code: public Date getInvalidityDate() {
          Extension ext = getExtensions().get("2.5.29.24");
          if (ext == null) {
              return null;
          } else {
              try {
                  Date invalidity = InvalidityDateExtension.toImpl(ext).get("DATE");
                  return new Date(invalidity.getTime());
              } catch (IOException ioe) {
                  return null;
              }
          }
      }
docs: Returns the invalidity date, as specified in the Invalidity Date
  extension of this {@code CertificateRevokedException}. The
  invalidity date is the date on which it is known or suspected that the
  private key was compromised or that the certificate otherwise became
  invalid. This implementation calls {@code getExtensions()} and
  checks the returned map for an entry for the Invalidity Date extension
  OID ("2.5.29.24"). If found, it returns the invalidity date in the
  extension; otherwise null. A new Date object is returned each time the
  method is invoked to protect against subsequent modification.
  
  @return the invalidity date, or {@code null} if not specified