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Java Enterprise Edition (EE)

Context


Package javax.enterprise.context

Annotations and interfaces relating to scopes and contexts.

See:
          Description

Interface Summary
Conversation Allows the application to manage the conversation context by marking the current conversation as transient or long-running, specifying a conversation identifier, or setting the conversation timeout.
 

Exception Summary
BusyConversationException Indicates that the container has rejected a request because a concurrent request is associated with the same conversation context.
ContextException Indicates a problem relating to context management.
ContextNotActiveException Indicates that a context is not active.
NonexistentConversationException Indicates that the conversation context could not be restored.
 

Annotation Types Summary
ApplicationScoped Specifies that a bean is application scoped.
ConversationScoped Specifies that a bean is conversation scoped.
Dependent Specifies that a bean belongs to the dependent pseudo-scope.
NormalScope Specifies that an annotation type is a normal scope type.
RequestScoped Specifies that a bean is request scoped.
SessionScoped Specifies that a bean is session scoped.
 

Package javax.enterprise.context Description

Annotations and interfaces relating to scopes and contexts.

A scope type is a Java annotation annotated @Scope or @NormalScope. The scope of a bean determines the lifecycle and visibility of its instances. In particular, the scope determines:

  • When a new instance of the bean is created
  • When an existing instance of the bean is destroyed
  • Which injected references refer to any instance of the bean

Built-in scopes

The following built-in scopes are provided: @Dependent, @RequestScoped, @ConversationScoped, @SessionScoped, @ApplicationScoped, @Singleton.

The container provides an implementation of the Context interface for each of the built-in scopes. The built-in request, session, and application contexts support servlet, web service and EJB invocations. The built-in conversation context supports JSF requests.

For other kinds of invocations, a portable extension may define a custom context object for any or all of the built-in scopes. For example, a third-party web application framework might provide a conversation context object for the built-in conversation scope.

The context associated with a built-in scope propagates across local, synchronous Java method calls, including invocation of EJB local business methods. The context does not propagate across remote method invocations or to asynchronous processes such as JMS message listeners or EJB timer service timeouts.

Normal scopes and pseudo-scopes

Most scopes are normal scopes. Normal scopes are declared using @NormalScope. If a bean has a normal scope, every client executing in a certain thread sees the same contextual instance of the bean. This instance is called the current instance of the bean. The operation Context.get(Contextual) of the context object for a normal scope type always returns the current instance of the given bean.

Any scope that is not a normal scope is called a pseudo-scope. Pseudo-scopes are declared using @Scope. The concept of a current instance is not well-defined in the case of a pseudo-scope. Different clients executing in the same thread may see different instances of the bean. In the extreme case of the @Dependent pseudo-scope, every client has its own private instance of the bean.

All built-in scopes are normal scopes, except for the @Dependent and @Singleton pseudo-scopes.

Contextual and injected reference validity

A reference to a bean obtained from the container via programmatic lookup is called a contextual reference. A contextual reference for a bean with a normal scope refers to the current instance of the bean. A contextual reference for a bean are valid only for a certain period of time. The application should not invoke a method of an invalid reference.

The validity of a contextual reference for a bean depends upon whether the scope of the bean is a normal scope or a pseudo-scope:

  • Any reference to a bean with a normal scope is valid as long as the application maintains a hard reference to it. However, it may only be invoked when the context associated with the normal scope is active. If it is invoked when the context is inactive, a ContextNotActiveException is thrown by the container.
  • Any reference to a bean with a pseudo-scope is valid until the bean instance to which it refers is destroyed. It may be invoked even if the context associated with the pseudo-scope is not active. If the application invokes a method of a reference to an instance that has already been destroyed, the behavior is undefined.

A reference to a bean obtained from the container via dependency injection is a special kind of contextual reference, called an injected reference. Additional restrictions apply to the validity of an injected reference:

  • A reference to a bean injected into a field, bean constructor or initializer method is only valid until the object into which it was injected is destroyed.
  • A reference to a bean injected into a producer method is only valid until the producer method bean instance that is being produced is destroyed.
  • A reference to a bean injected into a disposer method or observer method is only valid until the invocation of the method completes.

See Also:
javax.enterprise.inject


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