Sorting multiple conditions with null value

Question

I have this code, which sorts an array list based on 3 variables

        result.sort(Comparator.comparing(FeConsumptionChannelDTO::getMeterName)
                .thenComparing(FeConsumptionChannelDTO::getValueTypeSeq)
                .thenComparing(Comparator.comparing(FeConsumptionChannelDTO::getValidFrom).reversed())
        );

But the last variable, getValidFrom can be null since it is OffsetDateTime. If it is null, it throws a NullPointerException. Is there a way to handle null values sorting this way? Or I have to create my own comparing method?

Change method getValidFrom() so that rather than returning null, it returns a OffsetDateTime. If you want nulls to be low, then return a minimum value. — Abra
– Abra, Commented Apr 9, 2021 at 12:32

M A · Accepted Answer · 2021-04-09 12:32:32Z

4

Use the nullsFirst() (null < non-null) or nullsLast() to account for nullability:

result.sort(Comparator.comparing(FeConsumptionChannelDTO::getMeterName)
            .thenComparing(FeConsumptionChannelDTO::getValueTypeSeq)
            .thenComparing(Comparator.nullsFirst(Comparator.comparing(FeConsumptionChannelDTO::getValidFrom)).reversed())
    );

answered Apr 9, 2021 at 12:32

M A

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