In the ever-evolving landscape of software development, Spring Boot has emerged as a pivotal framework for building robust and scalable Java applications. Its simplicity, flexibility, and rapid development capabilities have made it a top choice for both developers and organizations. If you’re gearing up for a Spring Boot interview, you’re in the right place.
Preparing for an interview can be a nerve-wracking experience, but with the right knowledge and practice, you can increase your chances of success. This post is designed to be your ultimate ally in your Spring Boot interview journey. We’ve curated a comprehensive set of often-requested Spring Boot interview questions that are frequently posed by hiring managers and technical interviewers.
Below we will present 20 of the top most famous questions. Let’s get started!
1. What is Spring Boot, and how does it differ from the traditional Spring framework?
Spring Boot is an extension of the traditional Spring framework. It simplifies the process of setting up and developing Spring applications. Here’s how it differs:
| Aspect | Spring Framework | Spring Boot |
|---|---|---|
| Configuration | Requires extensive XML configuration | Emphasizes convention over configuration, with minimal XML |
| Boilerplate Code | Requires a lot of boilerplate code | Reduces boilerplate code through auto-configuration |
| Embedded Servers | Doesn’t provide embedded server support | Provides embedded server support (e.g., Tomcat) |
| Dependency Management | Manual management of dependencies | Simplified dependency management via Starter POMs |
2. What is a Spring Boot Starter?
A Spring Boot Starter is a pre-configured set of dependencies that are commonly used together in Spring Boot applications. They simplify dependency management by providing a single dependency that includes a group of related libraries. For example, spring-boot-starter-web includes dependencies for building web applications with Spring Boot.
3. Explain the concept of auto-configuration in Spring Boot.
Auto-configuration in Spring Boot is a feature that automatically configures your application based on the JARs on the classpath. It simplifies configuration by analyzing your project’s dependencies and providing sensible defaults. For example, if you have spring-boot-starter-web on the classpath, Spring Boot will configure a web application with sensible defaults, including embedded server setup and request mapping.
4. How can you create a Spring Boot application?
You can create a Spring Boot application in several ways:
- Using Spring Initializr: A web-based tool that generates a project with your chosen dependencies.
- Using the Spring Boot CLI: A command-line tool to quickly create Spring Boot projects.
- Using your IDE: Most integrated development environments have Spring Boot project templates.
- Manually: Create a Maven or Gradle project and add Spring Boot dependencies to the build file.
5. What is the @SpringBootApplication annotation, and how does it work?
The @SpringBootApplication annotation is a combination of three annotations: @Configuration, @EnableAutoConfiguration, and @ComponentScan. It marks the main class of a Spring Boot application.
@Configuration: Indicates that the class can be used as a source of bean definitions.@EnableAutoConfiguration: Enables Spring Boot’s auto-configuration capabilities.@ComponentScan: Scans for components (e.g., controllers, services) in the specified package.
Here’s an example:
@SpringBootApplication
public class MyApplication {
public static void main(String[] args) {
SpringApplication.run(MyApplication.class, args);
}
}
6. How do you define application properties or configuration in Spring Boot?
Υou can define application properties in the application.properties or application.yml file. Properties in these files can be used to configure various aspects of your application, such as database connections, server port, or custom settings.
Here’s an example in application.properties:
server.port=8080 spring.datasource.url=jdbc:mysql://localhost/mydb
Or in application.yml:
server:
port: 8080
spring:
datasource:
url: jdbc:mysql://localhost/mydb
7. What is the purpose of the @RestController annotation?
The @RestController annotation is used to indicate that a class is a RESTful controller in a Spring Boot application. It’s a specialization of @Controller and combines @Controller and @ResponseBody, which means that methods in the class return data to be serialized directly into the HTTP response body.
Here’s an example:
@RestController
public class MyController {
@GetMapping("/hello")
public String sayHello() {
return "Hello, World!";
}
}
8. Explain the difference between @RequestMapping, @GetMapping, and @PostMapping.
These annotations are used to map HTTP requests to methods in a controller:
@RequestMapping: The most generic annotation that can handle any HTTP method. You specify the method with themethodattribute.@GetMapping: Specifically for handling HTTP GET requests.@PostMapping: Specifically for handling HTTP POST requests.
Example:
@RequestMapping(value = "/example", method = RequestMethod.GET)
public String handleGetRequest() { /* ... */ }
@GetMapping("/example")
public String handleGetRequest() { /* ... */ }
@PostMapping("/example")
public String handlePostRequest() { /* ... */ }
9. What is Spring Boot’s Actuator, and how can you enable it?
Spring Boot Actuator provides production-ready features to help you monitor and manage your application. To enable it, add the spring-boot-starter-actuator dependency to your project. Actuator endpoints provide information about application health, metrics, and more. For example, you can access the health endpoint at /actuator/health to check the application’s health status.
