Configuring an ObjectMapper's DateFormat changes time zone when serialising Joda DateTime

[wilkinsona]

The serialisation of Joda DateTime instances behaves differently in 2.6.0 vs 2.5.4 when the ObjectMapper's had its DateFormat configured. The behaviour change is illustrated by the following code:

public static void main(String[] args) throws JsonProcessingException {
    System.out.println(createObjectMapper()
            .writeValueAsString(new DateTime(1988, 6, 25, 20, 30, DateTimeZone.UTC)));
}

private static ObjectMapper createObjectMapper() {
    ObjectMapper mapper = new ObjectMapper();
    mapper.registerModule(createJodaModule());
    mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
    System.out.println(mapper.getSerializationConfig().getTimeZone());
    mapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));
    System.out.println(mapper.getSerializationConfig().getTimeZone());
    return mapper;
}

private static SimpleModule createJodaModule() {
    SimpleModule module = new SimpleModule();
    module.addSerializer(DateTime.class, new DateTimeSerializer(
            new JacksonJodaDateFormat(DateTimeFormat.forPattern("yyyy-MM-dd HH:mm:ss")
                    .withZoneUTC())));
        return module;
    }

When run with Jackson 2.5.4 the output is:

sun.util.calendar.ZoneInfo[id="GMT",offset=0,dstSavings=0,useDaylight=false,transitions=0,lastRule=null]
sun.util.calendar.ZoneInfo[id="GMT",offset=0,dstSavings=0,useDaylight=false,transitions=0,lastRule=null]
"1988-06-25 20:30:00"

When run with Jackson 2.6.0 the output is:

sun.util.calendar.ZoneInfo[id="GMT",offset=0,dstSavings=0,useDaylight=false,transitions=0,lastRule=null]
sun.util.calendar.ZoneInfo[id="Europe/London",offset=0,dstSavings=3600000,useDaylight=true,transitions=242,lastRule=java.util.SimpleTimeZone[id=Europe/London,offset=0,dstSavings=3600000,useDaylight=true,startYear=0,startMode=2,startMonth=2,startDay=-1,startDayOfWeek=1,startTime=3600000,startTimeMode=2,endMode=2,endMonth=9,endDay=-1,endDayOfWeek=1,endTime=3600000,endTimeMode=2]]
"1988-06-25 21:30:00"

It looks like the fix for #824 is the cause. In 2.6, the call to mapper.setDateFormat causes the ObjectMapper's time zone to be set to the JVM's default time zone. In 2.5.x, calling mapper.setDateFormat has no effect on its time zone.

[cowtowncoder]

Ok, this does sound like a problem. Unfortunately timezone handling is a rather messy area of Jackson databinding. But sounds like in this case solution might be relatively easy, by trying to retain existing configured time zone and not taking it from DateFormat

[cowtowncoder]

The idea with the change was to allow piggy-backing timezone configuration, but all in all it is probably better not to try to be too clever. And since it changed behavior for existing code, it's a no-no.
Thank you for reporting this, and apologies for breakage. Fix will be in 2.6.1; we are getting enough fixes to release that relatively soon now, esp. considering couple of other issue with Joda / Java8 datetime datatype modules.