12.2 Writing Bean Properties
As explained in Managed Beans in JavaServer Faces Technology, a managed bean property can be bound to one of the following items:
-
A component value
-
A component instance
-
A converter implementation
-
A listener implementation
-
A validator implementation
These properties follow the conventions of JavaBeans components (also called beans). For more information on JavaBeans components, see the JavaBeans Tutorial at http://docs.oracle.com/javase/tutorial/javabeans/index.html
.
The component's tag binds the component's value to a managed bean property by using its value
attribute and binds the component's instance to a managed bean property by using its binding
attribute. Likewise, all the converter, listener, and validator tags use their binding
attributes to bind their associated implementations to managed bean properties. See Binding Component Values and Instances to Managed Bean Properties and Binding Converters, Listeners, and Validators to Managed Bean Properties for more information.
To bind a component's value to a managed bean property, the type of the property must match the type of the component's value to which it is bound. For example, if a managed bean property is bound to a UISelectBoolean
component's value, the property should accept and return a boolean
value or a Boolean
wrapper Object
instance.
To bind a component instance to a managed bean property, the property must match the type of component. For example, if a managed bean property is bound to a UISelectBoolean
instance, the property should accept and return a UISelectBoolean
value.
Similarly, to bind a converter, listener, or validator implementation to a managed bean property, the property must accept and return the same type of converter, listener, or validator object. For example, if you are using the convertDateTime
tag to bind a javax.faces.convert.DateTimeConverter
to a property, that property must accept and return a DateTimeConverter
instance.
The rest of this section explains how to write properties that can be bound to component values, to component instances for the component objects described in Adding Components to a Page Using HTML Tag Library Tags, and to converter, listener, and validator implementations.
12.2.1 Writing Properties Bound to Component Values
To write a managed bean property that is bound to a component's value, you must match the property type to the component's value.
Table 12-1 lists the javax.faces.component
classes and the acceptable types of their values.
Table 12-1 Acceptable Types of Component Values
Component Class | Acceptable Types of Component Values |
---|---|
|
Any of the basic primitive and numeric types or any Java programming language object type for which an appropriate |
|
|
|
|
|
|
|
|
When they bind components to properties by using the value
attributes of the component tags, page authors need to ensure that the corresponding properties match the types of the components' values.
12.2.1.1 UIInput and UIOutput Properties
The UIInput
and UIOutput
component classes are represented by the component tags that begin with h:input
and h:output
, respectively (for example, h:inputText
and h:outputText
).
In the following example, an h:inputText
tag binds the name
component to the name
property of a managed bean called CashierBean
.
<h:inputText id="name" size="30" value="#{cashierBean.name}" ...> </h:inputText>
The following code snippet from the managed bean CashierBean
shows the bean property type bound by the preceding component tag:
protected String name = null; public void setName(String name) { this.name = name; } public String getName() { return this.name; }
As described in Using the Standard Converters, to convert the value of an input or output component you can either apply a converter or create the bean property bound to the component with the matching type. Here is the example tag, from Using DateTimeConverter, that displays the date on which items will be shipped.
<h:outputText value="#{cashierBean.shipDate}"> <f:convertDateTime type="date" dateStyle="full" /> </h:outputText>
The bean property represented by this tag must have a type of java.util.Date
. The following code snippet shows the shipDate
property, from the managed bean CashierBean
, that is bound by the tag's value in the preceding example:
private Date shipDate; public Date getShipDate() { return this.shipDate; } public void setShipDate(Date shipDate) { this.shipDate = shipDate; }
12.2.1.2 UIData Properties
The UIData
component class is represented by the h:dataTable
component tag.
UIData
components must be bound to one of the managed bean property types listed in Table 12-1. Data components are discussed in Using Data-Bound Table Components. Here is part of the start tag of dataTable
from that section:
<h:dataTable id="items" ... value="#{cart.items}" ... var="item">
The value expression points to the items
property of a shopping cart bean named cart
. The cart
bean maintains a map of ShoppingCartItem
beans.
