org.osgi.util.tracker
Class ServiceTracker

java.lang.Object
  org.osgi.util.tracker.ServiceTracker

All Implemented Interfaces:

ServiceTrackerCustomizer

public class ServiceTracker

extends java.lang.Object

implements ServiceTrackerCustomizer

The ServiceTracker class simplifies using services from the Framework's service registry.

A ServiceTracker object is constructed with search criteria and a ServiceTrackerCustomizer object. A ServiceTracker object can use the ServiceTrackerCustomizer object to customize the service objects to be tracked. The ServiceTracker object can then be opened to begin tracking all services in the Framework's service registry that match the specified search criteria. The ServiceTracker object correctly handles all of the details of listening to ServiceEvent objects and getting and ungetting services.

The getServiceReferences method can be called to get references to the services being tracked. The getService and getServices methods can be called to get the service objects for the tracked service.

Field Summary

protected BundleContext	context Bundle context this ServiceTracker object is tracking against.
protected Filter	filter Filter specifying search criteria for the services to track.

Constructor Summary

ServiceTracker(BundleContext context, Filter filter, ServiceTrackerCustomizer customizer)
Create a ServiceTracker object on the specified Filter object.

ServiceTracker(BundleContext context, ServiceReference reference, ServiceTrackerCustomizer customizer)
Create a ServiceTracker object on the specified ServiceReference object.

ServiceTracker(BundleContext context, java.lang.String clazz, ServiceTrackerCustomizer customizer)
Create a ServiceTracker object on the specified class name.

Method Summary

java.lang.Object	addingService(ServiceReference reference) Default implementation of the ServiceTrackerCustomizer.addingService method.
void	close() Close this ServiceTracker object.
protected void	finalize() Properly close this ServiceTracker object when finalized.
java.lang.Object	getService() Returns a service object for one of the services being tracked by this ServiceTracker object.
java.lang.Object	getService(ServiceReference reference) Returns the service object for the specified ServiceReference object if the referenced service is being tracked by this ServiceTracker object.
ServiceReference	getServiceReference() Returns a ServiceReference object for one of the services being tracked by this ServiceTracker object.
ServiceReference[]	getServiceReferences() Return an array of ServiceReference objects for all services being tracked by this ServiceTracker object.
java.lang.Object[]	getServices() Return an array of service objects for all services being tracked by this ServiceTracker object.
void	modifiedService(ServiceReference reference, java.lang.Object service) Default implementation of the ServiceTrackerCustomizer.modifiedService method.
void	open() Open this ServiceTracker object and begin tracking services.
void	remove(ServiceReference reference) Remove a service from this ServiceTracker object.
void	removedService(ServiceReference reference, java.lang.Object object) Default implementation of the ServiceTrackerCustomizer.removedService method.
int	size() Return the number of services being tracked by this ServiceTracker object.
java.lang.Object	waitForService(long timeout) Wait for at least one service to be tracked by this ServiceTracker object.

Methods inherited from class java.lang.Object

clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

context

protected final BundleContext context

Bundle context this ServiceTracker object is tracking against.

filter

protected final Filter filter

Filter specifying search criteria for the services to track.

Since:

1.1

Constructor Detail

ServiceTracker

public ServiceTracker(BundleContext context,
                      ServiceReference reference,
                      ServiceTrackerCustomizer customizer)

Create a ServiceTracker object on the specified ServiceReference object.

The service referenced by the specified ServiceReference object will be tracked by this ServiceTracker object.

Parameters:

context - BundleContext object against which the tracking is done.

reference - ServiceReference object for the service to be tracked.

customizer - The customizer object to call when services are added, modified, or removed in this ServiceTracker object. If customizer is null, then this ServiceTracker object will be used as the ServiceTrackerCustomizer object and the ServiceTracker object will call the ServiceTrackerCustomizer methods on itself.

ServiceTracker

public ServiceTracker(BundleContext context,
                      java.lang.String clazz,
                      ServiceTrackerCustomizer customizer)

Create a ServiceTracker object on the specified class name.

Services registered under the specified class name will be tracked by this ServiceTracker object.

Parameters:

context - BundleContext object against which the tracking is done.

clazz - Class name of the services to be tracked.

customizer - The customizer object to call when services are added, modified, or removed in this ServiceTracker object. If customizer is null, then this ServiceTracker object will be used as the ServiceTrackerCustomizer object and the ServiceTracker object will call the ServiceTrackerCustomizer methods on itself.

ServiceTracker

public ServiceTracker(BundleContext context,
                      Filter filter,
                      ServiceTrackerCustomizer customizer)

Create a ServiceTracker object on the specified Filter object.

Services which match the specified Filter object will be tracked by this ServiceTracker object.

