Java 8 stream flatMap allow null check for each list in the nested list?

Question

I have a nested list to loop through in pre Java 8. My example is very similar to loop through nested list in java 8 which is a great example to follow then I realized that I need to check for null for each list. Plz refer to the below example. If the last condition is met then return true by short-circuiting.

However I am not sure how to check null for each list using list.stream().flatMap().

for(A a : ListA) {
        if(a.getListB() != null && !a.getListB().isEmpty()) {
            for(B b : a.getListB()) {
                if(b.getListC() != null && !p.getListC().isEmpty()) {
                    for(C c : b.getListC()) {
                        return (c.name.equalsIgnoreCase("john"));
                    }
                }
            }
        }
    }

Jason · Accepted Answer · 2020-04-16 20:22:04Z

3

This is kind of gross but it works. You essentially check if listB is not null and create a Stream of B. Then filter through Stream of B and check if ListC is null and if not map to a Stream of C. Then just simply check if any of C match the argument.

boolean found = listA.stream()
    .filter(a -> a.getListB() != null)
    .flatMap(a -> a.getListB().stream())
    .filter(b -> b.getListC() != null)
    .flatMap(b -> b.getListC().stream())
    .anyMatch(c -> c.name.equalsIgnoreCase("john"));

answered Apr 16, 2020 at 20:22

Jason

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