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<h1><a name="TemporalServiceDependency-Thetemporaldependencyhandler"></a>The temporal dependency handler</h1>
<p><em>Regular service dependencies participate to the instance
lifecycle. Moreover, the injected service object is either available or
not available. A temporal dependency handler is a little different and
provides a different resolution pattern. Indeed, the temporal
dependency does not invalidate the instance. Moreover, if not
available, the temporal dependency waits (and so blocks the current
thread) for a provider. Of course, the maximum waiting time can be
specified. If a timeout occurs, the handler throws a runtime exception.</em></p>
<div class="toc">
<ul>
<li><a href="#TemporalServiceDependency-Usingthehandler">Using the handler</a></li>
<li><a href="#TemporalServiceDependency-Collectioninjection">Collection injection</a></li>
<li><a href="#TemporalServiceDependency-Proxyinjection">Proxy injection</a></li>
<li><a href="#TemporalServiceDependency-Download">Download</a></li>
</ul></div>
<h2><a name="TemporalServiceDependency-Usingthehandler"></a>Using the handler</h2>
<p>First of all, you need to configure the component type to use the handler such as:</p>
<div class="code">
<div class="dp-highlighter"><table class="dp-xml" border="0" cellpadding="0" cellspacing="0"><tbody><tr><td class="line1"><span></span><span class="tag">&lt;</span><span>iPOJO&nbsp;xmlns:</span><span class="attribute">temporal</span><span>=</span><span class="attribute-value">"org.apache.felix.ipojo.handler.temporal"</span><span>&gt;&nbsp;</span></td></tr><tr><td class="line2"><span class="tag">&lt;</span><span>component&nbsp;</span></td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;<span class="attribute">className</span><span>=</span><span class="attribute-value">"org.apache.felix.ipojo.example.Temporal"</span><span>&gt;&nbsp;</span></td></tr><tr><td class="line2">&nbsp;</td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;<span class="comments">&lt;!--&nbsp;Temporal&nbsp;dependency&nbsp;configuration&nbsp;--&gt;</span><span>&nbsp;</span></td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;<span class="tag">&lt;</span><span>temporal:requires&nbsp;</span><span class="attribute">field</span><span>=</span><span class="attribute-value">"mytemporal"</span><span>/&gt;&nbsp;</span></td></tr><tr><td class="line1">&nbsp;</td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;<span class="tag">&lt;</span><span>provides</span><span class="tag">/&gt;</span><span>&nbsp;</span></td></tr><tr><td class="line1">&nbsp;</td></tr><tr><td class="line2"><span class="tag">&lt;/</span><span>component</span><span class="tag">&gt;</span><span>&nbsp;</span></td></tr><tr><td class="line1"><span class="tag">&lt;/</span><span>iPOJO</span><span class="tag">&gt;</span><span>&nbsp;</span></td></tr></tbody></table></div><textarea style="display: none;" name="newcodemacro" class="xml:nocontrols:nogutter" rows="10" readonly="readonly">&lt;iPOJO xmlns:temporal="org.apache.felix.ipojo.handler.temporal"&gt;
&lt;component
className="org.apache.felix.ipojo.example.Temporal"&gt;
&lt;!-- Temporal dependency configuration --&gt;
&lt;temporal:requires field="mytemporal"/&gt;
&lt;provides/&gt;
&lt;/component&gt;
&lt;/iPOJO&gt;</textarea>
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<p>Notice that, this handler is an external handler. So, it uses the "org.apache.felix.ipojo.handler.temporal" namespace.<br>
Once described, you can implement your component. The specified field
will be mapped to the temporal dependency. As for regular field
injection, aggregation, targeted service specification (i.e. interface)
is discovered automatically. Filter, comparator and binding policy are
also supported. However, the optional attribute is not supported. In
fact, this attribute is meaningless in the case of a temporal
dependency.<br>
Using the field in your code will try to find a matching service
provider. If a provider is available, the field receives the service
object immediately. Else, the thread is stopped and waits for a
provider. The default wait time is 3s (you can also specify this time).
