Bean Validation：把十几行 if 从接口里赶出去

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-validation</artifactId>
</dependency>

public record UserCreateReq(

        @NotBlank(message = "用户名不能为空白")
        @Size(min = 3, max = 20, message = "用户名长度须在 3-20 之间")
        String username,

        @NotBlank
        @Pattern(regexp = "^1\\d{10}$", message = "手机号格式不正确")
        String phone,

        @NotNull
        @Min(value = 14, message = "年龄不能小于 14")
        @Max(120)
        Integer age,

        @Email(message = "邮箱格式不正确")
        String email,

        @NotNull
        @Past(message = "生日必须是过去的时间")
        LocalDate birthday
) {}

@RestController
@RequestMapping("/api/users")
public class UserController {

    @PostMapping
    public String create(@Valid @RequestBody UserCreateReq req) {
        return "ok: " + req.username();
    }
}

public record AddressReq(
        @NotBlank(message = "城市不能为空") String city,
        @NotBlank String street
) {}

public record OrderCreateReq(
        @NotBlank String title,
        @NotNull @Valid AddressReq receiver    // @Valid 在这里，少了它内部规则全部静默失效
) {}

@RestController
@Validated                                        // 类上开启方法级校验，元素校验靠它触发
@RequestMapping("/api/user-batches")
public class UserBatchController {

    @PostMapping
    public int batch(@RequestBody List<@Valid UserCreateReq> items) {
        return items.size();
    }
}

public interface OnCreate {}
public interface OnUpdate {}

public record UserSaveReq(

        @Null(groups = OnCreate.class, message = "新增时不要携带 id")
        @NotNull(groups = OnUpdate.class, message = "更新必须携带 id")
        Long id,

        @NotBlank(groups = {OnCreate.class, OnUpdate.class}, message = "用户名不能为空白")
        String username
) {}

@PostMapping
public String create(@Validated(OnCreate.class) @RequestBody UserSaveReq req) {
    return "created";
}

@PutMapping("/{id}")
public String update(@Validated(OnUpdate.class) @RequestBody UserSaveReq req) {
    return "updated";
}

@ExceptionHandler(MethodArgumentNotValidException.class)
@ResponseStatus(HttpStatus.BAD_REQUEST)
public Result<Void> handleValidation(MethodArgumentNotValidException ex) {
    String detail = ex.getBindingResult().getFieldErrors().stream()
            .map(err -> err.getField() + " " + err.getDefaultMessage())
            .collect(Collectors.joining("; "));
    return Result.fail("1001", detail);
}

@ExceptionHandler(HandlerMethodValidationException.class)
@ResponseStatus(HttpStatus.BAD_REQUEST)
public Result<Void> handleMethodValidation(HandlerMethodValidationException ex) {
    String detail = ex.getAllErrors().stream()
            .map(MessageSourceResolvable::getDefaultMessage)
            .collect(Collectors.joining("; "));
    return Result.fail("1001", detail);
}

@Documented
@Constraint(validatedBy = PhoneNumberValidator.class)
@Target({ElementType.FIELD, ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
public @interface PhoneNumber {

    String message() default "手机号格式不正确";

    Class<?>[] groups() default {};

    Class<? extends Payload>[] payload() default {};
}

public class PhoneNumberValidator implements ConstraintValidator<PhoneNumber, String> {

    private static final Pattern PATTERN = Pattern.compile("^1\\d{10}$");

    @Override
    public void initialize(PhoneNumber annotation) {
        // 注解若带参数（如允许的号段），在这里读出来存成字段；本例规则固定，无需动作
    }

    @Override
    public boolean isValid(String value, ConstraintValidatorContext context) {
        if (value == null) {
            return true;    // null 一律放行：可不可空由 @NotNull 单独管，见第 4 节惯例
        }
        return PATTERN.matcher(value).matches();
    }
}

@NotBlank
@PhoneNumber
String phone,

@Service
@Validated
public class TaskService {

    public String rename(@NotNull Long id,
                         @NotBlank @Size(max = 50, message = "标题最长 50 字") String title) {
        return "ok";
    }
}

# 合法请求：200
curl -i -X POST http://localhost:8080/api/users \
  -H "Content-Type: application/json" \
  -d '{"username":"ada","phone":"13800138000","age":30,"email":"ada@ex.com","birthday":"1995-06-01"}'

# 用户名是空白：400
curl -i -X POST http://localhost:8080/api/users \
  -H "Content-Type: application/json" \
  -d '{"username":"  ","phone":"13800138000","age":30,"birthday":"1995-06-01"}'

# 手机号少一位：400
curl -i -X POST http://localhost:8080/api/users \
  -H "Content-Type: application/json" \
  -d '{"username":"ada","phone":"1380013800","age":30,"birthday":"1995-06-01"}'

# 生日在未来：400
curl -i -X POST http://localhost:8080/api/users \
  -H "Content-Type: application/json" \
  -d '{"username":"ada","phone":"13800138000","age":30,"birthday":"2995-06-01"}'

HTTP/1.1 400
Content-Type: application/json

{"code":"1001","message":"username 用户名长度须在 3-20 之间","data":null}

curl -i -X POST http://localhost:8080/api/orders \
  -H "Content-Type: application/json" \
  -d '{"title":"买键盘","receiver":{"city":"","street":"某某路 1 号"}}'