Summary

Instant.parse() method cannot parse hour-only zone offsets.

Problem

java.time.Instant.parse(CharSequence) method fails to parse the date/time text that includes an hour-only zone offset, such as "+02". For example,

 Instant .parse("2017-01-01T00:00:00.000+02")

this throws

java.time.format.DateTimeParseException: Text '2017-01-01T00:00:00.000+02' could not be parsed at index 23

Instant.parse() method uses DateTimeFormatter.ISO_INSTANT formatter, and its offset parsing behavior follows DateTimeFormatterBuilder.appendOffsetId() where it reads:

This is equivalent to calling appendOffset("+HH:mm:ss", "Z")

and in appendOffset(String, String):

+HH:mm:ss - hour, with minute if non-zero or with minute and second if non-zero, with colon

This implies the minutes are optional, while the actual behavior is not, because the actual implementation uses "+HH:MM:ss" for parsing/formatting the zone offset.

Solution

Replacing the pattern in the implementation from "+HH:mm:ss" to "+HH:MM:ss" will accept hour-only zone offsets. However, it will also cause compatibility problem on formatting, i.e., it won't print minutes if they are zero. For example "+02:00" would print "+02" which should be avoided. Thus, it would be desirable to align the specification to the actual implementation.

Specification

Replace the pattern in DateTimeFormatterBuilder.appendOffsetId() as follows:

      * Appends the zone offset, such as '+01:00', to the formatter.
      * <p>
      * This appends an instruction to format/parse the offset ID to the builder.
-     * This is equivalent to calling {@code appendOffset("+HH:mm:ss", "Z")}.
+     * This is equivalent to calling {@code appendOffset("+HH:MM:ss", "Z")}.
      * See {@link #appendOffset(String, String)} for details on formatting
      * and parsing.
      *