Top 10 High‑Frequency Spring Boot Interview Questions and Answers

Spring Boot has become a staple in Java developer interviews, and many candidates struggle with its core concepts. This article collects ten high‑frequency interview questions and provides concise, English‑language answers.

1. What is the biggest advantage of Spring Boot? It follows the "convention over configuration" principle, reducing the number of decisions developers must make while retaining flexibility.

2. Where does this principle manifest? In Spring Boot Starters and Spring Boot JPA, which automatically initialize resources and generate SQL based on conventions.

3. How does a Spring Boot Starter work? During startup Spring Boot scans the resources/META-INF/spring.factories files of its starter dependencies, loads the listed AutoConfigure classes, and registers beans according to @Conditional conditions.

4. How is automatic configuration implemented? The @SpringBootApplication annotation combines @Configuration, @ComponentScan, and @EnableAutoConfiguration. The latter imports AutoConfigurationImportSelector, which reads META-INF/spring.factories and registers the appropriate auto‑configuration classes.

5. What is an embedded server and why use it? An embedded server (e.g., Tomcat) is packaged inside the executable JAR, allowing the application to run with a single Java command without a separate servlet container installation.

6. How to handle distributed transactions? Spring Boot can integrate Atomikos, but it is usually discouraged due to latency; compensation via messaging is preferred.

7. Relationship among Shiro, OAuth, and CAS? CAS and OAuth provide single‑sign‑on, while Shiro handles authorization. They are often combined (e.g., CAS+Shiro or OAuth+Shiro) to achieve both authentication and permission control.

8. When to choose RESTful vs RPC for inter‑service communication? RPC can be slightly faster, but for most projects RESTful (via Spring Cloud) is simpler and language‑agnostic.

9. How to design a stateless service? Separate stateful data into dedicated data services (e.g., distributed caches) so business services become pure computation nodes that can scale horizontally.

10. Common Spring Cache annotations? @Cacheable (store method result), @CachePut (always execute and update cache), and @CacheEvict (remove entries).

11. Enabling CORS in Spring Boot

@Configuration
public class GlobalCorsConfig {
    @Bean
    public CorsFilter corsFilter() {
        CorsConfiguration config = new CorsConfiguration();
        config.addAllowedOrigin("*");
        config.setAllowCredentials(true);
        config.addAllowedMethod("*");
        config.addAllowedHeader("*");
        config.addExposedHeader("*");
        UrlBasedCorsConfigurationSource configSource = new UrlBasedCorsConfigurationSource();
        configSource.registerCorsConfiguration("/**", config);
        return new CorsFilter(configSource);
    }
}

Alternatively, override addCorsMappings in the main application class:

public class Application extends WebMvcConfigurerAdapter {
    @Override
    public void addCorsMappings(CorsRegistry registry) {
        registry.addMapping("/**")
                .allowCredentials(true)
                .allowedHeaders("*")
                .allowedOrigins("*")
                .allowedMethods("*");
    }
}

12. JPA vs Hibernate – JPA is a specification; Hibernate is one of its implementations. JPA defines interfaces, while Hibernate provides the actual ORM engine. Dynamic SQL is better supported by MyBatis, but JPA can achieve it with programmatic entity creation.

13. Relationship among Spring, Spring Boot, and Spring Cloud – Spring provides core IoC and AOP. Spring Boot builds on Spring to simplify configuration and packaging. Spring Cloud extends Spring Boot with distributed‑system utilities such as service discovery, configuration management, and circuit breaking.