How to parse JSON in Scala using standard Scala classes

Question

I am using the build in JSON class in Scala 2 8 to parse JSON code  I don t want to use the Liftweb one or any other due to minimizing dependencies   The way I am doing it seems too imperative  is there a better way to do it   import scala util parsing json       val json Option Any    JSON parseFull jsonString  val map Map String Any    json get asInstanceOf Map String  Any   val languages List Any    map get  languages   get asInstanceOf List Any   languages foreach  langMap   gt    val language Map String Any    langMap asInstanceOf Map String Any   val name String   language get  name   get asInstanceOf String  val isActive Boolean   language get  is active   get asInstanceOf Boolean  val completeness Double   language get  completeness   get asInstanceOf Double

User · Accepted Answer

This is a solution based on extractors which will do the class cast:

class CC[T] { def unapply(a:Any):Option[T] = Some(a.asInstanceOf[T]) }

object M extends CC[Map[String, Any]]
object L extends CC[List[Any]]
object S extends CC[String]
object D extends CC[Double]
object B extends CC[Boolean]

val jsonString =
    """
      {
        "languages": [{
            "name": "English",
            "is_active": true,
            "completeness": 2.5
        }, {
            "name": "Latin",
            "is_active": false,
            "completeness": 0.9
        }]
      }
    """.stripMargin

val result = for {
    Some(M(map)) <- List(JSON.parseFull(jsonString))
    L(languages) = map("languages")
    M(language) <- languages
    S(name) = language("name")
    B(active) = language("is_active")
    D(completeness) = language("completeness")
} yield {
    (name, active, completeness)
}

assert( result == List(("English",true,2.5), ("Latin",false,0.9)))

At the start of the for loop I artificially wrap the result in a list so that it yields a list at the end. Then in the rest of the for loop I use the fact that generators (using <-) and value definitions (using =) will make use of the unapply methods.

(Older answer edited away - check edit history if you're curious)

User · Answer

You can do like this  Very easy to parse JSON code  P  package org sqkb service common bean  import java text SimpleDateFormat  import org json4s import org json4s JValue import org json4s jackson JsonMethods     import org sqkb service common kit  IsvCode   import scala util Try               case class Order log  String       implicit lazy val formats   org json4s DefaultFormats    lazy val json  json4s JValue   parse log     lazy val create time  String    json    create time   extractOrElse  1970-01-01 00 00 00     lazy val site id  String    json    site id   extractOrElse       lazy val alipay total price  Double    json    alipay total price   extractOpt String  filter   nonEmpty  getOrElse  0   toDouble   lazy val gmv  Double   alipay total price   lazy val pub share pre fee  Double    json    pub share pre fee   extractOpt String  filter   nonEmpty  getOrElse  0   toDouble   lazy val profit  Double   pub share pre fee    lazy val trade id  String    json    trade id   extractOrElse       lazy val unid  Long   Try  json    unid   extractOpt String  filter   nonEmpty  get toLong  getOrElse 0L    lazy val cate id1  Int    json    cate id   extractOrElse 0    lazy val cate id2  Int    json    subcate id   extractOrElse 0    lazy val cate id3  Int    json    cate id3   extractOrElse 0    lazy val cate id4  Int    json    cate id4   extractOrElse 0    lazy val coupon id  Long    json    coupon id   extractOrElse 0     lazy val platform  Option String    Order siteMap get site id      def time fmt fmt  String    yyyy-MM-dd HH mm ss    String         val dateFormat   new SimpleDateFormat  yyyy-MM-dd HH mm ss       val date   dateFormat parse this create time      new SimpleDateFormat fmt  format date

