<chapter id="forms">
	<title>Using Forms</title>
	<para>This chapter will introduce you to the way in which Tapestry handles HTML forms. 
	It begins with basics on general form submission, covers server and client side 
	validation, use of multiple submit buttons and non-trivial components. </para>

	<para>The provided example tutorial code groups together the examples shown
	here into a single Tapestry application.  The examples provided will be developed
	in order, so that you can see how additional complexity and validation is added.</para>
	
	<para>The examples that you will firstly accept data from the user (probably you :-), validate
	that data, and then show the results. If there is any error during validation, this will be
	shown on the form and the user will be given the chance to fix the field values
	and re-enter the data.  Note: The validation and error handling functionality is 
	developed as the tutorial progresses so does not exist on the initial pages</para>
	
  	<section id="form-non-validated">
  		<title>Basic non-validated form</title>
		<para>
			Lets begin by creating a form that allows you to enter some information about yourself, 
			which is simply echoed back to you. Initially, we will use straight text fields - 
			but as the tutorial progresses we will replace these with smarter (and cooler!) 
			implementations which include error handling.
		</para>

		<para>The application specification below is used for all examples in this chapter.:</para>
	
		<figure>
			<title>The Application Specification</title>
			<programlisting>
&lt;application name="Forms Tutorial" engine-class="net.sf.tapestry.engine.SimpleEngine"&gt;
  &lt;property name="net.sf.tapestry.visit-class"&gt;tutorial.forms.VisitorState&lt;/property&gt;

  &lt;page name="Home" specification-path="/tutorial/forms/Home.page"/&gt;
  &lt;page name="Success" specification-path="/tutorial/forms/Success.page"/&gt;
  &lt;page name="Part1" specification-path="/tutorial/forms/Part1.page"/&gt;
  &lt;page name="Part2" specification-path="/tutorial/forms/Part2.page"/&gt;
  &lt;page name="Part3" specification-path="/tutorial/forms/Part3.page"/&gt;
  &lt;page name="Part4" specification-path="/tutorial/forms/Part4.page"/&gt;
&lt;/application&gt;
            </programlisting>
		</figure>
		
		<para>The Home page of this application provides some description of what the application is,
		and some links to various examples. We will skip it here for brevity. It can be found within
		the <filename>examples/tutorial</filename> directory if you wish to view it</para>
	
		<para>The following listing shows the HTML for the first example:</para>
		<figure>
			<title>HTML for Part One</title>
			<programlisting>
&lt;!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"&gt;
&lt;html&gt;
&lt;head&gt;
	&lt;title&gt;Forms Tutorial&lt;/title&gt;
&lt;/head&gt;
&lt;body&gt;

&lt;h1&gt;Form Tutorial&lt;/h1&gt;
Enter some fields on this page, and press the submit button. 

&lt;form jwcid="form"&gt;
	&lt;table&gt;
		&lt;tr&gt;
			&lt;td&gt;Your name:&lt;/td&gt;
			&lt;td&gt;&lt;input jwcid="name"&gt;Neil&lt;/input&gt;&lt;/td&gt;
		&lt;/tr&gt;

		&lt;tr&gt;
			&lt;td&gt;Date of birth:&lt;/td&gt;
			&lt;td&gt;&lt;input jwcid="dateOfBirth"/&gt;&lt;/td&gt;
		&lt;/tr&gt;

		&lt;tr&gt;
			&lt;td&gt;Favourite colour:&lt;/td&gt;
			&lt;td&gt;&lt;input jwcid="favColour"/&gt;&lt;/td&gt;
		&lt;/tr&gt;

		&lt;tr&gt;
			&lt;td colspan=2&gt;&lt;input type="submit" jwcid="submit"/&gt;&lt;/td&gt;
		&lt;/tr&gt;
	&lt;/table&gt;
&lt;/form&gt;

&lt;/body&gt;
&lt;/html&gt;
			</programlisting>				
		</figure>

		<para>We will now write a page specification to handle these fields, using standard &TextField;'s:</para>
		<figure>
			<title>Page Specification for Part One</title>
			<programlisting>
&lt;page-specification class="tutorial.forms.Part1"&gt;
	&lt;bean name="delegate" class="net.sf.tapestry.valid.ValidationDelegate"/&gt;

