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From conflue...@apache.org
Subject [CONF] Apache Felix > Apache Felix Dependency Manager - Using Annotations - Components
Date Sun, 22 Aug 2010 22:18:00 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>added</b> by             <a href="https://cwiki.apache.org/confluence/display/~pderop">Pierre
De Rop</a>
    <div class="notificationGreySide">
         <h1><a name="ApacheFelixDependencyManager-UsingAnnotations-Components-AnnotationsWritingComponents"></a>Annotations
- Writing Components</h1>

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

<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 your need:</p>

	<li><b>Service</b> component: This kind of component is rather like an
 OSGi Service: it's an implementation class that may publish an OSGi  service, and/or refer
to other dependencies, along with eventual service  properties. A Service has a lifecycle:
it is started once the component  bundle is started and all required dependencies are injected,
and it is  then stopped if a required dependency is lost, or if the bundle is  stopped. However,
notice that in DependencyManager, a Service may not  necessarily publish a Service into the
OSGi registry: in this case, the  component can still have a managed lifecycle, with dependencies.</li>

	<li><b>Aspect Service</b> component: 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
firsts  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

	<li><b>Adapter Service</b>&nbsp; component: 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>

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

	<li><b>@Service:</b> for declaring a component that 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>

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

	<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 have 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 provides  attribute. You can also set
this property to an emtpy 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>

	<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  values 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>

	<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, 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>

	<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/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  "dm.factory.name" property matching the
ID you specify in the attribute.  This Set&lt;Dictionary&gt; will act as a Factory
API, and another  component may use 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  factoryConfigure 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", excepts 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:
		<li>Each time a new Dictionary is added into the Set, then a new  instance of the
annotated service 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
Service 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>

	<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>

<p>Usage example:</p>

<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
<pre class="code-java">  @Service(factorySet=<span class="code-quote">"MyServiceFactory"</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 service. 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 specified in
the properties's Service attribute.
</span>      }

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

      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">// ... part of Z <span class="code-keyword">interface</span>
</span>      }

    * This class will instantiate some X Service instances
  class Y {
      @ServiceDependency(filter=<span class="code-quote">"(dm.factory.name=MyServiceFactory)"</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 Service
      void start() {
          <span class="code-comment">// Instantiate a X Service instance
</span>          Dictionary x1 = <span class="code-keyword">new</span> Hashtable()
{{ put(<span class="code-quote">"foo"</span>, <span class="code-quote">"bar1"</span>);

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

          <span class="code-comment">// Update the first X Service instance
</span>          x1.put(<span class="code-quote">"foo"</span>, <span

          <span class="code-comment">// Destroy X Services (Notice that invoking XFactory.clear()
will destroy all X Service instances)
</span>          _XFactory.remove(x1);

<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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