The getItems
method from the cart
bean populates a List
with ShoppingCartItem
instances that are saved in the items
map when the customer adds books to the cart, as shown in the following code segment:
public synchronized List<ShoppingCartItem> getItems() { List<ShoppingCartItem> results = new ArrayList<ShoppingCartItem>(); results.addAll(this.items.values()); return results; }
All the components contained in the UIData
component are bound to the properties of the cart
bean that is bound to the entire UIData
component. For example, here is the h:outputText
tag that displays the book title in the table:
<h:commandLink action="#{showcart.details}"> <h:outputText value="#{item.item.title}"/> </h:commandLink>
The title is actually a link to the bookdetails.xhtml
page. The h:outputText
tag uses the value expression #{item.item.title}
to bind its UIOutput
component to the title
property of the Book
entity. The first item in the expression is the ShoppingCartItem
instance that the h:dataTable
tag is referencing while rendering the current row. The second item in expression refers to the item
property of ShoppingCartItem
, which returns an Object
(in this case, a Book
). The title
part of the expression refers to the title
property of Book
. The value of the UIOutput
component corresponding to this tag is bound to the title
property of the Book
entity:
private String title; ... public String getTitle() { return title; } public void setTitle(String title) { this.title = title; }
12.2.1.3 UISelectBoolean Properties
The UISelectBoolean
component class is represented by the component tag h:selectBooleanCheckbox
.
Managed bean properties that hold a UISelectBoolean
component's data must be of boolean
or Boolean
type. The example selectBooleanCheckbox
tag from the section Displaying Components for Selecting One Value binds a component to a property. The following example shows a tag that binds a component value to a boolean
property:
<h:selectBooleanCheckbox title="#{bundle.receiveEmails}" value="#{custFormBean.receiveEmails}"> </h:selectBooleanCheckbox> <h:outputText value="#{bundle.receiveEmails}">
Here is an example property that can be bound to the component represented by the example tag:
private boolean receiveEmails = false; ... public void setReceiveEmails(boolean receiveEmails) { this.receiveEmails = receiveEmails; } public boolean getReceiveEmails() { return receiveEmails; }
12.2.1.4 UISelectMany Properties
The UISelectMany
component class is represented by the component tags that begin with h:selectMany
(for example, h:selectManyCheckbox
and h:selectManyListbox
).
Because a UISelectMany
component allows a user to select one or more items from a list of items, this component must map to a bean property of type List
or array
. This bean property represents the set of currently selected items from the list of available items.
The following example of the selectManyCheckbox
tag comes from Displaying Components for Selecting Multiple Values:
<h:selectManyCheckbox id="newslettercheckbox" layout="pageDirection" value="#{cashierBean.newsletters}"> <f:selectItems value="#{cashierBean.newsletterItems}"/> </h:selectManyCheckbox>
Here is the bean property that maps to the value
of the selectManyCheckbox
tag from the preceding example:
private String[] newsletters; public void setNewsletters(String[] newsletters) { this.newsletters = newsletters; } public String[] getNewsletters() { return this.newsletters; }
The UISelectItem
and UISelectItems
components are used to represent all the values in a UISelectMany
component. See UISelectItem Properties and UISelectItems Properties for information on writing the bean properties for the UISelectItem
and UISelectItems
components.
12.2.1.5 UISelectOne Properties
The UISelectOne
component class is represented by the component tags that begin with h:selectOne
(for example, h:selectOneRadio
and h:selectOneListbox
).
UISelectOne
properties accept the same types as UIInput
and UIOutput
properties, because a UISelectOne
component represents the single selected item from a set of items. This item can be any of the primitive types and anything else for which you can apply a converter.
Here is an example of the h:selectOneMenu
tag from Displaying a Menu Using the h:selectOneMenu Tag:
<h:selectOneMenu id="shippingOption" required="true" value="#{cashierBean.shippingOption}"> <f:selectItem itemValue="2" itemLabel="#{bundle.QuickShip}"/> <f:selectItem itemValue="5" itemLabel="#{bundle.NormalShip}"/> <f:selectItem itemValue="7" itemLabel="#{bundle.SaverShip}"/> </h:selectOneMenu>
Here is the bean property corresponding to this tag:
private String shippingOption = "2"; public void setShippingOption(String shippingOption) { this.shippingOption = shippingOption; } public String getShippingOption() { return this.shippingOption; }
Note that shippingOption
represents the currently selected item from the list of items in the UISelectOne
component.
The UISelectItem
and UISelectItems
components are used to represent all the values in a UISelectOne
component. This is explained in Displaying a Menu Using the h:selectOneMenu Tag.
For information on how to write the managed bean properties for the UISelectItem
and UISelectItems
components, see UISelectItem Properties and UISelectItems Properties.
12.2.1.6 UISelectItem Properties
A UISelectItem
component represents a single value in a set of values in a UISelectMany
or a UISelectOne
component. A UISelectItem
component must be bound to a managed bean property of type javax.faces.model.SelectItem
. A SelectItem
object is composed of an Object
representing the value along with two Strings
representing the label and the description of the UISelectItem
object.