	&lt;component id="form" type="Form"&gt;
		&lt;binding name="delegate" expression="beans.delegate"/&gt;
	&lt;/component&gt;

	&lt;component id="name" type="TextField"&gt;
		&lt;binding name="value" expression="visit.userName"/&gt;
	&lt;/component&gt;

	&lt;component id="dateOfBirth" type="TextField"&gt;
		&lt;binding name="value" expression="visit.dateOfBirthAsString"/&gt;
	&lt;/component&gt;

	&lt;component id="favColour" type="TextField"&gt;
		&lt;binding name="value" expression="visit.favoriteColour"/&gt;
	&lt;/component&gt;

	&lt;component id="submit" type="Submit"&gt;
		&lt;binding name="listener" expression="listeners.enterDetails"/&gt;
	&lt;/component&gt;
&lt;/page-specification&gt;
			</programlisting>				
		</figure>

		<para>An &TextField; component allows you to show simple &lt;input&gt; HTML tags, and have the value bound 
		to some property of an object. As we have have already seen, Tapestry is capable of getting the value which 
		will appear in the form from almost anywhere. In these examples, we will create a Visit object for the application 
		and bind the form's values to properties on that object. There is however nothing from stopping us using OGNL to 
		bind the component to some other object, (e.g: a static method, or property of some EJB object, for example).
		</para>
	
		<para>For the above specification, we have used simple OGNL bindings.  These will be used to both get the 
		property value when Tapestry renders the form, and also to set the value when the user submits the form.
		</para>
		
		<para>Moving along, lets examine the &Form; component. This has two properties, 
		<varname>delegate</varname> and <varname>listener</varname>.  The <varname>delegate</varname> is used to 
		store validataion error information.  This can be used by your submit handler to see if the form has any errors.
		We have bound the value to <varname>beans.delegate</varname> which is an instance of the Tapestry 
		supplied <varname>ValidationDelegate</varname> class.    This class handles the state required to 
		peform validation and associates error messages with components.</para>
		
		<para>In most applications, you can just use the Tapestry supplied validator - as we have done here.</para>
		
		<para>The second property, <varname>submit</varname> is used to tell Tapestry what method to call 
		on your Java object when the form is submitted.   The expression, <varname>listeners.submit</varname> 
		refers to the <varname>public void submit(IRequestCycle)</varname> method on the page object. </para>
		
		<para>Lastly, there is the actual submit button itself. This is rendered using a &Submit; component,
		which requires only two properties, the lable to use, and the method to call. 
		Here, since we are not implementing a localized version of the form, we will use a <varname>static-binding</varname> 
		for the button label, and we will refer to the same listener method that the form is using.</para>
	
		<para>Note that it is worth specifying the listener on both the &Form; and &Submit; components, 
		as by doing so the user will be able to use "default submit behavior" on the browser (i.e.: fill in the form and hit enter.)</para>
		
		<para>The Java object for the page and Visit Object is listed below. 
		You should be able to match up the OGNL expressions to JavaBean properties on the form. 
		The submit and form listeners refer to a method, not a property.</para>
	
		<figure>
			<title>Page1 Java Object, Part One</title>
			<programlisting>
package tutorial.forms;

import net.sf.tapestry.IRequestCycle;
import net.sf.tapestry.RequestCycleException;
import net.sf.tapestry.html.BasePage;

/**
 * Example code for the forms part of Tutorial
 * @author Neil Clayton
 */
public class Part1 extends BasePage {
	public void enterDetails(IRequestCycle cycle) throws RequestCycleException {
		// Submission has been performed. Do something here.
		cycle.setPage("Success");
	}
	
}
			</programlisting>
		</figure>

		<figure>
			<title>The Visit Object, Part One</title>
			<programlisting>
	public class VisitorState implements Serializable
	{
		/**
		 * Returns the dateOfBirth.
		 * @return String
		 */
		public Date getDateOfBirth()
		{
			return dateOfBirth;
		}

		public String getDateOfBirthAsString()
		{
			return DateFormat.getDateInstance().format(dateOfBirth);
		}

		/**
		 * Returns the favoriteColour.
		 * @return String
		 */
		public String getFavoriteColour()
		{
			return favoriteColour;
		}

