ArrayList gets duplicate values in jsp page

[Hare Shiva]

i am new to servlet and jsp..I retrieve values from database and set it in a arraylist of bean in servlet.That arraylist of bean is later displayed in jsp page...But after at second run of servlet duplicate values get printed in jsp..Guys help me....

/*****This is my servlet********************************/
public class FindDoctor extends HttpServlet {
    ConnectionFile connection = new ConnectionFile();
    
    List<Object> allData=new ArrayList<Object>();
    
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        
        try {
        // HttpSession session = request.getSession();
        //  session.removeAttribute("DoctorList");
            String Name,Category;
            int StartTime,EndTime,DoctorId;
            System.out.println("FindDoctor servlet started");
         //   HttpSession session = request.getSession();
          //  String Id = (String) session.getAttribute("Id");
          //  int id = Integer.parseInt("Id");

            /**Get Category and Day from Form*****************/

            String category = request.getParameter("category");
            System.out.println("Category is "+category);
            String day= request.getParameter("day");
            int i=0;
            /*****Form parameter received*********/

            /*****Select from Doctor Details table********/

            Connection con = connection.connectionfile();

            PreparedStatement pstmt = con.prepareStatement("select * from DoctorSchedule where Category=? and Day=?");
            pstmt.setString(1,category);
            pstmt.setString(2,day);

            ResultSet rs = pstmt.executeQuery();

            Connection con1 = connection.connectionfile();
            while(rs.next())
            {
                System.out.println("Match Found for DoctorId");
                /****Retrieve Doctor information from DoctorId*************/
                Category = rs.getString("Category");
                System.out.println("Category "+Category);
                StartTime = rs.getInt("StartTime");
                System.out.println("StartTime "+StartTime);
                EndTime = rs.getInt("EndTime");
                System.out.println("EndTime "+EndTime);
                PreparedStatement pstmt1 = con1.prepareStatement("select * from DoctorDetail where DoctorId=?");
                System.out.println("Here executed");
                DoctorId = rs.getInt("DoctorId");
                pstmt1.setInt(1,DoctorId);
                ResultSet rs1 = pstmt1.executeQuery();
                /****Create Bean to store all data************/
                rs1.next();
                Name = rs1.getString("Name");
              
                DataFields d=new DataFields(Name,DoctorId,Category,StartTime,EndTime);
                
                allData.add(i,d);
                i++;
            }
           
            HttpSession session1 = request.getSession();
            
            session1.setAttribute("DoctorList",allData);
            response.sendRedirect("appointmentview.jsp");
            con.close();
            con1.close();
        }
        catch(Exception error)
        {
            System.out.println("Error "+error);
        }
    } 

    // <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
    /** 
     * Handles the HTTP <code>GET</code> method.
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        processRequest(request, response);
    } 

    /** 
     * Handles the HTTP <code>POST</code> method.
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        processRequest(request, response);
    }

    /** 
     * Returns a short description of the servlet.
     * @return a String containing servlet description
     */
    @Override
    public String getServletInfo() {
        return "Short description";
    }// </editor-fold>

}
/******************************DatFields******************************/
 */
 public class DataFields
    {
       String name;
       
       String category;
       int DoctorId;
       int starttime;
       int endtime;

    
       public DataFields(String name,int DoctorId,String category,int starttime,int endtime)
       {
           this.name=name;
           this.category=category;
           this.starttime=starttime;
           this.endtime=endtime;
           this.DoctorId=DoctorId;
       }
    }
/***********ShowDataBean***************************/
public class ShowDataBean implements Serializable {

    public String name;
   
    public String category;
    public int starttime;
    public int endtime;
    public String photopath;
    int doctorid;
    ConnectionFile connection = new ConnectionFile();
    List<Object> allData=new ArrayList<Object>();
    Object obj=new Object();

    public int getDoctorid() {
        this.doctorid =((DataFields)obj).DoctorId;
        return doctorid;
    }

    public void setObj(Object obj)
    {
        this.obj=obj;
    }

    public String getName() {
        this.name=((DataFields)obj).name;
        return name;
    }

    public String getCategory() {
        this.category=((DataFields)obj).category;
        return category;
    }
  
    public int getEndtime() {
        this.endtime=((DataFields)obj).endtime;
        return endtime;
    }

    public String getPhotopath() {
        return photopath;
    }

    public int getStarttime() {
        this.starttime=((DataFields)obj).starttime;
        return starttime;
    }
}

[Ulf Dittmer]

You seem to assume that on each request a new instance of the servlet will be created, and hence you'll have a fresh and empty instance of "allData" to work with. That's not how servlets work - there will only ever be a single instance of the servlet class, and it is used to serve all requests.

But you can't just clear out that List before you use it, either, because instance variables are shared between simultaneous requests, so you might be interfering with other requests.

So it's best to avoid instance variables until you have a much better understanding about how concurrency works in web apps. Luckily, that's very easy to achieve in this case.

(I've also added code tags to your post - see how much easier it is to read that way? Please UseCodeTags in the future.)

[Seetharaman Venkatasamy]

why would you declare

PreparedStatement pstmt1 = con1.prepareStatement("select * from DoctorDetail where DoctorId=?");

inside while?
and use finally clause to close your connections

[Hare Shiva]

thanks a lot...all i had to do was clear alldata..its working now.