Java Platform, Enterprise Edition (Java EE) 8 The Java EE Tutorial

## 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.

### 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
`UIInput`, `UIOutput`, `UISelectItem`, `UISelectOne` | Any of the basic primitive and numeric types or any Java programming language object type for which an appropriate `javax.faces.convert.Converter` implementation is available
`UIData` | `array` of beans, `List` of beans, single bean, `java.sql.ResultSet`, `javax.servlet.jsp.jstl.sql.Result`, `javax.sql.RowSet`
`UISelectBoolean` | `boolean` or `Boolean`
`UISelectItems` | `java.lang.String`, `Collection`, `Array`, `Map`
`UISelectMany` | `array` or `List`, although elements of the `array` or `List` can be any of the standard types

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.

#### 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;
    }

#### 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;
    }

The UIData component (and UIRepeat) supports the `Map` and `Iterable` interfaces, as well as custom types.

For UIData and UIRepeat, the supported types are:

- `null` (becomes empty list)

- `javax.faces.model.DataMode`

- `java.util.List`

- `java.lang.Object`[]

- `java.sql.ResultSet`

- `javax.servlet.jsp.jstl.sql.Result`

- `java.util.Collection`

- `java.lang.Iterable`

- `java.util.Map`

- `java.lang.Object` (becomes ScalarDataModel)

#### 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;
    }

#### 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.

#### 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.

#### 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;
    }

#### 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.

### 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.

### 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.

Copyright © 2017, Oracle and/or its affiliates. All rights reserved.