Kotlin

Data Class

data class SportsActivity (
       val totalAveragePaceInMinutesPerKilometre: Double,
       val totalAverageSpeedInKilometresPerHour: Double,
       val totalDurationInSeconds: Int,
       val totalAverageDistanceInMetres: Double, 
       var dateOfActivity: Date
)

Reading and Writing to Gson

Given the following

    var mySportsActivity = SportsActivity(
           0.0,
           0.0,
           0,
           0.0,
           Date())

   val gson = Gson()
   val json = gson.toJson(mySportsActivity)

   var filename = "D:\\IAIN\\Output.json";

You can write to a file with

    FileWriter(filename).use {
       writer ->
       val gson = GsonBuilder().setPrettyPrinting().create()
       gson.toJson(mySportsActivity, writer)
    }

And read it back with

    FileReader("D:\\IAIN\\Output.json").use {
       reader ->
       val gson = GsonBuilder().setPrettyPrinting().create()
       mySportsActivity2 = gson.fromJson(reader,SportsActivity::class.java)
    }