[英]Java 8 stream filtering: IN clause
List<Y> tmp= new DATA<Y>().findEntities();
List<X> tmp1 = new DATA<X>().findEntities().stream().filter(
IN (tmp) ???
).collect(Collectors.toList());
How to simulate a tipical IN clause (like in mysql or JPA) using a Predicate ? 如何使用谓词模拟一个典型的IN子句(如在mysql或JPA中)?
I decided to update my comment to an answer. 我决定将我的评论更新为答案。 The lambda expression for your requested
Predicate<Y>
(where Y should be a concrete type) looks as following: 您请求的
Predicate<Y>
(其中Y应该是具体类型)的lambda表达式如下所示:
element -> tmp.contains(element)
Because the collection's contains
method has the same signature as the predicate's test
method, you can use a method reference (here an instance method reference): 因为集合的
contains
方法与谓词的test
方法具有相同的签名,所以您可以使用方法引用 (这里是实例方法引用):
tmp::contains
A full example: 一个完整的例子:
List<Number> tmp = Arrays.asList(1, 2, 3);
List<Integer> tmp1 = Arrays
.stream(new Integer[] { 1, 2, 3, 4, 5 })
.filter(tmp::contains)
.collect(Collectors.toList());
System.out.println(tmp1);
This prints 这打印
[1, 2, 3]
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