org.osgi.framework

Interface BundleContext

public interface BundleContext

A bundle's execution context within the Framework. The context is used to grant access to other methods so that this bundle can interact with the Framework.

BundleContext methods allow a bundle to:

• Subscribe to events published by the Framework.
• Register service objects with the Framework service registry.
• Retrieve ServiceReferences from the Framework service registry.
• Get and release service objects for a referenced service.
• Install new bundles in the Framework.
• Get the list of bundles installed in the Framework.
• Get the Bundle object for a bundle.
• Create File objects for files in a persistent storage area provided for the bundle by the Framework.

A BundleContext object will be created and provided to the bundle associated with this context when it is started using the BundleActivator.start(org.osgi.framework.BundleContext) method. The same BundleContext object will be passed to the bundle associated with this context when it is stopped using the BundleActivator.stop(org.osgi.framework.BundleContext) method. A BundleContext object is generally for the private use of its associated bundle and is not meant to be shared with other bundles in the OSGi environment.

The Bundle object associated with a BundleContext object is called the context bundle.

The BundleContext object is only valid during the execution of its context bundle; that is, during the period from when the context bundle is in the STARTING, STOPPING, and ACTIVE bundle states. If the BundleContext object is used subsequently, an IllegalStateException must be thrown. The BundleContext object must never be reused after its context bundle is stopped.

The Framework is the only entity that can create BundleContext objects and they are only valid within the Framework that created them.

Version:

$Revision$

Method Summary

Methods

Modifier and Type	Method and Description
void	addBundleListener(BundleListener listener) Adds the specified BundleListener object to the context bundle's list of listeners if not already present.
void	addFrameworkListener(FrameworkListener listener) Adds the specified FrameworkListener object to the context bundle's list of listeners if not already present.
void	addServiceListener(ServiceListener listener) Adds the specified ServiceListener object to the context bundle's list of listeners.
void	addServiceListener(ServiceListener listener, String filter) Adds the specified ServiceListener object with the specified filter to the context bundle's list of listeners.
Filter	createFilter(String filter) Creates a Filter object.
ServiceReference[]	getAllServiceReferences(String clazz, String filter) Returns an array of ServiceReference objects.
Bundle	getBundle() Returns the Bundle object associated with this BundleContext.
Bundle	getBundle(long id) Returns the bundle with the specified identifier.
Bundle[]	getBundles() Returns a list of all installed bundles.
File	getDataFile(String filename) Creates a File object for a file in the persistent storage area provided for the bundle by the Framework.
String	getProperty(String key) Returns the value of the specified property.
Object	getService(ServiceReference reference) Returns the service object referenced by the specified ServiceReference object.
ServiceReference	getServiceReference(String clazz) Returns a ServiceReference object for a service that implements and was registered under the specified class.
ServiceReference[]	getServiceReferences(String clazz, String filter) Returns an array of ServiceReference objects.
Bundle	installBundle(String location) Installs a bundle from the specified location identifier.
Bundle	installBundle(String location, InputStream input) Installs a bundle from the specified InputStream object.
ServiceRegistration	registerService(String[] clazzes, Object service, Dictionary properties) Registers the specified service object with the specified properties under the specified class names into the Framework.
ServiceRegistration	registerService(String clazz, Object service, Dictionary properties) Registers the specified service object with the specified properties under the specified class name with the Framework.
void	removeBundleListener(BundleListener listener) Removes the specified BundleListener object from the context bundle's list of listeners.
void	removeFrameworkListener(FrameworkListener listener) Removes the specified FrameworkListener object from the context bundle's list of listeners.
void	removeServiceListener(ServiceListener listener) Removes the specified ServiceListener object from the context bundle's list of listeners.
boolean	ungetService(ServiceReference reference) Releases the service object referenced by the specified ServiceReference object.

Method Detail

getProperty

String getProperty(String key)

Returns the value of the specified property. If the key is not found in the Framework properties, the system properties are then searched. The method returns null if the property is not found.

All bundles must have permission to read properties whose names start with "org.osgi.".

Parameters:

key - The name of the requested property.

Returns:

The value of the requested property, or null if the property is undefined.

Throws:

SecurityException - If the caller does not have the appropriate PropertyPermission to read the property, and the Java Runtime Environment supports permissions.

getBundle

Bundle getBundle()

Returns the Bundle object associated with this BundleContext. This bundle is called the context bundle.

