Transform Value In PlayJSon Mapping - scala

Question

I'm performing a standard mapping of JSON to a case class using PlayJson. I'd like to transform the value that gets mapped to a member, Test.foo below, if the validation succeeds. Is it possible to work that into the definition of a Reads converter?
val json = .....
case class Test(foo:String, bar:String)
val readsTest: Reads[Test] = (
(__ \ "foo").read[String](minLength(5)) and // And I want to transform this value if the validation succeeds
(__ \ "bar").read[String](minLength(10))
)(Test.apply _)
json.validate[Test] match {
case s: JsSuccess[Test] => s.get
case e: JsError => false
}

Answer 1

Reads.map can do just that, for example, say we want to reverse the value of foo field, then we could call .map(v => v.reverse) on the Reads like so
(__ \ "foo").read[String](minLength[String](5)).map(v => v.reverse)
Here is a working example
val json =
"""
|{
| "foo": "abcdefghijkl",
| "bar": "012345678910"
|}
|""".stripMargin
case class Test(foo: String, bar: String)
val readsTest: Reads[Test] = (
(__ \ "foo").read[String](minLength[String](5)).map(v => v.reverse)
(__ \ "bar").read[String](minLength[String](10))
)(Test.apply _)
Json.parse(json).validate[Test](readsTest)
which outputs
JsSuccess(Test(lkjihgfedcba,012345678910),)