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vineri, 27 noiembrie 2015

JSF Scopes Tutorial - CDI Dependent Pseudo-Scope

The CDI dependent pseudo-scope is the default CDI scope for a 
bean which does not explicitly declare a scope type
This is the default scope of a CDI bean (@Named) when nothing is specified. In this case, an object exists to serve exactly one bean and has the same life cycle as that bean; an instance of a dependent scoped bean is not shared between different users or different points of injection. It can also be explicitly specified by annotating the bean with the @Dependent annotation and importing javax.enterprise.context.Dependent. This scope is available only in CDI and is a non-contextual scope. All CDI scopes, except this one (and @Singleton), are known as normal scopes.

A normal scope is a scope annotated with @NormalScope. These are contextual scopes having a client proxy. Contextual scopes implements Contextual interface which provides operations to create and destroy contextual instances of a certain type (create() and destroy()). During create() and destroy() the Contextual interface uses the CreationalContext operations, push() and release().Contextual instances with a particular scope of any contextual type are obtained via Context interface operations (e.g.get()).

A pseudo-scope is a scope annotated with @Scope. So, dependent scope is a pseudo-scope. This is a non-contextual scope with no client proxy.  A bean annotated with @Dependent doesn't share injected instances between multiple injection points and the injected bean instance is bound to the lifecycle of the container newly created object. If the bean receives a producer field/method, disposer/observer method invocation then any instance of that bean is available for that invocation only. Moreover, with the exception of the container lifecycle events and observers, any instance of the bean that receives a producer field/method, disposer/observer method invocation is available for that invocation only.

For a  @Dependent bean, the bean constructor and a method annotated with @PostConstruct will be called for each request. Actually, they might be called multiple times during the same request, if the bean is used in several EL expressions. Initially, there is one instance of the bean, and this instance is reused if the bean EL name appears multiple times in the EL expression, but is not reused in the case of another EL expression or in the case of a re-evaluation of the same EL expression.

Check out the below simple example (in constructor, count is initialized with 5; in @PostConstruct is increased by 1; in increaseCount() action method is increased with 1):

public class CountBean implements Serializable {

 private static final Logger LOG = Logger.getLogger(CountBean.class.getName());

 private int count;

 public CountBean() {
  count = 5;
  LOG.log(Level.INFO, "CountBean Constructor! Current value: {0}", count);

 public void CountBean() {
  LOG.log(Level.INFO, "CountBean PostConstruct! Current value: {0}", count);

 public void increaseCount() {
  LOG.log(Level.INFO, "Current value: {0}", count);

 public int getCount() {
  return count;

 public void setCount(int count) {
  this.count = count;

  <h:commandButton value="Count" action="#{countBean.increaseCount()}"/>
 Current value: #{countBean.count}       

Now, if we press the Count button multiple times we can notice that the EL is re-evaluated during the same request:
The complete example is available here.

CDI: For CDI managed beans, injection is accomplished via @Inject. For example:

JSF & CDI mixed: CDI can be injected in JSF (vice versa is not true!)

See you in the next post about JSF none scope.

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