连接可选列表 [英] Concatenate Optional Lists

问题描述

我有三个Optional>，它们必须组合起来并返回.我尝试使用Optional.map()和flatmap()，但未成功.

I have three Optional> which have to be combined and returned. I tried to use Optional.map() and flatmap() but was not successful.

public Optional<List<Entiy>> getRecords() {
    Optional<List<Entiy>> entity1 = repo.findAllByStatus("1");
    Optional<List<Entiy>> entity2 = repo.findAllByStatus("2");
    Optional<List<Entiy>> entity3 = repo.findAllByStatus("3");
    //Need to return a concatenation of entity1, 2 and 3
}

任何有关如何有效执行操作的想法?

Any thoughts on how to do is efficiently?

推荐答案

类似的东西:

return Optional.of(Stream.of(entity1.orElse(new ArrayList<>()), entity2.orElse(new ArrayList<>()), entity3.orElse(new ArrayList<>()))
            .flatMap(List::stream)
            .collect(Collectors.toList()));

或更容易理解为:

return Optional.of(Stream.of(entity1, entity2, entity3)
        .filter(Optional::isPresent)
        .map(Optional::get)
        .flatMap(List::stream)
        .collect(Collectors.toList()));

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