
    userService.createUser(user);
    emailService.sendWelcomeEmail(user);
  }
}

In this example, if createUser or sendWelcomeEmail fails, all transactions are rolled back, and data consistency is guaranteed.

35. Explain the Use of Spring Data JPA With Spring Boot

One of the most integral components of the Spring Data family is the Spring Data JPA, having the responsibility of making it easy for data management and access to it.

JPA Databases are usually used while working with any of the source applications as it adds an abstraction layer on top of JAP.

Follow the below steps:

• Add Dependencies: If you are using Maven, you must first include the necessary dependencies in pom.xml. Usually, you need source-boot-starter-data-jpa and a database driver like mysql-connector-java.

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>Spring Boot-starter-data-jpa</artifactId>
    </dependency>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <scope>runtime</scope>
    </dependency>
</dependencies>

• Configure Database Connection: In your application.properties file, configure the database connection settings.

spring.datasource.url=jdbc:mysql://localhost:3306/yourdatabase
spring.datasource.username=yourusername
spring.datasource.password=yourpassword
spring.jpa.hibernate.ddl-auto=update

• Create Entity Classes: Define your entity classes using JPA annotations. For example, a User entity might look like this:

@Entity
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private String email;

    // Getters and setters
}

• Create Repository Interfaces: Create repository interfaces by extending JpaRepository. This interface provides CRUD operations out of the box.

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

• Service Layer: Create a service layer to handle business logic. This layer will use the repository to interact with the database.

@Service
public class UserService {
    @Autowired
    private UserRepository userRepository;

    public List<User> getAllUsers() {
        return userRepository.findAll();
    }

    public User saveUser(User user) {
        return userRepository.save(user);
    }
}

• Controller Layer: Finally, create a controller to handle HTTP requests.

@RestController
@RequestMapping("/users")
public class UserController {
    @Autowired
    private UserService userService;

    @GetMapping
    public List<User> getAllUsers() {
        return userService.getAllUsers();
    }

    @PostMapping
    public User createUser(@RequestBody User user) {
        return userService.saveUser(user);
    }
}

Merits of Spring Data JPA:

• Reduced Code: There is no longer a need for all the repetitive code required for data access layers while using Spring Data JPA.
• Query Methods: You can define query methods directly in the repository interface.
• Integration with Spring Boot: Seamless integration with Spring Boot makes it easy to set up and start using.

36. How Do You Implement Caching in a Spring Boot Application?

Caching is usually used to improve the performance of your application (which is basically the reads and writes that constantly happen to and from your DB).

Let's see the steps required for implementing a caching system for your application:

• Add Dependencies: Add the starter cache dependency in your pom.xml or build.gradle:

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

• Enable Caching: Enable caching in your Spring Boot application by adding the @EnableCaching annotation to one of your configuration classes:

import org.springframework.cache.annotation.EnableCaching;
import org.springframework.context.annotation.Configuration;

@Configuration
@EnableCaching
public class CacheConfig {
    // Additional configuration if needed
}

• Configure Cache Manager: Define a CacheManager bean. For simplicity, you can use ConcurrentMapCacheManager.

import org.springframework.cache.CacheManager;
import org.springframework.cache.concurrent.ConcurrentMapCacheManager;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class CacheConfig {
    @Bean
    public CacheManager cacheManager() {
        return new ConcurrentMapCacheManager("items");
    }
}

• Use Caching Annotations: Use caching annotations like @Cacheable, @CachePut, and @CacheEvict in your service methods:

import org.springframework.cache.annotation.Cacheable;
import org.springframework.stereotype.Service;

@Service
public class ItemService {
    @Cacheable("items")
    public Item getItemById(Long id) {
        // Method implementation
    }
}

• @Cacheable: Caches the result of the method.
• @CachePut: Updates the cache without interfering with the method execution.
• @CacheEvict: Removes the cache entry.
• Customize Cache Provider: If you need a more advanced cache provider like EhCache, Redis, or Caffeine, you can configure it in your application.properties or application.yml file and add the corresponding dependencies.