		/**
		 * Returns the name.
		 * @return String
		 */
		public String getUserName()
		{
			return userName;
		}

		/**
		 * Sets the dateOfBirth.
		 * @param dateOfBirth The dateOfBirth to set
		 */
		public void setDateOfBirth(Date dateOfBirth)
		{
			this.dateOfBirth = dateOfBirth;
		}

		/**
		 * Sets the favoriteColour.
		 * @param favoriteColour The favoriteColour to set
		 */
		public void setFavoriteColour(String favoriteColour)
		{
			this.favoriteColour = favoriteColour;
		}

		public void setDateOfBirthAsString(String newDOB) throws ParseException
		{
			dateOfBirth = DateFormat.getDateInstance().parse(newDOB);
		}

		/**
		 * Sets the name.
		 * @param name The name to set
		 */
		public void setUserName(String name)
		{
			this.userName = name;
		}

		private String userName;
		private Date dateOfBirth = new Date(0);
		private String favoriteColour;
	}
			</programlisting>
		</figure>

		<para>Compile and run this example. You should see the following form:</para>

		<figure>
			<title>Form Input, Part 1</title>
			<mediaobject>
				<imageobject>
					<imagedata fileref="images/forms-part1-form.gif" format="GIF"/>
				</imageobject>
			</mediaobject>
		</figure>

		<para>When you enter the data and hit the submit button, you should see:</para>
		
		<figure>
			<title>Form Input, Result - Part 1</title>
			<mediaobject>
				<imageobject>
					<imagedata fileref="images/forms-part1-result.gif" format="GIF"/>
				</imageobject>
			</mediaobject>
		</figure>

		<para>This section has shown basic form field handling using components with no validation. 
		The next section introduces some validation logic, and a method for showing errors on the page.</para>
	  	</section>

		<section id="server-side-validation">
  		<title>Adding Server-side Validation Logic</title>  	

		<para>Many Tapestry components use validators (they implement the <varname>IValidator</varname> interface) - 
		these validators encapsulate specific validation rules, such as 'required, mininum length of 5 and maximum length of 12'.
		Tapestry also provides some default validation implementations, to make life a little easier.</para>
	
		<para>The next example shows a complete page specification using a single StringValidator for the three
		input fields. A StringValidator will accept any string type value. In this example, the only real validation
		will be that a value for every field is that the value is <emphasis>required</emphasis>.  
		The example will also show some new components such 
		as &Delegator; and &Body; which are required in order to support validation. Here is the page specification:</para>

		<figure>
			<title>Component Specification, with StringValidator</title>
			<programlisting>
&lt;page-specification class="tutorial.forms.Part2"&gt;
	&lt;bean name="delegate" class="net.sf.tapestry.valid.ValidationDelegate"/&gt;

	&lt;bean name="stringValidator" class="net.sf.tapestry.valid.StringValidator" lifecycle="page"&gt;
		  &lt;set-property name="required" expression="true"/&gt;
		  &lt;set-property name="clientScriptingEnabled" expression="false"/&gt;
	 &lt;/bean&gt;

	&lt;component id="form" type="Form"&gt;
		&lt;binding name="delegate" expression="beans.delegate"/&gt;
	&lt;/component&gt;

	&lt;component id="body" type="Body"/&gt;

	&lt;component id="name" type="ValidField"&gt;
		&lt;binding name="value" expression="visit.userName"/&gt;
		&lt;binding name="validator" expression='beans.stringValidator'/&gt;
		&lt;static-binding name="displayName"&gt;User name&lt;/static-binding&gt;
	&lt;/component&gt;

	&lt;component id="dateOfBirth" type="ValidField"&gt;
		&lt;binding name="value" expression="visit.dateOfBirthAsString"/&gt;
		&lt;binding name="validator" expression='beans.stringValidator'/&gt;
		&lt;static-binding name="displayName"&gt;Date of birth&lt;/static-binding&gt;
	&lt;/component&gt;

	&lt;component id="favColour" type="ValidField"&gt;
		&lt;binding name="value" expression="visit.favoriteColour"/&gt;
		&lt;binding name="validator" expression='beans.stringValidator'/&gt;
		&lt;static-binding name="displayName"&gt;Favorite colour&lt;/static-binding&gt;
	&lt;/component&gt;

