Scala 多层隐式读写 map

Question

I have defined a multi-layered map:

import collection.mutable.Map
var modelsRef = Map[String,Map[String,Array[String]]]()

and filled it with data; for example by using:

myMap.update("a", Map("b1" -> Array("c","d","e","f")))
myMap("a").update("b2", Array("g","h"))

I'd like to write the result in a json file and later read it from the file and re-built the map structure. I am using the maven Scala and I am thinking to use the Play or an equivalent package. I read in other posts that I need to define a case class and then write an implicit Writer and Reader . I appreciate it if anyone can show me what it may look like for such a complicated multi-layered map?

Answer 1

You don't need to define any special case class as most of json libraries support "base" types like Map, String, Array, etc by default.

Example done with circe .

  import scala.collection.mutable
  import io.circe.parser._
  import io.circe.syntax._

  var map = mutable.Map[String, mutable.Map[String, mutable.ArrayBuffer[String]]]()
  map.update("a", mutable.Map("b1" -> mutable.ArrayBuffer("c", "d", "e", "f")))
  map("a").update("b2", mutable.ArrayBuffer("g", "h"))
  val json = map.asJson.pretty(Printer.noSpaces)

  println(json)
  // {"a":{"b2":["g","h"],"b1":["c","d","e","f"]}}
  println(decode[Map[String, Map[String, Seq[String]]]](json))
  // Right(Map(a -> Map(b2 -> List(g, h), b1 -> List(c, d, e, f))))

Notice that you aren't required to use mutable collections to read the json back into structure. In my example, I used immutable collections in decode method.

Update :

I tested the above code with Scala 2.12.8 and circe 0.11.2. Dependencies for maven are

<dependency>
    <groupId>io.circe</groupId>
    <artifactId>circe-core_2.12</artifactId>
    <version>0.11.2</version>
</dependency>
<dependency>
    <groupId>io.circe</groupId>
    <artifactId>circe-parser_2.12</artifactId>
    <version>0.11.2</version>
</dependency>