java-spring-boot

SKILL.md

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