IT. Expert System.

Java Enterprise Edition (EE)

Instance


javax.enterprise.inject
Interface Instance<T>

Type Parameters:
T - the required bean type
All Superinterfaces:
java.lang.Iterable<T>, Provider<T>
public interface Instance<T>
extends java.lang.Iterable<T>, Provider<T>

Allows the application to dynamically obtain instances of beans with a specified combination of required type and qualifiers.

In certain situations, injection is not the most convenient way to obtain a contextual reference. For example, it may not be used when:

  • the bean type or qualifiers vary dynamically at runtime, or
  • depending upon the deployment, there may be no bean which satisfies the type and qualifiers, or
  • we would like to iterate over all beans of a certain type.

In these situations, an instance of the Instance may be injected:

 @Inject Instance<PaymentProcessor> paymentProcessor;
 

Any combination of qualifiers may be specified at the injection point:

 @Inject @PayBy(CHEQUE) Instance<PaymentProcessor> chequePaymentProcessor;
 

Or, the @Any qualifier may be used, allowing the application to specify qualifiers dynamically:

 @Inject @Any Instance<PaymentProcessor> anyPaymentProcessor;
 

Finally, the @New qualifier may be used, allowing the application to obtain a @New qualified bean:

 @Inject @New(ChequePaymentProcessor.class) 
 Instance<PaymentProcessor> chequePaymentProcessor;
 

For an injected Instance:

  • the required type is the type parameter specified at the injection point, and
  • the required qualifiers are the qualifiers specified at the injection point.

The inherited Provider.get() method returns a contextual references for the unique bean that matches the required type and required qualifiers and is eligible for injection into the class into which the parent Instance was injected, or throws an UnsatisfiedResolutionException or AmbiguousResolutionException.

PaymentProcessor pp = chequePaymentProcessor.get();

The inherited Iterable.iterator() method returns an iterator over contextual references for beans that match the required type and required qualifiers and are eligible for injection into the class into which the parent Instance was injected.

for (PaymentProcessor pp: anyPaymentProcessor) pp.test();

Author:
Gavin King
See Also:
Provider.get(), Iterable.iterator(), AnnotationLiteral, TypeLiteral

Method Summary
 boolean isAmbiguous()
          Determines if there is more than one bean that matches the required type and qualifiers and is eligible for injection into the class into which the parent Instance was injected.
 boolean isUnsatisfied()
          Determines if there is no bean that matches the required type and qualifiers and is eligible for injection into the class into which the parent Instance was injected.
 Instance<T> select(java.lang.annotation.Annotation... qualifiers)
          Obtains a child Instance for the given additional required qualifiers.
<U extends T>
Instance<U>
select(java.lang.Class<U> subtype, java.lang.annotation.Annotation... qualifiers)
          Obtains a child Instance for the given required type and additional required qualifiers.
<U extends T>
Instance<U>
select(TypeLiteral<U> subtype, java.lang.annotation.Annotation... qualifiers)
          Obtains a child Instance for the given required type and additional required qualifiers.
 
Methods inherited from interface java.lang.Iterable
iterator
 
Methods inherited from interface javax.inject.Provider
get
 

Method Detail

select

Instance<T> select(java.lang.annotation.Annotation... qualifiers)

Obtains a child Instance for the given additional required qualifiers.

Parameters:
qualifiers - the additional required qualifiers
Returns:
the child Instance
Throws:
java.lang.IllegalArgumentException - if passed two instances of the same qualifier type, or an instance of an annotation that is not a qualifier type

select

<U extends T> Instance<U> select(java.lang.Class<U> subtype,
                                 java.lang.annotation.Annotation... qualifiers)

Obtains a child Instance for the given required type and additional required qualifiers.

Type Parameters:
U - the required type
Parameters:
subtype - a Class representing the required type
qualifiers - the additional required qualifiers
Returns:
the child Instance
Throws:
java.lang.IllegalArgumentException - if passed two instances of the same qualifier type, or an instance of an annotation that is not a qualifier type

select

<U extends T> Instance<U> select(TypeLiteral<U> subtype,
                                 java.lang.annotation.Annotation... qualifiers)

Obtains a child Instance for the given required type and additional required qualifiers.

Type Parameters:
U - the required type
Parameters:
subtype - a TypeLiteral representing the required type
qualifiers - the additional required qualifiers
Returns:
the child Instance
Throws:
java.lang.IllegalArgumentException - if passed two instances of the same qualifier type, or an instance of an annotation that is not a qualifier type

isUnsatisfied

boolean isUnsatisfied()

Determines if there is no bean that matches the required type and qualifiers and is eligible for injection into the class into which the parent Instance was injected.

Returns:
true if there is no bean that matches the required type and qualifiers and is eligible for injection into the class into which the parent Instance was injected, or false otherwise.

isAmbiguous

boolean isAmbiguous()

Determines if there is more than one bean that matches the required type and qualifiers and is eligible for injection into the class into which the parent Instance was injected.

Returns:
true if there is more than one bean that matches the required type and qualifiers and is eligible for injection into the class into which the parent Instance was injected, or false otherwise.


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