Spring Boot has revolutionized Java-based development by simplifying the process of creating stand-alone, production-ready applications. Its widespread adoption in the industry makers it a must-learn for aspiring developers. If you’re preparing for a Spring Boot interview in 2024, here’s a comprehensive list of the most frequently asked questions and their answers to help you succed.
Table of Contents
1. What is Spring Boot, and how does it differ from Spring Framework?
Answer:
Spring Boot is an extension of the Spring Framework that simplifies the development of Java applications. It allows developers to create stand-alone, production-ready Spring applictions without the need for extensive XML configuration. The primary differences between Spring Boot and Spring Framework are:
- Auto-configuration: Spring Boot automatically configures Spring applications based on the dependencide declared in the pom.xml or build.gradle.
- Embedded server: It comes with an embedded server (e.g., Tomcat or Jetty), so you don't need to deploy WAR files manually.
- Opinionated Default: Spring Boot provides sensible defaults, reducing boilerplate code.
2. What are the key features of Spring Boot?
Answer:
Some key features of Spring Boot include:
- Auto-configuration: Automatically configures Spring and third-party libraries when possible.
- Embedded Server: Comes with an embedded web server (Tomcat, Jetty, or Undertow) to simplify deployment.
- Starter Dependencies: Provides a set of pre-configured dependencies to start development quickly.
- Spring Boot CLI: Command-line interface that allows you to quickly build Spring Boot applications using Groovy.
- Actutor: Proviedes operational information like health checks, metrics, and application logs.
3. What is a Spring Boot starter?
Answer:
A Spring Boot starter is a set of convenient dependency descriptors you can include in your project. Spring Boot starters simplify dependency manajement by aggregating related libraties under a single starter dependency. For example, spring-boot-starter-web brings in all the dependencies you need for building web applications, such as Spring MVC, embedded Tomcat, and Jackson for JSON processing.
4. Explain Spring Boot auto-configuration deos it work?
Answer:
Spring Boot auto-configuration attomatically configure your Spring application based on the dependencies present in your classpath. For exaple, if you have spring-boot-starter-web in without requiring explicit configuration.
This is achieved using conditional annotations like @Conditionalonclass, which checks for the presence of specific classes in the classpath and then applies the corresponding configuration.
5. What is the use of @springBootApplication?
Answer:
@SpringBootApplication is a convenience annotation that combines the following three annotations:
- @configuration: Indicates that the class is a source of bean definitions.
- @EnableAutoConfiguration: Eanables auto-configuration, which automatically configures the Spring application based on the classpath.
- @ComponentScan: Scans the package where the application is located for Spring components like beans, controllers, and services.
By using @SpringBootApplication, you can avoid declaring these annotations separately, simplifying your codebase.
6. What are Spring Boot Actuators?
Spring Boot Actuator is a set of tools that provide real-time insights into the running Spring Boot application. It includes several buit-in-endpoints that expose various operational details, such as:
- /actuator/health: Displays the applications health status.
- /actuator/metrics: Shows various metrics, such as memory usaga, CPU utilization, and HTTP request counts.
- /actuator/loggers: Exposes and allows configuration of the logging levels.
You can also create custom actuator endpoints if needed.
7. What is Spring Boot DevTools, and why is it useful?
Answer:
Spring Boot DevTools is module that helps improve the development experience by providing features like.
- Automatic Restart: Automatically restarts the application when code changes are detected.
- LiveReload: Reloads the browser automatically whenever the resources (HTML, CSS, JS) are updated.
- Property Defaults: Disables caching of templates and static files during development to ensure changes are immediately reflected.
These features significantly speed up the development process by resucing the need to manually restart the server of refresh the browser.
8. What Spring Boot's Embedded Server, and how do you configure it?
Answer:
Spring Boot applications typically run with an embedded server like Tomcact, Jetty, or Undertow. This means that the server is bundled with your application, so you don’t need to deploy a WAR file to an external server. You can configure the embedded server by modifying properties in the application.properties or application.yml file.
Example configuration for Tomcat (in application.properties):
server.port=8081
server.tomcat.max-threads=200
9. How do you handle exceptions in Spring Boot?
Answer:
Spring Boot provides several mechainisms to handle exceptions, such as:
- @ExceptionHandler: Used in a controller class to handle exceptions raised in a specific request-handling method.
- @controllerAdvice: Global error-handling mechanism that allows you to define centralized exception handling local across multiple controllers.
- Response Entity Exception Handler: A convenient base class for handling standard Spring MVC exceptions and customizing the response.
Example:
@ControllerAdvice
public class GlobalExceptionHandler {
@ExceptionHandler(value = CustomException.class)
public ResponseEntity<Object> handleCustomException(CustomException e) {
return new ResponseEntity<>("Custom error message", HttpStatus.BAD_REQUEST);
}
}
10. What are Profiles in Spring Boot?
Answer:
Spring Boot profiles allow you to segregate different configurations for different environments (e.g. dev, test production). You can define property file like application-dev.properties, application-prod.properties, etc. You activate a profile using the spring.profiles.active property.
spring.profiles.active=dev
You can also define beans that should be loaded only in specific profiles using the @profile annotaion.
11. How do you secure a Spring Boot application?
Answer:
Securing a Spring Boot application involves integrating Security which provides comprehensive authentication and authorization features. The key steps include:
- Adding the dependency:
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-security</artifactId>
</dependency>
- Configuring security using WebSecurityConfigurerAdapter o define user roles, password policies, and access rules.
- Using @PreAuthorize or @Secured annotations for method-level security.
Exaple:
@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {
@Override
protected void configure(HttpSecurity http) throws Exception {
http
.authorizeRequests()
.antMatchers("/admin/**").hasRole("ADMIN")
.anyRequest().authenticated()
.and().formLogin();
}
}
12. What are Spring Boot Health Indicators?
Answer:
Spring Boot health indicators provide insight into the health of your application components. They are typically exposed via the Actuator’s /actuator/health endpoint. Built-in-health indicators monitor vatious components like database, messaging queues, and external services.
You can also create custom health indicators by implementing the HealthIndicator interface:
@Component
public class CustomHealthIndicator implements HealthIndicator {
@Override
public Health health() {
if (someService.isRunning()) {
return Health.up().build();
}
return Health.down().withDetail("Error", "Service not running").build();
}
}
Conclusion
These Spring Boot interview questions and answer cover some of the most essential concepts you’ll need to master. Wheter you’re a beginner or an experienced deveoper, this guide should give you a solid foundaton for your interview preparation in 2024. Make sure to explore each concept in detail, and be ready to demostrate your understanding through real-world example. Best of luck!
