code: public static long changeTimestampToLong(SimpleDateFormat simpleDateFormat,
              String timestamp) {
          try {
              synchronized (simpleDateFormat) {
                  return simpleDateFormat.parse(timestamp).getTime();
              }
          } catch (Exception e) {
              throw new RuntimeException(e);
          }
      }
docs: Change timestamp to long long.
  
  @param simpleDateFormat the simple date format
  @param timestamp        the timestamp
  @return the long