Initializing Managed Bean Properties

Sometimes you might want to create a bean that also references other managed beans so that you can construct a graph or a tree of beans. For example, suppose that you want to create a bean representing a customer’s information, including the mailing address and street address, each of which is also a bean. The following managed-bean declarations create a CustomerBean instance that has two AddressBean properties: one representing the mailing address, and the other representing the street address. This declaration results in a tree of beans with CustomerBean as its root and the two AddressBean objects as children.

<managed-bean>
    <managed-bean-name>customer</managed-bean-name>
    <managed-bean-class>
        com.mycompany.mybeans.CustomerBean
    </managed-bean-class>
    <managed-bean-scope> request </managed-bean-scope>
    <managed-property>
        <property-name>mailingAddress</property-name>
        <value>#{addressBean}</value>
    </managed-property>
    <managed-property>
        <property-name>streetAddress</property-name>
        <value>#{addressBean}</value>
    </managed-property>
    <managed-property>
        <property-name>customerType</property-name>
        <value>New</value>
    </managed-property>
</managed-bean>
<managed-bean>
    <managed-bean-name>addressBean</managed-bean-name>
    <managed-bean-class>
        com.mycompany.mybeans.AddressBean
    </managed-bean-class>
    <managed-bean-scope> none </managed-bean-scope>
    <managed-property>
        <property-name>street</property-name>
        <null-value/>
    <managed-property>
    ...
</managed-bean>

The first CustomerBean declaration (with the managed-bean-name of customer) creates a CustomerBean in request scope. This bean has two properties: mailingAddress and streetAddress. These properties use the value element to reference a bean named addressBean.

The second managed bean declaration defines an AddressBean but does not create it because its managed-bean-scope element defines a scope of none. Recall that a scope of none means that the bean is created only when something else references it. Because both the mailingAddress and the streetAddress properties reference addressBean using the value element, two instances of AddressBean are created when CustomerBean is created.

When you create an object that points to other objects, do not try to point to an object with a shorter life span because it might be impossible to recover that scope’s resources when it goes away. A session-scoped object, for example, cannot point to a request-scoped object. And objects with none scope have no effective life span managed by the framework, so they can point only to other none scoped objects. Table 14–2 outlines all of the allowed connections.

Be sure not allow cyclical references between objects. For example, neither of the AddressBean objects in the preceding example should point back to the CustomerBean object because CustomerBean already points to the AddressBean objects.