Pagination in toplink using custom query

Question

Re: Pagination using TopLink
Posted: Aug 31, 2006 10:42 PM in response to: Shaun Smith Reply
Hi,
I have my own customer query which is really complex with subqueries,joins,grouping,aggregation in the query etc etc for which I cant use toplink workbench to create a project and do the metadata mapping.
But we need to enable pagination without holding the database resources between customer's page time in the browser.
Is there any provision in toplink to just input the custom query (either statement/prepared statement) and do pagination without holding connection to the database between page time?
The example i got from the link makes use of LogicalCursor/ChunkingLogicalCursor etc.
LogicalCursor cursor = new LogicalCursor(Model.class,null);
for (CursorIterator it = cursor.iterator(session); it.hasNext();)
System.out.println(it.next(session));
Only parameter that is passed to the LogicalCursor is "Model" which is a java object mapped to a particular table.
But we had a java object which should be mapped to the output of a complex query involing complex query and pagination needs to be enabled.
Could you please let us know a sample by which we can do by simply passing the query during the runtime ?

Answer 1

It really seems weird.
We followed the toplink tutorial and wrote a servlet FindAddress which on receiving the request
1. instantiates ReadQuery and
2. setreferenceclass to Address.class,
3. setFetchSize(1000) and
4.sets useScrollableCursor.
5. It does session.executeQuery returning a ScrollableCursor.
6. We place the ScrollableCursor in HttpSession
and then redirect the page to viewAddress.jsp which
1. retrieves the ScrollableCursor from the session
2. i=0;     while(cursor.hasNext() && i<1000) {
     Address address = (Address)cursor.next();
//display via the jsp all these 1000 address objects
3. has a next button when a click on that it again goes to the same page retrieving the next set of 1000 records from ScrollableCursor from the session.
Through out this experimentation I could see the connection is still held. I was expecting that once the page gets displayed for 1000 records and untill you press next, the connection should be handled back to the J2EE application server but still the connection is held .
The logic of setFetchSize as mentioned in the documentation is that after reading the first set of records as per fetchSize ,connection should be returned to the pool and when we do iterator.next() after fetchsize limit, it has to again going to the database and fetch records but it doesnt seem to be.
Could you please help us. This is what we are trying to do as next step and we had been evaluating toplink could be the best choice for our business scneario:
We try to achieve pagination without holding the database resource when the user navigates between paged records.
Any help on this would make us to hit toplink for our huge application.
Here is the attached FindAddress.java and ViewAddress.jsp
FindAddress.java
=============
// Decompiled by DJ v2.9.9.61 Copyright 2000 Atanas Neshkov Date: 9/8/2006 6:32:21 PM
// Home Page : http://members.fortunecity.com/neshkov/dj.html - Check often for new version!
// Decompiler options: packimports(3)
// Source File Name: FindAddress.java
package examples.servletjsp;
import java.io.IOException;
import java.io.PrintStream;
import javax.servlet.*;
import javax.servlet.http.*;
import oracle.toplink.expressions.Expression;
import oracle.toplink.expressions.ExpressionBuilder;
import oracle.toplink.queryframework.ReadAllQuery;
import oracle.toplink.queryframework.ScrollableCursor;
import oracle.toplink.threetier.ClientSession;
import oracle.toplink.threetier.Server;
// Referenced classes of package examples.servletjsp:
// JSPDemoServlet
public class FindAddress extends JSPDemoServlet
public FindAddress()
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
doPost(request, response);
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
request.setCharacterEncoding("UTF-8");
getServletContext().log("FindAddress servlet - doPost");
java.util.Vector address = null;
ScrollableCursor cursor = null;
try
HttpSession session = request.getSession(true);
ReadAllQuery query = new ReadAllQuery();
query.setReferenceClass(examples.servletjsp.model.Address.class);
ExpressionBuilder builder = new ExpressionBuilder();
query.setSelectionCriteria(builder.get("id").greaterThan(100));
query.setFetchSize(5000);
query.useScrollableCursor();
System.out.println("########### Sleep Mode Before assigning to CURSOR ###############");
System.out.println("############ Back from Sleep Mode before CURSOR ############");
cursor = (ScrollableCursor)((Server)getSession()).acquireClientSession().executeQuery(query);
System.out.println("############ Sleep Mode After assigning to CURSOR ###########");
System.out.println("############ Back from Sleep Mode After CURSOR ############");
session.setAttribute("ScrollableCursor", cursor);
catch(Exception e)
request.setAttribute("source", "FindEmployees doPost");
request.setAttribute("header", "An Error Occurred");
request.setAttribute("errorMessage", e.getMessage());
request.getRequestDispatcher("./errorPage.jsp").forward(request, response);
return;
System.out.println("cursor------------" + (cursor == null));
if(cursor == null)
request.getRequestDispatcher("./EmployeesNotFound.jsp").forward(request, response);
} else
request.setAttribute("address", address);
request.getRequestDispatcher("./viewAddress.jsp").forward(request, response);
viewAddress.jsp
=============
<%@page import="java.util.*"%>
<%@page import="examples.servletjsp.*"%>
<%@page import="examples.servletjsp.model.*"%>
<%@page import="oracle.toplink.queryframework.ScrollableCursor"%>
<%@page import="java.math.*"%>
<%@page contentType = "text/html; charset=UTF-8"%>
<html>
<head><title>Employee Query Results</title></head>
<body>
<form name="test" method="post" action="viewAddress.jsp">
<!--      Prepare s heading.
     Get the employees passed in from ViewEmployees servlet. Show them in table format. Provide button
     to ViewEmployee -->
<%
     request.setCharacterEncoding("UTF-8");
     String searchString = request.getParameter("employeeString");
     ScrollableCursor cursor = (ScrollableCursor) session.getAttribute("ScrollableCursor");
     String heading = null;
          heading="Search Results for FindAll on Employee";
     String employeeData = "";
     //Iterator data = ((Vector)request.getAttribute("address")).iterator();
     int i =0;
     while(cursor.hasNext() && i<4995) {
          if(i<10){
               System.out.println("######### JSP Count TRhread Sleep ###########");
               //Thread.sleep(100);
               //System.out.println("######### JSP Count TRhread Sleep Over ###########");
          i++;
     Address address = (Address)cursor.next();
     BigDecimal id = address.getId();
     String city = address.getCity();
     String province = address.getProvince();
     String street = address.getStreet();
     String country = address.getCountry();
     String pCode = address.getPostalCode();
     employeeData += "<tr><td>" + id + "</td>"
          + "<td>" + province + "</td>"
          + "<td>" + street + "</td>"
          + "<td>" + city + "</td>"
          + "<td>" + pCode + "</td>"
          + "<td>" + country+ "</td>"
          + "</tr>";
     //cursor.close();
     System.out.println("abcdAfter closing the cursor ->plz see whether connpool monitorcnt = 0");
%>
<center>
     <h2><%=heading%></h2>
     <hr>
     Return to Main
     <p>
     <table border=1>
          <tr>
               <td align="center">Address Id</td>
               <td align="center">Province</td>
               <td align="center">Street</td>
               <td align="center">City</td>
               <td align="center">Postal Code</td>
               <td align="center">Country</td></tr>
          <%=employeeData %>
     </table>
</center>
<p>
<input type="submit" name ="next" value="next" >
<center>Return to Main</center>
</form>
</body>
</html>