使用Optional时面对NullPointerException

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.

Answer 1

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.