java11-jsr303-custom-validation

preface

• https://github.com/mtumilowicz/java-bean-validation2
• JSR303 - https://beanvalidation.org/2.0/spec/
• validating data is a common task that occurs throughout an application, from the presentation layer to the persistence layer
• often the same validation logic is implemented in each layer, proving to be time consuming and error-prone
• JSR defines a metadata model and API for JavaBean validation
• default metadata source is annotations, with the ability to override and extend the metadata through the use of XML validation descriptors
• declaring these constraints does not automatically cause their validation when the concerned methods are invoked - it’s the responsibility of an integration layer (Spring, Hibernate...) to trigger the validation of the constraints using a method interceptor, dynamic proxy or similar
• bean Validation itself doesn’t trigger the evaluation of method constraints
• just annotating any methods or constructors with parameter or return value constraints doesn’t automatically enforce these constraints, just as annotating any fields or properties with bean constraints doesn’t enforce these either
• @Valid - tells Spring to pass the object to a Validator before doing anything else
• if the input class contains a field with another complex type that should be validated, this field, needs to be annotated with @Valid

project description

• we have User

  public class User {
      String name;
  }
  

  and we want to validate if a name is a proper word
• regex for a word character ([a-zA-Z_0-9]): [\w]
• JSR303
  • annotation

    @Constraint(validatedBy = WordValidator.class)
    @Target(ElementType.FIELD)
    @Retention(RetentionPolicy.RUNTIME)
    public @interface Word {
        String message() default "is not a proper word!";
        Class<?>[] groups() default {};
        Class<? extends Payload>[] payload() default {};
    }
    

    • we need groups() and payload(), otherwise Internal Server Error, 500 - "HV000074: com.example.validation.app.domain.patterns.Word contains Constraint annotation, but does not contain a groups parameter."
  • validator

    class WordValidator implements ConstraintValidator<Word, String> {
    
        private static final Predicate<String> PATTERN = Pattern.compile("[\\w]+").asMatchPredicate();
    
        @Override
        public void initialize(Word word) {
        }
    
        @Override
        public boolean isValid(String word,
                               ConstraintValidatorContext cxt) {
            return isNull(word) || PATTERN.test(word);
        }
    
    }
    

• endpoint

  @RestController
  @RequestMapping("/users")
  public class UserController {
      
      @PostMapping("register")
      public ResponseEntity<User> register(@RequestBody @Valid User user) {
          return ResponseEntity.ok(user);
      }
  }
  

• final version of User

  @Value
  @Builder
  public class User {
  
      @NotBlank
      @Word
      String name;
  
      @JsonCreator(mode = JsonCreator.Mode.PROPERTIES)
      public User(@JsonProperty("name") String name) {
          this.name = name;
      }
  }
  

  • @JsonCreator and dedicated constructor are to prevent JSON parse error: cannot deserialize from Object value, note that User is immutable
• swagger: http://localhost:8080/swagger-ui.html#
  • users/register, response for a user with %%% as name:

    {
      "timestamp": "2019-03-11T09:03:53.983+0000",
      "status": 400,
      "error": "Bad Request",
      "errors": [
        {
          "codes": [
            "Word.user.name",
            "Word.name",
            "Word.java.lang.String",
            "Word"
          ],
          "arguments": [
            {
              "codes": [
                "user.name",
                "name"
              ],
              "arguments": null,
              "defaultMessage": "name",
              "code": "name"
            }
          ],
          "defaultMessage": "is not a proper word!",
          "objectName": "user",
          "field": "name",
          "rejectedValue": "%%%",
          "bindingFailure": false,
          "code": "Word"
        }
      ],
      "message": "Validation failed for object='user'. Error count: 1",
      "path": "/users/register"
    }