If no provider is available after this time, the thread throws a
RuntimeException. If a provider becomes available during this time, the
field receives immediately the value and the execution can continue.<br>
Configuration</p>
<p>The handler has only one mandatory attributes:</p>
<ul>
<li>Field: the implementation field supporting the dependency</li>
</ul>
<p>The handler supports on specific optional attributes:</p>
<ul>
<li>Timeout: the maximum time waited in order to find a provider
(default: 3s). For an infinite timeout, the timeout value is either
"infinite" or "-1".</li>
<li>OnTimeout: specifies the action to do
when the timeout occurs. Four actions are supported: null, nullable,
empty-array, default-implementation. By default, no action is
specified, and an exception occurs when the timeout is reached.</li>
</ul>
<p>The attributes from "regular" dependencies are also supported (like filter).<br>
OnTimeout actions</p>
<p>When a timeout occurs, you can specify what the handler must do. By
default, it throws a runtime exception. However, four others actions
can be set in the 'onTimeout' attribute.</p>
<ul>
<li>The null action (onTimeout="null") will return "null" instead of the service object.</li>
<li>The
"nullable" action (onTimeout="nullable") will return a "Nullable"
object instead of the service object. This object is a fake but can be
used a regular service object. However, invoking actions on this object
will do nothing. In the case of aggregate dependency, an array
containing a "nullable" object is returned.</li>
<li>The empty action
is only supported for aggregate dependency (the field must be an
array). In this case, an empty-array is returned. (In the 1.2.0
version, the <tt>empty-array</tt> attribute became <tt>empty</tt>)</li>
<li>The
default-implementation action is a little different. Instead of
specifying the action, you need to specify the default-implementation
(the qualified class name) that you want to use. For example
onTimeout="o.a.f.i.MyDefaultLogServiceImpl". In this case, the handler
will inject an instance of this object instead of a real service
object. On aggregate dependency, an array with one
default-implementation object is returned.</li>
</ul>
<div class="code">
<div class="dp-highlighter"><table class="dp-xml" border="0" cellpadding="0" cellspacing="0"><tbody><tr><td class="line1"><span></span><span class="tag">&lt;</span><span>iPOJO&nbsp;xmlns:</span><span class="attribute">temporal</span><span>=</span><span class="attribute-value">"org.apache.felix.ipojo.handler.temporal"</span><span>&gt;&nbsp;</span></td></tr><tr><td class="line2"><span class="tag">&lt;</span><span>component&nbsp;</span></td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;<span class="attribute">className</span><span>=</span><span class="attribute-value">"org.apache.felix.ipojo.example.Temporal"</span><span>&gt;&nbsp;</span></td></tr><tr><td class="line2">&nbsp;</td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;<span class="comments">&lt;!--&nbsp;Temporal&nbsp;dependency&nbsp;configuration&nbsp;--&gt;</span><span>&nbsp;</span></td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;<span class="tag">&lt;</span><span>temporal:requires&nbsp;</span><span class="attribute">field</span><span>=</span><span class="attribute-value">"fs"</span><span>&nbsp;</span><span class="attribute">timeout</span><span>=</span><span class="attribute-value">"300"</span><span>&nbsp;</span><span class="attribute">ontimeout</span><span>=</span><span class="attribute-value">"nullable"</span><span>/&gt;&nbsp;</span></td></tr><tr><td class="line1">&nbsp;</td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;<span class="tag">&lt;</span><span>provides</span><span class="tag">/&gt;</span><span>&nbsp;</span></td></tr><tr><td class="line1">&nbsp;</td></tr><tr><td class="line2"><span class="tag">&lt;/</span><span>component</span><span class="tag">&gt;</span><span>&nbsp;</span></td></tr><tr><td class="line1"><span class="tag">&lt;/</span><span>iPOJO</span><span class="tag">&gt;</span><span>&nbsp;</span></td></tr></tbody></table></div><textarea style="display: none;" name="newcodemacro" class="xml:nocontrols:nogutter" rows="10" readonly="readonly">&lt;iPOJO xmlns:temporal="org.apache.felix.ipojo.handler.temporal"&gt;
&lt;component
className="org.apache.felix.ipojo.example.Temporal"&gt;
&lt;!-- Temporal dependency configuration --&gt;
&lt;temporal:requires field="fs" timeout="300" ontimeout="nullable"/&gt;
&lt;provides/&gt;
&lt;/component&gt;
&lt;/iPOJO&gt;</textarea>
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<h2><a name="TemporalServiceDependency-Collectioninjection"></a>Collection injection</h2>
<p>Temporal dependencies can also be injected inside Collection. To
achieve this, the 'specification' attribute must indicates the looked
specification, and the field must be a Collection.</p>
<div class="code">
<div class="dp-highlighter"><table class="dp-xml" border="0" cellpadding="0" cellspacing="0"><tbody><tr><td class="line1"><span></span><span class="tag">&lt;</span><span>iPOJO&nbsp;xmlns:</span><span class="attribute">temporal</span><span>=</span><span class="attribute-value">"org.apache.felix.ipojo.handler.temporal"</span><span>&gt;&nbsp;</span></td></tr><tr><td class="line2"><span class="tag">&lt;</span><span>component&nbsp;</span></td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;<span class="attribute">className</span><span>=</span><span class="attribute-value">"org.apache.felix.ipojo.example.Temporal"</span><span>&gt;&nbsp;</span></td></tr><tr><td class="line2">&nbsp;</td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;<span class="comments">&lt;!--&nbsp;Temporal&nbsp;dependency&nbsp;configuration&nbsp;--&gt;</span><span>&nbsp;</span></td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;<span class="tag">&lt;</span><span>temporal:requires&nbsp;</span><span class="attribute">field</span><span>=</span><span class="attribute-value">"mycollection"</span><span>&nbsp;</span><span class="attribute">specification</span><span>=</span><span class="attribute-value">"my.service.specification"</span><span>/&gt;&nbsp;</span></td></tr><tr><td class="line1">&nbsp;</td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;<span class="tag">&lt;</span><span>provides</span><span class="tag">/&gt;</span><span>&nbsp;</span></td></tr><tr><td class="line1">&nbsp;</td></tr><tr><td class="line2"><span class="tag">&lt;/</span><span>component</span><span class="tag">&gt;</span><span>&nbsp;</span></td></tr><tr><td class="line1"><span class="tag">&lt;/</span><span>iPOJO</span><span class="tag">&gt;</span><span>&nbsp;</span></td></tr></tbody></table></div><textarea style="display: none;" name="newcodemacro" class="xml:nocontrols:nogutter" rows="10" readonly="readonly">&lt;iPOJO xmlns:temporal="org.apache.felix.ipojo.handler.temporal"&gt;
&lt;component
className="org.apache.felix.ipojo.example.Temporal"&gt;
&lt;!-- Temporal dependency configuration --&gt;
&lt;temporal:requires field="mycollection" specification="my.service.specification"/&gt;
&lt;provides/&gt;
&lt;/component&gt;
&lt;/iPOJO&gt;</textarea>
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<h2><a name="TemporalServiceDependency-Proxyinjection"></a>Proxy injection</h2>
<p>Temporal dependencies can also be injected as proxies. So it is possible to give the temporal dependency to helper object.<br>
On 'scalar' dependencies, the service lookup is executed during an
operation invocation. Timeout policies are also executed is the lookup
failed.<br>
On aggregate dependencies (necessary Collection), the service lookup is
executed when the iterator(), and toArray(...) methods are invoked.
