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From conflue...@apache.org
Subject [CONF] Apache Felix > Apache Felix Dependency Manager - Using Annotations - Components
Date Wed, 08 Sep 2010 20:51:00 GMT
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    <h2><a href="https://cwiki.apache.org/confluence/display/FELIX/Apache+Felix+Dependency+Manager+-+Using+Annotations+-+Components">Apache
Felix Dependency Manager - Using Annotations - Components</a></h2>
    <h4>Page <b>edited</b> by             <a href="https://cwiki.apache.org/confluence/display/~pderop">Pierre
De Rop</a>
    </h4>
        <br/>
                         <h4>Changes (1)</h4>
                                 
    
<div id="page-diffs">
            <table class="diff" cellpadding="0" cellspacing="0">
            <tr><td class="diff-snipped" >...<br></td></tr>
            <tr><td class="diff-unchanged" >* *Aspect Service*: A service that
provides a non-functional aspect on top of an existing service. In aspect oriented programming,
an aspect, or interceptor can sit between a client and another target service used by the
client. An Aspect Service first tracks a target service and is created once the target service
is detected. Then the Aspect Service is provided, but with a higher  ranking, and the client
is transparently updated with the aspect. Aspects can be chained and may apply to the same
target service (and in this case, the ranking of the Aspect service is used to chain aspects
in  the proper order). <br> <br></td></tr>
            <tr><td class="diff-changed-lines" >* *Adapter Service*: <span
class="diff-deleted-words"style="color:#999;background-color:#fdd;text-decoration:line-through;">component:</span>
A Service that adapts another existing service into a new one. Like with aspects, sometimes
you want to create adapters for certain services, which add certain behavior that results
in the publication of (in this case) a different service. Adapters can dynamically be added
and removed and allow you to keep your basic services implementations clean and simple, adding
extra features on top of them in a modular way. <br></td></tr>
            <tr><td class="diff-unchanged" > <br>Now we have introduced
the different types of components, here is the list of annotations, allowing to declare DependencyManager
service components: <br></td></tr>
            <tr><td class="diff-snipped" >...<br></td></tr>
        </table>
</div>                            <h4>Full Content</h4>
                    <div class="notificationGreySide">
        <h1><a name="ApacheFelixDependencyManager-UsingAnnotations-Components-AnnotationsWritingComponents"></a>Annotations
- Writing Components</h1>


<h2><a name="ApacheFelixDependencyManager-UsingAnnotations-Components-ComponentTypes"></a>Component
Types</h2>

<p>Before diving into all annotations, we must first introduce the  different types
of components DependencyManager is supporting. In  Dependency Manager, you may use the following
types of components,  depending on what you need:</p>


<ul>
	<li><b>Component</b>: Components are the main building blocks for OSGi
applications. They can publish themselves as a service, and/or they can have dependencies.
These dependencies will influence their life cycle as component will only be activated when
all required dependencies are available.</li>
</ul>


<ul>
	<li><b>Aspect Service</b>: A service that provides a non-functional aspect
on top of an existing service. In aspect oriented programming, an aspect, or interceptor can
sit between a client and another target service used by the client. An Aspect Service first
tracks a target service and is created once the target service is detected. Then the Aspect
Service is provided, but with a higher  ranking, and the client is transparently updated with
the aspect. Aspects can be chained and may apply to the same target service (and in this case,
the ranking of the Aspect service is used to chain aspects in  the proper order).</li>
</ul>


<ul>
	<li><b>Adapter Service</b>: A Service that adapts another existing service
into a new one. Like with aspects, sometimes you want to create adapters for certain services,
which add certain behavior that results in the publication of (in this case) a different service.
Adapters can dynamically be added and removed and allow you to keep your basic services implementations
clean and simple, adding extra features on top of them in a modular way.</li>
</ul>


<p>Now we have introduced the different types of components, here is the list of annotations,
allowing to declare DependencyManager service components:</p>

