how to custom validator for standard constraints in java

Old not from 2017. May be outdated.

Bean validation provides constraint annotations to check DTO parameters. However, what if we want to check a parameter type not supported by a standard constraint annotation?

Let’s say, we want to check a LocalDateTime is in the future. But, our parameter type is in String, a type not supported by the annotation @Future.

Instead of creating a new annotation, we will add configure so that it will support it.

First, let’s create our custom validator:

package lin.louis;
 
import java.time.LocalDateTime;
import java.time.format.DateTimeParseException;
 
import javax.validation.ConstraintValidator;
import javax.validation.ConstraintValidatorContext;
import javax.validation.constraints.Future;
 
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
 
 
public class FutureValidatorForString implements ConstraintValidator<Future, String> {
    private static final Logger LOGGER = LoggerFactory.getLogger(FutureValidatorForString.class);
 
    @Override
    public boolean isValid(String value, ConstraintValidatorContext context) {
        if (value == null || "".equals(value.trim())) {
            return true;
        }
        
        try {
            LocalDateTime localDateTime = LocalDateTime.parse(value);
            return LocalDateTime.now().isBefore(localDateTime);
        } catch (DateTimeParseException e) {
            LOGGER.debug("The timestamp is not valid.", e);
            return true;
        }
    }
}

Then provide this implementation in META-INF/services/javax.validation.ConstraintValidator:

lin.louis.FutureValidatorForString

Now, you can use the annotation for String type:

public class Apple {
    @Future
    private String expirationDate;
}

References

• in.relation.to