converting excel to json: reading problem when file too large

I have a excel file which stored my game data, and successfully converted to json file.
A sample on excel file and the converted json:

The pretty output on the sample data:
While if the excel file contain a lot of data, which exceed the size of String can hold (I believe), problem on reading the json will exceed.

Hence I would like to ask how should my json file be wrote and read so I need not to care about the file( or string) size.

 //function that create the json object ( using Simple Json library in eclipse)
  public void createJson(String outputpath,XSSFSheet sheet){
         XSSFRow singleRow;
         XSSFCell cell;
         int totalRows=getExcelTotalRow(sheet);
         int totalCol=getExcelTotalColumn(sheet);
                 
         JSONObject jsonObject=new JSONObject();    
         
         String[] attributes=getJsonAttributes(sheet.getRow(0));
         
         for(int i=1; i<totalRows;i++){
             JSONObject jRow = new JSONObject();
             singleRow=sheet.getRow(i);
             String chipRoot="";
             for(int j=0;j<totalCol;j++){
                 cell=singleRow.getCell(j);
                 cell.setCellType(Cell.CELL_TYPE_STRING);
                 jRow.put(attributes[j], cell.toString());
                 if(j==0){
                     chipRoot=cell.toString();
                 }
             }
             jsonObject.put(chipRoot, jRow);
             System.out.print("\n");
         }
         
         
         Gson gson = new GsonBuilder().setPrettyPrinting().create();
         String jsonOutput = gson.toJson(jsonObject);
         System.out.println(jsonOutput);
         writeJsonFile(outputpath,jsonObject);
     }

 //and function to create the json file
 public void writeJsonFile(String fileName, JSONObject jsonObject){
         try {
             //System.out.println(jsonObject);
             fileName=fileName.replace(".txt", "2.txt");
             FileWriter fw= new FileWriter(fileName);
             BufferedWriter bw = new BufferedWriter(fw);
             jsonObject.writeJSONString(fw);
             bw.close();
         } catch (IOException e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }
     }

The code for reading json in unity

 public class chipManager :MonoBehaviour {
 
     public string fileName;
     public string chipJson;
 
     public Dictionary<int, Chip> chipDictionary=new Dictionary<int, Chip>();
 
 
     void Start(){
         getChipData ();
         putAllChipToDictionary ();
         getChipByID (1);
         getChipByID (2);
         getChipByID (3);
         getChipByID (5);
     }
 
 
 
     public void getChipData(){
         try
         {
             string fileFullPath= Application.dataPath+"/textFiles/"+fileName;
             StreamReader theReader = new StreamReader(fileFullPath, Encoding.Default);
             chipJson=theReader.ReadToEnd();
             theReader.Close();
 
         }
         catch (Exception e)
         {
             Debug.Log(e);
         }
     }
 
     public void putAllChipToDictionary(){
         var N = JSON.Parse (chipJson);
         //Debug.Log (N.Count);
         for(int i=0;i<N.Count;i++){
             int id = N[i]["ChipID"].AsInt;
             string chipName = N[i]["Name"];
             int power = N[i]["Power"].AsInt;
             string desc = N[i]["Desc"];
             Chip tempChip= new Chip(id,chipName,power,desc);
             chipDictionary.Add(id, tempChip);
         }
     }
 
     public void getChipByID(int chipID){
         Debug.Log ("getting chip "+ chipID);
         Chip chipReturn= chipDictionary[chipID];
         Debug.Log (chipReturn.ToString ());
     }
 }