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")

Related Skills

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