	&lt;component id="errors" type="Delegator"&gt;
		&lt;binding name="delegate" expression="beans.delegate.firstError"/&gt;
	&lt;/component&gt;

	&lt;component id="submit" type="Submit"&gt;
		&lt;binding name="listener" expression="listeners.enterDetails"/&gt;
	&lt;/component&gt;
&lt;/page-specification&gt;
			</programlisting>
		</figure>

		<para>The fields themselves are now &ValidField;s. A ValidField requires two additional properties, 
		<varname>validator</varname> and <varname>displayName</varname>. The first specifies an instance of
		a validator, and the later is used as a textual description of the form element if an error occurs.</para>
		
		<para>The &Body; component is required and used to insert client side validation
		in the form of JavaScript at the top of the page (although for this example, client side
		validation is turned off).  Tapestry will provide server side validation
		all the time, and client side validation is possible if the user agent supports JavaScript.</para>
	
		<para>Finally, in order to show an error with validation on the page, we have added an
		<varname>errors</varname> component, which simply shows the first error.  The &Delegator; 
		component is an easy way to pass the responsibility for rendering to some other object. 
		As the first error of a validator implements &IRender;, we can use the &Delegator; component to 
		include its output into the page during the rendering process.  
		This is of course only one example of presenting errors. It
		would be possible to use an alternative error page, or a custom component to render all errors
		that are present in the validation delegate. The option presented here has been chosen for
		its simplicity.</para>

		<para>The new HTML template is as shown</para>
		<figure>
			<title>HTML Template, with StringValidator</title>
			<programlisting>
&lt;!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"&gt;
&lt;html&gt;
&lt;head&gt;
	&lt;title&gt;Forms Tutorial&lt;/title&gt;
&lt;/head&gt;
&lt;body&gt;

&lt;h1&gt;Form Tutorial&lt;/h1&gt;
Enter some fields on this page, and press the submit button. 

&lt;span jwcid="body"&gt;
	&lt;form jwcid="form"&gt;
		&lt;table&gt;
			&lt;tr&gt;
				&lt;td&gt;Your name:&lt;/td&gt;
				&lt;td&gt;&lt;input jwcid="name"&gt;Neil&lt;/input&gt;&lt;/td&gt;
			&lt;/tr&gt;
	
			&lt;tr&gt;
				&lt;td&gt;Date of birth:&lt;/td&gt;
				&lt;td&gt;&lt;input jwcid="dateOfBirth"/&gt;&lt;/td&gt;
			&lt;/tr&gt;
	
			&lt;tr&gt;
				&lt;td&gt;Favourite colour:&lt;/td&gt;
				&lt;td&gt;&lt;input jwcid="favColour"/&gt;&lt;/td&gt;
			&lt;/tr&gt;
	
			&lt;tr&gt;
				&lt;td colspan=2&gt;&lt;font color="red"&gt;&lt;span jwcid="errors"/&gt;&lt;/font&gt;&lt;/td&gt;
			&lt;/tr&gt;

			&lt;tr&gt;
				&lt;td colspan=2&gt;&lt;input type="submit" jwcid="submit"/&gt;&lt;/td&gt;
			&lt;/tr&gt;
		&lt;/table&gt;
	&lt;/form&gt;
&lt;/span&gt;

&lt;/body&gt;
&lt;/html&gt;
			</programlisting>
		</figure>
	
		<para>And lastly, the associated Java object:</para>
		<figure>
			<title>Java Object, with Validator</title>
			<programlisting>
package tutorial.forms;

import net.sf.tapestry.IRequestCycle;
import net.sf.tapestry.RequestCycleException;
import net.sf.tapestry.html.BasePage;
import net.sf.tapestry.valid.ValidationDelegate;

/**
 * Example code for the forms part of Tutorial
 * @author Neil Clayton
 */
public class Part2 extends BasePage {
	public void enterDetails(IRequestCycle cycle) throws RequestCycleException {
		// Submission has been performed. Validate the fields
		ValidationDelegate delegate = (ValidationDelegate)getBeans().getBean("delegate");
		if(delegate.getHasErrors()) {
			// there are errors
			return;
		}
		
		cycle.setPage("Success");
	}
	
}
			</programlisting>
		</figure>

		<para>In order to return the user to the previous page, we simply return from the
		submit method, without having set any alternative page for the rendering cycle. As a result,
		the same input page will show the user their error</para>
	
