CODEWITHSUNDEEP
jsonscalaparsingjson4s
codee
codee

Reputation: 31

Extracting string from JSON using Json4s using Scala

I have a JSON body in the following form:

val body = 
{
    "a": "hello",
    "b": "goodbye"
}

I want to extract the VALUE of "a" (so I want "hello") and store that in a val. I know I should use "parse" and "Extract" (eg. val parsedjson = parse(body).extract[String]) but I don't know how to use them to specifically extract the value of "a"

Upvotes: 2

Views: 2799

Answers (2)

Tim
Tim

Reputation: 27421

To use extract you need to create a class that matches the shape of the JSON that you are parsing. Here is an example using your input data:

val body ="""
{
  "a": "hello",
  "b": "goodbye"
}
"""

case class Body(a: String, b: String)

import org.json4s._
import org.json4s.jackson.JsonMethods._

implicit val formats = DefaultFormats

val b = Extraction.extract[Body](parse(body))

println(b.a) // hello

Upvotes: 3

Mateusz Kubuszok
Mateusz Kubuszok

Reputation: 27595

You'd have to use pattern matching/extractors:

val aOpt: List[String] = for {
  JObject(map) <- parse(body)
  JField("a", JString(value)) <- map
} yield value

alternatively use querying DSL

parse(body) \ "a" match {
  case JString(value) => Some(value)
  case _              => None
}

These are options as you have no guarantee that arbitrary JSON would contain field "a".

See documentation

extract would make sense if you were extracting whole JObject into a case class.

Upvotes: 1

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