Struts Paging Tutorial
This tutorial explain two ways to page
through a list in struts. The first way works with normal struts tags
and and the second with the really good display tag library.
General
Author:
Sascha
Wolski
Sebastian Hennebrueder
http://www.laliluna.de/tutorials.html
Date:
Updated:
December 2007
First
edition: March 2005
Software:
Eclipse
3.x
Display
Tag Library
Common-Lang
2.0
Struts
1.3 but can be easily ported to newer Struts versions as well
PDF
download: http://www.laliluna.de/download/struts-paging-en.pdf
Source
download: http://www.laliluna.de/download/struts-paging.zip
Requirments
First off all we require the display tag
library (http://www.displaytag.org)
and for the display tag library you need the commons-lang and
common-collections library.
Paging in Struts
Paging lists in struts costs a lot of
efforts and there is no standard way to do this. While writing the
example application for this tutorial, I found many problems on
paging lists with the standard tag libraries of struts. I think a
good alternative way to page through lists in struts is the display
tag library, I will also explain in this tutorial. But first we do a
paging of a list with the standard tag libraries.
Create a new Struts Project
Create a new struts project PagingExample
and add a package de.laliluna.tutorial.paging.
Object Class Customer
Create a new java class Customer in the
package de.laliluna.tutorial.object.
Add four properties, id of type int, name,
city and phone of type String.
Provide a getter and setter method for each
property.
Add a constructor which allow you to initialize
the properties.
The following source code shows the class
Customer:
/**<br> * Object Class Customer<br> */<br>public class Customer {<br><br> //properties<br> private int id;<br> private String name;<br> private String city;<br> private String phone;<br><br> //constructors<br> public Customer(){}<br> public Customer(int id, String name, String city, String phone){<br> this.id = id;<br> this.name = name;<br> this.city = city;<br> this.phone = phone;<br> }<br><br> //getter and setter methods<br> public String getCity() {<br> return city;<br> }<br> public void setCity(String city) {<br> this.city = city;<br> }<br> public int getId() {<br> return id;<br> }<br> public void setId(int id) {<br> this.id = id;<br> }<br> public String getName() {<br> return name;<br> }<br> public void setName(String name) {<br> this.name = name;<br> }<br> public String getPhone() {<br> return phone;<br> }<br> public void setPhone(String phone) {<br> this.phone = phone;<br> }<br>}
New Class TestList
Create a new java class TestList in
the package de.laliluna.tutorial.object.
This class provides methods for paging a
list.
Add three properties list of type
ArrayList, offset and
length of type int.
Provide a getter
and setter methods for each property.
Add a constructor
to initialize the properties and execute a method which fills the
property list with a list of dummy data.
The following
source code shows the class TestList:
/**<br> * Class TestList<br> */<br>public class TestList {<br><br> //properties<br> ArrayList list;<br> int offset;<br> int length;<br><br> //constructors<br> public TestList(int offset, int length){<br> this.offset = offset;<br> this.length = length;<br> fillList();<br> }<br><br> //fill the list with dummy data<br> public void fillList(){<br> list = new ArrayList();<br> list.add(new Customer(1, "Marie", "New York", "061/123456"));<br> list.add(new Customer(2, "Klaus", "Bouston", "071/654321"));<br> list.add(new Customer(3, "Peter", "Detroit", "091/3432432"));<br> list.add(new Customer(4, "Alex", "New York", "061/1324234"));<br> list.add(new Customer(5, "Eve", "Houston", "051/885656"));<br> list.add(new Customer(6, "Sebastian", "Seattle", "0811/8234240"));<br> list.add(new Customer(7, "Marie", "Ohio", "0771/23235"));<br> list.add(new Customer(8, "Gabriel", "Oklahoma", "011/9945461"));<br> list.add(new Customer(9, "John", "California", "0871/8230013"));<br> list.add(new Customer(10, "Dave", "Iowa", "0981/2320026"));<br> }<br><br> //get