Play: How to modify data while deserializing Json - json

Question

Here below is a simple case class that holds user information:
import play.api.libs.json._
import play.api.libs.functional.syntax._
case class User(
val username: String,
val password: String
)
... and here is the companion object that provides functionality for serializing/deserializing User objects to/from JSON:
object User {
implicit val userWrites: Writes[User] = (
(__ \ 'username).write[String] ~
(__ \ 'password).write[String]
)(unlift(User.unapply))
implict val userReads: Reads[User] = (
(__ \ 'username).read[String] ~
(__ \ 'password).read[String] // how do I invoke the password hasher here?
)(User.apply(_, _))
}
Let's assume User objects should always contain hashed passwords but incoming JSON always provide plaintext... how can I enhance my Reads so that it invokes the password hasher while deserializing?

Answer 1

You can use the map method on Reads:
def doSomething(s: String) = s * 3
case class User(val username: String, val password: String)
object User {
implicit val userWrites: Writes[User] = (
(__ \ 'username).write[String] ~
(__ \ 'password).write[String]
)(unlift(User.unapply))
implicit val userReads: Reads[User] = (
(__ \ 'username).read[String] ~
(__ \ 'password).read[String].map(doSomething)
)(User.apply(_, _))
}
And then:
scala> Json.parse("""{"username": "foo", "password": "bar"}""").as[User]
res0: User = User(foo,barbarbar)
Note, though, that this means that your Reads and Writes are no longer inverses of each other.