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h1. iPOJO {{Arch}} command
_Architecture introspection is required when the system doesn't work as expected. In this case, having a quick access to instances states and interconnection is a stringent requirement. The {{arch}} command allows getting these data from the Felix Shell and from the Equinox shell._

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h2. Download
The Felix command is available from the [download] page and in the {{arch}} folder of the iPOJO trunk [http://svn.apache.org/repos/asf/felix/trunk/ipojo/arch/|http://svn.apache.org/viewvc/felix/trunk/ipojo/arch].

The Equinox command sources are available [http://svn.apache.org/repos/asf/felix/sandbox/clement/ipojo-utils/arch-equinox/|http://svn.apache.org/viewvc/felix/sandbox/clement/ipojo-utils/arch-equinox/]. To compile sources, just launch the {{mvn clean install

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arch => displays instances name & state (equivalent to arch \-instances)
arch -instance $instance_name => displays complete information about the instance $instance_name
arch -factories => display the list of available factories
arch -factory $factory_name => display complete information about the factory $factory_name
arch -handlers => list available handlers

On the first line, are displayed the component type (i.e. factory), the instance state ({{valid}} or {{invalid}}), the bundle from which the instance is created, and the instance name.

Then, the information is organized handler by handler (a piece of container). For each handler plugged on the instance can participate to the instance architecture. For each handler its name (such as {{ org.apache.felix.ipojo.handlers.dependency.DependencyHandler}} for iPOJO service dependencies, {{ org.apache.felix.ipojo.handlers.providedservice.ProvidedServiceHandler}} for iPOJO service providing...) and the state (either {{valid}} or {{invalid}} are displayed. Remember that an instance is valid only and only if all plugged handlers are valid.

 
The {{org.apache.felix.ipojo.handlers.dependency.DependencyHandler}} provides data on service dependencies and more precisely on the state of service dependencies. In the previous example, the dependency on {{ spell.services.DictionaryService}} was resolved. On the following example, the same dependency is no more resolved:

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instance component.type="spell.checker.SpellCheck" state="invalid" bundle="8" name="spell.checker.SpellCheck-0"
	handler state="invalid" name="org.apache.felix.ipojo.handlers.dependency.DependencyHandler"
		requires optional="false" aggregate="false" state="unresolved" binding-policy="dynamic" specification="spell.services.DictionaryService"
	handler state="valid" name="org.apache.felix.ipojo.handlers.providedservice.ProvidedServiceHandler"
		provides state="unregistered" 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" 
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Notes that, the instance also becomes invalid and that the provided service is unregistered.

If the provider comes back, the dependency becomes {{resolved}} and the instance becomes

You can also check created POJO objects (implementation class objet). Here, only one object was created ({{spell.checker.SpellCheck@e222eb}}).
h2.

 List available factories

To list available factories (i.e. component types), launch the {{arch -factories}} command:

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-> arch -factories
Factory spell.checker.SpellCheck (VALID)
Factory spell.gui.SpellCheckerGui (VALID)
Factory spell.english.EnglishDictionary (VALID)
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For each available (public) factories,the name and the sate are displayed. A factory is valid if and only if all required handlers are available. To get more information on a factory launch the {{arch -factory factory_name}} command:

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factory implementation-class="spell.english.EnglishDictionary" state="valid" bundle="7" name="spell.english.EnglishDictionary"
	provides specification="spell.services.DictionaryService"
	missinghandlers list="[]"
	requiredhandlers list="[org.apache.felix.ipojo:provides, org.apache.felix.ipojo:architecture]"
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On the first line, you get the implementation class of the type, the state of the factory, the bundle declaring the type and the name of the type. Then you get the list of required and missing handlers.
h2.

 List available handlers

You can also list available handlers with the {{arch -handlers}} command.

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-> arch -handlers
Handler org.apache.felix.ipojo:controller (VALID)
Handler org.apache.felix.ipojo:callback (VALID)
Handler org.apache.felix.ipojo:requires (VALID)
Handler org.apache.felix.ipojo:provides (VALID)
Handler org.apache.felix.ipojo:properties (VALID)
Handler org.apache.felix.ipojo:architecture (VALID)
Handler org.apache.felix.ipojo.handler.whiteboard:wbp (VALID)
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Handlers with the {{org.apache.felix.ipojo}} namespace (section before {{:}}) are core handlers (provided by the iPOJO bundle). Others are external handlers (provided by others bundles).

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