Introspection and Architecture¶
The architecture feature allows obtaining an architectural / component view of your systems. It exposes a snapshot of the present instances & factories, the state of these instances... Moreover; iPOJO defines an 'arch' command displaying this architecture in Felix. You need to install the arch command.
Reflection on component instances¶
The architecture feature does "reflection" on the iPOJO containers. It gathers information about the component (state, class name ...), requirement (state, multiple, optional ...), provided services (state, properties) ... Each handler can participate to the architecture. This information allows you to know why an instance does not start, or why the component does not publish / provide a service.
Metadata¶
The architecture (i.e. instance introspection) is activated by default. To disable it, you need to add an attribute architecture="false"
to the component element:
<component classname="org.apache.felix.ipojo.hello.impl.HelloServiceImpl" architecture="false">
By default, the architecture feature is enabled.
The "arch" command¶
The Gogo commands are the following:
ipojo:instances
(or justinstances
) lists the instances and stateipojo:instance $instance_name
(or justinstance $instance_name
) displays the complete information about the specified $instance_nameipojo:factories
(or justfactories
) lists the available public factoriesipojo:factory $factory_name
(or justfactory $factory_name
) displays complete information about the factory $factory_nameipojo:handlers
(or justhandlers
lists available handlers
For example:
$ instances Instance ArchCommand -> valid Instance spell.english.EnglishDictionary-0 -> valid Instance spell.checker.SpellCheck-0 -> valid Instance spell.gui.SpellCheckerGui-0 -> valid $ instance spell.checker.SpellCheck-0 instance component.type="spell.checker.SpellCheck" state="valid" bundle="8" name="spell.checker.SpellCheck-0" handler state="valid" name="org.apache.felix.ipojo.handlers.dependency.DependencyHandler" requires optional="false" aggregate="false" state="resolved" binding-policy="dynamic" specification="spell.services.DictionaryService" handler state="valid" name="org.apache.felix.ipojo.handlers.providedservice.ProvidedServiceHandler" provides service.id="36" state="registered" specifications="[spell.services.SpellChecker]" property value="spell.checker.SpellCheck" name="factory.name" property value="spell.checker.SpellCheck-0" name="instance.name" handler state="valid" name="org.apache.felix.ipojo.handlers.architecture.ArchitectureHandler"
More info on the arch
command are available here.
Technical information¶
In fact, when a component enables the architecture introspection, its container exposes an Architecture
service. Any architecture requester can obtain information about the instance. For example, the arch command requests all the architecture services and prints the information.