How can I read Json as Map[String,String]?

Question

I got the problem when parsing JSON to Map[String, String]. The idea is to parse the nested object to a key separate by "."

Can we format this input JSON:

{
   "key-1":{
       "sub-key-1-1":{
           "sub-key-1-1-1":"value111"
        },
        "sub-key-1-2":{
           "sub-key-1-2-1":"value121"
        }
    },
    "key-2":{
       "sub-key-2-1":{
           "sub-key-2-1-1":"value211"
       }
    }
}

to this result as Map[String,String]:

("key-1.sub-key-1-1.sub-key-1-1-1"->"value111", 
"key-1.sub-key-1-2.sub-key-1-2-1"->"value121",
"key-2.sub-key-2-1.sub-key-2-1-1"->"value211")

Have you tried parsing it into a nested map, then traversing recursively to compact, then writing back to json? — Dima
– Dima, Commented Jun 29, 2022 at 11:03

AminMal · Accepted Answer · 2022-06-30 12:23:19Z

1

You can think about it this way, if the JsValue is a JsObject, you need to extract the key values and append them to the current state of your function, if it's anything else, you can just add them to the state of your function, and then return them. Thinking recursively:

import play.api.libs.json._

def iterateJson(js: JsValue, currentKey: Option[String] = None, acc: Map[String, String] = Map.empty): Map[String, String] = {
    js match {
      case obj: JsObject =>
        obj.keys.foldLeft(acc) {
          case (updatingMap, newKey) =>
            iterateJson(obj.value(newKey), currentKey.map(k => s"$k.$newKey") orElse Some(newKey), updatingMap)
        }
      case other =>
        (currentKey map (key => acc.updated(key, other.toString()))) getOrElse acc
    }
  }

See the code running on scastie

edited Jun 30, 2022 at 12:23

answered Jun 29, 2022 at 11:48

AminMal

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1 Comment

Andriy Plokhotnyuk Over a year ago

BEWARE about DoS vulnerability of Scala's maps if your system accepts untrusted input: github.com/scala/bug/issues/11203

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