list by offset and length<br> // returns a subset of the list, from offset to offset + length<br> public ArrayList getListByOffsetAndLength(){<br><br> ArrayList arrayList = new ArrayList();<br><br> //calc the to value<br> int to = this.offset + this.length;<br> //if offset or lenght exceed set them to list.size<br> if(this.offset > list.size()) this.offset = list.size();<br> if(to > list.size()) to = list.size();<br> //add the list items to the return collection <br> for(int i=this.offset;i<to;i++){<br> arrayList.add(list.get(i));<br> }<br> //return the collection<br> return arrayList;<br> }<br><br> //get list site<br> public int getListSize(){<br> return list.size();<br> }<br><br> //get pages returns a list of Integer values, representing the pages<br> public Collection getPages(){<br><br> Collection collection = new ArrayList(); <br> //calc how many pages are there<br> int pages = list.size() / this.length;<br> if(list.size() % this.length != 0)<br> pages = pages + 1;<br><br> //fill an collection with all pages<br> for(int i=1;i<=pages;i++){<br> collection.add(new Integer(i));<br> }<br><br> return collection;<br> }<br><br> // getter and setter methods<br> public ArrayList getList() {<br> return list;<br> }<br> public void setList(ArrayList list) {<br> this.list = list;<br> }<br> public int getLength() {<br> return length;<br> }<br> public void setLength(int length) {<br> this.length = length;<br> }<br> public int getOffset() {<br> return offset;<br> }<br> public void setOffset(int offset) {<br> this.offset = offset;<br> }<br>}
Action Class
Create a new java class ExampleAction in
the package de.laliluna.tutorial.paging.action, which extends
the class Action.
Add a variable maxEntriesPerPage to specify
how many entries are displayed per page.
Add a variable page which holds the current
page of the list. This variable will be set by the request parameter
page. You have to catch a
NumberFormatException,
because the exception can occur if the request parameter page
is null.
Calculate the offset
with the maxEntriesPerPage and the current page value.
Initialize the TestList
class and set it in the request.
Return the forward
example.
/**
* Action Class ExampleAction
*/
public class ExampleAction extends Action {
public ActionForward execute(
ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response) {
int maxEntriesPerPage = 3;
int page = 1;
try{
page = Integer.parseInt(request.getParameter(“page”));
}catch(NumberFormatException e){}
int offset = maxEntriesPerPage * (page – 1);
request.setAttribute(“testList”, new TestList(offset, maxEntriesPerPage));
return mapping.findForward(“example”);
}
}
Configure the struts-config.xml
Open the struts-config.xml and
configure the action mapping.
The folowing source code shows the
content of the struts-config.xml:
<?xml version=“1.0” encoding=“UTF-8”?>
<!DOCTYPE struts-config PUBLIC “-//Apache Software Foundation//DTD Struts Configuration 1.3//EN” “http://struts.apache.org/dtds/struts-config_1_3.dtd”>
<struts-config>
<action-mappings >
<action path=“/example” type=“de.laliluna.tutorial.paging.action.ExampleAction” >
<forward name=“example” path=“/example.jsp” />
</action>
</action-mappings>
<message-resources parameter=“de.laliluna.tutorial.paging.ApplicationResources” />
</struts-config>
The output (JSP File)
Create a new JSP file example.jsp in the
folder /WebRoot of your project.
Open the file and add the following content.
<%@ page language="java" pageEncoding="UTF-8"%><br><%@ taglib uri="http://struts.apache.org/tags-bean" prefix="bean"%><br><%@ taglib uri="http://struts.apache.org/tags-html" prefix="html"%><br><%@ taglib uri="http://struts.apache.org/tags-logic" prefix="logic" %><br><%@ taglib uri="http://displaytag.sf.net" prefix="display" %><br><br><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><br><html:html><br> <head><br> <html:base /><br> <title>example.jsp</title><br> </head><br><br> <body><br><br> ... example code ...<br><br> </body><br></html:html>
Inside the <body> element insert the
following examples.
