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

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.

这篇关于如何在Java中获取类的TypeTag的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！