If the result set is large, then having the entire result set in memory will not be feasible. With large result sets, you cannot afford to have them in memory. In such case, you have to fetch a chunk of data at a time (query based paging). The down side of using query based paging, is that there will be multiple calls to the database for multiple page requests. In this post, I will describe how to implement simple query based caching solution, using Hibernate and a simple JSP. Time permitting, I will soon post a hybrid of cache based and query based paging example. Here is the code for implementing simple paging using a JSP and Hibernate:
1)Download the latest version of hibernate from www.hibernate.org, and include all the required jars in your classpath.
2)Hibernate configuration
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | <code>
<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
<property name="connection.url">jdbc:oracle:thin:@localhost:1521/orcl</property>
<property name="connection.username">scott</property>
<property name="connection.password">tiger</property>
<property name="dialect">org.hibernate.dialect.Oracle9Dialect</property>
<property name="hibernate.current_session_context_class">thread</property>
<mapping resource="beans/Employee.hbm.xml" />
</session-factory>
</hibernate-configuration>
</code> |
3)The Employee bean class to hold the data
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 | <code>
public class Employee {
public long empId;
public String empName;
public String empJob;
public long empSal;
public long getEmpId() {
return empId;
}
public void setEmpId(long empId) {
this.empId = empId;
}
public String getEmpJob() {
return empJob;
}
public void setEmpJob(String empJob) {
this.empJob = empJob;
}
public String getEmpName() {
return empName;
}
public void setEmpName(String empName) {
this.empName = empName;
}
public long getEmpSal() {
return empSal;
}
public void setEmpSal(long empSal) {
this.empSal = empSal;
}
}
</code> |
4)The Employee Mapping file: This listing of the Data Access Object uses the setMaxResults, and setFirstResult method of the Query object to extract the appropriate set of results for each page.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 | <code>
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="beans.Employee" table="Emp">
<id name="empId" column="EMPNO" type="long">
<generator class="native"/>
</id>
<property name="empName" column="ENAME" />
<property name="empJob" column="JOB" />
<property name="empSal" column="SAL" type="long"/>
</class>
</hibernate-mapping>
</code> |
5)The Data Access Object
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | <code>
public class DAO {
private static int pageSize = 3;
public static List getData(int pageNumber) {
SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
Session session = sessionFactory.getCurrentSession();
List result = null;
try {
session.beginTransaction();
Query query = session.createQuery("from Employee");
query = query.setFirstResult(pageSize * (pageNumber - 1));
query.setMaxResults(pageSize);
result = query.list();
session.getTransaction().commit();
} catch (Exception e) {
e.printStackTrace();
}
return result;
}
}
</code> |
6)The JSP
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 | <code>
<jsp:root version="1.2" xmlns:jsp="http://java.sun.com/JSP/Page"
xmlns:c="urn:jsptld:http://java.sun.com/jsp/jstl/core">
<jsp:directive.page contentType="text/html; charset=UTF-8" />
<link rel="stylesheet" type="text/css" href="css/screen.css" />
<jsp:scriptlet>
int pageNumber=1;
if(request.getParameter("page") != null) {
session.setAttribute("page", request.getParameter("page"));
pageNumber = Integer.parseInt(request.getParameter("page"));
} else {
session.setAttribute("page", "1");
}
String nextPage = (pageNumber +1) + "";
session.setAttribute( "EmpList", data.DAO.getData(pageNumber));
System.out.println(((java.util.List)session.getAttribute("EmpList")).size());
String myUrl = "pagingEmp.jsp?page=" + nextPage;
System.out.println(myUrl);
pageContext.setAttribute("myUrl", myUrl);
</jsp:scriptlet>
<h2 align="center">Emp Table with Display tag</h2>
<jsp:useBean id="EmpList" scope="session" type="java.util.List"></jsp:useBean>
<table>
<tr>
<th>Employee Id</th>
<th>Name</th>
<th>Job</th>
<th>Salary</th>
</tr>
<c:forEach items="${EmpList}" var="emp" begin="0" end="10">
<tr>
<td><c:out value="${emp.empId}"></c:out></td>
<td><c:out value="${emp.empName}"></c:out></td>
<td><c:out value="${emp.empJob}"></c:out></td>
<td><c:out value="${emp.empSal}"></c:out></td>
</tr>
</c:forEach>
<tr>
<td colspan="2"></td>
<td colspan="2"><a href="${pageScope.myUrl}">nextPage</a></td>
</tr>
</table>
</jsp:root>
</code> |
This JSP uses the DAO class to retrieve the Employee information from the database. The page number is passed as a parameter to the DAO. Notice that I did not implement the “previous” page, but it is similar to next. I assumed that we do not know the number of results for this example.
Struts 2.0 and Spring