301-frameworks-spring-boot-core

# Spring Boot Core Guidelines Apply Spring Boot Core guidelines for annotations, bean management, configuration, and dependency injection. **What is covered in this Skill?** - @SpringBootApplication and main application class - Component annotations: @RestController, @Service, @Repository - Bean definition, scoping, lifecycle - Configuration classes and @ConfigurationProperties (with @Validated for fail-fast startup) - Component scanning and package organization - Conditional configuration and profiles (@Profile, @ConditionalOn*) - Constructor dependency injection - @Primary and @Qualifier for disambiguation when multiple beans share a type - Bean minimization and composition - Graceful shutdown for in-flight work - Virtual threads on supported stacks for concurrency-bound workloads - Jakarta EE namespace consistency (jakarta.* preferred; avoid mixing legacy javax.annotation / javax.validation) - Scheduled tasks and background processing **Scope:** Apply recommendations based on the reference rules and good/bad code examples. ## Constraints Before applying any Spring Boot changes, ensure the project compiles. If compilation fails, stop immediately. After applying improvements, run full verification. - **MANDATORY**: Run `./mvnw compile` or `mvn compile` before applying any change - **SAFETY**: If compilation fails, stop immediately — compilation failure is a blocking condition - **VERIFY**: Run `./mvnw clean verify` or `mvn clean verify` after applying improvements - *...