10. How does Spring Boot handle externalized configuration?
Spring Boot allows you to externalize configuration using property files (e.g., application.properties or application.yml). It follows a hierarchy for property resolution: system properties, environment variables, application-{profile}.properties, application-{profile}.yml, application.properties, and application.yml. Properties from more specific sources override those from less specific ones.
11. What is the purpose of the @Value annotation in Spring Boot?
The @Value annotation is used to inject values from properties files into Spring components. For example, you can inject a property value into a field like this:
@Value("${my.property}")
private String myProperty;
12. How do you secure a Spring Boot application?
Spring Boot provides security features through Spring Security. To secure a Spring Boot application, you can add the spring-boot-starter-security dependency, configure security rules, and provide user authentication details in your properties or a custom UserDetailsService.
Here’s an example of a basic security configuration:
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {
@Override
protected void configure(HttpSecurity http) throws Exception {
http
.authorizeRequests()
.antMatchers("/public/**").permitAll()
.anyRequest().authenticated()
.and()
.formLogin()
.loginPage("/login")
.permitAll()
.and()
.logout()
.permitAll();
}
}
13. What is Spring Boot’s data source auto-configuration, and how can you customize it?
Spring Boot auto-configures data sources based on the dependencies present in your project. If you need to customize the data source configuration, you can provide your own configuration by defining a DataSource bean and specifying it in your application.properties or application.yml file.
Example:
@Bean
@ConfigurationProperties("spring.datasource")
public DataSource dataSource() {
return DataSourceBuilder.create().build();
}
14. How can you create custom error pages in a Spring Boot application?
You can create custom error pages by defining error templates in the src/main/resources/templates/error folder. Spring Boot will automatically use these templates for error handling. For example, to create a custom 404 error page, you can create error/404.html.
15. What is the difference between @Repository and @Service annotations in Spring Boot?
Both @Repository and @Service are stereotypes for Spring components. However, they have different purposes:
@Repository: Used for DAO (Data Access Object) components, typically for database operations.@Service: Used for service components that contain business logic.
16. Explain the purpose of the Spring Boot TestSlice annotations: @DataJpaTest, @WebMvcTest, and @SpringBootTest.
@DataJpaTest: Focuses on testing JPA repositories and uses an embedded database. It’s suitable for testing data access components.@WebMvcTest: Focuses on testing Spring MVC controllers without starting the whole application. It’s ideal for testing web layer components.@SpringBootTest: Starts the complete Spring application context, suitable for integration testing.
17. What is Spring Boot’s embedded servlet container, and how can you change it?
Spring Boot includes an embedded servlet container by default, like Tomcat. You can change it by excluding the default and including the container you prefer in your pom.xml or build.gradle. For example, to use Jetty instead of Tomcat, exclude the spring-boot-starter-tomcat and include the spring-boot-starter-jetty.
18. How do you enable Cross-Origin Resource Sharing (CORS) in a Spring Boot application?
To enable CORS, you can configure it globally by extending the WebMvcConfigurer interface and overriding addCorsMappings method in a configuration class. Here’s an example:
@Configuration
public class CorsConfig implements WebMvcConfigurer {
@Override
public void addCorsMappings(CorsRegistry registry) {
registry.addMapping("/**")
.allowedOrigins("http://example.com")
.allowedMethods("GET", "POST", "PUT", "DELETE")
.maxAge(3600);
}
}
19. What is Spring Boot’s caching support, and how do you use it?
Spring Boot provides caching support using annotations like @Cacheable, @CachePut, and @CacheEvict. To enable caching, you can use the @EnableCaching annotation in your configuration class. Here’s an example:
@EnableCaching
@Configuration
public class CachingConfig { }
20. How can you create a custom Spring Boot starter?
To create a custom Spring Boot starter, you can follow these steps:
- Create a Maven or Gradle project.
- Organize your project structure with
src/main/resources/META-INF/spring.factoriesto define auto-configuration. - Package your custom starter as a JAR.
- Include the starter JAR in your Spring Boot application’s dependencies.
This is a high-level overview of the process, and creating a custom starter can involve more details. The key is to provide auto-configuration and make it available as a reusable dependency.
Wrapping Up
This comprehensive guide covers essential Spring Boot interview questions and provides in-depth answers, often accompanied by code examples. By mastering these concepts, you’ll be well-prepared to excel in your Spring Boot interviews and advance your career in the world of Java application development. Good luck!
