Java Coding Standards

// ✅ クラス/レコード: PascalCase
public class MarketService {}
public record Money(BigDecimal amount, Currency currency) {}

// ✅ メソッド/フィールド: camelCase
private final MarketRepository marketRepository;
public Market findBySlug(String slug) {}

// ✅ 定数: UPPER_SNAKE_CASE
private static final int MAX_PAGE_SIZE = 100;

// ✅ recordとfinalフィールドを優先
public record MarketDto(Long id, String name, MarketStatus status) {}

public class Market {
  private final Long id;
  private final String name;
  // getterのみ、setterなし
}

// ✅ find*メソッドからOptionalを返す
Optional<Market> market = marketRepository.findBySlug(slug);

// ✅ get()の代わりにmap/flatMapを使用
return market
    .map(MarketResponse::from)
    .orElseThrow(() -> new EntityNotFoundException("Market not found"));

// ✅ 変換にストリームを使用し、パイプラインを短く保つ
List<String> names = markets.stream()
    .map(Market::name)
    .filter(Objects::nonNull)
    .toList();

// ❌ 複雑なネストされたストリームを避ける; 明確性のためにループを優先

throw new MarketNotFoundException(slug);

public <T extends Identifiable> Map<Long, T> indexById(Collection<T> items) { ... }

src/main/java/com/example/app/
  config/
  controller/
  service/
  repository/
  domain/
  dto/
  util/
src/main/resources/
  application.yml
src/test/java/... (mainをミラー)

private static final Logger log = LoggerFactory.getLogger(MarketService.class);
log.info("fetch_market slug={}", slug);
log.error("failed_fetch_market slug={}", slug, ex);