How to convert java Map to scala Map of type LinkedHashMap[String,ArrayList[String]]?

Question

from Java API I get

java.util.LinkedHashMap[String,java.util.ArrayList[String]]

which I then need to pass as a parameter to a scala program

val rmap = Foo.baz(parameter)

This parameter is of scala type:

Map[String,List[String]]

So how can I easily convert

java.util.LinkedHashMap[String,java.util.ArrayList[String]]

to

Map[String,List[String]]

I tried using import scala.collection.JavaConversions._ but in my case this does not work (or at least thats what I guess) because the scala code is in template function and I can only place import scala.collection.JavaConversions._ inside the function. the template function is like:

def someFunc(param: java.util.LinkedHashMap[String,java.util.ArrayList[String]]) = {
import scala.collection.JavaConversions._
val rmap = Foo.baz(param) // param is of scala type Map[String,List[String]]
.......

Now scala is not auto converting java type to scala type.

This is the compiler error I get: Error raised is : type mismatch; found : java.util.LinkedHashMap[String,java.util.ArrayList[String]] required: Map[String,List[String]]

Matthew Farwell · Accepted Answer · 2011-09-02 10:44:53Z

6

You've got two problems: Map and List in scala are different from the java versions.

scala.collection.JavaConversions.mapAsScalaMap creates a mutable map, so using the mutable map, the following works:

import scala.collection.JavaConversions._
import scala.collection.mutable.Map

val f = new java.util.LinkedHashMap[String, java.util.ArrayList[String]]
var g: Map[String, java.util.ArrayList[String]] = f

The ArrayList is a bit harder. The following works:

import scala.collection.JavaConversions._
import scala.collection.mutable.Buffer

val a = new java.util.ArrayList[String]
var b: Buffer[String] = a

But if we try

import scala.collection.JavaConversions._
import scala.collection.mutable.Map
import scala.collection.mutable.Buffer

val f = new java.util.LinkedHashMap[String, java.util.ArrayList[String]]
var g: Map[String, Buffer[String]] = f

this doesn't work. Your best option is to define an explicit implicit conversion yourself for this.

edited Sep 2, 2011 at 10:44

answered Jul 5, 2011 at 11:02

Matthew Farwell

61.9k18 gold badges134 silver badges174 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

tsuna Over a year ago

"an explicit implicit conversion". <3 Scala. :)

rafalotufo · Accepted Answer · 2011-07-04 15:33:45Z

5

Just import scala.collection.JavaConversions and you should be set :) It performs conversions from Scala collections to Java collections and vice-versa.

If it doesn't work smoothly, try:

val m: Map[String,List[String]] = javaMap

You might also need to convert each one of the lists inside the map:

m.map {
  l => val sl: List[String] = l
  sl
}

answered Jul 4, 2011 at 15:33

rafalotufo

3,9524 gold badges27 silver badges28 bronze badges

2 Comments

Jean-Philippe Pellet Over a year ago

That's not correct; you need to import collection.JavaConversions._.

jilen Over a year ago

that is true. import scala.collection.JavaConversions._ than all collections are converted implicitly.

jilen · Accepted Answer · 2011-07-04 15:35:09Z

1

scala.collection.JavaConversions.mapAsScalaMap

or something similar in the JavaConversions Object

answered Jul 4, 2011 at 15:35

jilen

5,7833 gold badges38 silver badges87 bronze badges

Comments

Tunaki · Accepted Answer · 2017-02-11 14:21:29Z

0

You can try using

val rmap = Foo.baz(parameter.asScala.toMap.mapValues(v => v.asScala.toList))

Import below in your code -

import scala.collection.JavaConversions._
import scala.collection.JavaConverters._

edited Feb 11, 2017 at 14:21

Tunaki

138k46 gold badges370 silver badges443 bronze badges

answered Feb 11, 2017 at 14:01

Rahul Kosambi

1131 silver badge7 bronze badges

Collectives™ on Stack Overflow

How to convert java Map to scala Map of type LinkedHashMap[String,ArrayList[String]]?

4 Answers 4

1 Comment

2 Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

1 Comment

2 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related