java-spring-boot

# 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 ```java // 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 ```yaml # 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 ```java 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 ```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") ``` ## Related Skills - `java-testing` - Spring test patterns - `java-jpa-hibernate` - Data access