public class JsonStringToObect {

	public <T> T convertJsonValueToObjectByKey(String targetString, String key, Type ObjectType) {
		// using JsonParser When Json to JsonObject
		JsonObject jsonObject = new JsonParser().parse(targetString).getAsJsonObject();

		// using Gson When Json to Java Object (Class value)
		Gson gson = new Gson();
		return gson.fromJson(jsonObject.get(key), ObjectType);
	}

	public void example() {
		String testString = "{ \"code\" : \"200\", \"msg\" : \"OK\", \"products\" : [{\"product_id\":\"6216\",\"y\":\"0.6619\",\"point_id\":\"6216\",\"x\":\"0.6094\"},{\"product_id\":\"6217\",\"y\":\"0.6563\",\"point_id\":\"6217\",\"x\":\"0.5000\"}], \"top\": {\"product_id\":\"6216\",\"y\":\"0.6619\",\"point_id\":\"6216\",\"x\":\"0.6094\"} }";

		// ex. 1
		CoordinateModel result1 = convertJsonValueToObjectByKey(testString, "top", CoordinateModel.class);

		// ex. 2 ) List
		List<CoordinateModel> result2 = convertJsonValueToObjectByKey(testString, "products", new TypeToken<ArrayList<CoordinateModel>>(){}.getType());

		// ex. 3 ) String
		JsonObject jsonObject =  new JsonParser().parse(testString).getAsJsonObject();
		String result3 = jsonObject.get("code").getAsString()
	}

	public class CoordinateModel {
		@SerializedName(value = "product_id", alternate = {"id"})
		private Integer productsId;
		@SerializedName("x")
		private String positionX;
		@SerializedName("y")
		private String positionY;
	}
}