Unable to obtain ZonedDateTime from TemporalAccessor using DateTimeFormatter and ZonedDateTime in Java 8

This does not work because your input (and your Formatter) do not have time zone information. A simple way is to parse your date as a LocalDate first (without time or time zone information) then create a ZonedDateTime:

public static ZonedDateTime convertirAFecha(String fecha) {
  DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd/MM/yyyy");
  LocalDate date = LocalDate.parse(fecha, formatter);

  ZonedDateTime resultado = date.atStartOfDay(ZoneId.systemDefault());
  return resultado;
}

This is a bug, see JDK-bug-log. According to that information the problem was solved for Java 9 and Java 8u20. Try to download the latest Java 8 - version. Today on 2014-05-12: There is an early access release 8u20 available.

UPDATE:

Personally I think, since you only have and expect "dd/MM/yyyy" as pattern you should use LocalDate as your primary type as @assylias has already proposed. Regarding your context, it is almost sure a design failure to use ZonedDateTime. What do you want to do with objects of this type? I can only think of specialized timezone calculations as use-case. And you cannot even directly store these ZonedDateTime-objects in a database, so this type is far less useful than many people believe.

What I described as your use-case problem is indeed a new aspect introduced with Java-8 compared with the old GregorianCalendar-class (which is an all-in-one-type). Users have to start thinking about choosing the proper temporal type for their problems and use-cases.

In simple words, the line

ZonedDateTime.parse('2014-04-23', DateTimeFormatter.ISO_OFFSET_DATE_TIME)

throws an exception:

Text '2014-04-23' could not be parsed at index 10
java.time.format.DateTimeParseException: Text '2014-04-23' could not be parsed at index 10

It looks like a bug for me.

I used this workaround:

String dateAsStr = '2014-04-23';
if (dateAsStr.length() == 10) {
    dateAsStr += 'T00:00:00';
}
ZonedDateTime.parse(dateAsStr, DateTimeFormatter.ISO_OFFSET_DATE_TIME.withZone(ZoneId.systemDefault()));