spring boot one liner

Here’s a Spring Boot Interview One-Liners Cheat Sheet — designed for fast recall, last-minute prep, and real interview advantage, especially if you have 3–6 years of experience with Spring Boot, REST APIs, and Microservices.

⚡ Spring Boot Interview One-Liners

🔹 Core Concepts

• @SpringBootApplication = @Configuration + @EnableAutoConfiguration + @ComponentScan.
• Spring Boot uses embedded servers like Tomcat, Jetty, or Undertow.
• Spring Boot follows convention over configuration.
• application.properties / application.yml → externalized configuration.

🔹 Dependency Injection (DI)

• @Component → generic Spring-managed bean.
• @Service → service-layer bean.
• @Repository → persistence-layer bean with exception translation.
• @Controller vs @RestController: the latter = @Controller + @ResponseBody.

🔹 REST API Development

• @GetMapping, @PostMapping, etc. map HTTP methods.
• @RequestParam → for query parameters.
• @PathVariable → for URL path variables.
• @RequestBody → bind JSON to Java object.
• @ResponseEntity → customize status code and body in response.

🔹 Configuration & Properties

• Use @Value("${property.name}") to inject property.
• Use @ConfigurationProperties(prefix = "app") to bind multiple config values to a bean.
• Profiles: @Profile("dev") activates a bean for a specific environment.
• Activate profile with spring.profiles.active=dev.

🔹 Spring Boot Annotations

• @EnableAutoConfiguration scans the classpath and auto-configures beans.
• @Bean declares a Spring-managed bean manually.
• @Primary marks a bean as the default when multiple candidates exist.
• @ConditionalOnProperty conditionally loads a bean based on property value.

🔹 Data Access (Spring Data JPA)

• JpaRepository provides CRUD methods out of the box.
• Method names like findByEmailAndStatus() auto-generate queries.
• @Query lets you write custom JPQL or native queries.
• Transactions are handled via @Transactional.

🔹 Exception Handling

• @ControllerAdvice handles exceptions across the whole app.
• @ExceptionHandler(SomeException.class) maps specific exception handlers.
• Return ResponseEntity for flexible status + body responses.

🔹 Actuator & Monitoring

• Spring Boot Actuator exposes production-ready endpoints like /actuator/health.
• Enable endpoints via management.endpoints.web.exposure.include=*.
• Use for health checks, metrics, and tracing.

🔹 Security (Spring Security Basics)

• WebSecurityConfigurerAdapter is deprecated in Spring Security 5.7+; use SecurityFilterChain bean.
• @PreAuthorize("hasRole('ADMIN')") secures method-level access.
• Spring Security uses UserDetailsService for custom authentication logic.
• CSRF protection is enabled by default (disable for APIs if needed).

🔹 Dev Tools & Productivity

• spring-boot-devtools enables hot reload during development.
• @SpringBootTest loads the entire application context for integration tests.
• @WebMvcTest focuses only on web layer (controllers).

🔹 API Versioning

• Common methods: in URL path (/v1/users) or in headers (X-API-VERSION).
• Not supported out-of-box — must be handled manually or using libraries.

🔹 Application Startup

• CommandLineRunner and ApplicationRunner run code after app startup.
• Useful for initializations like database seeding or startup logs.

🔹 Profiles and Environments

• application-{profile}.properties allows profile-based config.
• Use @Profile("test") to conditionally load beans.

🔹 Embedded Server Config

• Change port: server.port=8081
• Customize context path: server.servlet.context-path=/api
• Add SSL by configuring server.ssl.* properties.

🔹 Logging

• Uses Spring Boot default logging (Logback).
• Customize with logging.level.root=DEBUG or per-package levels.
• Output format can be customized via logback-spring.xml.

🔹 Packaging & Deployment

• Spring Boot apps are self-contained JARs with an embedded server.
• Use mvn clean package or gradle bootJar to build.
• Run with java -jar target/app.jar

🔹 DevOps & Deployment Tips

• Use environment variables for secrets/configs.
• Spring Boot supports Docker and Kubernetes out-of-the-box.
• Health endpoints (/actuator/health) are useful in cloud deployments.

🔹 Best Practices

• Use DTOs to avoid exposing internal entities.
• Validate inputs using @Valid + @NotNull, @Size, etc.
• Use ModelMapper or MapStruct for converting Entity ↔ DTO.
• Use logging frameworks (Slf4j, Logback) instead of System.out.

✅ You’re now covered for:

• REST APIs
• Config, Security, and Persistence
• Error handling
• Profiles, Actuator, Deployment
• Interview-tricky annotations and behaviors

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