bundles/org.eclipse.osgi.services/src/org/osgi/service/component/ComponentContext.java

/*
 * Copyright (c) OSGi Alliance (2004, 2014). 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.service.component;

import java.util.Dictionary;
import org.osgi.annotation.versioning.ProviderType;
import org.osgi.framework.Bundle;
import org.osgi.framework.BundleContext;
import org.osgi.framework.ServiceReference;

/**
 * A Component Context object is used by a component instance to interact with
 * its execution context including locating services by reference name. Each
 * component instance has a unique Component Context.
 * 
 * <p>
 * A component instance may obtain its Component Context object through its
 * activate, modified, and deactivate methods.
 * 
 * @ThreadSafe
 * @author $Id$
 */
@ProviderType
public interface ComponentContext {
	/**
	 * Returns the component properties for this Component Context.
	 * 
	 * @return The properties for this Component Context. The Dictionary is read
	 *         only and cannot be modified.
	 */
	public Dictionary<String, Object> getProperties();

	/**
	 * Returns the service object for the specified reference name.
	 * 
	 * <p>
	 * If the cardinality of the reference is {@code 0..n} or {@code 1..n} and
	 * multiple services are bound to the reference, the service with the
	 * highest ranking (as specified in its {@code Constants.SERVICE_RANKING}
	 * property) is returned. If there is a tie in ranking, the service with the
	 * lowest service id (as specified in its {@code Constants.SERVICE_ID}
	 * property); that is, the service that was registered first is returned.
	 * 
	 * @param name The name of a reference as specified in a {@code reference}
	 *        element in this component's description.
	 * @return A service object for the referenced service or {@code null} if
	 *         the reference cardinality is {@code 0..1} or {@code 0..n} and no
	 *         bound service is available.
	 * @throws ComponentException If Service Component Runtime catches an
	 *         exception while activating the bound service.
	 */
	public Object locateService(String name);

	/**
	 * Returns the service object for the specified reference name and
	 * {@code ServiceReference}.
	 * 
	 * @param <S> Type of Service.
	 * @param name The name of a reference as specified in a {@code reference}
	 *        element in this component's description.
	 * @param reference The {@code ServiceReference} to a bound service. This
	 *        must be a {@code ServiceReference} provided to the component via
	 *        the bind or unbind method for the specified reference name.
	 * @return A service object for the referenced service or {@code null} if
	 *         the specified {@code ServiceReference} is not a bound service for
	 *         the specified reference name.
	 * @throws ComponentException If Service Component Runtime catches an
	 *         exception while activating the bound service.
	 */
	public <S> S locateService(String name, ServiceReference<S> reference);

	/**
	 * Returns the service objects for the specified reference name.
	 * 
	 * @param name The name of a reference as specified in a {@code reference}
	 *        element in this component's description.
	 * @return An array of service objects for the referenced service or
	 *         {@code null} if the reference cardinality is {@code 0..1} or
	 *         {@code 0..n} and no bound service is available. If the reference
	 *         cardinality is {@code 0..1} or {@code 1..1} and a bound service
	 *         is available, the array will have exactly one element.
	 * @throws ComponentException If Service Component Runtime catches an
	 *         exception while activating a bound service.
	 */
	public Object[] locateServices(String name);

	/**
	 * Returns the {@code BundleContext} of the bundle which contains this
	 * component.
	 * 
	 * @return The {@code BundleContext} of the bundle containing this
	 *         component.
	 */
	public BundleContext getBundleContext();

	/**
	 * If the component instance is registered as a service using the
	 * {@code servicescope="bundle"} or {@code servicescope="prototype"}
	 * attribute, then this method returns the bundle using the service provided
	 * by the component instance.
	 * <p>
	 * This method will return {@code null} if:
	 * <ul>
	 * <li>The component instance is not a service, then no bundle can be using
	 * it as a service.</li>
	 * <li>The component instance is a service but did not specify the
	 * {@code servicescope="bundle"} or {@code servicescope="prototype"}
	 * attribute, then all bundles using the service provided by the component
	 * instance will share the same component instance.</li>
	 * <li>The service provided by the component instance is not currently being
	 * used by any bundle.</li>
	 * </ul>
	 * 
	 * @return The bundle using the component instance as a service or
	 *         {@code null}.
	 */
	public Bundle getUsingBundle();

	/**
	 * Returns the Component Instance object for the component instance
	 * associated with this Component Context.
	 * 
	 * @return The Component Instance object for the component instance.
	 */
	public ComponentInstance getComponentInstance();

	/**
	 * Enables the specified component name. The specified component name must
	 * be in the same bundle as this component.
	 * 
	 * <p>
	 * This method must return after changing the enabled state of the specified
	 * component name. Any actions that result from this, such as activating or
	 * deactivating a component configuration, must occur asynchronously to this
	 * method call.
	 * 
	 * @param name The name of a component or {@code null} to indicate all
	 *        components in the bundle.
	 */
	public void enableComponent(String name);

	/**
	 * Disables the specified component name. The specified component name must
	 * be in the same bundle as this component.
	 * 
	 * <p>
	 * This method must return after changing the enabled state of the specified
	 * component name. Any actions that result from this, such as activating or
	 * deactivating a component configuration, must occur asynchronously to this
	 * method call.
	 * 
	 * @param name The name of a component.
	 */
	public void disableComponent(String name);

	/**
	 * If the component instance is registered as a service using the
	 * {@code service} element, then this method returns the service reference
	 * of the service provided by this component instance.
	 * <p>
	 * This method will return {@code null} if the component instance is not
	 * registered as a service.
	 * 
	 * @return The {@code ServiceReference} object for the component instance or
	 *         {@code null} if the component instance is not registered as a
	 *         service.
	 */
	public ServiceReference<?> getServiceReference();
}