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Struts: Paging and Sorting with Displaytag

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In the previous post, I described the use of Displaytag to implement paging in a simple JSP. In this example, I describe the use of Displaytag to implement sorting along with paging in Struts.
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In this example, we take a single input field, which is used to filter the employee list based on the minimum salary. Follow these steps to implement the solution.
  1. Start by importing struts-blank.war file into Eclipse.
  2. Follow the configuration steps 1, 2, 4, 5, and 6 in from the "Pagination with Displaytag" post.
  3. Create the search page as shown below
    <%@ page language="java" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-8859-1"%>
<%@ taglib uri="http://struts.apache.org/tags-bean" prefix="bean"%>
<%@ taglib uri="http://struts.apache.org/tags-html" prefix="html"%>
<%@ taglib uri="http://struts.apache.org/tags-logic" prefix="logic"%>
<%@ taglib uri="http://displaytag.sf.net" prefix="display"%>
<%@ page import="beans.Employee,data.DAO,java.util.List,org.displaytag.tags.TableTagParameters,org.displaytag.util.ParamEncoder"%>
<html:html>
<head>
<title>Search page</title>
<link rel="stylesheet" type="text/css"
href="/StrutsPaging/css/screen.css" />
</head>
<body bgcolor="white">
<html:form action="/search.do">
<table>
<tr>
<td>Minimum Salary:</td>
<td><html:text property="minSalary"></html:text></td>
</tr>
<tr>
<td colspan="2"><html:submit property="submit" /></td>
</tr>
</table>
</html:form>
<logic:notEqual name="empList" value="null">
<jsp:scriptlet>
if (session.getAttribute("empList") != null) {
String sortBy = request.getParameter((new ParamEncoder("empTable")).encodeParameterName(TableTagParameters.PARAMETER_SORT));
DAO.sort((List) session.getAttribute("empList"), sortBy);
}
</jsp:scriptlet>

<display:table name="sessionScope.empList" pagesize="4" id="empTable" sort="external" defaultsort="1" defaultorder="ascending">
<display:column property="empId" title="ID" sortable="true" sortName="empId" headerClass="sortable" />
<display:column property="empName" title="Name" sortName="empName" sortable="true" headerClass="sortable" />
<display:column property="empJob" title="Job" sortable="true" sortName="empJob" headerClass="sortable" />
<display:column property="empSal" title="Salary" sortable="true" headerClass="sortable" sortName="empSal" />
</display:table>
</logic:notEqual>
</body>
</html:html>
    pages/search.jsp
    Note that
    1. The display:table tag has the sort attribute defined as "external".
    2. Since the sort type is external, we have to provide for the actual sorting, which I implemented in the DAO class itself (see below).
    3. The column to sort by is obtained by the following peice of code
      request.getParameter((new ParamEncoder("empTable")).encodeParameterName(TableTagParameters.PARAMETER_SORT))
  4. Create the Action class and Form bean as shown below.
    public class SearchAction extends Action {
public ActionForward execute(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse httpservletresponse) throws Exception {
if (form == null) {
return mapping.findForward("success");
}
try {
SearchForm searchForm = (SearchForm) form;
if (searchForm.getMinSalary().equals("")) {
return mapping.findForward("success");
}
long minSal = Long.parseLong(searchForm.getMinSalary());
List data = DAO.getData(minSal);

request.getSession().setAttribute("empList", data);

} catch (Exception e) {
e.printStackTrace();
}
return mapping.findForward("success");
}
}
    actions.SearchAction
    public class SearchForm extends ActionForm {
private String minSalary;
public String getMinSalary() {
return minSalary;
}
public void setMinSalary(String minSalary) {
this.minSalary = minSalary;
}
}
    forms.SearchForm.java
  5. Modify the struts-config.xml to include the action and actionform as shown below
    <form-beans>
<form-bean name="searchForm" type="forms.SearchForm" />
</form-beans>
<action-mappings>
<action path="/Welcome" forward="/pages/Welcome.jsp" />
<action name="searchForm" path="/search"
type="actions.SearchAction" scope="session">
<forward name="success" path="/pages/search.jsp"></forward>
</action>
</action-mappings>
  6. Create the DAO class as shown below
    public class DAO {
public static List getData(long minSal) {
SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
Session session = sessionFactory.getCurrentSession();
List result = null;
try {
session.beginTransaction();
result = session.createQuery("from Employee as emp where emp.empSal >=?").setLong(0, minSal).list();
System.out.println("Result size : " + result.size());
session.getTransaction().commit();
} catch (Exception e) {
e.printStackTrace();
}
return result;
}

public static List sort(List<Employee> list, String sortBy) {
Comparator comp = getComparator(sortBy);
Collections.sort(list, comp);
return list;
}

private static Comparator getComparator(String sortBy) {
System.out.println("Sort by : " + sortBy);
if (sortBy ==null) {
return new NameComparator();
}
if (sortBy.equals("empName"))
return new NameComparator();
if (sortBy.equals("empId"))
return new IdComparator();
if (sortBy.equals("empSal"))
return new SalComparator();
if (sortBy.equals("empJob"))
return new JobComparator();

return null;

}

private static class NameComparator implements Comparator {
public int compare(Object emp1, Object emp2) {
Employee employee1 = (Employee) emp1;
Employee employee2 = (Employee) emp2;
return employee1.getEmpName().compareTo(employee2.getEmpName());
}
}

private static class IdComparator implements Comparator {
public int compare(Object emp1, Object emp2) {
Employee employee1 = (Employee) emp1;
Employee employee2 = (Employee) emp2;
return new Long(employee1.getEmpId()).compareTo(new Long(employee2.getEmpId()));
}
}

private static class SalComparator implements Comparator {
public int compare(Object emp1, Object emp2) {
Employee employee1 = (Employee) emp1;
Employee employee2 = (Employee) emp2;
return new Long(employee1.getEmpSal()).compareTo(new Long(employee2.getEmpSal()));
}
}

private static class JobComparator implements Comparator {
public int compare(Object emp1, Object emp2) {
Employee employee1 = (Employee) emp1;
Employee employee2 = (Employee) emp2;
return employee1.getEmpJob().compareTo(employee2.getEmpJob());
}
}

}
    DAO.java
    Note here that
    1. The list sorting is done in this class itself.
    2. The Comparators are used to compare order the list based on each individual field (there may be scope for improvement here).
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