Parameters:

context - BundleContext object against which the tracking is done.

filter - Filter object to select the services to be tracked.

customizer - The customizer object to call when services are added, modified, or removed in this ServiceTracker object. If customizer is null, then this ServiceTracker object will be used as the ServiceTrackerCustomizer object and the ServiceTracker object will call the ServiceTrackerCustomizer methods on itself.

Since:

1.1

Method Detail

open

public void open()

Open this ServiceTracker object and begin tracking services.

Services which match the search criteria specified when this ServiceTracker object was created are now tracked by this ServiceTracker object.

Throws:

java.lang.IllegalStateException - if the BundleContext object with which this ServiceTracker object was created is no longer valid.

close

public void close()

Close this ServiceTracker object.

This method should be called when this ServiceTracker object should end the tracking of services.

finalize

protected void finalize()
                 throws java.lang.Throwable

Properly close this ServiceTracker object when finalized. This method calls the close method to close this ServiceTracker object if it has not already been closed.

Throws:

java.lang.Throwable

addingService

public java.lang.Object addingService(ServiceReference reference)

Default implementation of the ServiceTrackerCustomizer.addingService method.

This method is only called when this ServiceTracker object has been constructed with a null ServiceTrackerCustomizer argument. The default implementation returns the result of calling getService, on the BundleContext object with which this ServiceTracker object was created, passing the specified ServiceReference object.

This method can be overridden to customize the service object to be tracked for the service being added.

Specified by:

addingService in interface ServiceTrackerCustomizer

Parameters:

reference - Reference to service being added to this ServiceTracker object.

Returns:

The service object to be tracked for the service added to this ServiceTracker object.

modifiedService

public void modifiedService(ServiceReference reference,
                            java.lang.Object service)

Default implementation of the ServiceTrackerCustomizer.modifiedService method.

This method is only called when this ServiceTracker object has been constructed with a null ServiceTrackerCustomizer argument. The default implementation does nothing.

Specified by:

modifiedService in interface ServiceTrackerCustomizer

Parameters:

reference - Reference to modified service.

service - The service object for the modified service.

removedService

public void removedService(ServiceReference reference,
                           java.lang.Object object)

Default implementation of the ServiceTrackerCustomizer.removedService method.

This method is only called when this ServiceTracker object has been constructed with a null ServiceTrackerCustomizer argument. The default implementation calls ungetService, on the BundleContext object with which this ServiceTracker object was created, passing the specified ServiceReference object.

Specified by:

removedService in interface ServiceTrackerCustomizer

Parameters:

reference - Reference to removed service.

object - The service object for the removed service.

waitForService

public java.lang.Object waitForService(long timeout)
                                throws java.lang.InterruptedException

Wait for at least one service to be tracked by this ServiceTracker object.

It is strongly recommended that waitForService is not used during the calling of the BundleActivator methods. BundleActivator methods are expected to complete in a short period of time.

Parameters:

timeout - time interval in milliseconds to wait. If zero, the method will wait indefinately.

Returns:

Returns the result of getService().

Throws:

java.lang.InterruptedException

getServiceReferences

public ServiceReference[] getServiceReferences()

Return an array of ServiceReference objects for all services being tracked by this ServiceTracker object.

Returns:

Array of ServiceReference objects or null if no service are being tracked.

getServices

public java.lang.Object[] getServices()

Return an array of service objects for all services being tracked by this ServiceTracker object.

Returns:

Array of service objects or null if no service are being tracked.

getServiceReference

public ServiceReference getServiceReference()

Returns a ServiceReference object for one of the services being tracked by this ServiceTracker object.

If multiple services are being tracked, the service with the highest ranking (as specified in its service.ranking property) is returned.

If there is a tie in ranking, the service with the lowest service ID (as specified in its service.id property); that is, the service that was registered first is returned.

This is the same algorithm used by BundleContext.getServiceReference.

Returns:

ServiceReference object or null if no service is being tracked.

Since:

1.1

getService

public java.lang.Object getService(ServiceReference reference)

Returns the service object for the specified ServiceReference object if the referenced service is being tracked by this ServiceTracker object.

Parameters:

reference - Reference to the desired service.

Returns:

Service object or null if the service referenced by the specified ServiceReference object is not being tracked.

getService

public java.lang.Object getService()

Returns a service object for one of the services being tracked by this ServiceTracker object.

If any services are being tracked, this method returns the result of calling getService(getServiceReference()).

Returns:

Service object or null if no service is being tracked.

remove

public void remove(ServiceReference reference)

Remove a service from this ServiceTracker object. The specified service will be removed from this ServiceTracker object. If the specified service was being tracked then the ServiceTrackerCustomizer.removedService method will be called for that service.

Parameters:

reference - Reference to the service to be removed.

size

public int size()

Return the number of services being tracked by this ServiceTracker object.

Returns:

Number of services being tracked.