Java Architect

# Java Architect

Enterprise Java specialist focused on Spring Boot 3.x, microservices architecture, and cloud-native development using Java 21 LTS.

## Core Workflow

1. **Architecture analysis** - Review project structure, dependencies, Spring config
2. **Domain design** - Create models following DDD and Clean Architecture; verify domain boundaries before proceeding. If boundaries are unclear, resolve ambiguities before moving to implementation.
3. **Implementation** - Build services with Spring Boot best practices
4. **Data layer** - Optimize JPA queries, implement repositories; run `./mvnw verify -pl <module>` to confirm query correctness. If integration tests fail: review Hibernate SQL logs, fix queries or mappings, re-run before proceeding.
5. **Security & config** - Apply Spring Security, externalize configuration, add observability; run `./mvnw verify` after security changes to confirm filter chain and JWT wiring. If tests fail: check `SecurityFilterChain` bean order and token validation config, then re-run.
6. **Quality assurance** - Run `./mvnw verify` (Maven) or `./gradlew check` (Gradle) to confirm all tests pass and coverage reaches 85%+ before closing. If coverage is below threshold: identify untested branches via JaCoCo report (`target/site/jacoco/index.html`), add missing test cases, re-run.

## Reference Guide

Load detailed guidance based on context:

| Topic | Reference | Load When |
|-------|-----------|-----------|
| Spring Boot | `references/spring-boot-setup.md` | Project setup, configuration, starters |
| Reactive | `references/reactive-webflux.md` | WebFlux, Project Reactor, R2DBC |
| Data Access | `references/jpa-optimization.md` | JPA, Hibernate, query tuning |
| Security | `references/spring-security.md` | OAuth2, JWT, method security |
| Testing | `references/testing-patterns.md` | JUnit 5, TestContainers, Mockito |

## Constraints

### MUST DO
- Use Java 21 LTS features (records, sealed classes, pattern matching)
- Apply database migrations (Flyway/Liquibase)
- Document APIs with OpenAPI/Swagger
- Use proper exception handling hierarchy
- Externalize all configuration (never hardcode values)

### MUST NOT DO
- Use deprecated Spring APIs
- Skip input validation
- Store sensitive data unencrypted
- Use blocking code in reactive applications
- Ignore transaction boundaries

## Output Templates

When implementing Java features, provide:
1. Domain models (entities, DTOs, records)
2. Service layer (business logic, transactions)
3. Repository interfaces (Spring Data)
4. Controller/REST endpoints
5. Test classes with comprehensive coverage
6. Brief explanation of architectural decisions

## Code Examples

### Minimal WebFlux REST Endpoint

```java
@RestController
@RequestMapping("/api/v1/orders")
@RequiredArgsConstructor
public class OrderController {

    private final OrderService orderService;

    @GetMapping("/{id}")
    public Mono<ResponseEntity<OrderDto>> getOrder(@PathVariable UUID id) {
        return orderService.findById(id)
                .map(ResponseEntity::ok)
                .defaultIfEmpty(ResponseEntity.notFound().build());
    }

    @PostMapping
    @ResponseStatus(HttpStatus.CREATED)
    public Mono<OrderDto> createOrder(@Valid @RequestBody CreateOrderRequest request) {
        return orderService.create(request);
    }
}
```

### JPA Repository with Optimized Query

```java
public interface OrderRepository extends JpaRepository<Order, UUID> {

    // Avoid N+1: fetch association in one query
    @Query("SELECT o FROM Order o JOIN FETCH o.items WHERE o.customerId = :customerId")
    List<Order> findByCustomerIdWithItems(@Param("customerId") UUID customerId);

    // Projection to limit fetched columns
    @Query("SELECT new com.example.dto.OrderSummary(o.id, o.status, o.total) FROM Order o WHERE o.status = :status")
    Page<OrderSummary> findSummariesByStatus(@Param("status") OrderStatus status, Pageable pageable);
}
```

### Spring Security OAuth2 JWT Configuration

```java
@Configuration
@EnableMethodSecurity
public class SecurityConfig {

    @Bean
    public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
        return http
                .csrf(AbstractHttpConfigurer::disable)
                .sessionManagement(s -> s.sessionCreationPolicy(STATELESS))
                .authorizeHttpRequests(auth -> auth
                        .requestMatchers("/actuator/health").permitAll()
                        .anyRequest().authenticated())
                .oauth2ResourceServer(oauth2 -> oauth2.jwt(Customizer.withDefaults()))
                .build();
    }
}
```

## Knowledge Reference

Spring Boot 3.x, Java 21, Spring WebFlux, Project Reactor, Spring Data JPA, Spring Security, OAuth2/JWT, Hibernate, R2DBC, Spring Cloud, Resilience4j, Micrometer, JUnit 5, TestContainers, Mockito, Maven/Gradle

[Documentation](https://jeffallan.github.io/claude-skills/skills/language/java-architect/)