Java Iterate over Map values

Question

I have a problem. I have the following JSON:

{
   "Market":"USDT",
   "Coin":"BTC",
   "Period":"1h",
   "EmergencyPerc":-25,
   "TakeProfitPerc":1.2,
   "ProtectiveOrdersEnabled":"no",
   "EMACrossMarginPerc":0.08,
   "EMABuySellPeriod":"5m",
   "EMABuySellNameLow":"EMA5",
   "EMABuySellNameHigh":"EMA20",
   "EMAUnfreezePeriod":"1h",
   "EMAUnfreezeNameLow":"EMA20",
   "EMAUnfreezeNameHigh":"EMA200",
   "SimTemplate":"t001",
   "PriceDropSells":[
      {
         "Period":"3h",
         "Number":"4",
         "Perc":"-1.0"
      },
      {
         "Period":"1h",
         "Number":"2",
         "Perc":"-2.0"
      }
   ]
}

In my java class I added the following code to parse the Json to the current class as object:

public class AgentStrategy {

    private String market;
    private String coin;
    private String period;
    private double emergencyPerc;
    private double takeProfitPerc;
    private String protectiveOrdersEnabled;
    private double EMACrossMarginPerc;
    private String EMABuySellPeriod;
    private String EMABuySellNameLow;
    private String EMABuySellNameHigh;
    private String EMAUnfreezePeriod;
    private String EMAUnfreezeNameLow;
    private String EMAUnfreezeNameHigh;
    private String simTemplate;
    private ArrayList<AgentStrategyPriceDropSells> priceDropSells = new ArrayList<>();

    public AgentStrategy parseJsonToObject(String jsonString) {
        Gson gson = new Gson();

        gson.fromJson(jsonString, AgentStrategy.class);

        Map map = gson.fromJson(jsonString, Map.class);
        this.market = map.get("Market").toString();
        this.coin = map.get("Coin").toString();
        this.period = map.get("Period").toString();
        this.emergencyPerc = Double.parseDouble(map.get("EmergencyPerc").toString());
        this.takeProfitPerc = Double.parseDouble(map.get("TakeProfitPerc").toString());
        this.protectiveOrdersEnabled = map.get("ProtectiveOrdersEnabled").toString();
        this.EMACrossMarginPerc = Double.parseDouble(map.get("EMACrossMarginPerc").toString());
        this.EMABuySellPeriod = map.get("EMABuySellPeriod").toString();
        this.EMABuySellNameLow = map.get("EMABuySellNameLow").toString();
        this.EMABuySellNameHigh = map.get("EMABuySellNameHigh").toString();
        this.EMAUnfreezePeriod = map.get("EMAUnfreezePeriod").toString();
        this.EMAUnfreezeNameLow = map.get("EMAUnfreezeNameLow").toString();
        this.EMAUnfreezeNameHigh = map.get("EMAUnfreezeNameHigh").toString();
        this.simTemplate = map.get("SimTemplate").toString();


        // PRICE DROP SELLS
        Map priceDropSellsMap = (Map) map.get("PriceDropSells");
        // ???

        return this;
    }

    private class PriceDropSell {

        private String period;
        private String number;
        private double perc;

    }
}

The function should return a full filled Object, but I am struggling with the ArrayList<PriceDropSell> . The problem is that I have no idea how to store the PriceDropSells from my JSON as ArrayList<PriceDropSell> . Every field gets stored in the class AgentStrategy, except the PriceDropSell. How can I parse that part to an ArrayList?

Answer 1

You don't need all the map stuff. Gson will parse directly into the object. But make sure the names match:

class Test
{
    private class PriceDropSell {
        private String Period;
        private String Number;
        private double Perc;
    }
    public class AgentStrategy {
        private String Market;
        private String Coin;
        private String Period;
        private double EmergencyPerc;
        private double TakeProfitPerc;
        private String ProtectiveOrdersEnabled;
        private double EMACrossMarginPerc;
        private String EMABuySellPeriod;
        private String EMABuySellNameLow;
        private String EMABuySellNameHigh;
        private String EMAUnfreezePeriod;
        private String EMAUnfreezeNameLow;
        private String EMAUnfreezeNameHigh;
        private String SimTemplate;
        private ArrayList<PriceDropSell> PriceDropSells;
    }

    public static void main (String[] args) throws java.lang.Exception
    {
        BufferedReader bufferedReader = new BufferedReader(new FileReader(path_to_json_file));
        Gson gson = new Gson();
        AgentStrategy agent = gson.fromJson(bufferedReader, AgentStrategy.class);
        
        System.out.println(agent.PriceDropSells.get(0).Perc);
    }
}

Answer 2

Why not inspect what the actual object for "PriceDropSells" is? Just get that property without any casts and check with a debugger it's type:

Object priceDropSellsMap = map.get("PriceDropSells");

I suppose it should be an array or a List.