Example 1
In the first example we use a normal logic:iterate
tag to display the list of dummy data. The attribute property of the
logic:iterate tag calls the getter Method
getListByOffsetAndLength()
and returns a list of items for the current page. For example if the
page is 1 it returns the items 0 to 2. Below the list we display the
pages which are existing. The attribute property of the second
logic:iterate element calls the getter method getPages() in
the TestList class and
returns a list of pages. Inside the logic:iterate
element a html:link
will be generated. The attribute paramId
sets a name for a parameter which is added to the link and the
attribute paramName
specifies the value for this parameter.
<h3>Simple paging with struts tags. </h3><br><br><tabl e border="1"><br><tr><br> <td><b>ID</b></td><br> <td><b>Name</b></td><br> <td><b>City</b></td><br> <td><b>Phone</b></td><br></tr><br><%-- Iteration over the list --%><br><logic:iterate name="testList" property="<b>listByOffsetAndLength</b>" id="var"><br><tr><br> <td><bean:write name="var" property="id" /></td><br> <td><bean:write name="var" property="name" /></td><br> <td><bean:write name="var" property="city" /></td><br> <td><bean:write name="var" property="phone" /></td><br></tr><br></logic:iterate> <br><tr><br> <td colspan="4"> <br> <logic:iterate name="testList" property="<b>pages</b>" id="varpage"><br> <html:link action="/example" paramName="varpage" paramId="page"><br> <bean:write name="varpage" /><br> </html:link><br> </logic:iterate><br> </td><br></tr><br></table>
The first example shows you a way to page a
list with standard tag libraries in struts. In my opinion, it is very
difficulty and costs a lot of time.
Example 2
Now I will show you, how you can use the display
tag library to do the same but more elegant.
Step 1
First off all, download the display tag library
(http://www.displaytag.org)
Download the commons-lang-2.0.jar
(http://jakarta.apache.org/commons/lang/)
Extract the archives.
Copy the display tag-1.0.jar
of the display tag archive to your lib folder /WEB-INF/lib/
Copy the
displaytag-11.tld of the display tag archive to your WEB-INF
folder
Copy the commons-lang-2.0.jar of the
commons-lang archive to your
lib folder /WEB-INF/lib/
Be sure you have delete
the old version of commons-lang.
That’s all.
Note: If you have some problems,
read the original install guide of the display tag library:
http://displaytag.sourceforge.net/install.html
Step 2
On the top of the JSP
file example.jsp add the reference to the tag library
<%@ taglib uri="http://displaytag.sf.net" prefix="display" %>
Step 3 Using the tag library
In example 2 we
use the display:table element to output the list. The
attribute name of the display:table element specify the
bean which holds the list. The attribute property specify list
of all items to display.
To use the
paging functionality you have to set the attribute pagesize,
in our case 3 item per page should be displayed. Thats all, very nice
and easy !!
The attribute
requestURI specifies the URI that is used for the links to
change a page. We have to specify this, because by default it refers
to the JSP file (example.jsp) and we fill and set the list in
the action class.
<h3>Simple use of display tag library for paging with struts. </h3><br> <display:table name="testList.list" <br> pagesize="3" <br> requestURI="/example.do" />
Example 3
The last example shows a advanced usage of the
display:table element for paging lists. If you want to specify
customer column names or display not all properties you have to
define the columns inside the body of the display:table
element. Furthermore you can specify if a column can be sorted or
some other functionality. The attribute property of the
display:column element specify the property you want to
display. The title attribute let you set a custom title for
each column and the sortable attribute specify if the column
is sortable.
<h3>Adavanced use of display tag library for paging with struts. </h3>
<display:table name=“testList.list”
pagesize=“3”
requestURI=“/example.do” >
<display:column property=“id” title=“ID” sortable=“true” />
<display:column property=“name” title=“Name” sortable=“true” />
<display:column property=“city” title=“City” sortable=“true” />
<display:column property=“phone” title=“Phone” sortable=“true” />
</display:table>
Detailed information about the elements you
will find on the display tag
homepage.
http://displaytag.sourceforge.net/tagreference-displaytag-12.html
That’s all you can test the project now.
Call the project with the link below.
http://localhost:8080/PagingExample/example.do