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How to return all valid enum values to API client as JSON when using custom validation annotation

I need to return to API client list of valid DecisionStates when the client passes invalid string that cannot be mapped to DecisionStates enum.
Annotataion definition:
#Target({METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER, TYPE_USE})
#Retention(RUNTIME)
#Documented
#Constraint(validatedBy = ValueOfEnumValidator.class)
public #interface ValueOfEnum {
Class<? extends Enum<?>> enumClass();
String message() default "must be any of enum {enumClass}: [" + Arrays.toString(enumClass().getEnumConstants()).replaceAll("^.|.$", "") + "]"; // <-- not compiling
Class<?>[] groups() default {};
Class<? extends Payload>[] payload() default {};
}
DTO:
#ValueOfEnum(enumClass = DecisionState.class)
String state;
ConstraintValidator implementation:
public class ValueOfEnumValidator implements ConstraintValidator<ValueOfEnum, CharSequence> {
private List<String> acceptedValues;
#Override
public void initialize(ValueOfEnum annotation) {
acceptedValues = Stream.of(annotation.enumClass().getEnumConstants())
.map(Enum::name)
.collect(Collectors.toList());
}
#Override
public boolean isValid(CharSequence value, ConstraintValidatorContext context) {
if (value == null) {
return true;
}
return acceptedValues.contains(value.toString());
}
}

Is it possible to overload SpringBoot's ConstraintValidator isValid method?

Essentially, my service takes the role of streamlining the delivery of Email Notifications for standardization/control. I've therefore exposed a POST endpoint which takes in an email Bean as the response body which holds information such as receiver, sender, cc, etc and I would like to verify the fields of the incoming bean (i.e. email address format).
Currently, I have written a custom validator for validating a list of email addresses (#EmailAddresses). Is there a way to reuse the same validator to validate the email address for the "from" property which isn't a list as opposed to introducing another validator?
My Bean:
public class Email {
#JsonProperty("from")
private String from;
#EmailAddresses
#JsonProperty("to")
private List<String> to;
#EmailAddresses
#JsonProperty("cc")
private List<String> cc;
// some other fields
}
My Controller:
#RestController
public class MyController {
#RequestMapping(value = "/", method = RequestMethod.POST)
public String deliverEmailNotification(#Valid #RequestBody Email email) {
// something
}
}
My Custom Validation Annotation:
#Target({ElementType.ANNOTATION_TYPE, ElementType.FIELD, ElementType.PARAMETER})
#Retention(RetentionPolicy.RUNTIME)
#Documented
#Constraint(validatedBy = EmailAddressesValidator.class)
public #interface EmailAddresses {
String message() default "Must be a valid email";
Class<?>[] groups() default {};
Class<? extends Payload>[] payload() default {};
}
Validation Implementation:
public class EmailAddressesValidator implements
ConstraintValidator<EmailAddresses, List<String>> {
#Override
public void initialize(EmailAddresses emailAddresses) {
// do nothing
}
#Override
public boolean isValid(final List<String> emails, ConstraintValidatorContext constraintValidatorContext) {
// do something
}
}
So essentially I'm wondering whether is it possible to do something like this:
public class EmailAddressesValidator implements
ConstraintValidator<EmailAddresses, List<String>>, ConstraintValidator<EmailAddresses, String> {
#Override
public void initialize(EmailAddresses emailAddresses) {
// do nothing
}
#Override
public boolean isValid(final List<String> emails, ConstraintValidatorContext constraintValidatorContext) {
// do something
}
#Override
public boolean isValid(final String email, ConstraintValidatorContext constraintValidatorContext) {
// do something
}
}
Or is there another way around it?

Didn't manage to implement two instances of the ConstraintValidator due to Duplicate class error. However, I was able to achieve the equivalent of overloading by having the validation interface be validated by two implementation classes.
Based on the field type annotated with the validation annotation (#EmailAddress in this case), the respective validation implementation will kick in.
#Target({ElementType.ANNOTATION_TYPE, ElementType.CONSTRUCTOR, ElementType.METHOD, ElementType.FIELD, ElementType.PARAMETER})
#Retention(RetentionPolicy.RUNTIME)
#Documented
#Constraint(validatedBy = { EmailAddressValidator.class, EmailAddressesValidator.class })
public #interface EmailAddress {
String message() default "Must be a valid email";
Class<?>[] groups() default {};
Class<? extends Payload>[] payload() default {};
}
Validation implementation for List of Strings
public class EmailAddressesValidator implements ConstraintValidator<EmailAddress, List<String>> {
...
}
Validation implementation for String
public class EmailAddressValidator implements ConstraintValidator<EmailAddress, String> {
...
}

How to interpolate message dynamically in ConstraintValidator with property node?

