如何使用Java8/StreamAPI列出、映射和“如果计数>0则打印”?

如果没有流,您当前的代码会更好,并且可以进一步缩短为:

if (!cats.isEmpty()) {
    logger.info("Processing for cats: " + cats.size());
}
cats.forEach(Cat::giveFood); // Assuming giveFood is a stateless operation

为什么? Stream<List<Cat>>

Stream.of(petStore.getCatsForSale())
    .filter(cats -> !cats.isEmpty())
    .flatMap(cats -> {
        logger.info("Processing for cats: " + cats.size());
        return cats.stream();
    })
    .forEach(Cat::giveFood);

可能是一种优化:

Stream.of(petStore.getCatsForSale())
    .filter(cats -> !cats.isEmpty())
    .peek(cats -> logger.info("Processing for cats: " + cats.size()))
    .flatMap(Collection::stream)
    .forEach(Cat::giveFood);

或者使用另一种变体:

Stream.of(petStore.getCatsForSale())
    .filter(cats -> !cats.isEmpty())
    .mapToInt(cats -> {
        cats.forEach(Cat::giveFood);
        return cats.size();
    })
    .findAny()
    .ifPresent(count -> logger.info("Processing for cats: " + count));

cats.stream()
    .peek(Cat::giveFood)
    .findAny().ifPresent(cat -> logger.info("Processing for cats: " + cats.size()));

我同意 with @Lino

List<Cat> cats = petStore.getCatsForSale();

cats.stream().limit(1)
    .flatMap(c -> {
        logger.info("Processing for cats: " + cats.size());
        return cats.stream();
    }).forEach(Cat::giveFood);