How to validate a List<BigDecimal> with @DecimalMin and @DecimalMax?

Question

In my Spring project I have a POJO class with a property for a CMYK color. I want this property to be represented by a JSON array with exactly 4 floating-point numbers. Each number must be in the range between 0.0 and 1.0. Currently I'm struggling with the validation of this property.

I have researched already and found that the @DecimalMin and @DecimalMax annotations cannot be used on Float or float (see the answers to this question). Therefore I already abandoned List<Float> and use List<BigDecimal> instead.

Here is my stripped down POJO class:

public class Settings {

    @NotNull
    @Size(min = 4, max = 4)
    @DecimalMin("0")
    @DecimalMax("1")
    private List<BigDecimal> cmykColor;

    public List<BigDecimal> getCmykColor() {
        return cmykColor;
    }

    public void setCmykColor(List<BigDecimal> cmykColor) {
        this.cmykColor = cmykColor;
    }
}

and here the JUnit test:

@RunWith(SpringRunner.class)
@SpringBootTest
public class SettingsTest extends Assert {

    @Autowired
    private ObjectMapper objectMapper;

    @Autowired
    private Validator validator; // from org.springframework.validation

    private Errors validate(String json) throws IOException {
        Settings settings = objectMapper.readValue(json, Settings.class);
        Errors errors = new BeanPropertyBindingResult(settings, "settings");
        validator.validate(settings, errors);
        return errors;
     }

    @Test
    public void testValid() throws IOException {
        String json = "{ \"cmykColor\": [0.5, 1.0, 0.3, 0.0] }";
        Errors errors = validate(json);
        assertEquals(0, errors.getErrorCount());
    }

    @Test
    public void testTooBig() throws IOException {
        String json = "{ \"cmykColor\": [0.5, 1.01, 0.3, 0.0] }";
        Errors errors = validate(json);
        assertEquals(1, errors.getErrorCount());    
    }

    @Test
    public void testTooMany() throws IOException {
        String json = "{ \"cmykColor\": [0.5, 1.0, 0.3, 0.0, 0.0] }";
        Errors errors = validate(json);
        assertEquals(1, errors.getErrorCount());
        assertNotNull(errors.getFieldError("cmykColor"));
    }
}

When I comment out the @DecimalMin("0") and @DecimalMax("1") annotations, all test-cases succeed, except of course the testTooBig test-case, which would rely on the @DecimalMax constraint.

But when I add the @DecimalMin("0") and @DecimalMax("1") annotations, I get the following exception on all test-cases, saying that there is no validator for DecimalMax to validate List<BigDecimal>.

javax.validation.UnexpectedTypeException: HV000030: No validator could be found for constraint 'javax.validation.constraints.DecimalMax' validating type 'java.util.List<java.math.BigDecimal>'. Check configuration for 'cmykColor'
    at org.hibernate.validator.internal.engine.constraintvalidation.ConstraintTree.getExceptionForNullValidator(ConstraintTree.java:108)
    at org.hibernate.validator.internal.engine.constraintvalidation.ConstraintTree.getInitializedConstraintValidator(ConstraintTree.java:140)
    at org.hibernate.validator.internal.engine.constraintvalidation.SimpleConstraintTree.validateConstraints(SimpleConstraintTree.java:55)
    at org.hibernate.validator.internal.engine.constraintvalidation.ConstraintTree.validateConstraints(ConstraintTree.java:73)
    at org.hibernate.validator.internal.metadata.core.MetaConstraint.doValidateConstraint(MetaConstraint.java:127)
    at org.hibernate.validator.internal.metadata.core.MetaConstraint.validateConstraint(MetaConstraint.java:120)
    at org.hibernate.validator.internal.engine.ValidatorImpl.validateMetaConstraint(ValidatorImpl.java:533)
    at org.hibernate.validator.internal.engine.ValidatorImpl.validateConstraintsForSingleDefaultGroupElement(ValidatorImpl.java:496)
    at org.hibernate.validator.internal.engine.ValidatorImpl.validateConstraintsForDefaultGroup(ValidatorImpl.java:465)
    at org.hibernate.validator.internal.engine.ValidatorImpl.validateConstraintsForCurrentGroup(ValidatorImpl.java:430)
    at org.hibernate.validator.internal.engine.ValidatorImpl.validateInContext(ValidatorImpl.java:380)
    at org.hibernate.validator.internal.engine.ValidatorImpl.validate(ValidatorImpl.java:169)
    at org.springframework.validation.beanvalidation.SpringValidatorAdapter.validate(SpringValidatorAdapter.java:104)
    at com.oce.spring.domain.SettingsTest.validate(SettingsTest.java:29)
    at com.oce.spring.domain.SettingsTest.testTooMany(SettingsTest.java:58)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    ...

So, how am I supposed to use @DecimalMin("0") and @DecimalMax("1") on a List<BigDecimal> correctly?

Answer 1

We implemented container element constraints in Hibernate Validator 6.0.x.

So upgrade to Hibernate Validator 6.0.x (6.0.9.Final is the latest) and Bean Validation 2.0.1 and do as follows:

@Size(...)
private List<@DecimalMin(...) @DecimalMax(...) BigDecimal> cmykColor;

Be careful, the groupId of Hibernate Validator 6.0 is org.hibernate.validator.