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Managed Bean Interdependence
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One of the most common criteria for IoC containers is that they be able to handle interdependencies between managed objects The JavaServer Faces Managed Bean Facility does not fall short in this regard Setting dependencies between managed beans can easily be done using the JSF expression language Consider the previous example where we declared a brand new moreSports managed bean from scratch that listed a new set of sports as moreSports This list can now be referred in another bean through an expression For example, you can add the values from the new list to the existing sportsInterests managed bean with the final result being a set of values from both lists
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<managed-bean> <managed-property> <property-name>sportsInterests</property-name> <list-entries> <value>Cycling</value> <value>Running</value> <value>Swimming</value> <value>Kayaking</value> <value>#{moreSports[0]}</value> <value>#{moreSports[1]}</value>
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Part I:
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The JavaServer Faces Framework
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<value>#{moreSports[2]}</value> </list-entries> </managed-property> </managed-bean>
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For a more general example of managed bean interdependency, consider a new custom class of type comjsfregregisterAddress that contains String properties for street, city and zipCode It can be registered as an independent managed bean using:
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<managed-bean> <managed-bean-name>addressBean</managed-bean-name> <managed-bean-class>comjsfregregisterAddress</managed-bean-class> <managed-bean-scope>none</managed-bean-scope> </managed-bean>
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Recall that a scope of none means that this bean is not initialized until requested by another managed bean Next, you could add two new properties homeAddress and shippingAddress of type comjsfregregisterAddress to the original UserBean You can then define these properties by using the following code:
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<managed-bean> <managed-bean-name>userBean</managed-bean-name> <managed-bean-class>comjsfregregisterUserBean</managed-bean-class> <managed-bean-scope>session</managed-bean-scope> <managed-property> <property-name>homeAddress</property-name> <value>#{addressBean}</value> </managed-property> <managed-property> <property-name>shippingAddress</property-name> <value>#{addressBean}</value> </managed-property> <managed-property> <property-name>firstName</property-name> </managed-property> </managed-bean>
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As a request is made to a page with an expression of #{userBeanhomeAddress}, a new instance of UserBean is created and stored in the session scope Its properties homeAddress and shippingAddress will also be initialized as well Subsequent postback operations could add values to the fields of the respective addresses of type AddressBean of the UserBean, using expressions that reference the address items:
<h:inputText value="#{userBeanhomeAddressstreet}"/>
The next question regarding managed bean interdependence is whether cyclical dependencies are possible with managed beans Although some other IoC containers can handle cyclical dependencies, this is not the case for JSF managed beans If two are made dependent on each other, a runtime error will occur
Setting Managed Properties Using EL
An important point to note is that in addition to offering the ability to establish inter-bean dependencies using EL, it is also possible to set managed properties to any value accessible
4:
Managed Beans and the JSF Expression Language
via EL For example, the implicit object param can be used in an EL expression to set a property This can be a handy trick that allows the application to assign a property based on an incoming Request parameter As an example, consider if the previous UserBean had a property, userid, also of type String It could be set as a managed property using a value from the implicit param object
<managed-property> <property-name>userid</property-name> <value>#{paramuserid}</value> </managed-property>
PART I PART I PART I
In your JSP you could value-bind this property to a UI component:
Userid entered:<h:inputText value="#{UserBeanuserid}"/>
To provide a value, of course, you would have to add the userid value as a request parameter:
http://host:port/yourapp/faces/yourpagejsp userid=cschalk
You can now see that it is possible to declare the entire initial state of your model tier using the managed bean facility This makes for a very powerful and flexible system
Controlling Managed Bean Life Spans
Similar to standard JSP, JavaServer Faces provides a way to define the scope of a managed bean instance by using a scope setting A scope defines the lifetime of a bean, and is similar to the concept of scope in the Java language In contrast to JSP, however, there is no page scope because managed beans have to exist and be accessible on postback, which is outside the scope of JSP As you have seen in previous managed bean examples, the <managedbean-scope> element of a managed bean defines how long the instance of the managed bean will survive The different managed bean scopes are described in Table 4-5
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