Java 8 Stream

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我的情况类似于:

public class A { private String id; @ManyToMany private Set<B> bSet; // getters and setters }

和

public class B { private String id; // other attributes // getters and setters }

当使用stream() API拥有B的实例时，如何找到A的实例?我正在尝试类似的东西:

How can I find an instance of A when I have an instance of B using the stream() API? I was trying something like:

public A findAFromB(B b) { List<A> aList = aService.findAll(); Optional<A> matchingObject = aList.stream().filter({find a where a.getBSet().contains(b)}).getA(); return (A) matchingObject.get(); }

如何正确编写此过滤器?

How to properly write this filter?

推荐答案

类似使用findFirst或findAny作为终端操作的事情:

Soemthing like using a findFirst or findAny as a terminal operation:

Optional<A> matchingObject = aList.stream() .filter(a -> a.getbSet().contains(b)) .findFirst();