Hi, I was trying to get parameters from a request ...

# ktor

[Rui]

Hi, I was trying to get parameters from a request body by using

call.receive<Parameters>()

and got:

Unable to invoke no-args constructor for interface io.ktor.http.Parameters. Registering an InstanceCreator with Gson for this type may fix this problem

Any ideas?

[Dominik wuttke]

Your server doesn't know what type of data are you receiving and what it should do with it. Installing a contentnegotiator like Gson for example tells your server what it should do with received data of a specific type. For example this

install(ContentNegotiation) {
    gson {
        setDateFormat(DateFormat.LONG)
        setPrettyPrinting()
        register(ContentType.Text.Plain, GsonConverter(GsonBuilder().create()))

    }
}

For received data with a ContentType of plain text, the received data will be converted with the GsonConverter. In my example I am calling

call.receive<FormMessage>()

at a later stage, FormMessage is a JSONObject from this class

data class FormMessage(val name: String, val email : String, val message: String)

[Rustam Siniukov]

Gson doesn’t know how to create Parameters instance, because it is an interface. You can create class that will represent request body or use Map<String, Any>

[Rui]

@Rustam Siniukov thanks for your reply. After I change Parameters to Map<String, String>, it works now. Funny that I saw several examples that they simply use call.receive<Parameters>() and it worked for them. Kinda wonder why does that happen.

[Rui]

@Dominik wuttke Thanks for your reply. I did add a gson ContentNegotiation as you recommended (with or without "register" line), but still no luck here.
My request body is quite simple, only contains String->String and String-> Gson.toJson(Obj). Not sure what was missing here.

[Rustam Siniukov]

@Rui receive<Parameters>() should work when your content type is multipart/form-data or application/x-www-form-urlencoded