Java Spring Boot Skill Build production-ready Spring Boot applications with modern best practices. Overview This skill covers Spring Boot development including REST APIs, security configuration, data access, actuator monitoring, and cloud integration. Follows Spring Boot 3.x patterns with emphasis on production readiness. When to Use This Skill Use when you need to: Create REST APIs with Spring MVC/WebFlux Configure Spring Security (OAuth2, JWT) Set up database access with Spring Data Enable monitoring with Actuator Integrate with Spring Cloud Topics Covered Spring Boot Core Auto-configuration and starters Application properties and profiles Bean lifecycle and configuration DevTools and hot reload REST API Development @RestController and @RequestMapping Request/response handling Validation with Bean Validation Exception handling with @ControllerAdvice Spring Security SecurityFilterChain configuration OAuth2 and JWT authentication Method security (@PreAuthorize) CORS and CSRF configuration Spring Data JPA Repository pattern Query methods and @Query Pagination and sorting Auditing and transactions Actuator & Monitoring Health checks and probes Metrics with Micrometer Custom endpoints Prometheus integration Quick Reference // REST Controller @RestController @RequestMapping ( "/api/users" ) @Validated public class UserController { @GetMapping ( "/{id}" ) public ResponseEntity < User

getUser ( @PathVariable Long id ) { return userService . findById ( id ) . map ( ResponseEntity :: ok ) . orElse ( ResponseEntity . notFound ( ) . build ( ) ) ; } @PostMapping public ResponseEntity < User

createUser ( @Valid @RequestBody UserRequest request ) { User user = userService . create ( request ) ; URI location = URI . create ( "/api/users/" + user . getId ( ) ) ; return ResponseEntity . created ( location ) . body ( user ) ; } } // Security Configuration @Configuration @EnableWebSecurity public class SecurityConfig { @Bean public SecurityFilterChain filterChain ( HttpSecurity http ) throws Exception { return http . csrf ( csrf -> csrf . disable ( ) ) . sessionManagement ( s -> s . sessionCreationPolicy ( STATELESS ) ) . authorizeHttpRequests ( auth -> auth . requestMatchers ( "/actuator/health/" ) . permitAll ( ) . requestMatchers ( "/api/public/" ) . permitAll ( ) . anyRequest ( ) . authenticated ( ) ) . oauth2ResourceServer ( oauth2 -> oauth2 . jwt ( Customizer . withDefaults ( ) ) ) . build ( ) ; } } // Exception Handler @RestControllerAdvice public class GlobalExceptionHandler { @ExceptionHandler ( EntityNotFoundException . class ) public ProblemDetail handleNotFound ( EntityNotFoundException ex ) { return ProblemDetail . forStatusAndDetail ( NOT_FOUND , ex . getMessage ( ) ) ; } } Configuration Templates

application.yml

spring : application : name : $ { APP_NAME : my - service } profiles : active : $ { SPRING_PROFILES_ACTIVE : local } jpa : open-in-view : false properties : hibernate : jdbc.batch_size : 50 management : endpoints : web : exposure : include : health , info , metrics , prometheus endpoint : health : probes : enabled : true server : error : include-stacktrace : never Common Patterns Layer Architecture Controller → Service → Repository → Database ↓ ↓ ↓ DTOs Entities Entities Validation Patterns public record CreateUserRequest ( @NotBlank @Size ( max = 100 ) String name , @Email @NotBlank String email , @NotNull @Min ( 18 ) Integer age ) { } Troubleshooting Common Issues Problem Cause Solution Bean not found Missing @Component Add annotation or @Bean Circular dependency Constructor injection Use @Lazy or refactor 401 Unauthorized Security config Check permitAll paths Slow startup Heavy auto-config Exclude unused starters Debug Properties debug = true logging.level.org.springframework.security = DEBUG spring.jpa.show-sql = true Debug Checklist □ Check /actuator/conditions □ Verify active profiles □ Review security filter chain □ Check bean definitions □ Test health endpoints Usage Skill("java-spring-boot")