I was having trouble with safely parsing Gson objects without loads of try catch statements or a single try catch which would cause the whole object parsing to fail if a single field was incorrect. I also wanted to replicate org.json.JSONObject opt style functions to return null instead of throwing an exception so I can use Kotlin's null handlin…

JsonElement_Safe.kt

import com.google.gson.*
import java.math.BigDecimal
import java.math.BigInteger

/**
 * Created by Terence Baker on 13/02/2018.
 */

val JsonElement.optString: String?
    get() = safeConversion { asString }

val JsonElement.optLong: Long?
    get() = safeConversion { asLong }

val JsonElement.optBoolean: Boolean?
    get() = safeConversion { asBoolean }

val JsonElement.optFloat: Float?
    get() = safeConversion { asFloat }

val JsonElement.optDouble: Double?
    get() = safeConversion { asDouble }

val JsonElement.optJsonObject: JsonObject?
    get() = safeConversion { asJsonObject }

val JsonElement.optJsonArray: JsonArray?
    get() = safeConversion { asJsonArray }

val JsonElement.optJsonPrimitive: JsonPrimitive?
    get() = safeConversion { asJsonPrimitive }

val JsonElement.optInt: Int?
    get() = safeConversion { asInt }

val JsonElement.optBigDecimal: BigDecimal?
    get() = safeConversion { asBigDecimal }

val JsonElement.optBigInteger: BigInteger?
    get() = safeConversion { asBigInteger }

val JsonElement.optByte: Byte?
    get() = safeConversion { asByte }

val JsonElement.optShort: Short?
    get() = safeConversion { asShort }

val JsonElement.optJsonNull: JsonNull?
    get() = safeConversion { asJsonNull }

val JsonElement.optCharacter: Char?
    get() = safeConversion { asCharacter }

private fun <T> JsonElement.safeConversion(converter: () -> T?): T? {

    return try {
        converter()
    }
    catch (e: Exception) {
        null
    }
}

JsonObject_Safe.kt

import com.google.gson.JsonArray
import com.google.gson.JsonElement
import com.google.gson.JsonObject
import com.google.gson.JsonPrimitive

/**
 * Created by Terence Baker on 13/02/2018.
 */

fun JsonObject.optGet(key: String): JsonElement? = get(key)

fun JsonObject.optGetJsonArray(key: String): JsonArray? = getAsJsonArray(key)

fun JsonObject.optGetJsonObject(key: String): JsonObject? = getAsJsonObject(key)

fun JsonObject.optGetJsonPrimitive(key: String): JsonPrimitive? = getAsJsonPrimitive(key)

fun JsonObject.optString(key: String) = optGet(key)?.asString

fun JsonObject.optLong(key: String) = optGet(key)?.asLong

fun JsonObject.optBoolean(key: String) = optGet(key)?.asBoolean

fun JsonObject.optFloat(key: String) = optGet(key)?.asFloat

fun JsonObject.optDouble(key: String) = optGet(key)?.asDouble

fun JsonObject.optJsonObject(key: String) = optGet(key)?.asJsonObject

fun JsonObject.optJsonArray(key: String) = optGet(key)?.asJsonArray

fun JsonObject.optJsonPrimitive(key: String) = optGet(key)?.asJsonPrimitive

fun JsonObject.optInt(key: String) = optGet(key)?.asInt

fun JsonObject.optBigDecimal(key: String) = optGet(key)?.asBigDecimal

fun JsonObject.optBigInteger(key: String) = optGet(key)?.asBigInteger

fun JsonObject.optByte(key: String) = optGet(key)?.asByte

fun JsonObject.optShort(key: String) = optGet(key)?.asShort

fun JsonObject.optJsonNull(key: String) = optGet(key)?.asJsonNull

fun JsonObject.optCharacter(key: String) = optGet(key)?.asCharacter

Sample.kt

open class MyClass {
  
  var myString = ""
  var myDouble = 0.0
  var myInt = 0
  
  fun setup(json:JsonObject) {
  
      json.optString("stringJsonKey")?.let { myString = it }
      json.optGet("doubleJsonKey")?.optDouble?.let { myDouble = it }
      json.optInt("intJsonKey")?.let { myInt = it }
  }
}

/*
{
  "stringJsonKey":"I am a string",
  "doubleJsonKey":2.5,
  "intJsonKey":5
}
*/