如何使用 Java 8 / 流 API 列出、映射和“打印 if count>0”？

Question

这是我现在的代码。

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

if (!cats.empty) 

    logger.info("Processing for cats: " + cats.size());

for (Cat cat : cats) {

    cat.giveFood();

}

我的同事使用 Java 流 API 编写了非常好的代码。我试图将它重写为一个流式语句，但我被卡住了。

petStore.getCatsForSale().stream.forEach(cat -> cat.giveFood)

    .countTheCats().thenDo(logger.info("Total number of cats: " + x)); // Incorrect... is this possible?

我怎样才能做到这一点？理想情况下，我想要一个流式声明......

Answer 1

您当前的代码在没有流的情况下要好得多，并且可以进一步缩短为：if (!cats.isEmpty()) {&nbsp; &nbsp; logger.info("Processing for cats: " + cats.size());}cats.forEach(Cat::giveFood); // Assuming giveFood is a stateless operation

Answer 2

我不确定为什么要在当前循环解决方案中使用流，但您也可以使用Stream<List<Cat>>：Stream.of(petStore.getCatsForSale())&nbsp; &nbsp; .filter(cats -> !cats.isEmpty())&nbsp; &nbsp; .flatMap(cats -> {&nbsp; &nbsp; &nbsp; &nbsp; logger.info("Processing for cats: " + cats.size());&nbsp; &nbsp; &nbsp; &nbsp; return cats.stream();&nbsp; &nbsp; })&nbsp; &nbsp; .forEach(Cat::giveFood);也许是优化：Stream.of(petStore.getCatsForSale())&nbsp; &nbsp; .filter(cats -> !cats.isEmpty())&nbsp; &nbsp; .peek(cats -> logger.info("Processing for cats: " + cats.size()))&nbsp; &nbsp; .flatMap(Collection::stream)&nbsp; &nbsp; .forEach(Cat::giveFood);或使用其他变体：Stream.of(petStore.getCatsForSale())&nbsp; &nbsp; .filter(cats -> !cats.isEmpty())&nbsp; &nbsp; .mapToInt(cats -> {&nbsp; &nbsp; &nbsp; &nbsp; cats.forEach(Cat::giveFood);&nbsp; &nbsp; &nbsp; &nbsp; return cats.size();&nbsp; &nbsp; })&nbsp; &nbsp; .findAny()&nbsp; &nbsp; .ifPresent(count -> logger.info("Processing for cats: " + count));

Answer 3

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