I have a custom Java Bean Validation constraint annotation and apply it to a single Jakarta Part field using:

@AllowedFileExtensions({".jpg", ".png"})
private Part file;

This is the constraint annotation class:

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD})
@Constraint(validatedBy = {AllowedFileExtensionsValidator.class})
public @interface AllowedFileExtensions {

  Class<?>[] groups() default {};
  Class<? extends Payload>[] payload() default {};
  String message() default
      "{com.annotation.constraint.AllowedFileExtensions}";

  String[] value() default {};
}

And this is the constraint validator class:

import com.annotation.constraint.AllowedFileExtensions;
import jakarta.servlet.http.Part;
import jakarta.validation.ConstraintValidator;
import jakarta.validation.ConstraintValidatorContext;
import java.util.Arrays;

public class AllowedFileExtensionsValidator
    implements ConstraintValidator<AllowedFileExtensions, Part> {

  private String[] extensions;

  @Override
  public void initialize(AllowedFileExtensions constraintAnnotation) {
    this.extensions = constraintAnnotation.value();
  }

  @Override
  public boolean isValid(Part part, ConstraintValidatorContext context) {
    return Arrays.stream(extensions).anyMatch(type -> part.getSubmittedFileName().endsWith(type));
  }
}

I know this constraint annotation is designed to only work on a single Part field, but is it possible to refactor it to support reuse of the same constraint annotation on a field that is either a single Part or a field that is an array Part[] or a list List<Part>?

Example:

@AllowedFileExtensions({".jpg", ".png"})
private Part[] files;
// or
@AllowedFileExtensions({".jpg", ".png"})
private List<Part> files;

What would be best practice in this case from the perspective of Bean Validation, should a separate constraint annotation be created to specifically handle the array or list of Parts? Or should I aim to reuse the same constraint annotation across the different types somehow?