Assume I have simple dto with one field and this dto is also annotated with custom validation annotation:
#CustomAnnotation
public class SimpleDto {
private String field;
}
// setters and getters omited
Custom annotation:
#Target(TYPE)
#Retention(RUNTIME)
#Constraint(validatedBy = CustomValidator.class)
#Documented
public #interface CheckMondialRelayShopOrderWeight {
String message() default "{temp.key.message}";
Class<?>[] groups() default {};
Class<? extends Payload>[] payload() default {};
}
and finally validator itself:
public class CustomValidator implements
ConstraintValidator<CustomAnnotation, SimpleDto> {
#Override
public void initialize(CustomAnnotation constraintAnnotation) {}
#Override
public boolean isValid(SimpleDto value,
ConstraintValidatorContext context) {
HibernateConstraintValidatorContext hibernateContext = context.unwrap(HibernateConstraintValidatorContext.class);
hibernateContext.addMessageParameter("dynamicValue", 130);
hibernateContext.buildConstraintViolationWithTemplate(hibernateContext.getDefaultConstraintMessageTemplate()).addPropertyNode("field").addConstraintViolation().disableDefaultConstraintViolation();
return false;
}
}
and in application.properties:
CustomAnnotation.simpleDto.field=Your dynamic value is {dynamicValue}
But this doesn't work, this works just fine if I put hibernateContext.buildConstraintViolationWithTemplate("Your dynamic value is {dynamicValue}").addConstraintViolation().disableDefaultConstraintViolation(); instead of hibernateContext.buildConstraintViolationWithTemplate(hibernateContext.getDefaultConstraintMessageTemplate()).addPropertyNode("field").addConstraintViolation().disableDefaultConstraintViolation();
I can't figure out how to use the interpolation with addPropertyNode. Any suggestions?

Java annotation for Null but neither Empty nor Blank

Is there are any java annotation(s) that can validate like the example below?
String test;
test = null; //valid
test = ""; //invalid
test = " "; //invalid
test = "Some values"; //valid

You need to create a custom annotation: #NullOrNotBlank
First create the custom annotation: NullOrNotBlank.java
#Target( {ElementType.FIELD})
#Retention(RUNTIME)
#Documented
#Constraint(validatedBy = NullOrNotBlankValidator.class)
public #interface NullOrNotBlank {
String message() default "{javax.validation.constraints.NullOrNotBlank.message}";
Class<?>[] groups() default { };
Class<? extends Payload>[] payload() default {};
}
Then the actual validator: NullOrNotBlankValidator.java
public class NullOrNotBlankValidator implements ConstraintValidator<NullOrNotBlank, String> {
public void initialize(NullOrNotBlank parameters) {
// Nothing to do here
}
public boolean isValid(String value, ConstraintValidatorContext constraintValidatorContext) {
return value == null || value.trim().length() > 0;
}
}

There isn't such an annotation in either javax.validation or Hibernate Validator. There was a request to add one to Hibernate Validator but it was closed as "won't fix" due to the possibility of writing your own relatively easily. The suggest solution was to either use your own annotation type defined like this:
#ConstraintComposition(OR)
#Null
#NotBlank
#ReportAsSingleViolation
#Target({ METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER })
#Retention(RUNTIME)
#Constraint(validatedBy = { })
public #interface NullOrNotBlank {
String message() default "{org.hibernate.validator.constraints.NullOrNotBlank.message}";
Class<?>[] groups() default { };
Class<? extends Payload>[] payload() default { };
}
or to use the #Pattern annotation with a regular expression that requires a non-whitespace character to be present (as the Pattern annotation accepts nulls and does not match them against the pattern).

Where is a nice javax.validation.constraints.Pattern annotation.
You can annotate the field with:
#Pattern(regexp = "^(?!\\s*$).+", message = "must not be blank")
This checks if field matches regex. The regex itself is something but not blank (see details here). It uses negative lookahead.

This is possible without creating a custom annotation, by using javax.validation.constraints.Size
// Null values are considered valid
#Size(min=1) String test;

The best way is to create your own constraint validator,
//custom annotation
#Documented
#Constraint(validatedBy = CustomCheck.class)
#Target( { ElementType.METHOD, ElementType.FIELD })
#Retention(RetentionPolicy.RUNTIME)
public #interface CustomConstarint {
String message() default "Invalid data";
Class<?>[] groups() default {};
Class<? extends Payload>[] payload() default {};
}
//validation logic goes here
public class CustomCheck implements
ConstraintValidator<CustomConstarint, String> {
#Override
public void initialize(CustomConstarint customConstarint) {
}
#Override
public boolean isValid(String field,
ConstraintValidatorContext cxt) {
//write your logic to validate the field
}
}

Did you try Hibernate-Validator? I think that's what you are looking for.
import javax.validation.constraints.NotNull;
import org.hibernate.validator.constraints.NotBlank;
import org.hibernate.validator.constraints.NotEmpty;
public class MyModel {
#NotNull
private String str1;
#NotEmpty
private String str2;
#NotBlank
private String str3;
}

How to use an annotation element inside a custom constraint validator

I wrote a custom annotation in my project called CGC:
#Target({ METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER })
#Retention(RUNTIME)
#Documented
#Constraint(validatedBy = CGCValidator.class)
public #interface CGC {
String message() default "{person.cgc.error}";
Class<?>[] groups() default {};
Class<? extends Payload>[] payload() default {};
boolean canBeNull() default false;
#Target({ METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER })
#Retention(RUNTIME)
#Documented
public #interface List {
CGC[] value();
}
}
I have a validator class that uses the annotation and basically, as my first validation I wanna check if the field is null, but only If the annotation for that field has specified the "canBeNull" element as true (#CGC(canBeNull="true")). My question is: how can I access the canBeNull element inside my validator class?
*The validator should be something like this:
public class CGCValidator implements ConstraintValidator<CGC, String> {
#Override
public void initialize(CGC annotation) {
}
#Override
public boolean isValid(String cgc, ConstraintValidatorContext constraintValidatorContext) {
if(!canBeNull() && cgc == null) {
return false;
}
...

You can capture the canBeNull value in the initialize function:
class CGCValidator implements ConstraintValidator<CGC, String> {
boolean canBeNull;
#Override
public void initialize(CGC constraintAnnotation) {
canBeNull = constraintAnnotation.canBeNull();
}
#Override
public boolean isValid(String value, ConstraintValidatorContext context) {
return canBeNull || value != null;
}
}