如何在Java中获取类的TypeTag [英] How to get the TypeTag for a class in Java
问题描述
我正在尝试从它要求输入两个参数,即文字对象及其类型(TypeTag
).
I'm trying to call the functions.typedLit
from Spark library in my other question. And it asks for two parameters, a literal object and its type (a TypeTag
).
第一个论点,我可以提出自己(我认为).但是对于第二个对象,我不知道如何为它实例化一个对象.我正在尝试将TypeTag<Seq<Integer>>
作为第二个参数传递.
The first argument, I can come up with myself (I think). But as for the second one, I don't know how to instantiate an object for it. I'm trying to pass the TypeTag<Seq<Integer>>
as the second parameter.
有人可以告诉我如何在 Java 中为Seq<Integer>
创建TypeTag
吗?这是我要完成的代码:
Can someone please tell how to create the TypeTag
for Seq<Integer>
in Java? Here's the code I'm trying to complete:
Seq<Integer> seq = JavaConverters
.asScalaIteratorConverter((new ArrayList<Integer>()).iterator())
.asScala()
.toSeq();
Column litColumn = functions.<Seq<Integer>>typedLit(seq, ???)
推荐答案
在我说的另一个问题中
并从Java提供CanBuildFrom参数是...从技术上来说是可行的,但您不希望这样做.
and supplying the CanBuildFrom argument from Java is... technically possible, but not something you want to do.
不幸的是,对于TypeTag
,它的可能性更低:与CanBuildFrom
不同,它们不是由库提供的,而是内置在Scala编译器中的.
Unfortunately, for TypeTag
it's even less possible: unlike CanBuildFrom
, they aren't supplied by a library, but built into Scala compiler.
我能提供的最佳建议是创建一个Scala文件,提供需要从Java使用的类型标签,因为您只需要有限数量的标签即可:
The best advice I can give is to create a Scala file supplying the type tags you need to use from Java, since you only should need a limited number of them:
object TypeTags {
val SeqInteger = typeTag[Seq[Integer]]
...
// or
val Integer = typeTag[Integer]
def Seq[A](implicit tt: TypeTag[A]) = typeTag[Seq[A]]
}
,然后从Java TypeTags.SeqInteger
或TypeTags.Seq(TypeTags.Integer)
.
and then from Java TypeTags.SeqInteger
or TypeTags.Seq(TypeTags.Integer)
.
在其他地方,Spark提供了可从Java使用的特殊API(查找.java
软件包),但是我找不到用于functions.typedLit
的API.
In other places Spark provides special API for use from Java (look for .java
packages), but I couldn't find one for functions.typedLit
.
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