Java 8 Time API - ZonedDateTime - specify default ZoneId when parsing

I am trying to write a generic method to return a ZonedDateTime given a date as String and its format.

How do we make ZonedDateTime to use the default ZoneId if it is not specified in the date String?

It can be done with java.util.Calendar, but I want to use the Java 8 time API.

This question here is using a fixed time zone. I am specifying the format as an argument. Both the date and its format are String arguments. More generic.

Code and output below:

public class DateUtil {
    /** Convert a given String to ZonedDateTime. Use default Zone in string does not have zone.  */
    public ZonedDateTime parseToZonedDateTime(String date, String dateFormat) {
        //use java.time from java 8
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern(dateFormat);
        ZonedDateTime zonedDateTime = ZonedDateTime.parse(date, formatter);
        return zonedDateTime;
    }

    public static void main(String args[]) {
        DateUtil dateUtil = new DateUtil();
        System.out.println(dateUtil.parseToZonedDateTime("2017-09-14 15:00:00+0530", "yyyy-MM-dd HH:mm:ssZ"));
        System.out.println(dateUtil.parseToZonedDateTime("2017-09-14 15:00:00", "yyyy-MM-dd HH:mm:ss"));
    }
}

Output

2017-09-14T15:00+05:30
Exception in thread "main" java.time.format.DateTimeParseException: Text '2017-09-14 15:00:00' could not be parsed: Unable to obtain ZonedDateTime from TemporalAccessor: {},ISO resolved to 2017-09-14T15:00 of type java.time.format.Parsed
    at java.time.format.DateTimeFormatter.createError(DateTimeFormatter.java:1920)
    at java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1855)
    at java.time.ZonedDateTime.parse(ZonedDateTime.java:597)
    at com.nam.sfmerchstorefhs.util.DateUtil.parseToZonedDateTime(DateUtil.java:81)
    at com.nam.sfmerchstorefhs.util.DateUtil.main(DateUtil.java:97)
Caused by: java.time.DateTimeException: Unable to obtain ZonedDateTime from TemporalAccessor: {},ISO resolved to 2017-09-14T15:00 of type java.time.format.Parsed
    at java.time.ZonedDateTime.from(ZonedDateTime.java:565)
    at java.time.format.Parsed.query(Parsed.java:226)
    at java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1851)
    ... 3 more
Caused by: java.time.DateTimeException: Unable to obtain ZoneId from TemporalAccessor: {},ISO resolved to 2017-09-14T15:00 of type java.time.format.Parsed
    at java.time.ZoneId.from(ZoneId.java:466)
    at java.time.ZonedDateTime.from(ZonedDateTime.java:553)
    ... 5 more