src/java.base/share/classes/java/time/format/DateTimeFormatterBuilder.java

*** 829,838 ****
--- 829,842 ----
       * The {@linkplain ResolverStyle resolver style} has no effect on instant parsing.
       * The end-of-day time of '24:00' is handled as midnight at the start of the following day.
       * The leap-second time of '23:59:59' is handled to some degree, see
       * {@link DateTimeFormatter#parsedLeapSecond()} for full details.
       * <p>
+      * When formatting, the instant will always be suffixed by 'Z' to indicate UTC.
+      * When parsing, the behaviour of {@link DateTimeFormatterBuilder#appendOffsetId()} will be used to parse the offset,
+      * converting the instant to UTC as necessary.
+      * <p>
       * An alternative to this method is to format/parse the instant as a single
       * epoch-seconds value. That is achieved using {@code appendValue(INSTANT_SECONDS)}.
       *
       * @return this, for chaining, not null
       */
*** 3460,3470 ****
                      .append(DateTimeFormatter.ISO_LOCAL_DATE).appendLiteral('T')
                      .appendValue(HOUR_OF_DAY, 2).appendLiteral(':')
                      .appendValue(MINUTE_OF_HOUR, 2).appendLiteral(':')
                      .appendValue(SECOND_OF_MINUTE, 2)
                      .appendFraction(NANO_OF_SECOND, minDigits, maxDigits, true)
!                     .appendLiteral('Z')
                      .toFormatter().toPrinterParser(false);
              DateTimeParseContext newContext = context.copy();
              int pos = parser.parse(newContext, text, position);
              if (pos < 0) {
                  return pos;
--- 3464,3474 ----
                      .append(DateTimeFormatter.ISO_LOCAL_DATE).appendLiteral('T')
                      .appendValue(HOUR_OF_DAY, 2).appendLiteral(':')
                      .appendValue(MINUTE_OF_HOUR, 2).appendLiteral(':')
                      .appendValue(SECOND_OF_MINUTE, 2)
                      .appendFraction(NANO_OF_SECOND, minDigits, maxDigits, true)
!                     .appendOffsetId()
                      .toFormatter().toPrinterParser(false);
              DateTimeParseContext newContext = context.copy();
              int pos = parser.parse(newContext, text, position);
              if (pos < 0) {
                  return pos;
*** 3478,3487 ****
--- 3482,3492 ----
              int min = newContext.getParsed(MINUTE_OF_HOUR).intValue();
              Long secVal = newContext.getParsed(SECOND_OF_MINUTE);
              Long nanoVal = newContext.getParsed(NANO_OF_SECOND);
              int sec = (secVal != null ? secVal.intValue() : 0);
              int nano = (nanoVal != null ? nanoVal.intValue() : 0);
+             int offset = newContext.getParsed(OFFSET_SECONDS).intValue();
              int days = 0;
              if (hour == 24 && min == 0 && sec == 0 && nano == 0) {
                  hour = 0;
                  days = 1;
              } else if (hour == 23 && min == 59 && sec == 60) {
*** 3490,3500 ****
              }
              int year = (int) yearParsed % 10_000;
              long instantSecs;
              try {
                  LocalDateTime ldt = LocalDateTime.of(year, month, day, hour, min, sec, 0).plusDays(days);
!                 instantSecs = ldt.toEpochSecond(ZoneOffset.UTC);
                  instantSecs += Math.multiplyExact(yearParsed / 10_000L, SECONDS_PER_10000_YEARS);
              } catch (RuntimeException ex) {
                  return ~position;
              }
              int successPos = pos;
--- 3495,3505 ----
              }
              int year = (int) yearParsed % 10_000;
              long instantSecs;
              try {
                  LocalDateTime ldt = LocalDateTime.of(year, month, day, hour, min, sec, 0).plusDays(days);
!                 instantSecs = ldt.toEpochSecond(ZoneOffset.ofTotalSeconds(offset));
                  instantSecs += Math.multiplyExact(yearParsed / 10_000L, SECONDS_PER_10000_YEARS);
              } catch (RuntimeException ex) {
                  return ~position;
              }
              int successPos = pos;