Java Spring Boot

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")

Related Skills

• java-testing - Spring test patterns
• java-jpa-hibernate - Data access