<ul>
	<li><b>@Component:</b> for declaring a Component that eventually publishes
a singleton OSGi service as long as its dependencies are resolved.</li>
	<li><b>@AspectService</b>: provides a non-functional aspect on top of an
existing service.</li>
	<li><b>@AdapterService</b>: creates an OSGi service that adapts another
existing service into a new interface.</li>
	<li><b>@BundleAdapterService</b>: creates an OSGi service a service on
top of a given bundle.</li>
	<li><b>@ResourceAdapterService</b>: creates an OSGi service on top of a
specific Resource.</li>
	<li><b>@FactoryConfigurationAdapterService</b>: creates an OSGi service
from ConfigAdmin, using a factoryPid, and a ManagedServiceFactory.</li>
</ul>


<h2><a name="ApacheFelixDependencyManager-UsingAnnotations-Components-@Component"></a>@Component</h2>

<p>This annotation annotates an implementation class that optionally publishes an OSGi
service, and optionally has some dependencies, with a managed lifecycle. The annotation has
the following attributes:</p>

<ul>
	<li><b>provides</b>: By default, the component is registered into the OSGi
registry under all directly implemented interfaces. If no interfaces are implemented, then
the component is not registered, but it still has a managed lifecycle, and may have some dependencies.
If you need to  explicitly define the list of interfaces (or classes) under which the  component
must be registered in the OSGi registry, then use the <em>provides</em> attribute.
You can also set this property to an empty array of classes  if you don't want at all your
component to be exposed in the OSGi  registry (even if it implements some interfaces).</li>
</ul>


<ul>
	<li><b>properties</b>: enumerates the list of properties that are part
 of the Service exposed by the component in the OSGi Registry. Each  property is defined using
the @Property annotation, which represents a  key/value pair. When a value is actually an
array of strings, then the <em>values</em> attribute of the @Property annotation
can be used. This attribute  is not the only way to specify OSGi Service properties (see Setting
 Service properties in the lifecycle section).</li>
</ul>


<ul>
	<li><b>factoryMethod</b>: may match a static method name from the annotated
class which can be used to instantiate the component instance. Normally, DependencyManager
instantiates the component using its class name, and with the default constructor of the class,
but there are some cases where it is required to take control of  how the component is created.
For instance, this method may be used to create the component as a dynamic proxy ...</li>
</ul>


<ul>
	<li><b>factorySet</b>: The component factory ID. By default, a Service
component is automatically instantiated as a singleton when the bundle is started, and when
all required dependencies are satisfied. But when a component must be created, configured,
or disposed dynamically, and when multiple instances of the same component are needed, a factorySet
should  be used. When you use this attribute, a java.util.Set&lt;Dictionary&gt;  object
is registered into the OSGi regitry, with a specific <b><em>dm.factory.name</em></b>
property matching the ID you specify in the attribute. This Set&lt;Dictionary&gt;
will act as a Factory API, and another component may define a dependency on this Set and add
some configuration dictionaries in  it, in order to fire some component instantiation/activation.
There is one component instantiated per added dictionary, which is passed to component instances
via a configurable callback method (using the <b><em>factoryConfigure</em></b>
attribute). All public properties will be propagated  along with eventual published service.
A public property is a property  which does not start with a dot ("."). Properties starting
with a dot are considered private to the component, and won't be propagated to published service.
This model is actually similar to the Declarative Service "Component Factories" concept, except
that you don't have a dependency on a specific API, but rather on a basic jdk class  (java.util.Set&lt;Dictionary&gt;).
Notice that, unlike in Declarative Service, the component factory is&nbsp; provided once
the component bundle is started, even if required dependencies are not satisfied. This is
useful when the component want  to dynamically configure its dependency filters. So, to summarize:
	<ul>
		<li>Each time a new Dictionary is added into the Set, then a new instance of the annotated
component will be instantiated, and this dictionary is passed to the component callback specified
with the factoryConfigure attribute.</li>
		<li>Each time an existing Dictionary is re-added into the Set, then the corresponding
component instance is updated, and the updated dictionary is also passed to the callback specified
in the factoryConfigure attribute.</li>
		<li>Each time an existing Dictionary is removed from the Set, then the  corresponding
component instance will be stopped and destroyed.</li>
	</ul>
	</li>
</ul>


<ul>
	<li><b>factoryConfigure</b>: Sets the "configure" callback method name
to be called with the factory configuration. This attribute only makes sense if the factorySet()
attribute is used. If specified, then this attribute references a component callback method,
which is called for providing the configuration supplied by the factory that instantiated
this Service. The current Service properties will be also updated with all public properties
(which don't start with a dot).</li>
</ul>


