extracting keys from json string using json4s

Question

can someone tell me how to extract keys from json using json4s. My use case: json stored as string in scala variable:

 {
 "key1" : "val1",
 "key2" : ["12", "32"],
 "key3" : {"keyN" : "valN"}
 }

I'd like to transform this into a following Map[String, String]:

 (key1 -> "val1", key2 -> "[\"12\",\"32\"]", key3 -> "{\"keyN\":\"valN\"}"

is there a simple way to achieve this with json4s? Thanks in advance

chengpohi · Accepted Answer · 2015-12-15 13:45:10Z

4

val result: Map[String, String] = parse( """ {
                                           | "key1" : "val1",
                                           | "key2" : ["12", "32"],
                                           | "key3" : {"keyN" : "valN"}
                                           | }""".stripMargin).mapField(k => {
  val v: String = k._2 match {
    case s: JString => k._2.extract[String]
    case _ => write(k._2)
  }
  (k._1, JString(v))
}).extract[Map[String, String]]
println(result)

You can use mapField map the JValue toString

if the value's type is String just extract as String
if the value's type is others, use the json4s to parse it to as JSON string
finally extract the JValue as Map[String, String].

answered Dec 15, 2015 at 13:45

chengpohi

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1 Comment

homar Over a year ago

thanks, works fine. I didn't see mapField method which is a key here :(

phil · Accepted Answer · 2018-05-24 13:13:56Z

0

implicit val formats = DefaultFormats

val a = parse(""" { "numbers" : [1, 2, 3, 4] } """)
println(a.extract[Map[String, Any]].keySet)

answered May 24, 2018 at 13:13

phil

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