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/*
* Copyright (c) OSGi Alliance (2000, 2015). All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.osgi.framework;
import java.util.Dictionary;
import org.osgi.annotation.versioning.ProviderType;
/**
* A reference to a service.
*
* <p>
* The Framework returns {@code ServiceReference} objects from the
* {@code BundleContext.getServiceReference} and
* {@code BundleContext.getServiceReferences} methods.
* <p>
* A {@code ServiceReference} object may be shared between bundles and can be
* used to examine the properties of the service and to get the service object.
* <p>
* Every service registered in the Framework has a unique
* {@code ServiceRegistration} object and may have multiple, distinct
* {@code ServiceReference} objects referring to it. {@code ServiceReference}
* objects associated with a {@code ServiceRegistration} object have the same
* {@code hashCode} and are considered equal (more specifically, their
* {@code equals()} method will return {@code true} when compared).
* <p>
* If the same service object is registered multiple times,
* {@code ServiceReference} objects associated with different
* {@code ServiceRegistration} objects are not equal.
*
* @param <S> Type of Service.
* @see BundleContext#getServiceReference(Class)
* @see BundleContext#getServiceReference(String)
* @see BundleContext#getServiceReferences(Class, String)
* @see BundleContext#getServiceReferences(String, String)
* @see BundleContext#getService(ServiceReference)
* @see BundleContext#getServiceObjects(ServiceReference)
* @ThreadSafe
* @author $Id$
*/
@ProviderType
public interface ServiceReference<S> extends Comparable<Object> {
/**
* Returns the property value to which the specified property key is mapped
* in the properties {@code Dictionary} object of the service referenced by
* this {@code ServiceReference} object.
*
* <p>
* Property keys are case-insensitive.
*
* <p>
* This method must continue to return property values after the service has
* been unregistered. This is so references to unregistered services (for
* example, {@code ServiceReference} objects stored in the log) can still be
* interrogated.
*
* @param key The property key.
* @return The property value to which the key is mapped; {@code null} if
* there is no property named after the key.
*/
public Object getProperty(String key);
/**
* Returns an array of the keys in the properties {@code Dictionary} object
* of the service referenced by this {@code ServiceReference} object.
*
* <p>
* This method will continue to return the keys after the service has been
* unregistered. This is so references to unregistered services (for
* example, {@code ServiceReference} objects stored in the log) can still be
* interrogated.
*
* <p>
* This method is <i>case-preserving </i>; this means that every key in the
* returned array must have the same case as the corresponding key in the
* properties {@code Dictionary} that was passed to the
* {@link BundleContext#registerService(String[],Object,Dictionary)} or
* {@link ServiceRegistration#setProperties(Dictionary)} methods.
*
* @return An array of property keys.
*/
public String[] getPropertyKeys();
/**
* Returns the bundle that registered the service referenced by this
* {@code ServiceReference} object.
*
* <p>
* This method must return {@code null} when the service has been
* unregistered. This can be used to determine if the service has been
* unregistered.
*
* @return The bundle that registered the service referenced by this
* {@code ServiceReference} object; {@code null} if that service has
* already been unregistered.
* @see BundleContext#registerService(String[],Object,Dictionary)
*/
public Bundle getBundle();
/**
* Returns the bundles that are using the service referenced by this
* {@code ServiceReference} object. Specifically, this method returns the
* bundles whose usage count for that service is greater than zero.
*
* @return An array of bundles whose usage count for the service referenced
* by this {@code ServiceReference} object is greater than zero;
* {@code null} if no bundles are currently using that service.
*
* @since 1.1
*/
public Bundle[] getUsingBundles();
/**
* Tests if the bundle that registered the service referenced by this
* {@code ServiceReference} and the specified bundle use the same source for
* the package of the specified class name.
* <p>
* This method performs the following checks:
* <ol>
* <li>Get the package name from the specified class name.</li>
* <li>For the bundle that registered the service referenced by this
* {@code ServiceReference} (registrant bundle); find the source for the
* package. If no source is found then return {@code true} if the registrant
* bundle is equal to the specified bundle; otherwise return {@code false}.</li>
* <li>If the package source of the registrant bundle is equal to the
* package source of the specified bundle then return {@code true};
* otherwise return {@code false}.</li>
* </ol>
*
* @param bundle The {@code Bundle} object to check.
* @param className The class name to check.
* @return {@code true} if the bundle which registered the service
* referenced by this {@code ServiceReference} and the specified
* bundle use the same source for the package of the specified class
* name. Otherwise {@code false} is returned.
* @throws IllegalArgumentException If the specified {@code Bundle} was not
* created by the same framework instance as this
* {@code ServiceReference}.
* @since 1.3
*/
public boolean isAssignableTo(Bundle bundle, String className);
/**
* Compares this {@code ServiceReference} with the specified
* {@code ServiceReference} for order.
*
* <p>
* If this {@code ServiceReference} and the specified
* {@code ServiceReference} have the same {@link Constants#SERVICE_ID
* service id} they are equal. This {@code ServiceReference} is less than
* the specified {@code ServiceReference} if it has a lower
* {@link Constants#SERVICE_RANKING service ranking} and greater if it has a
* higher service ranking. Otherwise, if this {@code ServiceReference} and
* the specified {@code ServiceReference} have the same
* {@link Constants#SERVICE_RANKING service ranking}, this
* {@code ServiceReference} is less than the specified
* {@code ServiceReference} if it has a higher {@link Constants#SERVICE_ID
* service id} and greater if it has a lower service id.
*
* @param reference The {@code ServiceReference} to be compared.
* @return Returns a negative integer, zero, or a positive integer if this
* {@code ServiceReference} is less than, equal to, or greater than
* the specified {@code ServiceReference}.
* @throws IllegalArgumentException If the specified
* {@code ServiceReference} was not created by the same framework
* instance as this {@code ServiceReference}.
* @since 1.4
*/
@Override
public int compareTo(Object reference);
}
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