In my Scala code I need to interact with Java libraries.
The method I want to use expects parameter of type List<java.util.Long>
, but I have Scala type Option[List[Long]]
. The problem I faced is that I need manually apply Predef.long2Long
function to convert from Scala Long
to java.util.Long
:
val userIds = Option(List(1,2,3,4))
val methodParameter = userIds.map(list => list.map(long2Long).asJava).orNull
is there some way to convert this list in more elegant and concise way?
EDIT: I can even simplify question: how to convert Option[scala.Boolean]
to java.util.Boolean
? Here I need to do same:
isUsed.map(isUsedVal => boolean2Boolean(isUsedVal)).orNull,
For the List[Long]
:
import scala.collection.JavaConverters._
val l = List(1L,2L,3L,4L)
l.map(java.lang.Long.valueOf).asJava
// or
l.map(_.asInstanceOf[AnyRef]).asJava
// or
l.map(Long.box).asJava
For the Option[Boolean]
:
val mb = Some(true)
mb.map(java.lang.Boolean.valueOf).orNull
// or
mb.map(_.asInstanceOf[AnyRef]).orNull
// or
mb.map(Boolean.box).orNull
Can you use JavaConverters ? and do something like that
val sl = new scala.collection.mutable.ListBuffer[Int]
val jl : java.util.List[Int] = sl.asJava
It's worth mentioning that long2Long
and boolean2Boolean
are implicit, but that doesn't help you much to make this more elegant or clear, I think. It does allow you to things like:
type JB = java.lang.Boolean
isUsed.fold(null : JB)(implicitly)
//Or:
isUsed.map { b => b : JB }.orNull
//Or even:
isUsed.map[JB](identity).orNull
But that's not particularly readable, in my opinion.
These sorts of methods are perfect candidates for an implicit class method . You can enrich your classes with these methods so that you only have to write the tedious or inelegant code once. For example, you might consider:
object MoreJavaConversions {
import scala.collection.JavaConverters._
implicit class RichListLong(val list: Option[List[Long]]) extends AnyVal {
def asJava : java.util.List[java.lang.Long] = list.map(_.map(long2Long).asJava).orNull
}
implicit class RichOptionBoolean(val bool: Option[Boolean]) extends AnyVal {
def asJava : java.lang.Boolean = bool.map(boolean2Boolean).orNull
}
}
Which would later allow you to do:
import MoreJavaConversions._
val myUsers = Option(List(1l, 2l, 3l))
myUsers.asJava //java.util.List[java.lang.Long]
Option(true).asJava //java.lang.Boolean
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.