类成员顺序

public class Example {
    // 1. 静态常量
    public static final String CONSTANT = "value";

    // 2. 静态变量
    private static Logger logger = LoggerFactory.getLogger(Example.class);

    // 3. 实例变量
    private Long id;

    // 4. 构造函数
    public Example() { }

    // 5. 静态方法
    public static Example create() { return new Example(); }

    // 6. 实例方法（公共 → 私有）
    public void doSomething() { }
    private void helperMethod() { }

    // 7. getter/setter（或使用 Lombok）
}

DTO/VO 类规范

// ❌ 手写 getter/setter
public class UserDTO {
    private Long id;
    private String name;
    public Long getId() { return id; }
    public void setId(Long id) { this.id = id; }
    // ... 大量样板代码
}

// ✅ 使用 Lombok
@Data
public class UserDTO {
    private Long id;
    private String name;
}

批量查询规范

// ❌ 1700 个 ID 一次查询
List<User> users = userRepository.findByIdIn(allIds); // IN 子句过长

// ✅ 分批查询工具方法
public static <T, R> List<R> batchQuery(List<T> params, int batchSize,
                                         Function<List<T>, List<R>> queryFn) {
    List<R> result = new ArrayList<>();
    for (int i = 0; i < params.size(); i += batchSize) {
        List<T> batch = params.subList(i, Math.min(i + batchSize, params.size()));
        result.addAll(queryFn.apply(batch));
    }
    return result;
}

// 使用
List<User> users = batchQuery(allIds, 500, ids -> userRepository.findByIdIn(ids));

N+1 查询防范

// ❌ N+1：循环内逐行查询 count
records.forEach(record -> {
    long count = deviceRepo.countByDeviceId(record.getDeviceId()); // 每条触发一次查询
    record.setDeviceCount(count);
});

// ✅ 循环外批量查询 + Map 查找
List<String> deviceIds = records.stream()
    .map(Record::getDeviceId).distinct().collect(Collectors.toList());
Map<String, Long> countMap = deviceRepo.countByDeviceIdIn(deviceIds).stream()
    .collect(Collectors.toMap(CountDTO::getDeviceId, CountDTO::getCount));
records.forEach(r -> r.setDeviceCount(countMap.getOrDefault(r.getDeviceId(), 0L)));

常见 N+1 场景及修复模式：

并发安全规范

// ❌ read-modify-write 竞态条件
PointsAccount account = accountRepo.findById(id);
account.setBalance(account.getBalance() + points); // 并发时丢失更新
accountRepo.save(account);

// ✅ 方案一：原子更新 SQL
@Modifying
@Query("UPDATE PointsAccount SET balance = balance + :points WHERE id = :id")
int addBalance(@Param("id") Long id, @Param("points") int points);

// ✅ 方案二：乐观锁
@Version
private Long version; // Entity 中添加版本字段



// ❌ check-then-act 无兜底（并发下可能重复结算）
if (!rewardRepo.existsByTenantIdAndPeriod(tenantId, period)) {
    rewardRepo.save(new RankingReward(...));
}

// ✅ 唯一索引兜底 + 异常捕获
// DDL: UNIQUE INDEX uk_tenant_period (tenant_id, ranking_type, period, rank_position)
try {
    rewardRepo.save(new RankingReward(...));
} catch (DataIntegrityViolationException e) {
    log.warn("重复结算已被唯一索引拦截: tenantId={}, period={}", tenantId, period);
}

异常处理

// ✅ 好：捕获具体异常，添加上下文
try {
    user = userRepository.findById(id);
} catch (DataAccessException e) {
    throw new ServiceException("Failed to find user: " + id, e);
}

// ✅ 好：资源自动关闭
try (InputStream is = new FileInputStream(file)) {
    // 使用资源
}

// ❌ 差：捕获过宽
catch (Exception e) { e.printStackTrace(); }

空值处理

// ✅ 使用 Optional
public Optional<User> findById(Long id) {
    return userRepository.findById(id);
}

// ✅ 参数校验
public void updateUser(User user) {
    Objects.requireNonNull(user, "user must not be null");
}