The example selectOneMenu
tag from UISelectOne Properties contains selectItem
tags that set the values of the list of items in the page. Here is an example of a bean property that can set the values for this list in the bean:
SelectItem itemOne = null; SelectItem getItemOne(){ return itemOne; } void setItemOne(SelectItem item) { itemOne = item; }
12.2.1.7 UISelectItems Properties
UISelectItems
components are children of UISelectMany
and UISelectOne
components. Each UISelectItems
component is composed of a set of either UISelectItem
instances or any collection of objects, such as an array, a list, or even POJOs.
The following code snippet from CashierBean
shows how to write the properties for selectItems
tags containing SelectItem
instances.
private String[] newsletters; private static final SelectItem[] newsletterItems = { new SelectItem("Duke's Quarterly"), new SelectItem("Innovator's Almanac"), new SelectItem("Duke's Diet and Exercise Journal"), new SelectItem("Random Ramblings") }; ... public void setNewsletters(String[] newsletters) { this.newsletters = newsletters; } public String[] getNewsletters() { return this.newsletters; } public SelectItem[] getNewsletterItems() { return newsletterItems; }
Here, the newsletters
property represents the SelectItems
object, whereas the newsletterItems
property represents a static array of SelectItem
objects. The SelectItem
class has several constructors; in this example, the first argument is an Object
representing the value of the item, whereas the second argument is a String
representing the label that appears in the UISelectMany
component on the page.
12.2.2 Writing Properties Bound to Component Instances
A property bound to a component instance returns and accepts a component instance rather than a component value. The following components bind a component instance to a managed bean property:
<h:selectBooleanCheckbox id="fanClub" rendered="false" binding="#{cashierBean.specialOffer}" /> <h:outputLabel for="fanClub" rendered="false" binding="#{cashierBean.specialOfferText}" value="#{bundle.DukeFanClub}" /> </h:outputLabel>
The selectBooleanCheckbox
tag renders a check box and binds the fanClub
UISelectBoolean
component to the specialOffer
property of CashierBean
. The outputLabel
tag binds the value of the value
attribute, which represents the check box's label, to the specialOfferText
property of CashierBean
. If the user orders more than $100 worth of books and clicks the Submit button, the submit
method of CashierBean
sets both components' rendered
properties to true
, causing the check box and label to display when the page is re-rendered.
Because the components corresponding to the example tags are bound to the managed bean properties, these properties must match the components' types. This means that the specialOfferText
property must be of type UIOutput
, and the specialOffer
property must be of type UISelectBoolean
:
UIOutput specialOfferText = null; UISelectBoolean specialOffer = null; public UIOutput getSpecialOfferText() { return this.specialOfferText; } public void setSpecialOfferText(UIOutput specialOfferText) { this.specialOfferText = specialOfferText; } public UISelectBoolean getSpecialOffer() { return this.specialOffer; } public void setSpecialOffer(UISelectBoolean specialOffer) { this.specialOffer = specialOffer; }
For more general information on component binding, see Managed Beans in JavaServer Faces Technology.
For information on how to reference a managed bean method that performs navigation when a button is clicked, see Referencing a Method That Performs Navigation.
For more information on writing managed bean methods that handle navigation, see Writing a Method to Handle Navigation.
12.2.3 Writing Properties Bound to Converters, Listeners, or Validators
All the standard converter, listener, and validator tags included with JavaServer Faces technology support binding attributes that allow you to bind converter, listener, or validator implementations to managed bean properties.
The following example shows a standard convertDateTime
tag using a value expression with its binding
attribute to bind the javax.faces.convert.DateTimeConverter
instance to the convertDate
property of LoginBean
:
<h:inputText value="#{loginBean.birthDate}"> <f:convertDateTime binding="#{loginBean.convertDate}" /> </h:inputText>
The convertDate
property must therefore accept and return a DateTimeConverter
object, as shown here:
private DateTimeConverter convertDate; public DateTimeConverter getConvertDate() { ... return convertDate; } public void setConvertDate(DateTimeConverter convertDate) { convertDate.setPattern("EEEEEEEE, MMM dd, yyyy"); this.convertDate = convertDate; }
Because the converter is bound to a managed bean property, the managed bean property can modify the attributes of the converter or add new functionality to it. In the case of the preceding example, the property sets the date pattern that the converter uses to parse the user's input into a Date
object.
The managed bean properties that are bound to validator or listener implementations are written in the same way and have the same general purpose.