Struts Iteration with nested tags

Since the version 1.1 of Struts, the tag library *nested* is included in Struts. In this tutorial we want to explain what are the features of the new nested tag library and show some little examples how you can use it.

General

Author:

Sascha Wolski

Sebastian Hennebrueder

http://www.laliluna.de/tutorials.html

Date: February, 29th 2004

Software:

Eclipse 3.x

Struts 1.1

PDF Version:

http://www.laliluna.de/assets/tutorials/struts-nested-iteration-en.pdf

Source code:

http://www.laliluna.de/assets/tutorials/struts-nested-iteration-sources.zip

The nested tag library

Nested tags make it easy to manage nested beans. For example a list like the following:

Department A
Customer A
Customer B
Customer C
Department B
Customer D

All nested tags inside a nested tag refers to the tag which surrounds them. For example your form bean holds an object department and you want the property name of the department. Normally you can use a dot notation to get the name of the department.

With a nested:nest tag you do not need the dot notation any more.

The following example shows a dot notation to output the name of a department bean:

<nested:write property="department.id" />

This example shows the usage of a nested:nest element to output the same property.

<nested:nest property="department">
	<nested:write property="id" />
</nested:nest>

The tags inside the nested:nest can refers directly to the properties of the department. When you have many properties this is quite an advantage.

The most functionality elements of the other tag libraries are rebuild as nested tags, like bean:write is nested:write, logic:iterate is nested:iterate etc. You will find a complete list of all supported tags by the nested tab library in the Apache Struts Nested Tag Library API.

Usage of the nested tags

Create a new struts 1.1 project to get more familiar with the nested tags.

Add a package de.laliluna.tutorial.nested to the src folder of the project.

Object class Customer

Create a new java class Customer in the package de.laliluna.tutorial.nested.object.

Add two properties, id of type int and name of type String.

Provide a getter and setter method for each property.

Create a constructor that allow you to set the properties on initialization.

The following source code shows the class Customer :

/**
 * Object Class Customer
 */
public class Customer {

	private int id;
	private String name;

	//constructors
	public Customer(){}
	public Customer(int id, String name){
		this.id = id;
		this.name = name;
	}

	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
}

Object class Department

Create a second java class Departments in the same package de.laliluna.tutorial.nested.object.

Add two properties, id of type int and name of type String and one property customers of type Collection, which holds a list of customers.

Provide a getter and setter method for each property.

Create a constructor that allows you to set the properties on initialization.

The following source code shows the class Department :

/**
 * Object Class Department
 */
public class Department {

	private int id;
	private String name;

	//customers collection
	private Collection customers;

	//constructors
	public Department() {}
	public Department(int id, String name, Collection customers){
		this.id = id;
		this.name = name;
		this.customers = customers;
	}

	public Collection getCustomers() {
		return customers;
	}
	public void setCustomers(Collection customers) {
		this.customers = customers;
	}
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
}

Action form class ExampleForm

Create a java class ExampleForm in the package de.laliluna.tutorial.nested.form, which extends the class ActionForm of struts.

Add a property department of type Department.

Provide a getter and setter method for the property department.

Implement the reset() method of the ActionForm class and provide some dummy data.

The following source code shows the class ExampleForm:

/** 
 * Action Form Class ExampleForm
 */
public class ExampleForm extends ActionForm {

	Department department;

	public Department getDepartment() {
		return department;
	}
	public void setDepartment(Department department) {
		this.department = department;
	}

	/**
	 * Reset method
	 * @param mapping
	 * @param request
	 */
	public void reset(ActionMapping mapping, 
					  HttpServletRequest request) {

		//initial a dummy collection of customers
		Collection customers = new ArrayList();
		customers.add(new Customer(1, "Maria"));
		customers.add(new Customer(2, "Klaus"));
		customers.add(new Customer(3, "Peter"));

		//initial a dummy department
		department = new Department(1, "Department A", customers);

	}
}

Action class ExampleAction

Create a java class ExampleAction in the package de.laliluna.tutorial.nested.action, which extends the class Action of struts.

Return the forward example.

The following source code shows the class ExampleAction:

/** 
 * Action Class ExampleAction
 */
public class ExampleAction extends Action {

	/**
	 * Method execute
	 * @param mapping
	 * @param form
	 * @param request
	 * @param response
	 * @return ActionForward
	 */
	public ActionForward execute(
		ActionMapping mapping,
		ActionForm form,
		HttpServletRequest request,
		HttpServletResponse response) {
		ExampleForm exampleForm = (ExampleForm) form;

		return mapping.findForward("example");
	}

}

Configure the struts-config.xml

Open the struts-config.xml and add the form bean and action mapping.

The following source code shows the content of the struts-config.xml.

<struts-config>
   <form-beans >
      <form-bean name="exampleForm" type="de.laliluna.tutorial.nested.form.ExampleForm" />
   </form-beans>

   <action-mappings >
      <action
         attribute="exampleForm"
         input="/form/example.jsp"
         name="exampleForm"
         path="/example"
         scope="request"
         type="de.laliluna.tutorial.nested.action.ExampleAction"
         validate="false" >
         <forward name="example" path="/form/example.jsp" />
      </action>
   </action-mappings>
</struts-config>

The JSP file

Create a new JSP file example.jsp in the folder /WebRoot/form.

Add the reference to the tag library nested at the top of the file.

The following source code shows the JSP file. The bold line at the top is the reference to the nested tag library.

<%@ page language="java"%>
<%@ taglib uri="http://jakarta.apache.org/struts/tags-bean" prefix="bean"%> 
<%@ taglib uri="http://jakarta.apache.org/struts/tags-html" prefix="html"%>
<%@ taglib uri="http://jakarta.apache.org/struts/tags-nested" prefix="nested"%>

<html> 
	<head>
		<title>JSP for exampleForm form</title>
	</head>
	<body>
		<html:form action="/example">

			... example code ...

			<br />
			<br />
			<html:submit/><html:cancel/>
		</html:form>
	</body>
</html>

Inside the <html:form> element you insert the following examples.

Example 1

In the first example we show the usage of dot notation to get the properties form the department object of the form bean.

<h3>Use of nested:text tag with dot notation</h3>

DEP. ID: <nested:text property="department.id" /> <br />
NAME: <nested:text property="department.name" /> <br />

<br />

Example 2

The second example shows the usage of the nested:nest tag to use the properties inside the nested:nest tag without dot notation. The attribute property of the nested:nest element refers to the property department of our form bean.

The nested:text elements inside the nested:nest element refers to the properties of the surrounds nested tag. The attribute property of the nested:text element refers to a property of the object class Department.

<h3>Use of nested:nest tag</h3>

<nested:nest property="department">
	DEP. ID: <nested:text property="id"/> <br />
	NAME: <nested:text property="name"/> <br />
</nested:nest>

<br />

Example 3

Example 3 shows the usage of an iteration inside a nested:nest tag. The nested:iteration element works like the logic:iteration element, but refers to a property of the parent nested tag.

<h3>Use of nested:iteration tag</h3>

<nested:nest property="department">
	DEP. ID: <nested:text property="id"/> <br />
	NAME: <nested:text property="name"/> <br /><br />
<nested:iterate property="customers">
		<b>Customer info</b><br />
		CUST. ID: <nested:text property="id"/> <br />
		NAME: <nested:text property="name"/> <br />
	</nested:iterate>
</nested:nest>

You see that the usage of the nested tags is very comfortable and easy to understand. Now you can deploy your project to your favorite application server (we recommend jboss or tomcat) and call the project with the following link:

http://localhost:8080/NestedExample/example.do