Timeout policies <br>
are also executed if the lookup failed.</p>
<p>To set a temporal dependency as a proxy, just add the <tt>proxy</tt> attribute as follows:</p>
<div class="code">
<div class="dp-highlighter"><table class="dp-xml" border="0" cellpadding="0" cellspacing="0"><tbody><tr><td class="line1"><span></span><span class="tag">&lt;</span><span>iPOJO&nbsp;xmlns:</span><span class="attribute">temporal</span><span>=</span><span class="attribute-value">"org.apache.felix.ipojo.handler.temporal"</span><span>&gt;&nbsp;</span></td></tr><tr><td class="line2"><span class="tag">&lt;</span><span>component&nbsp;</span></td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;<span class="attribute">className</span><span>=</span><span class="attribute-value">"org.apache.felix.ipojo.example.Temporal"</span><span>&gt;&nbsp;</span></td></tr><tr><td class="line2">&nbsp;</td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;<span class="comments">&lt;!--&nbsp;Temporal&nbsp;dependencies&nbsp;configuration&nbsp;--&gt;</span><span>&nbsp;</span></td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;<span class="tag">&lt;</span><span>temporal:requires&nbsp;</span><span class="attribute">proxy</span><span>=</span><span class="attribute-value">"true"</span><span>&nbsp;</span><span class="attribute">field</span><span>=</span><span class="attribute-value">"fs"</span><span>/&gt;&nbsp;</span></td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;<span class="tag">&lt;</span><span>temporal:requires&nbsp;</span><span class="attribute">proxy</span><span>=</span><span class="attribute-value">"true"</span><span>&nbsp;</span><span class="attribute">field</span><span>=</span><span class="attribute-value">"mycollection"</span><span>&nbsp;</span><span class="attribute">specification</span><span>=</span><span class="attribute-value">"my.service.specification"</span><span>/&gt;&nbsp;</span></td></tr><tr><td class="line2">&nbsp;</td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;<span class="tag">&lt;</span><span>provides</span><span class="tag">/&gt;</span><span>&nbsp;</span></td></tr><tr><td class="line2">&nbsp;</td></tr><tr><td class="line1"><span class="tag">&lt;/</span><span>component</span><span class="tag">&gt;</span><span>&nbsp;</span></td></tr><tr><td class="line2"><span class="tag">&lt;/</span><span>iPOJO</span><span class="tag">&gt;</span><span>&nbsp;</span></td></tr></tbody></table></div><textarea style="display: none;" name="newcodemacro" class="xml:nocontrols:nogutter" rows="10" readonly="readonly">&lt;iPOJO xmlns:temporal="org.apache.felix.ipojo.handler.temporal"&gt;
&lt;component
className="org.apache.felix.ipojo.example.Temporal"&gt;
&lt;!-- Temporal dependencies configuration --&gt;
&lt;temporal:requires proxy="true" field="fs"/&gt;
&lt;temporal:requires proxy="true" field="mycollection" specification="my.service.specification"/&gt;
&lt;provides/&gt;
&lt;/component&gt;
&lt;/iPOJO&gt;</textarea>
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<p>By default, proxies are disabled.</p>
<h2><a name="TemporalServiceDependency-Download"></a>Download </h2>
<p>The handler is available on the <a href="http://felix.apache.org/site/download.html" title="Download">download</a> page.<br>
Sources are available on the Felix trunk at the following location: <a href="http://svn.apache.org/repos/asf/felix/trunk/ipojo/handler/temporal" rel="nofollow">http://svn.apache.org/repos/asf/felix/trunk/ipojo/handler/temporal</a>.
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