		<para>Compile and run the example. If you are using the precompiled examples, choose
		the second link on the forms tutorial page. If you ommit a value for any field, you 
		will see an error just above the submit button:</para>

		<figure>
			<title>Form Input, Part 2 - Required fields</title>
			<mediaobject>
				<imageobject>
					<imagedata fileref="images/forms-part2-form.gif" format="GIF"/>
				</imageobject>
			</mediaobject>
		</figure>

		<para>The next section shows some more advanced validation</para>
	</section>
	
	<section id="better-validation">
		<title>Advanced Validation</title>
		<para>The previous section showed some simple server side validation. 
		This next section shows how to use client side Javascript validation, as well as some further validators.
		Enabling client side validation is very simple in Tapestry. First, the page itself requires a &Body; component - 
		then we just need to turn it on! If this is sounding too good to be true, 
		it isn't.. really :-)</para>
			
		<para>Lets get started.  For this example, you don't need to do much, as the previous example code contained
		all of the required components (&Body;). To enable client side scripting, change the page specification 
		so that the <varname>stringValidator</varname> definition looks like this:</para>
			
		<figure>
			<title>Part3 Component Specification, with client side enabled StringValidator</title>
			<programlisting>
...
&lt;bean name="stringValidator" class="net.sf.tapestry.valid.StringValidator" lifecycle="page"&gt;
  		&lt;set-property name="required" expression="true"/>
  		&lt;set-property name="clientScriptingEnabled" expression="true"/>
&lt;/bean>
...
 			</programlisting>
		</figure>
		<para>This example can be found in <filename>Part3.page</filename> and is referred to as 'client and server side scripting
		from the index page of the complete forms example.	Compile and run the example.  
		Again, submit the form. If your browser supports JavaScript, you should see a popup 
		telling you that a field value is required.</para>

		<figure>
			<title>Form Input, Part 3 - Required fields with Client Side Validation</title>
			<mediaobject>
				<imageobject>
					<imagedata fileref="images/forms-part3-result.gif" format="GIF"/>
				</imageobject>
			</mediaobject>
		</figure>

		<para>Note that enabling client side validation does not <emphasis>disable</emphasis> server side validation. 
		If the browser does not support JavaScript, any incorrect values will still be caught and handled correctly.</para>

		<section id="date-validator">
			<title>A more specific Validator</title>
			<para>Now, lets use a more suitable validator for the "date of birth" field.  
			First, we need to instantiate an alternative IValidator instance. To do this, we will use another bean definition:</para>

			<figure>
				<title>Date Validator - bean definition</title>
				<programlisting>
...
&lt;bean name="stringValidator" class="net.sf.tapestry.valid.DateValidator" lifecycle="page"&gt;
  		&lt;set-property name="required" expression="true"/>
  		&lt;set-property name="clientScriptingEnabled" expression="true"/>
&lt;/bean>
...
	 			</programlisting>
			</figure>

			<para>Update the validator binding for the <varname>dateOfBirth</varname> component, to use the new validator.
			That done, you shoul be able to compile and run the code. Enter any non valid date, and you will get an appropriate 
			error message</para>
			<figure>
				<title>Updated Component Properties, for dateOfBirth</title>
				<programlisting>
...
&lt;component id="dateOfBirth" type="ValidField"&gt;
	&lt;binding name="value" expression="visit.dateOfBirth"/&gt;
    &lt;binding name="validator" expression='beans.dateValidator'/&gt;
    &lt;static-binding name="displayName"&gt;Date of birth&lt;/static-binding&gt;
&lt;/component&gt;
...
	 			</programlisting>
			</figure>
			<para>If you enter an incorrect value for date of birth, you will see:</para>
			<figure>
				<title>Form Input, Part 3 - Required fields with Client Side Validation</title>
				<mediaobject>
					<imageobject>
						<imagedata fileref="images/forms-part3-date-result.gif" format="GIF"/>
					</imageobject>
				</mediaobject>
			</figure>
		</section>
		<section id="validation-summary">
			<title>Summary</title>
			<para>This section has the basics of validation. By now you should be familiar with simple string based
			validation, and also the use of alternative validators such as the <varname>DateValidator</varname>.
			All standard Tapestry supplied component validation follows a similar pattern to what you have seen here.
			You need to first choose the validator, and then setup its properties.
			</para>
			
