Page History

...

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 exceptionRuntime Exception.

...

Using the handler

First of all, you need to configure the component type to use the handler such as:

...

Notice that, this handler is an external handler. So, it uses the "org.apache.felix.ipojo.handler.temporal" namespace.
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.
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.

You can also use annotations:

@Component
public class Temporal {

    @Temporal // was org.apache.felix.ipojo.handler.temporal.Requires before the 1.7.0
    private FooService mytemporal;

}

Configuration

The handler has only one mandatory attributes:

• Field: the implementation field supporting the dependency (not needed with annotations)

The handler supports on specific optional attributes:

...

<iPOJO xmlns:temporal="org.apache.felix.ipojo.handler.temporal">
<component
    className="org.apache.felix.ipojo.example.Temporal">

    <!-- Temporal dependency configuration -->
    <temporal:requires field="fs" timeout="300" ontimeout="nullable"/>

    <provides/>

</component>
</iPOJO>

This is equivalent to:

@Component
public class Temporal {

    @Temporal(timeout=300, ontimeout="nullable")
    private FooService mytemporal;

}

Collection injection

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.

<iPOJO xmlns:temporal="org.apache.felix.ipojo.handler.temporal">
<component
    className="org.apache.felix.ipojo.example.Temporal">

    <!-- Temporal dependency configuration -->
    <temporal:requires field="mycollection" specification="my.service.specification"/>

    <provides/>

</component>
</iPOJO>

This is equivalent to:

@Component
public class Temporal {

    @Temporal(specification="my.service.specification")
    private List<FooService> mycollection;

}

Proxy injection

Temporal dependencies can also be injected as proxies. So it is possible to give the temporal dependency to helper object.
On 'scalar' dependencies, the service lookup is executed during an operation invocation. Timeout policies are also executed is the lookup failed.
On aggregate dependencies (necessary Collection), the service lookup is executed when the iterator(), and toArray(...) methods are invoked. Timeout policies
are also executed if the lookup failed. Proxies are enabled by default since the 1.7.0 version.

To set a temporal dependency as a proxy, just add the proxy attribute as follows:

<iPOJO xmlns:temporal="org.apache.felix.ipojo.handler.temporal">
<component
    className="org.apache.felix.ipojo.example.Temporal">

    <!-- Temporal dependencies configuration -->
    <temporal:requires proxy="true" field="fs"/>
    <temporal:requires proxy="true" field="mycollection" specification="my.service.specification"/>

    <provides/>

</component>
</iPOJO>

By default, proxies are disabled enabled. Setting proxy to false disables them.

Download

The handler is available on the download page.
Sources are available on the Felix trunk at the following location: http://svn.apache.org/repos/asf/felix/trunk/ipojo/handler/temporal.