// ✅ 安全的空值处理
String name = Optional.ofNullable(user)
    .map(User::getName)
    .orElse("Unknown");

并发编程

// ✅ 使用 ExecutorService
ExecutorService executor = Executors.newFixedThreadPool(10);
Future<Result> future = executor.submit(() -> doWork());

// ✅ 使用 CompletableFuture
CompletableFuture<User> future = CompletableFuture
    .supplyAsync(() -> findUser(id))
    .thenApply(user -> enrichUser(user));

// ❌ 差：直接创建线程
new Thread(() -> doWork()).start();

测试规范 (JUnit 5)

class UserServiceTest {
    @Test
    @DisplayName("根据 ID 查找用户 - 用户存在时返回用户")
    void findById_whenUserExists_returnsUser() {
        // given
        when(userRepository.findById(1L)).thenReturn(Optional.of(expected));

        // when
        Optional<User> result = userService.findById(1L);

        // then
        assertThat(result).isPresent();
        assertThat(result.get().getName()).isEqualTo("test");
    }
}

Spring Boot 规范

// ✅ 构造函数注入
@Service
@RequiredArgsConstructor
public class UserService {
    private final UserRepository userRepository;
    private final EmailService emailService;
}

// ✅ REST Controller
@RestController
@RequestMapping("/api/users")
public class UserController {
    @GetMapping("/{id}")
    public ResponseEntity<UserDto> findById(@PathVariable Long id) {
        return userService.findById(id)
            .map(ResponseEntity::ok)
            .orElse(ResponseEntity.notFound().build());
    }
}

Auth Filter 降级原则

输入校验规范

常见 DTO 字段校验速查 ：

// ❌ 无校验，任意输入直接进入业务逻辑
@PostMapping("/ship")
public Result ship(@RequestBody ShippingRequest request) { ... }

// ✅ 完整校验
@PostMapping("/ship")
public Result ship(@RequestBody @Valid ShippingRequest request) { ... }

public record ShippingRequest(
    @NotNull Long orderId,
    @NotBlank @Size(max = 500) String shippingInfo,
    @Pattern(regexp = "pending|shipped|delivered") String giftStatus
) {}

// ❌ quantity 只有 @NotNull，负数会导致 Redis DECRBY 反向加库存
public record CreateOrderRequest(
    @NotNull Integer quantity  // 可提交 0 或负数
) {}

// ✅ 数量必须 >= 1
public record CreateOrderRequest(
    @NotNull @Min(1) Integer quantity
) {}

// ❌ 分页无上限，用户可传 size=999999
@GetMapping("/orders")
public Result list(@RequestParam int page, @RequestParam int size) { ... }

// ✅ 分页参数加约束
@GetMapping("/orders")
public Result list(@RequestParam @Min(1) int page,
                   @RequestParam @Min(1) @Max(100) int size) { ... }

性能优化

Native SQL 规范

别名避免 MySQL 保留字

@Query(nativeQuery = true) 中的列别名如果是 MySQL 保留字，会导致语法错误。

高频踩坑保留字 ：year_month, order, status, key, value, name, type, date, time, rank, range, rows, column, user, role, group

// ❌ year_month 是 MySQL 保留字（INTERVAL YEAR_MONTH）
@Query(value = """
    SELECT DATE_FORMAT(o.order_date, '%Y-%m') as year_month,
           COUNT(*) as cnt
    FROM orders o
    GROUP BY year_month
    """, nativeQuery = true)

// ✅ 改用非保留字别名
@Query(value = """
    SELECT DATE_FORMAT(o.order_date, '%Y-%m') as ym,
           COUNT(*) as cnt
    FROM orders o
    GROUP BY ym
    """, nativeQuery = true)

日志规范

// ✅ 参数化日志
log.debug("Finding user by id: {}", userId);
log.info("User {} logged in successfully", username);
log.error("Failed to process order {}", orderId, exception);

// ❌ 差：字符串拼接
log.debug("Finding user by id: " + userId);

详细参考

📋 本回复遵循：java-dev - [具体章节]

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