Scala convert ArrayList in Map[String, Any] to Seq

Question

I'm trying to read in a .yaml file into my Scala code. Assume I have the following yaml file:

animals: ["dog", "cat"]

I am trying to read it using the following code:

val e = yaml.load(os.read("config.yaml")).asInstanceOf[java.util.Map[String, Any]] val arr = e.getOrDefault("animals", new Java.util.ArrayList[String]()) // arr is Option[Any], but I know it contains java.util.ArrayList<String> arr.asInstanceOf[Buffer[String]] // ArrayList cannot be cast to Buffer

The ArrayList is type Any, so how do I cast to a Scala Collection e.g. Buffer? (Or Seq, List...)

Donald, your question has enough answers. Will you please comments/accept/else on those? Please read What should I do when someone answers my question? — Tomer Shetah
– Tomer Shetah, Commented Nov 23, 2020 at 12:48

tentacle · Accepted Answer · 2020-11-22 05:53:31Z

SnakeYaml (assuming what you're using) can't give you a scala collection like Buffer directly.

But you can ask it for ArrayList of string and then convert it to whatever you need.

import scala.jdk.CollectionConverters._ val list = arr.asInstanceOf[util.ArrayList[String]].asScala

results in:

list: scala.collection.mutable.Buffer[String] = Buffer(dog, cat)

Tomer Shetah · Accepted Answer · 2020-11-22 13:16:36Z

Another option you have is to define the model of you configuration, for example:

class Sample { @BeanProperty var animals = new java.util.ArrayList[String]() }

The following will create an instance of Sample:

val input = new StringReader("animals: [\"dog\", \"cat\"]") val yaml = new Yaml(new Constructor(classOf[Sample])) val sample = yaml.load(input).asInstanceOf[Sample]

Then, using CollectionConverters in Scala 2.13, or JavaConverters in Scala 2.12 or prior, convert animals into a Scala structure:

val buffer = sample.getAnimals.asScala

Code run at Scastie.

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