Returns:

The Bundle object associated with this BundleContext.

Throws:

IllegalStateException - If this BundleContext is no longer valid.

installBundle

Bundle installBundle(String location,
                   InputStream input)
                     throws BundleException

Installs a bundle from the specified InputStream object.

If the specified InputStream is null, the Framework must create the InputStream from which to read the bundle by interpreting, in an implementation dependent manner, the specified location.

The specified location identifier will be used as the identity of the bundle. Every installed bundle is uniquely identified by its location identifier which is typically in the form of a URL.

The following steps are required to install a bundle:

1. If a bundle containing the same location identifier is already installed, the Bundle object for that bundle is returned.
2. The bundle's content is read from the input stream. If this fails, a BundleException is thrown.
3. The bundle's associated resources are allocated. The associated resources minimally consist of a unique identifier and a persistent storage area if the platform has file system support. If this step fails, a BundleException is thrown.
4. The bundle's state is set to INSTALLED.
5. A bundle event of type BundleEvent.INSTALLED is fired.
6. The Bundle object for the newly or previously installed bundle is returned.

Postconditions, no exceptions thrown

• getState() in { INSTALLED, RESOLVED }.
• Bundle has a unique ID.

Postconditions, when an exception is thrown

• Bundle is not installed and no trace of the bundle exists.

Parameters:

location - The location identifier of the bundle to install.

input - The InputStream object from which this bundle will be read or null to indicate the Framework must create the input stream from the specified location identifier. The input stream must always be closed when this method completes, even if an exception is thrown.

Returns:

The Bundle object of the installed bundle.

Throws:

BundleException - If the input stream cannot be read or the installation failed.

SecurityException - If the caller does not have the appropriate AdminPermission[installed bundle,LIFECYCLE], and the Java Runtime Environment supports permissions.

IllegalStateException - If this BundleContext is no longer valid.

installBundle

Bundle installBundle(String location)
                     throws BundleException

Installs a bundle from the specified location identifier.

This method performs the same function as calling installBundle(String,InputStream) with the specified location identifier and a null InputStream.

Parameters:

location - The location identifier of the bundle to install.

Returns:

The Bundle object of the installed bundle.

Throws:

BundleException - If the installation failed.

SecurityException - If the caller does not have the appropriate AdminPermission[installed bundle,LIFECYCLE], and the Java Runtime Environment supports permissions.

IllegalStateException - If this BundleContext is no longer valid.

See Also:

installBundle(String, InputStream)

getBundle

Bundle getBundle(long id)

Returns the bundle with the specified identifier.

Parameters:

id - The identifier of the bundle to retrieve.

Returns:

A Bundle object or null if the identifier does not match any installed bundle.

getBundles

Bundle[] getBundles()

Returns a list of all installed bundles.

This method returns a list of all bundles installed in the OSGi environment at the time of the call to this method. However, since the Framework is a very dynamic environment, bundles can be installed or uninstalled at anytime.

Returns:

An array of Bundle objects, one object per installed bundle.

addServiceListener

void addServiceListener(ServiceListener listener,
                      String filter)
                        throws InvalidSyntaxException

Adds the specified ServiceListener object with the specified filter to the context bundle's list of listeners. See Filter for a description of the filter syntax. ServiceListener objects are notified when a service has a lifecycle state change.

If the context bundle's list of listeners already contains a listener l such that (l==listener), then this method replaces that listener's filter (which may be null) with the specified one (which may be null).

The listener is called if the filter criteria is met. To filter based upon the class of the service, the filter should reference the Constants.OBJECTCLASS property. If filter is null, all services are considered to match the filter.

When using a filter, it is possible that the ServiceEvents for the complete lifecycle of a service will not be delivered to the listener. For example, if the filter only matches when the property x has the value 1, the listener will not be called if the service is registered with the property x not set to the value 1. Subsequently, when the service is modified setting property x to the value 1, the filter will match and the listener will be called with a ServiceEvent of type MODIFIED. Thus, the listener will not be called with a ServiceEvent of type REGISTERED.

If the Java Runtime Environment supports permissions, the ServiceListener object will be notified of a service event only if the bundle that is registering it has the ServicePermission to get the service using at least one of the named classes the service was registered under.

Parameters:

listener - The ServiceListener object to be added.

filter - The filter criteria.

