private static StringBuilder ymd(StringBuilder b, int year, int month, int day) {
    int4(b, year);
    b.append('-');
    int2(b, month);
    b.append('-');
    int2(b, day);
    return b;
  }
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