Package org.qi4j.api.service.qualifier

Service Qualifiers.

See:
Description

Interface Summary

AnnotationQualifier<QUALIFIER extends Annotation>

Constructs a Specification for a given qualifier annotation

Class Summary

Active.ActiveQualifier	Active Annotation Qualifier.
Available.AvailableQualifier	Available Annotation Qualifier.
HasMetaInfo.HasMetaInfoQualifier	HasMetaInfo Annotation Qualifier.
IdentifiedBy.IdentifiedByQualifier	IdentifiedBy Annotation Qualifier.
ServiceQualifier	This class helps you select a particular service from a list.
ServiceTags	Use this as metainfo about a Service to specify tags.
Tagged.TaggedQualifier	Tagged Annotation Qualifier.

Annotation Types Summary

Active	Filter services based on whether they are active or not.
Available	Filter services based on whether they are available or not.
HasMetaInfo	Filter services based on Meta Info being declared on the Service.
IdentifiedBy	Filter services based on identity.
Qualifier	Annotation used to declare Qualifiers annotations.
Tagged	Filter services based on tags.

Package org.qi4j.api.service.qualifier Description

Service Qualifiers.

The @Service injection is only able to specify the type of the service to be injected. If any other type of qualification has to be done it has to be done manually but for common cases it's more convenient to use annotations to do this filtering. This package contains annotations to perform this qualification.

Example:

@Service @Tagged( "sometag" ) MyService service;

This will only inject instances of MyService that have been tagged with "sometag". If none exist an exception will occur at injection time since it is not optional.

It also works with iterables:

@Service @Tagged( "sometag" ) Iterable<MyService> services;

The qualification will be evaluated upon each call to iterator(), and since the qualifier has access to a ServiceReference, which contains the isActive() method, it can even provide some dynamicity.

@Service @Active Iterable<SomeImportedService> importedServices;

Let's say these SomeImportedService are only sometimes available. Then whenever iterator() is called the Active tag can kick in and filter out those whose ServiceReference.isActive() returns false.

Standard ones defined in the API are:

• Active
• Available
• HasMetaInfo
• IdentifiedBy
• Tagged

See tests and API for more examples, and how to implement your own qualifiers.