如何从 java.util.Map 转换为 Scala Map

How to convert from from java.util.Map to a Scala Map

提问by George

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 返回一个java.util.Map<java.lang.String,java.lang.Boolean>;。我想把它变成一个Map[String,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:

你不能这样做Map.empty ++ javaMap，因为 ++ 方法不知道 Java 映射。我试过：

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

and:

和：

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.Stringis not the same as a scala String.

由于泛型，这些都无法编译 -java.lang.String与 scala String 不同。

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

除了手动复制地图之外，是否有一种很好的方法可以做到这一点？

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，我从他们那里学到了很多东西。但是，我在这里发布了一个比我实际遇到的问题更简单的问题，这是一个错误。所以，如果你允许我，我会概括这个问题 - API 实际返回的是

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]]

我需要将它移动到 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.

它可能看起来不太复杂，但它增加了额外的类型擦除级别，我发现将其移动到 Scala 映射的唯一方法是深度复制它（使用您在下面建议的一些技术） . 有人有任何提示吗？我通过为我的确切类型定义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征中，但仍然感觉有点笨拙，深度复制很多。

回答by Andrew E

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

至少在 Scala 2.9.2 中，集合转换有一种更简单的方法：导入“import collection.JavaConversions._”并使用“toMap”。

Example:

例子：

// 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.

它适用于字符串到布尔值的 java.util.map。

回答by oxbow_lakes

A Scala Stringis a java.lang.Stringbuta Scala Booleanis nota java.lang.Boolean. Hence the following works:

Scala的String是java.lang.String，但Scala的Boolean是不是一个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 Booleandifference. You'll have to "fold" the Java map into the scala one: try again using the Scala Booleantype:

但是您的问题仍然是Boolean差异的问题。您必须将 Java 映射“折叠”到 Scala 映射中：再次尝试使用 ScalaBoolean类型：

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

Then mmis 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 映射，其中包含原始 Scala 映射的内容以及 Java 映射中的内容

回答by jitter

useJavaMap.scala

使用JavaMap.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

测试/测试.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

命令行

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

回答by thatismatt

I think I have a partial answer...

我想我有一个部分的答案......

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 映射转换为具有 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 scalaMapis 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?!

这个计划的缺陷是类型scalaMap是 Iterable[(java.lang.String, Boolean)] 而不是映射。我感觉很亲近，有比我更聪明的人可以修改最后一条语句来使这项工作成功吗？！