karaf-2.2.x/deployer/features/src/main/resources/OSGI-INF/blueprint/features-deployer.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--

    Licensed to the Apache Software Foundation (ASF) under one or more
    contributor license agreements.  See the NOTICE file distributed with
    this work for additional information regarding copyright ownership.
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    (the "License"); you may not use this file except in compliance with
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       http://www.apache.org/licenses/LICENSE-2.0

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    distributed under the License is distributed on an "AS IS" BASIS,
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    See the License for the specific language governing permissions and
    limitations under the License.

-->
<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0"
           default-activation="lazy">

    <service id="featureUrlHandler" interface="org.osgi.service.url.URLStreamHandlerService">
    	<service-properties>
            <entry key="url.handler.protocol" value="feature"/>
        </service-properties>
        <bean class="org.apache.karaf.deployer.features.FeatureURLHandler"/>
    </service>

    <bean id="featureDeploymentListener" class="org.apache.karaf.deployer.features.FeatureDeploymentListener"
          init-method="init" destroy-method="destroy" activation="lazy">
        <property name="bundleContext" ref="blueprintBundleContext"/>
        <property name="featuresService">
            <reference interface="org.apache.karaf.features.FeaturesService"/>
        </property>
    </bean>

    <!-- Force a reference to the url handler above from the osgi registry to (try to) make sure
         the url handler is registered inside the framework.  Else we can run into timing issues
         where fileinstall will use the featureDeploymentListener before the url can be actually
         used.  In order to not block the bundle, the blueprint.graceperiod=false flag must be
         set on the SymbolicName osgi header -->
    <reference id="featureUrlHandlerRef" interface="org.osgi.service.url.URLStreamHandlerService" filter="url.handler.protocol=feature" />

    <service ref="featureDeploymentListener" auto-export="interfaces" depends-on="featureUrlHandlerRef"/>

</blueprint>