code: @Override
    public final boolean isValid(final String pvalue, final ConstraintValidatorContext pcontext) {
      if (StringUtils.isEmpty(pvalue)) {
        return true;
      }
      if (pvalue.length() > LENGTH_URL) {
        // url is to long, but that's handled by size annotation
        return true;
      }
      return org.apache.commons.validator.routines.UrlValidator.getInstance().isValid(pvalue);
    }
docs: {@inheritDoc} check if given string is a valid url.
  
  @see javax.validation.ConstraintValidator#isValid(java.lang.Object,
  javax.validation.ConstraintValidatorContext)