如何从java.util.Map转换为Scala Map

A Java API returns a java.util.Map<java.lang.String,java.lang.Boolean>;. I would like to put that into a Map[String,Boolean]

Java API返回java.util.Map ;。我想把它放到Map [String,Boolean] ,java.lang.boolean>

So imagine we have:

所以想象我们有:

var scalaMap : Map[String,Boolean] = Map.empty
val javaMap = new JavaClass().map()   // Returns java.util.Map<java.lang.String,java.lang.Boolean>

You can't do Map.empty ++ javaMap, because the ++ method does not know about Java maps. I tried:

你不能做Map.empty ++ javaMap,因为++方法不了解Java地图。我试过了:

scalaMap = Map.empty ++ new collection.jcl.MapWrapper[String,Boolean] {
    override def underlying = javaMap
}

and:

scalaMap = Map.empty ++ new collection.jcl.MapWrapper[java.lang.String,java.lang.Boolean] {
    override def underlying = javaMap
  }

These both fail to compile, because of the generics - java.lang.String is not the same as a scala String.

这两个都无法编译,因为泛型 - java.lang.String与scala String不同。

Is there a good way of doing this, short of copying the map manually?

有没有一种好方法可以做到这一点,而不是手动复制地图?

EDIT: Thanks, all good answers, I learned a lot from all of them. However, I made a mistake by posting a simpler problem here than the one I actually have. So, if you allow me, I'll generalise the question - What the API actually returns is

编辑:谢谢,所有好的答案,我从他们所有人那里学到了很多东西。但是,我在这里发布一个比我实际拥有的更简单的问题犯了一个错误。所以,如果你允许我,我会概括一个问题 - API实际返回的是什么

java.util.Map<java.lang.String, java.util.Map<SomeJavaEnum,java.lang.String>>

And I need to move this to Map[String, Map[SomeJavaEnum,String]]

我需要将其移动到Map [String,Map [SomeJavaEnum,String]]

It probably does not seem like too much of a complication, but it adds an extra level of type erasure, and the only way I found of moving this to a Scala map was deep-copying it (using some of the techniques you suggested below). Anyone any hints? I kind of solved my problem by defining an implicit conversion for my exact types, so at least the ugliness is hidden in its own trait, but still feels a bit clumsy deep copying the lot.

它似乎不太复杂,但它增加了额外级别的类型擦除,我发现将其移动到Scala地图的唯一方法是深度复制它(使用下面建议的一些技术) 。任何提示?我通过为我的确切类型定义一个隐式转换来解决我的问题,所以至少丑陋隐藏在它自己的特性中,但仍然感觉有点笨拙的深层复制。

4 个解决方案

#1

At least with Scala 2.9.2 there's an easier way with the collections conversions: import "import collection.JavaConversions._" and use "toMap".

至少使用Scala 2.9.2,集合转换更简单:导入“import collection.JavaConversions._”并使用“toMap”。

Example:

// show with Java Map:

scala> import java.util.{Map=>JMap}
scala> val jenv: JMap[String,String] = System.getenv()
jenv: java.util.Map[String,String] = {TERM=xterm, ANT_OPTS=-Xmx512m ...}

scala> jenv.keySet()
res1: java.util.Set[String] = [TERM, ANT_OPTS...]

// Now with Scala Map:

scala> import collection.JavaConversions._
scala> val env: Map[String,String] = System.getenv.toMap // <--- TADA <---
env: Map[String,String] = Map(ANT_OPTS -> -Xmx512m, TERM -> xterm ...)

// Just to prove it's got Scala functionality:

scala> env.filterKeys(_.indexOf("TERM")>=0)
res6: scala.collection.immutable.Map[String,String] = Map(TERM -> xterm, 
  TERM_PROGRAM -> iTerm.app, ITERM_PROFILE -> Default)

It works fine with a java.util.map of String to Boolean.

使用String的java.util.map到Boolean可以正常工作。

#2

A Scala String is a java.lang.String but a Scala Boolean is not a java.lang.Boolean. Hence the following works:

Scala String是java.lang.String,但Scala Boolean不是java.lang.Boolean。因此以下工作:

import collection.jcl.Conversions._
import collection.mutable.{Map => MMap}
import java.util.Collections._
import java.util.{Map => JMap}

val jm: JMap[String, java.lang.Boolean] = singletonMap("HELLO", java.lang.Boolean.TRUE)

val sm: MMap[String, java.lang.Boolean] = jm //COMPILES FINE

But your problem is still the issue with the Boolean difference. You'll have to "fold" the Java map into the scala one: try again using the Scala Boolean type:

但是你的问题仍然是布尔差异的问题。您必须将Java地图“折叠”到scala中:使用Scala布尔类型再次尝试:

val sm: MMap[String, Boolean] = collection.mutable.Map.empty + ("WORLD" -> false)
val mm = (sm /: jm) { (s, t2) => s + (t2._1 -> t2._2.booleanValue) }

Then mm is a scala map containing the contents of the original scala map plus what was in the Java map

然后mm是一个scala地图,其中包含原始scala地图的内容以及Java地图中的内容

#3

useJavaMap.scala

import test._
import java.lang.Boolean
import java.util.{Map => JavaMap}
import collection.jcl.MapWrapper

object useJavaMap {
  def main(args: Array[String]) {
    var scalaMap : Map[String, Boolean] = Map.empty
    scalaMap = toMap(test.testing())
    println(scalaMap)
  }

  def toMap[K, E](m: JavaMap[K, E]): Map[K, E] = {
    Map.empty ++ new MapWrapper[K, E]() {
      def underlying = m
    }
  }
}

test/test.java

package test;

import java.util.*;

public class test {
    public static Map<String, Boolean> testing() {
        Map<String, Boolean> x = new HashMap<String, Boolean>();
        x.put("Test",Boolean.FALSE);
        return x;
    }
    private test() {}
}

Commandline

javac test\test.java
scalac useJavaMap.scala
scala useJavaMap
> Map(Test -> false)

#4

I think I have a partial answer...

我想我有部分答案......

If you convert the java map to a scala map with the java types. You can then map it to a scala map of scala types:

如果将java映射转换为带有java类型的scala映射。然后,您可以将其映射到scala类型的scala映射:

val javaMap = new java.util.TreeMap[java.lang.String, java.lang.Boolean]
val temp = new collection.jcl.MapWrapper[java.lang.String,java.lang.Boolean] {
    override def underlying = javaMap
}
val scalaMap = temp.map{
    case (k, v) => (k.asInstanceOf[String] -> v.asInstanceOf[Boolean])
}

The flaw in this plan is that the type of scalaMap is Iterable[(java.lang.String, Boolean)] not a map. I feel so close, can someone cleverer than me fix the last statement to make this work?!

这个计划的缺陷是scalaMap的类型是Iterable [(java.lang.String,Boolean)]而不是map。我觉得如此接近,有人比我更聪明地修复最后的声明来使这项工作?!

#1