Here’s an example for using EhCache:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>Spring Boot-starter-cache</artifactId>
</dependency>
<dependency>
    <groupId>net.sf.ehcache</groupId>
    <artifactId>ehcache</artifactId>
</dependency>

And in your configuration class:

import org.springframework.cache.CacheManager;
import org.springframework.cache.ehcache.EhCacheCacheManager;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.io.ClassPathResource;

@Configuration
public class CacheConfig {
    @Bean
    public CacheManager cacheManager() {
        net.sf.ehcache.CacheManager cacheManager = new net.sf.ehcache.CacheManager(new ClassPathResource("ehcache.xml").getInputStream());
        return new EhCacheCacheManager(cacheManager);
    }
}

37. What Are the Different Strategies for Database Migration in Spring Boot?

Maintaining and updating the database schema for your application requires database migration. There are various techniques in Spring Boot that you may apply to efficiently manage database migrations.

Let's see some of the most popular ones:

• Flyway: A well-liked database migration tool that works well with Spring Boot is called Flyway. Versioned SQL scripts are used to handle database modifications.

Steps to use Flyway:

• Add Dependency: Add the Flyway dependency in your pom.xml or build.gradle:

<dependency>
    <groupId>org.flywaydb</groupId>
    <artifactId>flyway-core</artifactId>
</dependency>

• Create Migration Scripts: Place your SQL migration scripts in the src/main/resources/db/migration directory. The scripts should follow a naming convention like V1__initial_setup.sql.
• Configuration: Spring Boot auto-configures Flyway, so you typically don’t need additional setup. However, you can customize it in application.properties: spring.flyway.locations=classpath:db/migration
• Liquibase: Liquibase is another powerful tool for database migrations, offering more flexibility with XML, YAML, JSON, or SQL for defining changes.

Steps to use Liquibase:

• Add Dependency: Include the Liquibase dependency in your pom.xml:

<dependency>
    <groupId>org.liquibase</groupId>
    <artifactId>liquibase-core</artifactId>
</dependency>

• Create ChangeLog File: Define your database changes in a changelog file (e.g., db/changelog/db.changelog-master.xml).
• Configuration: Spring Boot auto-configures Liquibase, but you can customize it in application.properties: spring.liquibase.change-log=classpath:db/changelog/db.changelog-master.xml
• Manual SQL Scripts: For smaller projects or specific use cases, you might prefer to manage migrations manually using SQL scripts.

Steps to use Manual SQL Scripts:

• Configure Scripts: Write your SQL scripts and save them in a directory (such as src/main/resources/db/scripts) to start creating SQL scripts.
• Run Scripts: Employ a command-line tool or incorporate the running of scripts into your construction procedure.
• JPA Schema Generation: Spring Boot can automatically generate database schemas based on your JPA entities. This is useful for development but not recommended for production.

Steps to use JPA Schema Generation:

• Configuration: Enable schema generation in application.properties: spring.jpa.hibernate.ddl-auto=update

Choosing the Right Strategy:

• Flyway: Best for simple, versioned migrations with SQL scripts.
• Liquibase: Ideal for complex migrations requiring more flexibility.
• Manual SQL Scripts: Suitable for small projects or specific scenarios.
• JPA Schema Generation: Useful for rapid development but not for production.

38. How Do You Deploy a Spring Boot Application to a Cloud Platform Like AWS, Azure, or Google Cloud?

Below are the steps on how you deploy a Spring Boot application across various cloud platforms:

Deploying to AWS

• AWS Account Creation:
• Go to AWS and create an account if you don’t have one already. AWS provides a free tier to help you get started without any cost.
• Launch an EC2 Instance:
• Navigate to the "Launch Instance" section of the EC2 dashboard and select an Amazon Linux 2 AMI (Amazon Machine Image).
• Choose the appropriate instance type. For a basic Spring Boot application, a free tier-eligible t2.micro instance is typically sufficient.
• Set up a security group. Ensure port 8080 is open to allow Spring Boot applications to communicate.
• Install Java:
• Connect to your EC2 instance using SSH. On Windows, use PuTTY, or on macOS/Linux, use the terminal.