			<para>
			Tapestry contains more validators that those shown here, and of course it is not that hard to write
			your own.  Also, there are specific components that help in this regard. For example, the <varname>DateField</varname>
			component sets it's own validator, saving you the time in having to declare and attach it yourself.
			</para>
		</section>
	</section>		  		
  			
  	<section id="built-in">
  		<title>Smart Components</title>
		<para>The final part of this chapter shows the use of some smarter components for appropriate fields. 
		In terms of getting user input "right", prevention of bad input data is the best strategy. 
		If the user can't enter invalid input - your form processing is going to be simpler.  
		An excellent example is using the DatePicker, so that rather than the user having to type a date, they can just select one.
		For the user, this is 100% more intuitive, easier to use and virtually eliminates all entry errors.</para>

		<para>Tapestry includes some more advanced form components, which are used in this example. 
		We will use a DatePicker for the date of birth field, and a PropertySeletion for favouriteColour.<footnote>
		<para>DatePicker uses JavaScript to perform its work, so you will required something like IE5 (or above), Mozilla or Konqueror to use it</para></footnote>
		</para>

		<para>This example is named <varname>Part4</varname>. It is identical to <varname>Part3</varname>
		except that there are additional component definitions, and the definition for <varname>dateOfBirth</varname> and
		<varname>favColour</varname> have been modified. The specification below is highlighted to show those parts that differ:
		</para>
		
		<figure>
			<title>Full page specification for exampe - Part4</title>
			<programlisting>
&lt;page-specification class="tutorial.forms.Part4"&gt;
	&lt;bean name="delegate" class="net.sf.tapestry.valid.ValidationDelegate"/&gt;

	&lt;bean name="stringValidator" class="net.sf.tapestry.valid.StringValidator" lifecycle="page"&gt;
  		&lt;set-property name="required" expression="true"/&gt;
  		&lt;set-property name="clientScriptingEnabled" expression="true"/&gt;
 	&lt;/bean&gt;

	&lt;component id="form" type="Form"&gt;
		&lt;binding name="delegate" expression="beans.delegate"/&gt;	
	&lt;/component&gt;
	
	<emphasis role="bold">&lt;component id="shell" type="Shell"&gt;
		&lt;static-binding name="title"&gt;Smarter Components&lt;/static-binding&gt;	
	&lt;/component&gt;
	&lt;component id="body" type="Body"/&gt;</emphasis>
	
	&lt;component id="name" type="ValidField"&gt;
		&lt;binding name="value" expression="visit.userName"/&gt;
        &lt;binding name="validator" expression='beans.stringValidator'/&gt;
        &lt;static-binding name="displayName"&gt;User name&lt;/static-binding&gt;
	&lt;/component&gt;
	
	<emphasis role="bold">&lt;component id="dateOfBirth" type="DatePicker"&gt;
		&lt;binding name="value" expression="visit.dateOfBirth"/&gt;
	&lt;/component&gt;</emphasis>
	
	&lt;component id="favColour" type="ValidField"&gt;
		&lt;binding name="value" expression="visit.favoriteColour"/&gt;
        &lt;binding name="validator" expression='beans.stringValidator'/&gt;
        &lt;static-binding name="displayName"&gt;Favorite colour&lt;/static-binding&gt;
	&lt;/component&gt;
	
	&lt;component id="errors" type="Delegator"&gt;
		&lt;binding name="delegate" expression="beans.delegate.firstError"/&gt;
	&lt;/component&gt;
	
	&lt;component id="submit" type="Submit"&gt;
		&lt;binding name="listener" expression="listeners.enterDetails"/&gt;
	&lt;/component&gt;
&lt;/page-specification&gt;
 			</programlisting>
		</figure>

		<para>
		Because we have introduced a &Shell; component (required for the date picker to work), we need to modify the
		HTML. The HTML for part four is provided here:
		</para>
		<figure>
			<title>Full HTML for exampe - Part4</title>
			<programlisting>
&lt;span jwcid="shell"&gt;
	&lt;span jwcid="body"&gt;
		&lt;h1&gt;Form Tutorial&lt;/h1&gt;
		Enter some fields on this page, and press the submit button. 
		