Throws:

InvalidSyntaxException - If filter contains an invalid filter string that cannot be parsed.

IllegalStateException - If this BundleContext is no longer valid.

See Also:

ServiceEvent, ServiceListener, ServicePermission

addServiceListener

void addServiceListener(ServiceListener listener)

Adds the specified ServiceListener object to the context bundle's list of listeners.

This method is the same as calling BundleContext.addServiceListener(ServiceListener listener, String filter) with filter set to null.

Parameters:

listener - The ServiceListener object to be added.

Throws:

IllegalStateException - If this BundleContext is no longer valid.

See Also:

addServiceListener(ServiceListener, String)

removeServiceListener

void removeServiceListener(ServiceListener listener)

Removes the specified ServiceListener object from the context bundle's list of listeners.

If listener is not contained in this context bundle's list of listeners, this method does nothing.

Parameters:

listener - The ServiceListener to be removed.

Throws:

IllegalStateException - If this BundleContext is no longer valid.

addBundleListener

void addBundleListener(BundleListener listener)

Adds the specified BundleListener object to the context bundle's list of listeners if not already present. BundleListener objects are notified when a bundle has a lifecycle state change.

If the context bundle's list of listeners already contains a listener l such that (l==listener), this method does nothing.

Parameters:

listener - The BundleListener to be added.

Throws:

IllegalStateException - If this BundleContext is no longer valid.

SecurityException - If listener is a SynchronousBundleListener and the caller does not have the appropriate AdminPermission[context bundle,LISTENER], and the Java Runtime Environment supports permissions.

See Also:

BundleEvent, BundleListener

removeBundleListener

void removeBundleListener(BundleListener listener)

Removes the specified BundleListener object from the context bundle's list of listeners.

If listener is not contained in the context bundle's list of listeners, this method does nothing.

Parameters:

listener - The BundleListener object to be removed.

Throws:

IllegalStateException - If this BundleContext is no longer valid.

SecurityException - If listener is a SynchronousBundleListener and the caller does not have the appropriate AdminPermission[context bundle,LISTENER], and the Java Runtime Environment supports permissions.

addFrameworkListener

void addFrameworkListener(FrameworkListener listener)

Adds the specified FrameworkListener object to the context bundle's list of listeners if not already present. FrameworkListeners are notified of general Framework events.

If the context bundle's list of listeners already contains a listener l such that (l==listener), this method does nothing.

Parameters:

listener - The FrameworkListener object to be added.

Throws:

IllegalStateException - If this BundleContext is no longer valid.

See Also:

FrameworkEvent, FrameworkListener

removeFrameworkListener

void removeFrameworkListener(FrameworkListener listener)

Removes the specified FrameworkListener object from the context bundle's list of listeners.

If listener is not contained in the context bundle's list of listeners, this method does nothing.

Parameters:

listener - The FrameworkListener object to be removed.

Throws:

IllegalStateException - If this BundleContext is no longer valid.

registerService

ServiceRegistration registerService(String[] clazzes,
                                  Object service,
                                  Dictionary properties)

Registers the specified service object with the specified properties under the specified class names into the Framework. A ServiceRegistration object is returned. The ServiceRegistration object is for the private use of the bundle registering the service and should not be shared with other bundles. The registering bundle is defined to be the context bundle. Other bundles can locate the service by using either the getServiceReferences(java.lang.String, java.lang.String) or getServiceReference(java.lang.String) method.

A bundle can register a service object that implements the ServiceFactory interface to have more flexibility in providing service objects to other bundles.

The following steps are required to register a service:

1. If service is not a ServiceFactory, an IllegalArgumentException is thrown if service is not an instanceof all the specified class names.
2. The Framework adds the following service properties to the service properties from the specified Dictionary (which may be null):
   A property named Constants.SERVICE_ID identifying the registration number of the service
   A property named Constants.OBJECTCLASS containing all the specified classes.
   Properties with these names in the specified Dictionary will be ignored.
3. The service is added to the Framework service registry and may now be used by other bundles.
4. A service event of type ServiceEvent.REGISTERED is fired.
5. A ServiceRegistration object for this registration is returned.

Parameters:

clazzes - The class names under which the service can be located. The class names in this array will be stored in the service's properties under the key Constants.OBJECTCLASS.

service - The service object or a ServiceFactory object.

properties - The properties for this service. The keys in the properties object must all be String objects. See Constants for a list of standard service property keys. Changes should not be made to this object after calling this method. To update the service's properties the ServiceRegistration.setProperties(java.util.Dictionary) method must be called. The set of properties may be null if the service has no properties.