<p>Usage example:</p>

<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
<pre class="code-java">
 /**
   * This component will be activated once the bundle is started and when all required dependencies
   * are available.
   */
 @Component
 class X <span class="code-keyword">implements</span> Z {
     @ConfigurationDependency(pid=<span class="code-quote">"MyPid"</span>)
     void configure(Dictionary conf) {
          <span class="code-comment">// Configure or reconfigure our service.
</span>     }

     @Start
     void start() {
         <span class="code-comment">// Our Service is starting and is about to be registered
in the OSGi registry as a Z service.
</span>     }

     <span class="code-keyword">public</span> void doService() {
         <span class="code-comment">// ...
</span>     }
 }

</pre>
</div></div>
<p>Example using a factorySet, where the X component is instantiated/updated/disposed
by another Y component:</p>


<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
<pre class="code-java">
  @Component(factorySet=<span class="code-quote">"MyComponentFactory"</span>,
factoryConfigure=<span class="code-quote">"configure"</span>)
  class X <span class="code-keyword">implements</span> Z {
      void configure(Dictionary conf) {
          <span class="code-comment">// Configure or reconfigure our component. The
conf is provided by the factory,
</span>          <span class="code-comment">// and all <span class="code-keyword">public</span>
properties (which don't start with a dot) are propagated with the
</span>          <span class="code-comment">// Service properties eventually specified
in the properties annotation attribute.
</span>      }

      @ServiceDependency
      void bindOtherService(OtherService other) {
          <span class="code-comment">// store <span class="code-keyword">this</span>
require dependency
</span>      }

      @Start
      void start() {
          <span class="code-comment">// Our component is starting and is about to be
registered in the OSGi registry as a Z service.
</span>      }

      <span class="code-keyword">public</span> void doService() {
          <span class="code-comment">// ... part of Z <span class="code-keyword">interface</span>
</span>      }
  }

  /**
    * This class will instantiate some X component instances
    */
  @Component
  class Y {
      @ServiceDependency(filter=<span class="code-quote">"(dm.factory.name=MyComponentFactory)"</span>)
      Set&lt;Dictionary&gt; _XFactory; <span class="code-comment">// This Set
acts as a Factory API <span class="code-keyword">for</span> creating X component
instances.
</span>
      @Start
      void start() {
          <span class="code-comment">// Instantiate a X component instance
</span>          Dictionary x1 = <span class="code-keyword">new</span> Hashtable()
{{ put(<span class="code-quote">"foo"</span>, <span class="code-quote">"bar1"</span>);
}};
          _XFactory.add(x1);

          <span class="code-comment">// Instantiate another X component instance
</span>          Dictionary x2 = <span class="code-keyword">new</span> Hashtable()
{{ put(<span class="code-quote">"foo"</span>, <span class="code-quote">"bar2"</span>);
}};
          _XFactory.add(x2);

          <span class="code-comment">// Update the first X component instance
</span>          x1.put(<span class="code-quote">"foo"</span>, <span
class="code-quote">"bar1_modified"</span>);
          _XFactory.add(x1);

          <span class="code-comment">// Destroy all components (Notice that invoking
_XFactory.clear() also destroys every X instances)
</span>          _XFactory.remove(x1);
          _XFactory.remove(x2);
      }
  }
</pre>
</div></div>

<h2><a name="ApacheFelixDependencyManager-UsingAnnotations-Components-@AspectService"></a>@AspectService</h2>


<h2><a name="ApacheFelixDependencyManager-UsingAnnotations-Components-@AdapterService"></a>@AdapterService</h2>


<h2><a name="ApacheFelixDependencyManager-UsingAnnotations-Components-@BundleAdapterService"></a>@BundleAdapterService</h2>


<h2><a name="ApacheFelixDependencyManager-UsingAnnotations-Components-@ResourceAdapterService"></a>@ResourceAdapterService</h2>


<h2><a name="ApacheFelixDependencyManager-UsingAnnotations-Components-@FactoryConfigurationAdapterService"></a>@FactoryConfigurationAdapterService</h2>
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