//size of input obj is around 15K
public generateQuery(List<DBObj> objs){

 StringBuffer sb = new StringBuffer();
 sb.append(SOMEINSERTQUERYPREFIX)

 for(DBObj obj : objs){
           //add some prefix
            sb.append(append(checkNULLforDBInsert(obj.getF1())).append(" , ");
            sb.append(checkNULLforDBInsert(obj.getField2())).append(" , ");
            sb.append(checkNULLforDBInsert(obj.getField3())).append(" , ");
         //app sufix
  }

}


private String checkNULLforDBInsert(String str)
    {

        if (str == null || str.toLowerCase().equals("null"))
        {

            return "null";
        } else {
            //suspecting this for leak
            return "'" + str + "'";
        }

    }