如何通过自定义spring invalidator注解校验数据合法性

package com.elon.springbootdemo.manager.invalidator;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import javax.validation.Constraint;
import javax.validation.Payload;

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy = FieldLengthInvalidatorImpl.class)
@Documented
public @interface FieldLengthInvalidator {
    // 字段支持的最大长度(字符数)
    int maxLength() default 50;
    // 校验失败后返回的错误信息
    String message() default "";
    // 分组
    Class<?>[] groups() default {};
    // 负载
    Class<? extends Payload>[] payload() default {};
}

package com.elon.springbootdemo.manager.invalidator;
import javax.validation.ConstraintValidator;
import javax.validation.ConstraintValidatorContext;

public class FieldLengthInvalidatorImpl implements ConstraintValidator<FieldLengthInvalidator, String> {
    private int maxLength = 0;
    @Override
    public void initialize(FieldLengthInvalidator invalidator) {
        maxLength = invalidator.maxLength();
    }
    @Override
    public boolean isValid(String fieldValue, ConstraintValidatorContext context) {
        if (fieldValue.length() > maxLength) {
            context.disableDefaultConstraintViolation();
            context.buildConstraintViolationWithTemplate("对象属性长度超过限制。").addConstraintViolation();
            // 校验失败返回false。返回true上游收集不到错误信息。
            return false;
        }
        return true;
    }
}

public class User
{
    private int userId = -1;
    @FieldLengthInvalidator(maxLength=10)
    private String name = "";
}

package com.elon.springbootdemo.manager;
import java.util.ArrayList;
import java.util.List;
import java.util.Set;
import javax.validation.ConstraintViolation;
import javax.validation.Validation;
import javax.validation.Validator;
import javax.validation.ValidatorFactory;

public class InvalidatORMgr {
    private InvalidatorMgr() {
        
    }
    
    
    public static InvalidatorMgr instance() {
        return InvalidatorMgrBuilder.instance;
    }
    
    
    public <T> List<String> validate(T model) {
        
        ValidatorFactory validatorFactory = Validation.buildDefaultValidatorFactory();
        Validator validator = validatorFactory.getValidator();
        Set<ConstraintViolation<T>> resultSet = validator.validate(model);
        
        List<String> messageList = new ArrayList<>();
        resultSet.forEach((r)->messageList.add(r.getMessage()));        
        return messageList;
    }
    
    
    private static class InvalidatorMgrBuilder{
        private static InvalidatorMgr instance = new InvalidatorMgr();
    }
}

        User user = new User();
        user.setName("ahskahskhqlwjqlwqlwhqlhwlqjwlqhwlhqwhqlwjjqlwl");
        List<String> messageList = InvalidatorMgr.instance().validate(user);
        System.out.println(messageList);

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-WEB</artifactId>
</dependency>
<dependency> 
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency> 
<dependency> 
    <groupId>com.h2database</groupId> 
    <artifactId>h2</artifactId>
    <version>1.4.197</version> 
    <scope>runtime</scope>
</dependency>

@Entity
public class User {
    
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;
     
    @NotBlank(message = "Name is mandatory")
    private String name;
     
    @NotBlank(message = "Email is mandatory")
    private String email;
    
    // standard constructors / setters / getters / toString    
    
}

@Repository
public interface UserRepository extends CrudRepository<User, Long> {}

@RestController
public class UserController {
 
    @PostMapping("/users")
    ResponseEntity<String> addUser(@Valid @RequestBody User user) {
        // persisting the user
        return ResponseEntity.ok("User is valid");
    }
     
    // standard constructors / other methods
     
}

@ResponseStatus(httpstatus.BAD_REQUEST)
@ExceptionHandler(MethodArgumentNotValidException.class)
public Map<String, String> handleValidationExceptions(
  MethodArgumentNotValidException ex) {
    Map<String, String> errors = new HashMap<>();
    ex.getBindingResult().getAllErrors().forEach((error) -> {
        String fieldName = ((FieldError) error).getField();
        String errorMessage = error.getDefaultMessage();
        errors.put(fieldName, errorMessage);
    });
    return errors;
}

@RunWith(SpringRunner.class) 
@WebmvcTest
@AutoConfigureMockMvc
public class UserControllerIntegrationTest {
 
    @MockBean
    private UserRepository userRepository;
     
    @Autowired
    UserController userController;
 
    @Autowired
    private MockMvc mockMvc;
 
    //...     
}

@Test
public void whenPostRequestToUsersAndValidUser_thenCorrectResponse() throws Exception {
    MediaType textPlainUtf8 = new MediaType(MediaType.TEXT_PLAIN, Charset.forName("UTF-8"));
    String user = "{\"name\": \"bob\", \"email\" : \"bob@domain.com\"}";
    mockMvc.perform(MockMvcRequestBuilders.post("/users")
      .content(user)
      .contentType(MediaType.APPLICATION_JSON_UTF8))
      .andExpect(MockMvcResultMatchers.status().isOk())
      .andExpect(MockMvcResultMatchers.content()
        .contentType(textPlainUtf8));
}
 
@Test
public void whenPostRequestToUsersAndInValidUser_thenCorrectResponse() throws Exception {
    String user = "{\"name\": \"\", \"email\" : \"bob@domain.com\"}";
    mockMvc.perform(MockMvcRequestBuilders.post("/users")
      .content(user)
      .contentType(MediaType.APPLICATION_JSON_UTF8))
      .andExpect(MockMvcResultMatchers.status().isBadRequest())
      .andExpect(MockMvcResultMatchers.jsonPath("$.name", Is.is("Name is mandatory")))
      .andExpect(MockMvcResultMatchers.content()
        .contentType(MediaType.APPLICATION_JSON_UTF8));
    }
}

@SpringBootApplication
public class Application {
     
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
     
    @Bean
    public CommandLineRunner run(UserRepository userRepository) throws Exception {
        return (String[] args) -> {
            User user1 = new User("Bob", "bob@domain.com");
            User user2 = new User("Jenny", "jenny@domain.com");
            userRepository.save(user1);
            userRepository.save(user2);
            userRepository.findAll().forEach(System.out::println);
        };
    }
}

{
  "name":"Name is mandatory",
  "email":"Email is mandatory"
}