User · Answer

scala util parsing json JSON is deprecated  Here is another approach with circe  FYI documentation  https   circe github io circe cursors html Add the dependency in build sbt  I used scala 2 13 4  note the scala version must align with the library version  val circeVersion    quot 0 14 0-M2 quot   libraryDependencies     Seq     quot io circe quot       quot circe-core quot        circeVersion     quot io circe quot       quot circe-generic quot     circeVersion     quot io circe quot       quot circe-parser quot      circeVersion    Example 1  case class Person name  String  age  Int   object Main     def main args  Array String    Unit         val input          quot  quot  quot                         quot kind quot    quot Listing quot               quot data quot                                    quot name quot    quot Frodo quot                   quot age quot   51                                                quot name quot    quot Bilbo quot                   quot age quot   60                                                  quot  quot  quot  stripMargin      implicit val decoderPerson  Decoder Person    deriveDecoder Person     decoder required to parse to custom object      val parseResult  Json   circe parser parse input  getOrElse Json Null      val data  ACursor   parseResult hcursor downField  quot data quot      get the data field     val personList  List Person    data as List Person   getOrElse null     parse the dataField to a list of Person     for         person  lt - personList       println person name    quot  is  quot    person age         Example 2  json has an object within an object  case class Person name  String  age  Int  position  Position  case class Position x  Int  y  Int   object Main     def main args  Array String    Unit         val input          quot  quot  quot                         quot kind quot    quot Listing quot               quot data quot                                    quot name quot    quot Frodo quot                   quot age quot   51                  quot position quot                       quot x quot   10                    quot y quot   20                                                                 quot name quot    quot Bilbo quot                   quot age quot   60                  quot position quot                       quot x quot   75                    quot y quot   85                                                                   quot  quot  quot  stripMargin      implicit val decoderPosition  Decoder Position    deriveDecoder Position     must be defined before the Person decoder     implicit val decoderPerson  Decoder Person    deriveDecoder Person       val parseResult   circe parser parse input  getOrElse Json Null      val data   parseResult hcursor downField  quot data quot       val personList   data as List Person   getOrElse null      for         person  lt - personList       println person name    quot  is  quot    person age    quot  at  quot    person position

User · Answer

I tried a few things  favouring pattern matching as a way of avoiding casting but ran into trouble with type erasure on the collection types    The main problem seems to be that the complete type of the parse result mirrors the structure of the JSON data and is either cumbersome or impossible to fully state  I guess that is why Any is used to truncate the type definitions  Using Any leads to the need for casting   I ve hacked something below which is concise but is extremely specific to the JSON data implied by the code in the question  Something more general would be more satisfactory but I m not sure if it would be very elegant   implicit def any2string a  Any     a toString implicit def any2boolean a  Any    a asInstanceOf Boolean  implicit def any2double a  Any     a asInstanceOf Double   case class Language name  String  isActive  Boolean  completeness  Double   val languages   JSON parseFull jstr  match     case Some x    gt        val m   x asInstanceOf Map String  List Map String  Any          m  languages   map  l   gt  Language l  name    l  isActive    l  completeness           case None   gt  Nil    languages foreach  println

User · Answer

This is the way I do the pattern match   val result   JSON parseFull jsonStr  result match        Matches if jsonStr is valid JSON and represents a Map of Strings to Any   case Some map  Map String  Any     gt  println map    case None   gt  println  Parsing failed     case other   gt  println  Unknown data structure      other

User · Answer

val jsonString                       languages                 name    English              is active   true             completeness   2 5                       name    Latin              is active   false             completeness   0 9                       stripMargin  val result   JSON parseFull jsonString  map     case json  Map String  List Map String  Any      gt      json  languages   map l   gt   l  name    l  is active    l  completeness       get  println result   assert  result    List   English   true  2 5     Latin   false  0 9

User · Answer

This is the way I do the Scala Parser Combinator Library   import scala util parsing combinator   class ImprovedJsonParser extends JavaTokenParsers      def obj  Parser Map String  Any               gt  repsep member        lt           Map            def array  Parser List Any               gt  repsep value        lt          def member  Parser  String  Any         stringLiteral         value      case name         value   gt   name  value       def value  Parser Any          obj         array         stringLiteral         floatingPointNumber       toDouble          true          false           object ImprovedJsonParserTest extends ImprovedJsonParser     def main args  Array String         val jsonString                            languages                   name    English                is active   true               completeness   2 5                           name    Latin                is active   false               completeness   0 9                            stripMargin       val result   parseAll value  jsonString      println result

User · Answer

I like  huynhjl s answer  it led me down the right path  However  it isn t great at handling error conditions  If the desired node does not exist  you get a cast exception  I ve adapted this slightly to make use of Option to better handle this   class CC T      def unapply a Option Any   Option T    if  a isEmpty        None     else       Some a get asInstanceOf T          object M extends CC Map String  Any   object L extends CC List Any   object S extends CC String  object D extends CC Double  object B extends CC Boolean   for     M map   lt - List JSON parseFull jsonString     L languages    map get  languages     language  lt - languages   M lang    Some language    S name    lang get  name     B active    lang get  is active     D completeness    lang get  completeness     yield      name  active  completeness      Of course  this doesn t handle errors so much as avoid them  This will yield an empty list if any of the json nodes are missing  You can use a match to check for the presence of a node before acting     for     M map   lt - Some JSON parseFull jsonString     yield     map get  languages   match       case L languages    gt          for           language  lt - languages         M lang    Some language          S name    lang get  name           B active    lang get  is active           D completeness    lang get  completeness           yield            name  active  completeness                            case None   gt   bad json

[json] How to parse JSON in Scala using standard Scala classes?

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