Question 263033 in Json Question posted in
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Gson FromJson returns null. What am i missing?

I tried to use gson fromJson but i got this print => Countries(countries=null) everytime. what am i missing ?

//CODE

data class Countries(val countries: Map<String, List<String>>)

val jsonString = """
    {
      "Afghanistan": [
        "Herat",
        "Kabul",
        "Kandahar",
        "Molah",
        "Rana",
        "Shar",
        "Sharif",
        "Wazir Akbar Khan"
      ],
      "Albania": [
        "Elbasan",
        "Petran",
        "Pogradec",
        "Shkoder",
        "Tirana",
        "Ura Vajgurore"
      ]
    }
""".trimIndent()

        val countries = Gson().fromJson(jsonString, Countries::class.java)
        println(countries)
Tags:

2

Answers


  1. 0

    It couldn’t find the countries key. There are basically 3 options here.

    1. You can modify json itself:
    val jsonString = """
{
  "countries": {
    "Afghanistan": [
      "Herat",
      "Kabul",
      "Kandahar",
      "Molah",
      "Rana",
      "Shar",
      "Sharif",
      "Wazir Akbar Khan"
    ],
    "Albania": [
      "Elbasan",
      "Petran",
      "Pogradec",
      "Shkoder",
      "Tirana",
      "Ura Vajgurore"
    ]
  }
}
""".trimIndent()

    1. Alternatively, you can change an entity you deserialize to (e.g. use object : TypeToken<Map<String, List<String>>>() {}.type as the second parameter).

    2. Another option is to create a custom deserializer for your existing json and Countries class as follows:

    val countriesDeserializer =
    JsonDeserializer { json, _, context ->
        Countries(
            context.deserialize(json, object : TypeToken<Map<String, List<String>>>() {}.type)
        )
    }

    And use GsonBuilder().registerTypeAdapter(Countries::class.java, countriesDeserializer).create() instead of simply Gson()

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  2. 0

    To determine type

    val countryCityType = object : TypeToken<Map<String, List<String>>>() {}.type

    Gson parse

    val countryCityData: Map<String, List<String>> = Gson().fromJson(jsonString, countryCityType)

println(countryCityData)
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