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| <h1 id="instance-controller-or-service-controller">Instance Controller or Service Controller ?<a class="headerlink" href="#instance-controller-or-service-controller" title="Permanent link">¶</a></h1> |
| <p>When the component implementation needs to impact the instance container, it uses <em>controllers</em> on Boolean fields. iPOJO provides two controllers:</p> |
| <ul> |
| <li>Instance Lifecycle Controller (<code>@Controller</code>)</li> |
| <li>Service Lifecycle Controller (<code>@ServiceController</code>)</li> |
| </ul> |
| <p>This page explains the differences between the two kinds of controllers.</p> |
| <h2 id="the-instance-lifecycle-controller">The Instance Lifecycle Controller<a class="headerlink" href="#the-instance-lifecycle-controller" title="Permanent link">¶</a></h2> |
| <p>The instance lifecycle controller impacts the instance state. Such controller must only be used if the instance code has detected an irremediable situation, where the instance cannot behave correctly.</p> |
| <p>Such controller is generally used when the component code:</p> |
| <ul> |
| <li>check the configuration</li> |
| <li>has caught an error</li> |
| </ul> |
| <p>Instance Lifecycle Controller cannot be initialized, and generally are only set to <code>false</code>:</p> |
| <div class="codehilite"><pre><span class="nd">@Component</span> |
| <span class="kd">public</span> <span class="kd">class</span> <span class="nc">MyComponent</span> <span class="o">{</span> |
| |
| <span class="nd">@Controller</span> |
| <span class="kd">private</span> <span class="kt">boolean</span> <span class="n">controller</span><span class="o">;</span> |
| |
| <span class="nd">@Property</span><span class="o">(</span><span class="n">name</span><span class="o">=</span><span class="s">"my-property"</span><span class="o">)</span> |
| <span class="kd">public</span> <span class="kt">void</span> <span class="nf">setMyProperty</span><span class="o">(</span><span class="n">String</span> <span class="n">value</span><span class="o">)</span> <span class="o">{</span> |
| <span class="k">if</span> <span class="o">(!</span> <span class="n">ACCEPTABLE_VALUES</span><span class="o">.</span><span class="na">contains</span><span class="o">(</span><span class="n">value</span><span class="o">)</span> <span class="o">{</span> |
| <span class="c1">// Let's image that if the given </span> |
| <span class="c1">// value is not acceptable, we invalidate</span> |
| <span class="c1">// the instance</span> |
| <span class="n">controller</span> <span class="o">=</span> <span class="kc">false</span><span class="o">;</span> |
| <span class="o">}</span> |
| <span class="o">}</span> |
| <span class="o">}</span> |
| </pre></div> |
| |
| |
| <p>When set to <code>false</code>:</p> |
| <ul> |
| <li>the service exposed by the instance are withdrawn from the service registry</li> |
| <li>the <code>@Invalidate</code> callback is called</li> |
| </ul> |
| <h2 id="the-service-lifecycle-controller">The service lifecycle controller<a class="headerlink" href="#the-service-lifecycle-controller" title="Permanent link">¶</a></h2> |
| <p>The service lifecycle controller impacts only the services exposed by the instance. It is used when the component implementation decides whether or not to publish the services. </p> |
| <p>Unlike the instance lifecycle controller, such controller can:</p> |
| <ul> |
| <li>be set to <code>false</code> at startup (to not publish the services by default).</li> |
| <li>fluctuate between <code>true</code> and <code>false</code> to reflect the decision of the component implementation to publish or not the services.</li> |
| </ul> |
| <p>The following example publishes the component's provided service only after initialization.</p> |
| <div class="codehilite"><pre><span class="nd">@Component</span> |
| <span class="nd">@Provides</span> |
| <span class="kd">public</span> <span class="kd">class</span> <span class="nc">MyComponent</span> <span class="kd">implements</span> <span class="n">MyService</span> <span class="o">{</span> |
| |
| <span class="c1">// Service not published by default</span> |
| <span class="nd">@ServiceController</span><span class="o">(</span><span class="n">value</span><span class="o">=</span><span class="kc">false</span><span class="o">)</span> |
| <span class="kd">private</span> <span class="kt">boolean</span> <span class="n">controller</span><span class="o">;</span> |
| |
| <span class="nd">@Validate</span> |
| <span class="kd">public</span> <span class="kt">void</span> <span class="nf">initialize</span><span class="o">()</span> <span class="o">{</span> |
| <span class="c1">//...</span> |
| <span class="c1">// publish the service once the initialization</span> |
| <span class="c1">// is completed.</span> |
| <span class="n">controller</span> <span class="o">=</span> <span class="kc">true</span><span class="o">;</span> |
| <span class="o">}</span> |
| <span class="o">}</span> |
| </pre></div> |
| |
| |
| <p>When the controller is set to <code>true</code>, the <code>@PostRegistration</code> callback is called. When it is set to <code>false</code> the <code>@PostUnregistration</code> callback is called. In both cases, the service is already registered or unregistered when the callback is invoked.</p> |
| <p>Notice that a <code>@ServiceController</code> controls all exposed services by default, but can be restricted to specific service interface with the <code>specification</code> attribute.</p> |
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| Rev. 1700393 by cziegeler on Tue, 1 Sep 2015 06:04:06 +0000 |
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