public class User {
@NotNull
private Long id;

@NotBlank
@Size(min = 2, max = 50)
private String firstName;
@NotBlank
@Size(min = 2, max = 50)
private String lastName;
@Email
private String email;
@NotNull
@Min(18)
@Max(99)
private Integer age;
@NotEmpty
private List<String> hobbies;
@Pattern(regexp = "[A-Z]{2}\d{4}")
private String employeeId;

@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy = UniqueTitleValidator.class)
public @interface UniqueTitle {
String message() default “Title must be unique”;
Class<?>[] groups() default {};
Class<? extends Payload>[] payload() default {};
}

public interface PostRepository extends JpaRepository<Post, Long> {
Post findByTitle(String title);
}

@Component
public class UniqueTitleValidator implements ConstraintValidator<UniqueTitle, String> {
@Autowired
private PostRepository postRepository;
@Override
public boolean isValid(String title, ConstraintValidatorContext context) {
    if (title == null) {
        return true;
    }
    return Objects.isNull(postRepository.findByTitle(title));
}
}

public class Post {
@UniqueTitle
private String title;
@NotNull
private String body;
}

public class UserDTO {
@NotBlank
private String username;
@NotBlank
private String password;
}

@RestController
@RequestMapping(“/users”)
@Validated
public class UserController {
@Autowired
private UserService userService;
@PostMapping
public ResponseEntity<String> createUser(@Valid @RequestBody UserDTO userDto) {
    userService.createUser(userDto);
    return ResponseEntity.status(HttpStatus.CREATED).body("User created successfully");
}
}

public class User {
@NotBlank(message = "用戶名不能為空")
private String name;
@NotBlank(message = "Email不能為空")
@Email(message = "無(wú)效的Emaild地址")
private String email;
@NotNull(message = "年齡不能為空")
@Min(value = 18, message = "年齡必須大于18")
@Max(value = 99, message = "年齡必須小于99")
private Integer age;
}

@RestController
@RequestMapping(“/users”)
public class UserController {
@Autowired
private UserService userService;
@PostMapping
public ResponseEntity<String> createUser(@Valid @RequestBody User user, BindingResult result) {
    if (result.hasErrors()) {
        List<String> errorMessages = result.getAllErrors().stream()
                .map(DefaultMessageSourceResolvable::getDefaultMessage)
                .collect(Collectors.toList());
        return ResponseEntity.badRequest().body(errorMessages.toString());
    }
    // save the user to the database using UserService
    userService.saveUser(user);
    return ResponseEntity.status(HttpStatus.CREATED).body("User created successfully");
}
}

user.name.required=Name is required.
user.email.invalid=Invalid email format.
user.age.invalid=Age must be a number between 18 and 99.

user.name.required=名稱不能為空.
user.email.invalid=無(wú)效的email格式.
user.age.invalid=年齡必須在18到99歲之間.

public class User {
@NotNull(message = “{user.id.required}”)
private Long id;
@NotBlank(message = "{user.name.required}")
private String name;
@Email(message = "{user.email.invalid}")
private String email;
@NotNull(message = "{user.age.required}")
@Min(value = 18, message = "{user.age.invalid}")
@Max(value = 99, message = "{user.age.invalid}")
private Integer age;
}

@Configuration
public class AppConfig {
@Bean
public MessageSource messageSource() {
ResourceBundleMessageSource messageSource = new ResourceBundleMessageSource();
messageSource.setBasename(“messages”);
messageSource.setDefaultEncoding(“UTF-8”);
return messageSource;
}
@Bean
public LocalValidatorFactoryBean validator() {
    LocalValidatorFactoryBean validatorFactoryBean = new LocalValidatorFactoryBean();
    validatorFactoryBean.setValidationMessageSource(messageSource());
    return validatorFactoryBean;
}
}

public class User {
@NotBlank(groups = Default.class)
private String firstName;
@NotBlank(groups = Default.class)
private String lastName;
@Email(groups = EmailNotEmpty.class)
private String email;
// getters and setters omitted for brevity
public interface EmailNotEmpty {}
public interface Default {}
}

@RestController
@RequestMapping(“/users”)
@Validated
public class UserController {
public ResponseEntity createUser(
@Validated({org.example.model.ex6.User.EmailNotEmpty.class}) @RequestBody User userWithEmail,
@Validated({User.Default.class}) @RequestBody User userWithoutEmail)
{
// Create the user and return a success response
}

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy = EndDateAfterStartDateValidator.class)
public @interface EndDateAfterStartDate {
String message() default “End date must be after start date”;
Class<?>[] groups() default {};
Class<? extends Payload>[] payload() default {};
}

public class EndDateAfterStartDateValidator implements ConstraintValidator<EndDateAfterStartDate, TaskForm> {
@Override
public boolean isValid(TaskForm taskForm, ConstraintValidatorContext context) {
if (taskForm.getStartDate() == null || taskForm.getEndDate() == null) {
return true;
}
    return taskForm.getEndDate().isAfter(taskForm.getStartDate());
}
}

@EndDateAfterStartDate
public class TaskForm {
@NotNull
@DateTimeFormat(pattern = “yyyy-MM-dd”)
private LocalDate startDate;
@NotNull
@DateTimeFormat(pattern = "yyyy-MM-dd")
private LocalDate endDate;
}

@RestControllerAdvice
public class RestExceptionHandler extends ResponseEntityExceptionHandler {
@ExceptionHandler(MethodArgumentNotValidException.class)
protected ResponseEntity<Object> handleMethodArgumentNotValid(MethodArgumentNotValidException ex,
                                                              HttpHeaders headers, HttpStatus status,
                                                              WebRequest request) {
    Map<String, Object> body = new LinkedHashMap<>();
    body.put("timestamp", LocalDateTime.now());
    body.put("status", status.value());
    // Get all errors
    List<String> errors = ex.getBindingResult()
            .getFieldErrors()
            .stream()
            .map(x -> x.getDefaultMessage())
            .collect(Collectors.toList());
    body.put("errors", errors);
    return new ResponseEntity<>(body, headers, status);
}
}

@DataJpaTest
public class UserValidationTest {
@Autowired
private TestEntityManager entityManager;
@Autowired
private Validator validator;
@Test
public void testValidation() {
    User user = new User();
    user.setFirstName("John");
    user.setLastName("Doe");
    user.setEmail("invalid email");
    Set<ConstraintViolation<User>> violations = validator.validate(user);
    assertEquals(1, violations.size());
    assertEquals("must be a well-formed email address", violations.iterator().next().getMessage());
}
}