		&lt;form jwcid="form"&gt;
			&lt;table&gt;
				&lt;tr&gt;
					&lt;td&gt;Your name:&lt;/td&gt;
					&lt;td&gt;&lt;input jwcid="name"&gt;Neil&lt;/input&gt;&lt;/td&gt;
				&lt;/tr&gt;
		
				&lt;tr&gt;
					&lt;td&gt;Date of birth:&lt;/td&gt;
					&lt;td&gt;&lt;input jwcid="dateOfBirth"/&gt;&lt;/td&gt;
				&lt;/tr&gt;
		
				&lt;tr&gt;
					&lt;td&gt;Favourite colour:&lt;/td&gt;
					&lt;td&gt;&lt;input jwcid="favColour"/&gt;&lt;/td&gt;
				&lt;/tr&gt;
		
				&lt;tr&gt;
					&lt;td colspan=2&gt;&lt;font color="red"&gt;&lt;span jwcid="errors"/&gt;&lt;/font&gt;&lt;/td&gt;
				&lt;/tr&gt;
	
				&lt;tr&gt;
					&lt;td colspan=2&gt;&lt;input type="submit" jwcid="submit"/&gt;&lt;/td&gt;
				&lt;/tr&gt;
			&lt;/table&gt;
		&lt;/form&gt;
	&lt;/span&gt;
&lt;/span&gt;
 			</programlisting>
		</figure>

		<para>The Java code itself requires no modification, because the <varname>DatePicker</varname> component uses the
		same data type as our previous &ValidField; did.  So, we have made it easier for the user to enter date values, by providing a date picker 
		component. We can also restrict the possible values for favorite colour, using another built in Tapestry
		component.
		</para>

		<para>
		To restrict the inputs for favourite colour, we will use the &PropertySelection; component. This component 
		takes as one of it's inputs a <emphasis>model</emphasis>. The model describes the data available 
		(it's very MVC like). Tapestry provides a number of pre-built models, one of which is the StringPropertySelection.
		</para>
		
		<para>The StringPropertySelection exposes an array of strings - which is very good if you have a 
		discrete set of values from whih a user must choose. Modify the component property for favouriteColour to read:
		</para>

		<figure>
			<title>PropertySelection for Favorite Colour - Part4</title>
			<programlisting>
&lt;component id="favColour" type="PropertySelection"&gt;
	&lt;binding name="value" expression="visit.favoriteColour"/&gt;
	&lt;binding name="model" expression="@getColourModel()"/&gt;
&lt;/component&gt;
 			</programlisting>
		</figure>

		<para>What happens here is that Tapestry takes care of rending a selection HTML element for you, 
		and sticks whatever value the user chooses into the favouriteColour property. Finally we need to 
		add the following method to Page4.java, to construct and return the model for the component:</para>
		<figure>
			<title>PropertySelection Code for Favorite Colour - Part4</title>
			<programlisting>
/**
 * Returns a set of colours that the user may choose from.
 */
public static IPropertySelectionModel getColourModel() {
	return new StringPropertySelectionModel(
		new String[] { "Black", "Fiji Blue", "Green", "Red", "Yellow" });
}
 			</programlisting>
		</figure>

		<para>Upon compiling and running this new code, your form should look like this:</para>

		<figure>
			<title>Form, with DatePicker and PropertySelection components</title>
			<mediaobject>
				<imageobject>
					<imagedata fileref="images/forms-part4-result.gif" format="GIF"/>
				</imageobject>
			</mediaobject>
		</figure>

		<section id="forms-part4-summary">
			<title>Summary</title>
			<para>We've looked at basic form handling, including different form fields, 
			binding values of a form to properties on an object, and Tapestry supplied error handling. We 
			have also introduced a couple of the smarter components - and seen how easy it is to switch 
			a component type without having to modify the page template.
			</para>
			<para>
			The usage of the components shown here is somewhat basic, due to the fact that this is a tutorial.
			Keep in mind that something like the IPropertySelection (along with the PropertySelection component) interface 
			allows you to make available any kind of object in both drop down lists and multi line lists, and handle selections
			of those components.
			</para>
		</section>
  	</section>
  </chapter>