Question

I’m trying to process some JSON into a Java object using some beans and GSON. However, the keys in the JSON code I am using can change over time, based on what is most recently traded. I can manually make a bean file that includes each currency code, but in the end, they can all be different, and my program broken.

Here is my code:

From my main class:

public void updateData() {
    Data data;
    String s = null;
    try {
        s = DataGetter.getJSON("http://bitcoincharts.com/t/weighted_prices.json");
    } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    s = s.replaceAll("7d", "week");
    s = s.replaceAll("30d", "month");
    s = s.replaceAll("24h", "day");
    s = s.toLowerCase();
    data = new Gson().fromJson(s, Data.class);
}

Data.java:

package tehsusenoh.bittick.get;

import java.util.ArrayList;
import java.util.List;

public class Data {

public enum Currency {
    USD, AUD, RUB, GAU, BGN, CNY, SLL, INR, GBP, PLN, SAR, EUR, CLP, CAD
}

private CurrencyData usd;
private CurrencyData aud;
private CurrencyData rub;
private CurrencyData gau;
private CurrencyData bgn;
private CurrencyData cny;
private CurrencyData sll;
private CurrencyData inr;
private CurrencyData gbp;
private CurrencyData pln;
private CurrencyData sar;
private CurrencyData eur;
private CurrencyData clp;
private CurrencyData cad;

public List<CurrencyData> getData() {
    List<CurrencyData> d = new ArrayList<CurrencyData> ();
    d.add(usd);
    d.add(aud);
    d.add(rub);
    d.add(gau);
    d.add(bgn);
    d.add(cny);
    d.add(sll);
    d.add(inr);
    d.add(gbp);
    d.add(pln);
    d.add(sar);
    d.add(eur);
    d.add(clp);
    d.add(cad);
    return d;
}

public CurrencyData get(Currency c) {
    switch (c) {
    case USD: {
        return usd;
    }
    case AUD: {
        return aud;
    }
    case RUB: {
        return rub;
    }
    case GAU: {
        return gau;
    }
    case BGN: {
        return bgn;
    }
    case CNY: {
        return sll;
    }
    case INR: {
        return inr;
    }
    case GBP: {
        return gbp;
    }
    case PLN: {
        return pln;
    }
    case SAR: {
        return sar;
    }
    case EUR: {
        return eur;
    }
    case CLP: {
        return clp;
    }
    case CAD: {
        return cad;
    }
    default: {
        return null;
    }
    }
}

public void addCodes() {
    usd.setCode("USD");
    aud.setCode("AUD");
    rub.setCode("RUB");
    gau.setCode("GAU");
    bgn.setCode("BGN");
    cny.setCode("CNY");
    sll.setCode("SLL");
    inr.setCode("INR");
    gbp.setCode("GBP");
    pln.setCode("PLN");
    sar.setCode("SAR");
    eur.setCode("EUR");
    clp.setCode("CLP");
    cad.setCode("CAD");

}

public String toString() {
    return "" + getData();
}
}

And finally, CurrencyData.java:

package tehsusenoh.bittick.get;

public class CurrencyData {

private Double week;
private Double month;
private Double day;
private String code;

public CurrencyData() {}

public Double getWeek() { return week; }
public Double getMonth() { return month; }
public Double getDay() { return day; }
public String getCode() { return code; }

public void setWeek(Double d) { week = d; }
public void setMonth(Double d) { month = d; }
public void setDay(Double d) { day = d; }
public void setCode(String aCode) { code = aCode; }

public String toString() {
    return code + ":: week:" + week + " month:" + month + " day:" + day;
}
}

Answer 1

Since the nice person that generated the JSON chose to use a JSON object to hold a collection of things, instead of using a JSON array, Jim’s suggestion to use a Java Map is a natural fit.

With Gson, here’s what that solution would look like.

import java.io.FileReader;
import java.lang.reflect.Type;
import java.math.BigDecimal;
import java.util.Map;

import com.google.gson.Gson;
import com.google.gson.annotations.SerializedName;
import com.google.gson.reflect.TypeToken;

public class Foo
{
  public static void main(String[] args) throws Exception
  {
    Gson gson = new Gson();
    Type currencyMapType = new TypeToken<Map<String, Currency>>() {}.getType();
    Map<String, Currency> currencyMap = gson.fromJson(new FileReader("input.json"), currencyMapType);
    System.out.println(currencyMap);
  }
}

class Currency
{
  @SerializedName("7d")
  BigDecimal _7d;
  @SerializedName("30d")
  BigDecimal _30d;
  @SerializedName("24h")
  BigDecimal _24h;

  @Override
  public String toString()
  {
    return String.format("{7d:%s, 30d:%s, 24h:%s}", _7d, _30d, _24h);
  }
}

---

The following update generates a list of currencies from the currency data in the deserialized map.

import java.io.FileReader;
import java.lang.reflect.Type;
import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

import com.google.gson.Gson;
import com.google.gson.annotations.SerializedName;
import com.google.gson.reflect.TypeToken;

public class Foo
{
  public static void main(String[] args) throws Exception
  {
    Gson gson = new Gson();
    Type currencyDataMapType = new TypeToken<Map<String, CurrencyData>>() {}.getType();
    Map<String, CurrencyData> currencyDataMap = gson.fromJson(new FileReader("input.json"), currencyDataMapType);
    List<Currency> currencies = fromDataMap(currencyDataMap);
    System.out.println(currencies);
  }

  static List<Currency> fromDataMap(Map<String, CurrencyData> currencyDataMap)
  {
    List<Currency> currencies = new ArrayList<Currency>(currencyDataMap.size());
    for (Entry<String, CurrencyData> entry : currencyDataMap.entrySet())
    {
      String code = entry.getKey();
      currencies.add(new Currency(code, currencyDataMap.get(code)));
    }
    return currencies;
  }
}

class Currency
{
  String code;
  CurrencyData data;

  Currency(String code, CurrencyData data)
  {
    this.code = code;
    this.data = data;
  }

  @Override
  public String toString()
  {
    return String.format("{code:%s, 7d:%s, 30d:%s, 24h:%s}", code, data._7d, data._30d, data._24h);
  }
}

class CurrencyData
{
  @SerializedName("7d")
  BigDecimal _7d;
  @SerializedName("30d")
  BigDecimal _30d;
  @SerializedName("24h")
  BigDecimal _24h;
}