如何从 groovy 调用 Java 的 Stream.collect()？
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How to call Java's Stream.collect() from groovy?
提问by Jerzyna
Having some background with FP from Scala I really don't like Groovy's names for collections methods. Given that and some architectural choices made above, I found using a Java 8 streams API (plus java.util.Optional) in Groovy code an appealing solution.
有一些 Scala 的 FP 背景，我真的不喜欢 Groovy 的集合方法名称。鉴于此以及上面做出的一些架构选择，我发现在 Groovy 代码中使用 Java 8 流 API（加上 java.util.Optional）是一个有吸引力的解决方案。
Until I hit this:
直到我击中这个：
def finalCollection = [ 'some', 'items', 'really', 'not', 'important' ].stream()
.map { aMethodReturningOptional(it) } //map String to Optional<Item>
.flatMap { it.map(Stream.&of).orElseGet(Stream.&empty) } //convert to Stream<Item>
.collect() //Groovy's collect, not stream's!
Note it works only in Groovy 2+ - treating closure as lambda.
What bothers me is the last line of the example code. Groovy translates the call to the DefaultGroovyMethods.collect()instead of Stream.collect()that I originally wanted to use. Of course then the last line would be:
请注意，它仅适用于 Groovy 2+ -将闭包视为 lambda。困扰我的是示例代码的最后一行。Groovy 将调用转换为DefaultGroovyMethods.collect()而不是Stream.collect()我最初想要使用的。当然，最后一行将是：
.collect(Collectors.toList()) //Should call Java collect, but it doesn't
It seems counter-intuitive to me, that some extension method is called instead of native, 'built-in' method of the class.
对我来说似乎违反直觉，调用一些扩展方法而不是类的本机“内置”方法。
How can I rewrite the example so the Stream.collect()method would be called?
如何重写示例以便Stream.collect()调用该方法？
UPDATE: After some more fiddling, I've found out what problem I had originally. I wrote .collect{Collectors.toList()}(note curly braces), which of course called Groovy method, not Java. Note to self: remember to quadruple-check before posting...
更新：经过更多的摆弄之后，我发现了我最初遇到的问题。我写的.collect{Collectors.toList()}（注意大括号），当然叫Groovy方法，而不是Java。自我注意：记得在发帖前四重检查......
采纳答案by jalopaba
Using Collectors.toList()you can get what you want to do:
使用Collectors.toList()你可以获得你想做的事情：
import java.util.stream.*
class Item {
final String name
Item(name) {
this.name = name
}
@Override
String toString() {
name
}
}
def itemize(String name) {
Optional.of(new Item(name))
}
def finalCollection = [ 'some', 'items', 'really', 'not', 'important' ].stream()
.map { itemize(it) } //map String to Optional<Item>
.flatMap { it.map(Stream.&of).orElseGet(Stream.&empty) } //convert to Stream<Item>
.collect (Collectors.toList())
assert 'java.util.ArrayList' == finalCollection.class.name
assert finalCollection.collect { it.name } == ['some', 'items', 'really', 'not', 'important']
Anyway, with groovy 2.4.5 the above is working also with
无论如何，使用 groovy 2.4.5 以上也适用
def finalCollection = [ 'some', 'items', 'really', 'not', 'important' ].stream()
.map { itemize(it) } //map String to Optional<Item>
.flatMap { it.map(Stream.&of).orElseGet(Stream.&empty) } //convert to Stream<Item>
.collect()
that uses groovy's collect:
transforming each item into a new value using Closure.IDENTITY as a transformer, basically returning a list of items copied from the original object.
使用 Closure.IDENTITY 作为转换器将每个项目转换为新值，基本上返回从原始对象复制的项目列表。