Returns:

A ServiceRegistration object for use by the bundle registering the service to update the service's properties or to unregister the service.

Throws:

IllegalArgumentException - If one of the following is true:

• service is null.
• service is not a ServiceFactory object and is not an instance of all the named classes in clazzes.
• properties contains case variants of the same key name.

SecurityException - If the caller does not have the ServicePermission to register the service for all the named classes and the Java Runtime Environment supports permissions.

IllegalStateException - If this BundleContext is no longer valid.

See Also:

ServiceRegistration, ServiceFactory

registerService

ServiceRegistration registerService(String clazz,
                                  Object service,
                                  Dictionary properties)

Registers the specified service object with the specified properties under the specified class name with the Framework.

This method is otherwise identical to registerService(String[], Object, Dictionary) and is provided as a convenience when service will only be registered under a single class name. Note that even in this case the value of the service's Constants.OBJECTCLASS property will be an array of string, rather than just a single string.

Parameters:

clazz - The class name under which the service can be located.

service - The service object or a ServiceFactory object.

properties - The properties for this service.

Returns:

A ServiceRegistration object for use by the bundle registering the service to update the service's properties or to unregister the service.

Throws:

IllegalStateException - If this BundleContext is no longer valid.

See Also:

registerService(String[], Object, Dictionary)

getServiceReferences

ServiceReference[] getServiceReferences(String clazz,
                                      String filter)
                                        throws InvalidSyntaxException

Returns an array of ServiceReference objects. The returned array of ServiceReference objects contains services that were registered under the specified class, match the specified filter expression, and the packages for the class names under which the services were registered match the context bundle's packages as defined in ServiceReference.isAssignableTo(Bundle, String).

The list is valid at the time of the call to this method. However since the Framework is a very dynamic environment, services can be modified or unregistered at any time.

The specified filter expression is used to select the registered services whose service properties contain keys and values which satisfy the filter expression. See Filter for a description of the filter syntax. If the specified filter is null, all registered services are considered to match the filter. If the specified filter expression cannot be parsed, an InvalidSyntaxException will be thrown with a human readable message where the filter became unparsable.

The result is an array of ServiceReference objects for all services that meet all of the following conditions:

• If the specified class name, clazz, is not null, the service must have been registered with the specified class name. The complete list of class names with which a service was registered is available from the service's objectClass property.
• If the specified filter is not null, the filter expression must match the service.
• If the Java Runtime Environment supports permissions, the caller must have ServicePermission with the GET action for at least one of the class names under which the service was registered.
• For each class name with which the service was registered, calling ServiceReference.isAssignableTo(Bundle, String) with the context bundle and the class name on the service's ServiceReference object must return true

Parameters:

clazz - The class name with which the service was registered or null for all services.

filter - The filter expression or null for all services.

Returns:

An array of ServiceReference objects or null if no services are registered which satisfy the search.

Throws:

InvalidSyntaxException - If the specified filter contains an invalid filter expression that cannot be parsed.

IllegalStateException - If this BundleContext is no longer valid.

getAllServiceReferences

ServiceReference[] getAllServiceReferences(String clazz,
                                         String filter)
                                           throws InvalidSyntaxException

Returns an array of ServiceReference objects. The returned array of ServiceReference objects contains services that were registered under the specified class and match the specified filter expression.

The list is valid at the time of the call to this method. However since the Framework is a very dynamic environment, services can be modified or unregistered at any time.

The specified filter expression is used to select the registered services whose service properties contain keys and values which satisfy the filter expression. See Filter for a description of the filter syntax. If the specified filter is null, all registered services are considered to match the filter. If the specified filter expression cannot be parsed, an InvalidSyntaxException will be thrown with a human readable message where the filter became unparsable.

The result is an array of ServiceReference objects for all services that meet all of the following conditions:

• If the specified class name, clazz, is not null, the service must have been registered with the specified class name. The complete list of class names with which a service was registered is available from the service's objectClass property.
• If the specified filter is not null, the filter expression must match the service.
• If the Java Runtime Environment supports permissions, the caller must have ServicePermission with the GET action for at least one of the class names under which the service was registered.

