How to get time difference between two ZonedDateTimes and pretty print it like "4 hours, 1 minute, 40 seconds ago"?

This is how I call getTimeBetween function:

getTimeBetween(ZonedDateTime.now().minusHours(4).minusMinutes(1).minusSeconds(40), ZonedDateTime.now());

And I expect this output:

4 hours, 1 minute, 40 seconds ago

This is my getTimeBetween function:

private String getTimeBetween(ZonedDateTime zonedDateTime1, ZonedDateTime zonedDateTime2) {
    Duration timeDifference = Duration.between(zonedDateTime1, zonedDateTime2);
    if (timeDifference.getSeconds() == 0) return "now";
    String timeDifferenceAsPrettyString = "";
    Boolean putComma = false;
    if (timeDifference.toDays() > 0) {
        if (timeDifference.toDays() == 1) timeDifferenceAsPrettyString += timeDifference.toDays() + " day";
        else timeDifferenceAsPrettyString += timeDifference.toDays() + " days";
        putComma = true;
    }
    if (timeDifference.toHours() > 0) {
        if (putComma) timeDifferenceAsPrettyString += ", ";
        if (timeDifference.toHours() == 1) timeDifferenceAsPrettyString += timeDifference.toHours() + " hour";
        else timeDifferenceAsPrettyString += timeDifference.toHours() % 24 + " hours";
        putComma = true;
    }
    if (timeDifference.toMinutes() > 0) {
        if (putComma) timeDifferenceAsPrettyString += ", ";
        if (timeDifference.toMinutes() == 1) timeDifferenceAsPrettyString += timeDifference.toMinutes() + " minute";
        else timeDifferenceAsPrettyString += timeDifference.toMinutes() % 60 + " minutes";
        putComma = true;
    }
    if (timeDifference.getSeconds() > 0) {
        if (putComma) timeDifferenceAsPrettyString += ", ";
        if (timeDifference.getSeconds() == 1) timeDifferenceAsPrettyString += timeDifference.getSeconds() + " second";
        else timeDifferenceAsPrettyString += timeDifference.getSeconds() % 60 + " seconds";
    }
    timeDifferenceAsPrettyString += " ago";
    return timeDifferenceAsPrettyString;
}

This function works as expected but is it really necessary to do it like this? Perhaps there is a better way to achieve this?

I'm using Java 8.

How about this?

static String getTimeBetween(ZonedDateTime from, ZonedDateTime to) {
    StringBuilder builder = new StringBuilder();
    long epochA = from.toEpochSecond(), epochB = to.toEpochSecond();
    long secs = Math.abs(epochB - epochA);
    if (secs == 0) return "now";
    Map<String, Integer> units = new LinkedHashMap<>();
    units.put("day", 86400);
    units.put("hour", 3600);
    units.put("minute", 60);
    units.put("second", 1);
    boolean separator = false;
    for (Map.Entry<String, Integer> unit : units.entrySet()) {
        if (secs >= unit.getValue()) {
            long count = secs / unit.getValue();
            if (separator) builder.append(", ");
            builder.append(count).append(' ').append(unit.getKey());
            if (count != 1) builder.append('s');
            secs %= unit.getValue();
            separator = true;
        }
    }
    return builder.append(epochA > epochB ? " ago" : " in the future").toString();
}

You could probably store the LinkedHashMap instead of instantiating it every method call, but this should work.