Event subject=Title

public static EventObj upsertEvents(String sEventObj, String sObjectName, String titleField, String startDateTimeField, String endDateTimeField, String descriptionField, String userField,string whatIdField,string whoIdField){
    EventObj upsertingEvent = (EventObj)JSON.deserialize(sEventObj, EventObj.class);
      system.debug('upserting event###########'+upsertingEvent);
    sObject newRecord = Schema.getGlobalDescribe().get(sObjectName).newSObject();
     Datetime EventStartDate= datetime.valueOf(upsertingEvent.startDateTime);
     Datetime EventEndDate= datetime.valueOf(upsertingEvent.endDateTime);
  if (upsertingEvent.Id != null && isAccessible(sObjectName,'Id')){
        newRecord.put('Id',upsertingEvent.Id);
    }
    if (isAccessible(sObjectName,titleField)) {
        newRecord.put(titleField, upsertingEvent.title);

    }
    if (isAccessible(sObjectName,startDateTimeField)) {
        newRecord.put(startDateTimeField, upsertingEvent.startDateTime);
    }
    if (isAccessible(sObjectName,endDateTimeField)) {
        newRecord.put(endDateTimeField, upsertingEvent.endDateTime);
    }
    if (isAccessible(sObjectName,descriptionField)) {
        newRecord.put(descriptionField, upsertingEvent.description);
    }


    if (isAccessible(sObjectName,whatIdField)) {
        newRecord.put(whatIdField, upsertingEvent.whatId);
    }
    if (isAccessible(sObjectName,whoIdField)) {
        newRecord.put(whoIdField,upsertingEvent.whoId);
    }

    System.debug('WhoId--'+upsertingEvent.whoId );
    try {
        upsert  newRecord;

        Account acc1 = null;
            if(newRecord.get(whatIdField) != null && String.valueOf(newRecord.get(whatIdField)) != '')
            {
                acc1 = [Select Id, Name from Account where Id =: String.valueOf(newRecord.get(whatIdField))];
            }

            Contact cont1 = null;

            if(newRecord.get(whoIdField) != null && String.valueOf(newRecord.get(whoIdField)) != '')
            {
                cont1 = [Select Id,Interceptor_ID__c, Name from Contact where Id =: String.valueOf(newRecord.get(whoIdField))];
            }
      //New line of code
      Datetime start= DateTime.valueOf(newRecord.get(startDateTimeField));
      Datetime enddate=DateTime.valueOf(newRecord.get(endDateTimeField));

        Map<Integer, String> MonthMap = new Map<Integer, String>();
        MonthMap.put(1, 'Jan');
        MonthMap.put(2, 'Feb');
        MonthMap.put(3, 'Mar');
        MonthMap.put(4, 'Apr');
        MonthMap.put(5, 'May');
        MonthMap.put(6, 'Jun');
        MonthMap.put(7, 'Jul');
        MonthMap.put(8, 'Agu');
        MonthMap.put(9, 'Sep');
        MonthMap.put(10, 'Oct');
        MonthMap.put(11, 'Nov');
        MonthMap.put(12, 'Dec');
         string TitleName;
             if(cont1!=null){
                System.debug('InterceptorId--' + cont1.Interceptor_ID__c);
             TitleName=cont1.Interceptor_ID__c+':'+' '+' '+MonthMap.get(start.month())+String.valueOf(start.day())+'-'+start.format('HH:mm a')+'-'+enddate.format('HH:mm a');
             }