Accessing attributes in objects Scala - json

Question

An example of the sort of objects I need to grab from my json can be found in the following example(src):
{
"test": {
"attra": "2017-10-12T11:17:52.971Z",
"attrb": "2017-10-12T11:20:58.374Z"
},
"dummyCheck": false,
"type": "object",
"ruleOne": {
"default": 2557
},
"ruleTwo": {
"default": 2557
}
}
From the example above I want to access the default value under "ruleOne".
I've tried messing about with several different things below but I seem to be struggling. I can grab values like "dummyCheck" ok. What's the best way to key into where I need to go?
Example of how I am trying to get the value below:
import org.json4s._
import org.json4s.native.JsonMethods._
import org.json4s.DefaultFormats
implicit val formats = DefaultFormats
val test = parse(src)
println((test \ "ruleOne.default").extract[Integer])
Edit:
To further extend what is above:
def extractData(data: java.io.File) = {
val json = parse(data)
val result = (json \ "ruleOne" \ "default").extract[Int]
result
}
If I was to extend the above into a function that is called by passing in:
extractData(src)
That would only ever give me RuleOne.default.. is there a way I could extend it so that I could dynamically pass it multiple string arguments to parse (like a splat)
def extractData(data: java.io.File, path: String*) = {
val json = parse(data)
val result = (json \ path: _*).extract[Int]
result
}
so consuming it would be like
extractData(src, "ruleOne", "default")

Answer 1

This here works with "json4s-jackson" % "3.6.0-M2", but it should work in exactly the same way with native backend.
val src = """
|{
| "test": {
| "attra": "2017-10-12T11:17:52.971Z",
| "attrb": "2017-10-12T11:20:58.374Z"
| },
| "dummyCheck": false,
| "type": "object",
| "ruleOne": {
| "default": 2557
| },
| "ruleTwo": {
| "default": 2557
| }
|}""".stripMargin
import org.json4s._
import org.json4s.jackson.JsonMethods._
import org.json4s.DefaultFormats
implicit val formats = DefaultFormats
val test = parse(src)
println((test \ "ruleOne" \ "default").extract[Int])
Output:
2557
To make it work with native, simply replace
import org.json4s.jackson.JsonMethods._
by
import org.json4s.native.JsonMethods._
and make sure that you have the right dependencies.
EDIT
Here is a vararg method that transforms string parameters into a path:
def extract(json: JValue, path: String*): Int = {
path.foldLeft(json)(_ \ _).extract[Int]
}
With this, you can now do:
println(extract(test, "ruleOne", "default"))
println(extract(test, "ruleTwo", "default"))
Note that it accepts a JValue, not a File, because the version with File would be unnecessarily painful to test, whereas JValue-version can be tested with parsed string constants.