private static void int4(StringBuilder buf, int i) {
    buf.append((char) ('0' + (i / 1000) % 10));
    buf.append((char) ('0' + (i / 100) % 10));
    buf.append((char) ('0' + (i / 10) % 10));
    buf.append((char) ('0' + i % 10));
  }
Appends year-month-day to a buffer; assumes they are valid.
amoro-format-mixed/amoro-mixed-flink/amoro-mixed-flink-common/src/main/java/org/apache/amoro/flink/util/DateTimeUtils.java