A comprehensive guide to the most common interview questions for Spring Boot developers, including explanations and answers to topics like application configuration, security, Actuator, logging, and more.
🔍 Introduction
Spring Boot simplifies the development of Spring applications by offering production-ready features with minimal configuration. If you’re preparing for a Spring Boot developer interview, understanding the core components and tools associated with Spring Boot is essential. Below are some commonly asked Spring Boot interview questions, along with their answers.
Spring Boot Basics
1️⃣ What is Spring Boot?
Answer:
Spring Boot is a project from the Spring team designed to simplify the development of new Spring applications. It is used to create stand-alone, production-grade Spring-based applications with minimal configuration. Spring Boot makes it easy to get started with Spring by providing defaults for application settings and dependencies.
2️⃣ What are the main features of Spring Boot?
Answer:
- Auto-Configuration: Automatically configures Spring applications based on the dependencies present in the classpath.
- Standalone: Spring Boot applications can run independently with an embedded server (e.g., Tomcat, Jetty).
- Production-ready: Provides production-ready features such as metrics, health checks, and externalized configuration.
- Spring Initializer: A web-based tool to generate initial Spring Boot projects.
- Opinionated Defaults: Provides default configurations to help developers get started quickly.
3️⃣ How does Spring Boot simplify the development process?
Answer:
Spring Boot simplifies development by:
- Reducing boilerplate code and configurations.
- Automatically configuring Spring and third-party libraries based on dependencies.
- Providing an embedded server to run the application without needing an external web server.
- Offering production-ready features and tools to monitor and manage the application.
4️⃣ Explain the use of the @SpringBootApplication annotation.
Answer:
The @SpringBootApplication annotation is a convenience annotation that combines three annotations:
- @Configuration: Marks the class as a source of bean definitions for the application context.
- @EnableAutoConfiguration: Tells Spring Boot to start adding beans based on classpath settings, other beans, and various property settings.
- @ComponentScan: Instructs Spring to look for other components, configurations, and services in the specified package.
5️⃣ What is a Spring Boot Starter?
Answer:
Spring Boot Starters are a set of convenient dependency descriptors that you can include in your application. They provide all the dependencies and transitive dependencies needed to get started with a particular functionality. For example, spring-boot-starter-web for web applications, and spring-boot-starter-data-jpa for JPA and Hibernate.
Application Configuration
6️⃣ How can you run a Spring Boot application?
Answer:
You can run a Spring Boot application in several ways:
- Using the main method in the application class with
SpringApplication.run(). - Using the Maven command:
mvn spring-boot:run. - Using the Gradle command:
gradle bootRun. - By building a JAR file with
mvn package or gradle build, and then running it with java -jar.
7️⃣ What is the purpose of the application.properties or application.yml file in Spring Boot?
Answer:
The application.properties or application.yml file is used for externalizing configuration. It allows you to define various settings for your application in a centralized place, including database configurations, server port, logging levels, and more. These files help in managing different environments and make your application more flexible and maintainable.
8️⃣ How do you configure a datasource in Spring Boot?
Answer:
To configure a datasource in Spring Boot, you typically add properties to your application.properties or application.yml file, such as:
properties
spring.datasource.url=jdbc:mysql://localhost:3306/mydb
spring.datasource.username=root
spring.datasource.password=root
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
Spring Boot will auto-configure the datasource based on these properties.
Production-Ready Features
9️⃣ What is Spring Boot Actuator?
Answer:
Spring Boot Actuator provides production-ready features to help you monitor and manage your application. It includes several endpoints that provide information about the application's health, metrics, beans, environment, and more. For example, /actuator/health provides the health status, and /actuator/metrics provides application metrics.
🔟 How do you enable Spring Boot Actuator in your application?
Answer:
To enable Spring Boot Actuator, add the Actuator starter dependency to your pom.xml or build.gradle file:
xml
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
You can then configure the available endpoints and their security in your application.properties file.
1️⃣1️⃣ What is the difference between @RestController and @Controller?
Answer:
@RestController: A convenience annotation that combines @Controller and @ResponseBody. It is used for RESTful web services and automatically serializes return objects to JSON/XML and writes them to the HTTP response.@Controller: Used to define a standard controller that handles HTTP requests. You need to explicitly use @ResponseBody or a ViewResolver to handle the response.
Error Handling and Development Tools
1️⃣2️⃣ How do you handle exceptions in Spring Boot?
Answer:
You can handle exceptions in Spring Boot using:
@ControllerAdvice: A special annotation to handle exceptions globally across multiple controllers.@ExceptionHandler: Used within a controller to handle specific exceptions.
Example:
java
@ControllerAdvice
public class GlobalExceptionHandler {
@ExceptionHandler(ResourceNotFoundException.class)
public ResponseEntity<String> handleResourceNotFoundException(ResourceNotFoundException ex) {
return new ResponseEntity<>(ex.getMessage(), HttpStatus.NOT_FOUND);
}
}
1️⃣3️⃣ What is Spring Boot DevTools?
Answer:
Spring Boot DevTools provides a set of tools that enhance the development experience, including:
- Automatic restarts when files on the classpath change.
- LiveReload support to automatically refresh the browser.
- Additional configurations to improve debugging and development speed.
To enable DevTools, add the following dependency:
xml
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-devtools</artifactId>
<optional>true</optional>
</dependency>
Security and Customization
1️⃣4️⃣ What are Spring Boot Profiles?
Answer:
Spring Boot Profiles provide a way to segregate parts of your application configuration and make them available only in certain environments. For example, you might have a dev, test, and prod profile, each with different settings for the database, logging, etc. You can activate a profile using the spring.profiles.active property in your application.properties file or as a command-line argument.
1️⃣5️⃣ How do you implement security in a Spring Boot application?
Answer:
To implement security in a Spring Boot application, you typically add the Spring Security starter dependency:
xml
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-security</artifactId>
</dependency>
Then, you configure security settings by extending WebSecurityConfigurerAdapter and overriding the configure methods. This allows you to define custom authentication and authorization rules.
1️⃣6️⃣ How do you create a custom Spring Boot starter?
Answer:
To create a custom Spring Boot starter:
- Create a new Maven or Gradle project.
- Define the necessary dependencies in the project’s
pom.xml or build.gradle. - Create auto-configuration classes and annotate them with
@Configuration and @ConditionalOnMissingBean or other conditional annotations. - Package the project as a JAR and publish it to a repository.
- Use this custom starter in other Spring Boot projects by including it as a dependency.
Miscellaneous
1️⃣7️⃣ What is the purpose of the spring-boot-maven-plugin?
Answer:
The spring-boot-maven-plugin is used to package Spring Boot applications as executable JAR or WAR files. It simplifies the build process by allowing you to run the application directly from the command line using mvn spring-boot:run and also provides goals to build and run Spring Boot applications.
1️⃣8️⃣ How do you configure logging in Spring Boot?
Answer:
Spring Boot uses Logback as the default logging framework. You can configure logging by:
- Setting properties in the
application.properties file (e.g., logging.level.root=INFO). - Using a custom
logback-spring.xml or logback.xml configuration file for advanced logging configurations. - Setting environment variables or command-line arguments to override logging settings.
1️⃣9️⃣ What is a Spring Boot actuator endpoint and give an example?
Answer:
A Spring Boot actuator endpoint is a URL mapping that exposes operational information about the running application. For example, the /actuator/health endpoint provides health information about the application.
2️⃣0️⃣ How do you externalize configuration in Spring Boot?
Answer:
You can externalize configuration in Spring Boot by using:
application.properties or application.yml files.- Environment variables.
- Command-line arguments.