Install Java using the command:

sudo yum install java-17-openjdk



• Deploy Your Application
• Build your Spring Boot application into a JAR file using Maven:

mvn clean package

• Use SCP to transfer the JAR file to the EC2 instance:

scp -i your-key.pem target/your-application.jar ec2-user@your-ec2-ip:/home/ec2-user/

• SSH into your instance and run the JAR file:

 java -jar your-application.jar

Deploying to Azure

• Create an Azure Account:
• Sign up for Azure. Azure offers a free tier with credits to get started.
• Set Up Azure App Service:
• In the Azure portal, create a new App Service. Choose your subscription resource group, and give your app a name.
• Select Java 17 as the runtime stack and choose either Linux or Windows as the operating system.
• Deploy Your Application:
• Install and log in to the Azure CLI.
• Use the Azure CLI to deploy your JAR file:

 az webapp deploy --resource-group yourResourceGroup --name yourAppName --src-path target/your-application.jar

Deploying to Google Cloud

• Create a Google Cloud Account:
• Sign up for Google Cloud, which also offers a free tier with credits for new users.
• Set Up Google App Engine:
• Download and install the Google Cloud SDK. Initialize it by running:

gcloud init

• Create an app.yaml File:
• In your project root, create an app.yaml file that defines your application’s runtime and entry point:

runtime: java17
entrypoint: java -jar your-application.jar

• Deploy Your Application:
• Use the following command to deploy the application to Google Cloud:

gcloud app deploy

General Tips:

• Environment Variables: Use environment variables to manage sensitive information like database credentials and API keys. These can be set securely on each cloud platform.
• Logging and Monitoring: Incorporating logging and monitoring is crucial. You can use tools like AWS CloudWatch, Azure Monitor, and Google Cloud Logging to keep track of application performance and troubleshoot issues effectively.
• Re-Scaling: As your application grows, monitor its traffic and set up auto-scaling to handle various loads. This ensures that your application remains responsive during high-traffic times.

39. What Is Spring Boot Admin, and How Do You Use It?

Spring Boot Admin, as the name says, is an Admin tool that is primarily responsible for managing and keeping an eye on Spring Boot applications.

Let's look at the steps for setting up Spring Boot Admin:

• First, create a Spring Boot web application.
• Add the following Maven dependency to your pom.xml:

<dependency>
    <groupId>de.codecentric</groupId>
    <artifactId>Spring Boot-admin-starter-server</artifactId>
    <version>3.1.5</version>
</dependency>

• Enable the admin server by adding @EnableAdminServer to your main application class:

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

• To register your Spring Boot application as a client, add the following dependency:

<dependency>
    <groupId>de.codecentric</groupId>
    <artifactId>Spring Boot-admin-starter-client</artifactId>
    <version>3.1.5</version>
</dependency>

• Configure the client to know about the admin server’s base URL by adding this property to your application.properties.

spring.boot.admin.client.url=http://localhost:8080
management.endpoints.web.exposure.include=*
management.endpoint.health.show-details=always

• Since the admin server has access to sensitive endpoints, it’s a good idea to secure it. Add the following dependencies:

<dependency>
    <groupId>de.codecentric</groupId>
    <artifactId>Spring Boot-admin-server-ui</artifactId>
    <version>1.5.7</version>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>Spring Boot-starter-security</artifactId>
    <version>3.1.5</version>
</dependency>

• Implement a security configuration class to secure your admin server.

40. How Do You Monitor a Spring Boot Application in Production?

Once your Spring Boot application is live, you need a couple of tools to support post-production monitoring and issues.

This can be done via a myriad of approaches, one of them being:

• Spring Boot Actuator: The Spring Boot Actuator is like your Swiss Army knife for monitoring. It provides a bunch of endpoints that give you insights into your application’s health, metrics, and more.
• Add an Actuator: The first step would be to add an Actuator to your project by including the Actuator dependency in your pom.xml:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>Spring Boot-starter-actuator</artifactId>
</dependency>

• Configure Endpoints: Open your application.properties and expose the necessary endpoints:

management.endpoints.web.exposure.include=health,info,metrics
management.endpoint.health.show-details=always

• Prometheus and Grafana: Prometheus is great for collecting metrics, and Grafana helps you visualize them beautifully.
• Add Prometheus Dependency: Add this to your pom.xml:

<dependency>
    <groupId>io.micrometer</groupId>
    <artifactId>micrometer-registry-prometheus</artifactId>
</dependency>

• Update your application.properties.

management.metrics.export.prometheus.enabled=true
management.endpoints.web.exposure.include=prometheus

• Set up Logstash: Captures logs from your app and transmits them to Elasticsearch.
• Kibana Visualization: Leverage Kibana to create interactive dashboards and explore your log data.
• Notifying: It is not desirable to constantly stare at your monitoring dashboards. To get informed when something goes wrong, set up notifications.
• Notifications via SMS/Email: Connect email or SMS services to get alerts.

41. What Are the Different Logging Mechanisms Available in Spring Boot?

There are various alternatives available to you in Spring Boot for logging, each having advantages of its own.

