Hello im trying to read a JSON file and sorting with a template that things would be in a specific order, can i get some pointers on how to do it? - scala

Question

I found how to read from it but , can't seem to find the information i need on how to order it using my own template. and writing it on a diffrent json file. Im using Scala.

Answer 1

Usually to transform data from one JSON file to another you will need to parse it to some data structures in memory (case classes, Scala collections, etc.), transform them and serialize back to file.
Circe is most inefficient JSON parser, especially when it is need to parse files. Its core parser works only with strings that requires reading whole file to RAM and convert it to string from encoded bytes (usually UTF-8), even its alternative Jawn parser reads whole file to a byte array, then convert it to a string and then start parsing. Its formatter also have lot of overheads: serialization of whole output to string or byte buffer before you can start writing it to file.
Much better would be to use circe-jackson integration or even better to use jackson-module-scala: both support reading from FileInputStream and writing to FileOutputStream.
Most efficient Scala parser and serializer that can be used for buffered reading/writing from/to files is here and example of parse-transform-serialize code with it is below.
Let we have a following content of the JSON file:
{
"name": "John",
"devices": [
{
"id": 1,
"model": "HTC One X"
}
]
}
And we are going to transform it to:
{
"name": "John",
"devices": [
{
"id": 1,
"model": "HTC One X"
},
{
"id": 2,
"model": "iPhone X"
}
]
}
Here is how we can do it with jsoniter-scala:
libraryDependencies ++= Seq(
"com.github.plokhotnyuk.jsoniter-scala" %% "jsoniter-scala-core" % "0.29.2" % Compile,
"com.github.plokhotnyuk.jsoniter-scala" %% "jsoniter-scala-macros" % "0.29.2" % Provided // required only in compile-time
)
// import required packages
import java.io._
import com.github.plokhotnyuk.jsoniter_scala.macros._
import com.github.plokhotnyuk.jsoniter_scala.core._
// define your model that mimic JSON format
case class Device(id: Int, model: String)
case class User(name: String, devices: Seq[Device])
// create codec for type that corresponds to root of JSON
implicit val codec = JsonCodecMaker.make[User](CodecMakerConfig())
// read & parse JSON from file to your data structures
val user = {
val fis = new FileInputStream("/tmp/input.json")
try readFromStream(fis)
finally fis.close()
}
// transform your data
val newUser = user
.copy(devices = user.devices :+ Device(id = 2, model = "iPhone X"))
// write your transformed data to json file
val fos = new FileOutputStream("/tmp/output.json")
try writeToStream(newUser, fos)
finally fos.close()

Answer 2

you question is very abstract, but here's a good library for JSON parsing and manipulation in Scala
https://github.com/circe/circe