Develop Reference

Converting an JSON string to Gson object

I have an JSONObject which is creating in the following way.
For a special reason, I have to convert it to Gson in this way, as i can modify only extractDataToString() method. But I do not get proper value after conversion.
fun createJsonString() {
val headerJson = JSONObject()
headerJson.put("typ1", "value1")
headerJson.put("typ2", "value2")
extractData(headerJson.toString())
}
fun extractDataToString(jsonString: String) {
val headerJson = Gson().fromJson(jsonString, JsonObject::class.java)
val resultType1 = headerJson.remove("typ1")?.toString() // Here, resultType1 becomes
"value1", but it should be
value1 that is extra qutomation
mark is being added.
}
Why extra quotation mark is being added? Can anyone please help? I am a newbie.

Call
.getAsString()
Instead of
toString()
at the end
ref : docs

How to parse a data class into JSON string for Kotlin?

I wonder what is the way to convert a Kotlin data class into its equivalent json string. Json keys should be configurable.
Let's say I have a class,
data class Student(name: String?, roll: Int?, mark: Int?) {
}
I want to make a Json from this Student object where keys will be,
stundent_name, stundent_roll, stundent_mark
Moreover, I may also need to make a json from list of student with key students. How can I do so? I know using Gson I can create object from json string. How to do the reverse?

data class Student(
#SerializedName("stundent_name")
val name: String?,
#SerializedName("stundent_roll")
val roll: Int?,
#SerializedName("stundent_mark")
val mark: Int?
)
And the code for convertion is:
val gson = Gson()
val student = Student("John", 1, 5)
gson.toJson(student)
This code makes String like this:
{"stundent_mark":5,"stundent_name":"John","stundent_roll":1}
And if you need to create JsonArray, just do the same with your List of students:
gson.toJson(list)

how to parse custom json array list in kotlin using GSON

this is my data class, need to parse the arraylist of type link
class DetailResponse {
data class BasicInfo (
#SerializedName("favorite") val isFavorite: Boolean,
#SerializedName("screenshots") val screenshots: ArrayList<Link>
)
data class Link (
#SerializedName("href") val href: String
)
}

What you have done is correct. Now you just have to use Gson to convert this JSON to object
val gson = Gson()
val detailResponse = gson.fromJson(resp,DetailedResponse::class.java)
where "resp" is your json string.

How to use gson deserialize to ArrayList in Kotlin

I use this class to store data
public class Item(var name:String,
var description:String?=null){
}
And use it in ArrayList
public var itemList = ArrayList<Item>()
Use this code to serialize the object
val gs=Gson()
val itemListJsonString = gs.toJson(itemList)
And deserialize
itemList = gs.fromJson<ArrayList<Item>>(itemListJsonString, ArrayList::class.java)
But this method will give me LinkedTreeMap, not Item, I cannot cast LinkedTreeMap to Item
What is correct way to deserialize to json in Kotlin?

Try this code for deserialize list
val gson = Gson()
val itemType = object : TypeToken<List<Item>>() {}.type
itemList = gson.fromJson<List<Item>>(itemListJsonString, itemType)

You can define a inline reified extension function like:
internal inline fun <reified T> Gson.fromJson(json: String) =
fromJson<T>(json, object : TypeToken<T>() {}.type)
And use it like:
val itemList: List<Item> = gson.fromJson(itemListJsonString)
By default, types are erased at runtime, so Gson cannot know which kind of List it has to deserialize. However, when you declare the type as reified you preserve it at runtime. So now Gson has enough information to deserialize the List (or any other generic Object).

In my code I just use:
import com.google.gson.Gson
Gson().fromJson(string_var, Array<Item>::class.java).toList() as ArrayList<Type>
I give here a complete example.
First the type and the list array:
class Item(var name:String,
var description:String?=null)
var itemList = ArrayList<Item>()
The main code:
itemList.add( Item("Ball","round stuff"))
itemList.add(Item("Box","parallelepiped stuff"))
val striJSON = Gson().toJson(itemList) // To JSON
val backList = Gson().fromJson( // Back to another variable
striJSON, Array<Item>::class.java).toList() as ArrayList<Item>
val striJSONBack = Gson().toJson(backList) // To JSON again
if (striJSON==striJSONBack) println("***ok***")
The exit:
***OK***

Instead of the accepted answer (that works but creates an object to get its type), you could just do:
val gson = Gson()
itemList = gson.fromJson(itemListJsonString, Array<Item>::class.java)
There "Array" represents a Java array when targeting the JVM platform. That's not an ArrayList but you can access the items (that's usually all is needed after parsing JSON).
If you still need to manipulate the list you could easily convert it to mutable by doing:
itemsList.toMutableList()

How to parse JSON from an url using Kotlin on Android?

I've been trying to parse JSON from an url for hours now but I'm too stupid I guess
I have tried
val result = URL("http://date.jsontest.com/").readText()
but it crashes
java.net.MalformedURLException: no protocol: date.jsontest.com
I have tried Klaxon's library
fun parse(name: String) : Any? {
val cls = Parser::class.java
return cls.getResourceAsStream(name)?.let {
inputStream -> return Parser().parse(inputStream)
}
}
val obj = parse("http://date.jsontest.com/") as JsonObject
but it also crashes
kotlin.TypeCastException: null cannot be cast to non-null type com.beust.klaxon.JsonObject
Can someone please write in Kotlin the simpliest way to parse data from this link http://date.jsontest.com/

Hard to say why you are getting an error. Since this line is correct and working.
val result = URL("http://date.jsontest.com/").readText()
For the parse method. It does not work, becase it expects path to a JSON file but is getting a URL String.
Simplest example using Klaxon would be this.
val result = URL("http://date.jsontest.com/").readText()
val parser: Parser = Parser()
val stringBuilder: StringBuilder = StringBuilder(result)
val json: JsonObject = parser.parse(stringBuilder) as JsonObject
println("Time : ${json.string("time")}, Since epoch : ${json.long("milliseconds_since_epoch")}, Date : ${json.string("date")}, ")