How to parse json with spray json that uses snake case (underscore notation) instead of camel case

Question

How to parse json with spray json that uses snake case (underscore notation) instead of camel case?

E.g.

case class Test(subjectDescription: String)
"{\"subject_description\":\"Medicine\"}".parseJson.convertTo[Test]

should work and not throw exception.

Answer 1

Like this:

case class Test(subjectDescription: String)
implicit val testFormat = jsonFormat(Test.apply, "subject_description")
"{\"subject_description\":\"Medicine\"}".parseJson.convertTo[Test]

The trick here is jsonFormat function takes string arguments for json object keys.

Answer 2

This answer is taken from https://groups.google.com/forum/#!msg/spray-user/KsPIqWDK0AY/HcanflgRzMcJ. Putting it on SO since the SEO is better.

/**
 * A custom version of the Spray DefaultJsonProtocol with a modified field naming strategy
 */
trait SnakifiedSprayJsonSupport extends DefaultJsonProtocol {
  import reflect._

  /**
   * This is the most important piece of code in this object!
   * It overrides the default naming scheme used by spray-json and replaces it with a scheme that turns camelcased
   * names into snakified names (i.e. using underscores as word separators).
   */
  override protected def extractFieldNames(classTag: ClassTag[_]) = {
    import java.util.Locale

    def snakify(name: String) = PASS2.replaceAllIn(PASS1.replaceAllIn(name, REPLACEMENT), REPLACEMENT).toLowerCase(Locale.US)

    super.extractFieldNames(classTag).map { snakify(_) }
  }

  private val PASS1 = """([A-Z]+)([A-Z][a-z])""".r
  private val PASS2 = """([a-z\d])([A-Z])""".r
  private val REPLACEMENT = "$1_$2"
}

object SnakifiedSprayJsonSupport extends SnakifiedSprayJsonSupport

import SnakifiedSprayJsonSupport._

object MyJsonProtocol extends SnakifiedSprayJsonSupport {
  implicit val testFormat = jsonFormat1(Test.apply)
}