The primary logging systems that you can utilize are listed below:

• Logback (Default): Spring Boot uses Logback as the default logging framework. It’s powerful and flexible, making it a popular choice.
• Configuration: Spring Boot comes with logback preconfigured, so you don't need to install any additional dependencies. It can be altered with the help of a logback-spring.xml file.

<configuration>
    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <pattern>%d{yyyy-MM-dd HH:mm:ss} - %msg%n</pattern>
        </encoder>
    </appender>
    <root level="INFO">
        <appender-ref ref="STDOUT" />
    </root>
</configuration>

• Log4j2: Log4j2 is another popular logging framework that you can use with Spring Boot.

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>Spring Boot-starter-log4j2</artifactId>
</dependency>

• Configuration: You can configure Log4j2 using a log4j2-spring.xml file.

<Configuration status="WARN">
    <Appenders>
        <Console name="Console" target="SYSTEM_OUT">
            <PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss} - %msg%n"/>
        </Console>
    </Appenders>
    <Loggers>
        <Root level="info">
            <AppenderRef ref="Console"/>
        </Root>
    </Loggers>
</Configuration>

• Java Util Logging (JUL): Java Util Logging is a built-in logging framework in Java. While not as feature-rich as Logback or Log4j2, it’s still a viable option.
• Configuration: You can configure JUL using a logging.properties file.

handlers= java.util.logging.ConsoleHandler
.level= INFO
java.util.logging.ConsoleHandler.level = INFO
java.util.logging.ConsoleHandler.formatter = java.util.logging.SimpleFormatter

• SLF4J (Simple Logging Facade for Java): SLF4J is not a logging implementation but a facade that allows you to plug in the logging framework of your choice (like Logback or Log4j2).
• Usage: You typically use SLF4J in your code, and it delegates the logging calls to the underlying framework.

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class Employee {
    String Name;
    private static final Logger logger = LoggerFactory.getLogger(MyClass.class);

    public String getEmployeeName() {
        logger.info("Sending Employee Name");
        return this.name;
    }
}

• Customizing Logging Levels: You can easily customize logging levels in your application.properties or application.yml file.

Example:

logging.level.org.springframework=DEBUG
logging.level.com.yourpackage=TRACE

42. How Do You Troubleshoot and Debug Issues in a Spring Boot Application?

Let's check out the steps that would be required for troubleshooting issues:

• Logs: Logs provide a wealth of information about what’s happening inside your application.
• Log Levels: Adjust log levels in your application.properties to get more detailed information:

logging.level.org.springframework=DEBUG
logging.level.com.yourpackage=TRACE

• Logback Configuration: Customize your logging with a logback-spring.xml file to format and filter logs as needed.
• Using a Debugger: A debugger allows you to step through your code and inspect variables at runtime.

IntelliJ IDEA:

• Set breakpoints in your code.
• Run your application in debug mode.
• Use the debugger to step through the code and inspect variables.
• Spring Boot Actuator: The Actuator provides endpoints that give insights into your application’s health, metrics, and more.
• Add Actuator Dependency:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>Spring Boot-starter-actuator</artifactId>
</dependency>

• Expose Endpoints: Configure your application.properties:

management.endpoints.web.exposure.include=health,info,metrics
management.endpoint.health.show-details=always

• Live Reload with Spring Boot DevTools: Spring Boot DevTools can automatically restart your application whenever you make changes, making the development process faster.
• Add DevTools Dependency:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>Spring Boot-devtools</artifactId>
    <optional>true</optional>
</dependency>

• Profiling and Performance Monitoring: Tools like JProfiler or VisualVM can help you profile your application and identify performance bottlenecks.

Conclusion

Spring Boot has indeed been a game-changing technology, making the development of robust Java applications seamless. This set of Spring Boot interview questions covers both basic and advanced concepts, helping me gain a deeper understanding of its capabilities. From effortless autoconfiguration to the convenience of embedded servers, Spring Boot empowers developers to build efficient and scalable solutions with minimal setup overhead.

Answering these questions has reinforced my knowledge and highlighted areas for improvement. This framework strikes the perfect balance between simplicity and flexibility, making it indispensable for modern application development. The learning experience has been both insightful and rewarding, leaving me better equipped to leverage Spring Boot in real-world projects.

Note : We have compiled all Spring Boot Interview Questions for you in a template format. Check it out now!