Facing NullPointerException while using Optional

Question

I am using a Map<String, Optional<List<String>>>. I am getting an obvious NullPointerException because the result is null for that key.

Is there any way to handle the null situation?

public Map<MyEnum, Optional<List<String>>> process(Map<MyEnum, Optional<List<String>>> map) {
    Map<MyEnum, Optional<List<String>>> resultMap = new HashMap<>();
    // Getting NullPointerException here, since map.get(MyEnum.ANIMAL) is NULL
    resultMap.put(MyEnum.ANIMAL, doSomething(map.get(MyEnum.ANIMAL).get()));
    // do something more here
}

private Optional<List<String>> doSomething(List<String> list) {
    // process and return a list of String
    return Optional.of(resultList);
}

I am trying to avoid a if-else check for null by using Optional.

rgettman · Accepted Answer · 2018-03-10 01:06:05Z

5

You can use Map's getOrDefault method.

Returns the value to which the specified key is mapped, or defaultValue if this map contains no mapping for the key.

resultMap.put(MyEnum.ANIMAL,
    map.getOrDefault(MyEnum.ANIMAL, Optional.of(new ArrayList<>())) );

This avoids the null by having that method check for you.

answered Mar 10, 2018 at 1:06

rgettman

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2 Comments

RDM Over a year ago

Thanks for helping me out here.

Radiodef Over a year ago

I was also thinking of something like map.getOrDefault(MyEnum.ANIMAL, Optional.empty()).flatMap(this::doSomething).... It was kind of ambiguous to me what the OP actually wanted to do in case that the mapping was not present, though.

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