The Scala Toolkit

How to access values inside JSON?

Getting upickle

Using Scala CLI, you can require the entire toolkit in a single line:

//> using toolkit latest

Alternatively, you can require just a specific version of UPickle:

//> using dep com.lihaoyi::upickle:4.1.0

In your build.sbt file, you can add the dependency on the Toolkit:

lazyvalexample=project.in(file(".")).settings(scalaVersion:="3.4.2",libraryDependencies+="org.scala-lang"%%"toolkit"%"0.7.0")

Alternatively, you can require just a specific version of UPickle:

libraryDependencies+="com.lihaoyi"%%"upickle"%"4.1.0"

In your build.sc file, you can add the dependency to the upickle library:

objectexampleextendsScalaModule{defscalaVersion="3.4.2"defivyDeps=Agg(ivy"org.scala-lang::toolkit:0.7.0")}

Alternatively, you can require just a specific version of UPickle:

ivy"com.lihaoyi::upickle:4.1.0"

Accessing values inside JSON

To parse a JSON string and access fields inside it, you can use uJson, which is part of uPickle.

The method ujson.read parses a JSON string into memory:

valjsonString="""{"name": "Peter", "age": 13, "pets": ["Toolkitty", "Scaniel"]}"""valjson:ujson.Value=ujson.read(jsonString)println(json("name").str)// prints: Peter

To access the "name" field, we do json("name") and then call str to type it as a string.

To access the elements by index in a JSON array,

valpets:ujson.Value=json("pets")valfirstPet:String=pets(0).strvalsecondPet:String=pets(1).strprintln(s"The pets are $firstPet and $secondPet")// prints: The pets are Toolkitty and Scaniel

You can traverse the JSON structure as deeply as you want, to extract any nested value. For instance, json("field1")(0)("field2").str is the string value of field2 in the first element of the array in field1.

JSON types

In the previous examples we used str to type a JSON value as a string. Similar methods exist for other types of values, namely:

num for numeric values, returning Double
bool for boolean values, returning Boolean
arr for arrays, returning a mutable Buffer[ujson.Value]
obj for objects, returning a mutable Map[String, ujson.Value]

importscala.collection.mutablevaljsonString="""{"name": "Peter", "age": 13, "pets": ["Toolkitty", "Scaniel"]}"""valjson=ujson.read(jsonString)valperson:mutable.Map[String, ujson.Value]=json.objvalage:Double=person("age").numvalpets:mutable.Buffer[ujson.Value]=person("pets").arr

If a JSON value does not conform to the expected type, uJson throws a ujson.Value.InvalidData exception.

valname:Boolean=person("name").bool// throws a ujson.Value.InvalidData: Expected ujson.Bool (data: "Peter")

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How to access values inside JSON?

Accessing values inside JSON

JSON types

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