Json Data assign to java class

Question

I'm having problem to assign json data into java class.Please do help anyone, My java class is like,

public class ListofGridRecords<T> {
    public int Totalrecords;
    public List<T> GridRecords;//using TraderTransaction class.
}

and TraderTransaction class is,

public class TraderTransaction {

  public Date AddedTime;
  public String TransactId;
  public TransactStatus Status;
  public String OtherPartyAccountNo;
  public Double AmountPaid;
  public Double AmountRecieved;
  public Double ClosingBalance;
  public TransactionTypes TransType;
  public String Narration;

  public TraderTransaction() {
    super();
  }
}

and my json conversion function look like,

JsonObject returndata = JsonObject.parse(responseString);
String operationresult = returndata.get("OperationResult").toString();

if (Result.values()[Integer.parseInt(operationresult)] == Result.Success) {
  Gson gson = new Gson();

  @SuppressWarnings("unchecked")
  ListofGridRecords<TraderTransaction> traderlist = 
        gson.fromJson(returndata.get("ResultData").toString(), ListofGridRecords.class);

  Log.i("LIST DATA:", "" + traderlist);
  for (TraderTransaction trader: traderlist.GridRecords) {
    HashMap<String, String> map = new HashMap<String, String>();
    map.put(TRANS_FIRST_COLUMN, currentformatter.format(trader.AddedTime));
    map.put(TRANS_SECOND_COLUMN, trader.TransactId);
    map.put(TRANS_THIRD_COLUMN, trader.OtherPartyAccountNo);
    map.put(TRANS_FOURTH_COLUMN, trader.AmountPaid.toString());
    map.put(TRANS_FIFTH_COLUMN, trader.AmountRecieved.toString());
    map.put(TRANS_SIXTH_COLUMN, OpenOrClosed.values()[Integer.parseInt(trader.TransType.toString())].toString());
    list.add(map);
  }
}

I'm getting conversion error at for (TraderTransaction trader : traderlist.GridRecords).

My Json data look like,

{
   "Messages":"RESULTS_RETRIEVAL_SUCCESSFULL",
   "OperationResult":0,
   "ResultData":{
      "GridRecords":[
         {
            "AddedBy":"Distributor-9787457361-Rathinavel",
            "AddedTime":"2013-04-12T16:26:24.0140117",
            "AmountPaid":0.0,
            "AmountRecieved":10000.0,
            "ClosingBalance":10000.0,
            "Narration":null,
            "OtherPartyAccountNo":"0102849015327675",
            "Status":2,
            "TransType":2,
            "TransactId":"TDRF483679051236"
         },
         {
            "AddedBy":"Distributor-9787457361-Rathinavel",
            "AddedTime":"2013-04-12T16:20:54.8681857",
            "AmountPaid":0.0,
            "AmountRecieved":0.0,
            "ClosingBalance":0.0,
            "Narration":null,
            "OtherPartyAccountNo":"0102849015327675",
            "Status":0,
            "TransType":2,
            "TransactId":"TDRF706925413802"
         }
      ],
      "Totalrecords":2
   },
   "UpdateAvailable":"0"
}

I'm getting error like can not convert class on for (TraderTransaction trader : traderlist.GridRecords) — Vinoth Kumar
– Vinoth Kumar, Commented Apr 16, 2013 at 5:45
You should probably not use JSON for this. In general, it's not powerful enough to represent Java classes. You might get problems when you have circular references (e.g. A includes a B object and vice versa). My suggestion is to switch to XML. XStream worked good for me; also, it returned better error messages when e.g. failing with JSON. — Cedric Reichenbach
– Cedric Reichenbach, Commented Apr 16, 2013 at 9:54

MikO · Accepted Answer · 2013-04-16 13:35:19Z

In order to parse your JSON, I'd use a slightly different strategy. As you seem to be interested in parsing only the "ResultData", I'd create classes to wrap the response, very similar to those you have already created, namely:

public class Response {
  @SerializedName("ResultData")
  public ResultData resultData;
}

and,

public class ResultData {
  @SerializedName("GridRecords")
  public List<GridRecord> gridRecords;
  @SerializedName("Totalrecords")
  public int totalrecords;
}

and,

public class GridRecord {
  @SerializedName("AddedTime")
  public String addedTime;
  @SerializedName("TransactId")
  public String transactId;
  //other fields...
}

and other classes if necessary...

Then, in order to parse your JSON reponse, you just have to do:

Gson gson = new Gson();
Response data = gson.fromJson(responseString, Response.class);

and you'll be able to access any field, for example:

data.resultData.gridRecords.transactId;

Note 1: If you are interested in more fields of the JSON response, you just have to add more fields to your wrap classes, according to the JSON response...

Note 2: I've changed the type of addedTime to String, instead of Date because it throws an exception for unparseable date. Anyway I usually leave the types in the Response objects as simple String and then in the class from where I retrieve the response, I do the correct formatting while creating my objects, for example, when you put the values in your Map...

Note 3: The use of the annotation @SerializedName is interesting to separate the name of a field in the JSON response and in your app, in order to follow Java naming conventions, which your attributes are not following...

Note 4: You shouldn't use public attributes in your classes. It's more recommendable to use private/protected attributes and their correspondent getters and setters...

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