Blogs

JSF has a simple Inversion-of-Control (IoC) container called the JSF Managed Bean Facility (MBF). Although it has a verbose XML syntax, and is not as robust as the Spring BeanFactory, PicoContainer, or the JBoss Microcontainer, the MBF does have the basics of an IoC container, and offers features like dependency injection.

When a POJO is managed by the JSF MBF, it is typically referred to as a managed-bean. But if you're going to create a maintainable JSF webapp/portlet, it is necessary to distinguish between different kinds of managed-beans. This practice will also preserve the clean separation of concerns that JSF provides by implementing the Model-View-Controller (MVC) design pattern:

Now... One of the main benefits in making fine distinctions like this is loose coupling. What's that you ask? Well let's first take a look at an example of tight coupling, where MVC concerns can be smashed/confused into a single managed-bean:

public class ModelAndBackingAndControllerBean {

	private String fullName; // model-bean property
	private boolean privacyRendered; // backing-bean property

	// model-bean getter
	public String getFullName() {
		return fullName;
	}
	
	// model-bean setter
	public void setFullName(String fullName) {
		this.fullName = fullName;
	}

	// backing-bean getter
	public boolean isPrivacyRendered() {
		return privacyRendered;
	}

	// backing-bean setter
	public void setPrivacyRendered(boolean privacyRendered) {
		this.privacyRendered = privacyRendered;
	}

	// backing-bean actionListener for UI support logic
	public void togglePrivacySection(ActionEvent actionEvent) {
		privacyRendered = !privacyRendered;
	}

	// controller-bean business logic
	public String submit() {
		System.out.println("fullName=" + fullName);
		return "success";
	}
}

The problem here is that the bean would have to be kept in session scope because of the model-bean property. Additionally, what if we wanted to do some unit testing with mock model data? Can't do it. So in order to fix these problems, and to promote loose coupling, we would have three separate Java classes:

public class ModelBean {

	private String fullName;

	public void setFullName(String fullName) {
		this.fullName = fullName;
	}

	public String getFullName() {
		return fullName;
	}
}

public class BackingBean {

	private boolean privacyRendered;

	public void setPrivacyRendered(boolean privacyRendered) {
		this.privacyRendered = privacyRendered;
	}

	public boolean isPrivacyRendered() {
		return privacyRendered;
	}

	public void togglePrivacySection(ActionEvent actionEvent) {
		privacyRendered = !privacyRendered;
	}

}

public class ControllerBean {

	private ModelBean modelBean;
	
	public ModelBean getModelBean() {
		return modelBean;
	}

	public void setModelBean(ModelBean modelBean) {
		// Dependency injected from the JSF managed-bean facility
		this.modelBean = modelBean;
	}

	public String submit() {
    	System.out.println("fullName=" + getModelBean().getFullName());
        return "success";
    }

}

Now that the beans are found in different classes, they can all be kept in their appropriate scopes. The model-bean can be kept in session scope, and the backing-bean and controller-bean can be kept in request scope, thus saving memory resources on the server.

Finally, we can use the dependency injection features of the JSF MBF in order to inject the model-bean into the controller-bean. This can be seen in the following WEB-INF/faces-config.xml example, where the #{modelBean} Expression Language (EL) binding is used:

<?xml version="1.0" encoding="UTF-8"?>
<faces-config xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-facesconfig_1_2.xsd"
	version="1.2">
	<managed-bean>
		<managed-bean-name>modelBean</managed-bean-name>
		<managed-bean-class>myproject.ModelBean</managed-bean-class>
		<managed-bean-scope>session</managed-bean-scope>
	</managed-bean>
	<managed-bean>
		<managed-bean-name>backingBean</managed-bean-name>
		<managed-bean-class>myproject.BackingBean</managed-bean-class>
		<managed-bean-scope>request</managed-bean-scope>
	</managed-bean>
	<managed-bean>
		<managed-bean-name>controllerBean</managed-bean-name>
		<managed-bean-class>myproject.ControllerBean</managed-bean-class>
		<managed-bean-scope>request</managed-bean-scope>
		<managed-property>
			<property-name>modelBean</property-name>
			<value>#{modelBean}</value>
		</managed-property>
	</managed-bean>
</faces-config>