Parameters:

clazz - The class name with which the service was registered or null for all services.

filter - The filter expression or null for all services.

Returns:

An array of ServiceReference objects or null if no services are registered which satisfy the search.

Throws:

InvalidSyntaxException - If the specified filter contains an invalid filter expression that cannot be parsed.

IllegalStateException - If this BundleContext is no longer valid.

Since:

1.3

getServiceReference

ServiceReference getServiceReference(String clazz)

Returns a ServiceReference object for a service that implements and was registered under the specified class.

The returned ServiceReference object is valid at the time of the call to this method. However as the Framework is a very dynamic environment, services can be modified or unregistered at any time.

This method is the same as calling getServiceReferences(String, String) with a null filter expression. It is provided as a convenience for when the caller is interested in any service that implements the specified class.

If multiple such services exist, the service with the highest ranking (as specified in its Constants.SERVICE_RANKING property) is returned.

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

Parameters:

clazz - The class name with which the service was registered.

Returns:

A ServiceReference object, or null if no services are registered which implement the named class.

Throws:

IllegalStateException - If this BundleContext is no longer valid.

See Also:

getServiceReferences(String, String)

getService

Object getService(ServiceReference reference)

Returns the service object referenced by the specified ServiceReference object.

A bundle's use of a service is tracked by the bundle's use count of that service. Each time a service's service object is returned by getService(ServiceReference) the context bundle's use count for that service is incremented by one. Each time the service is released by ungetService(ServiceReference) the context bundle's use count for that service is decremented by one.

When a bundle's use count for a service drops to zero, the bundle should no longer use that service.

This method will always return null when the service associated with this reference has been unregistered.

The following steps are required to get the service object:

1. If the service has been unregistered, null is returned.
2. The context bundle's use count for this service is incremented by one.
3. If the context bundle's use count for the service is currently one and the service was registered with an object implementing the ServiceFactory interface, the ServiceFactory.getService(Bundle, ServiceRegistration) method is called to create a service object for the context bundle. This service object is cached by the Framework. While the context bundle's use count for the service is greater than zero, subsequent calls to get the services's service object for the context bundle will return the cached service object.
   If the service object returned by the ServiceFactory object is not an instanceof all the classes named when the service was registered or the ServiceFactory object throws an exception, null is returned and a Framework event of type FrameworkEvent.ERROR containing a ServiceException describing the error is fired.
4. The service object for the service is returned.

Parameters:

reference - A reference to the service.

Returns:

A service object for the service associated with reference or null if the service is not registered, the service object returned by a ServiceFactory does not implement the classes under which it was registered or the ServiceFactory threw an exception.

Throws:

SecurityException - If the caller does not have the ServicePermission to get the service using at least one of the named classes the service was registered under and the Java Runtime Environment supports permissions.

IllegalStateException - If this BundleContext is no longer valid.

IllegalArgumentException - If the specified ServiceReference was not created by the same framework instance as this BundleContext.

See Also:

ungetService(ServiceReference), ServiceFactory

ungetService

boolean ungetService(ServiceReference reference)

Releases the service object referenced by the specified ServiceReference object. If the context bundle's use count for the service is zero, this method returns false. Otherwise, the context bundle's use count for the service is decremented by one.

The service's service object should no longer be used and all references to it should be destroyed when a bundle's use count for the service drops to zero.

The following steps are required to unget the service object:

1. If the context bundle's use count for the service is zero or the service has been unregistered, false is returned.
2. The context bundle's use count for this service is decremented by one.
3. If the context bundle's use count for the service is currently zero and the service was registered with a ServiceFactory object, the ServiceFactory.ungetService(Bundle, ServiceRegistration, Object) method is called to release the service object for the context bundle.
4. true is returned.

Parameters:

reference - A reference to the service to be released.

Returns:

false if the context bundle's use count for the service is zero or if the service has been unregistered; true otherwise.

Throws:

IllegalStateException - If this BundleContext is no longer valid.

IllegalArgumentException - If the specified ServiceReference was not created by the same framework instance as this BundleContext.

See Also:

getService(org.osgi.framework.ServiceReference), ServiceFactory

getDataFile

File getDataFile(String filename)

Creates a File object for a file in the persistent storage area provided for the bundle by the Framework. This method will return null if the platform does not have file system support.

A File object for the base directory of the persistent storage area provided for the context bundle by the Framework can be obtained by calling this method with an empty string as filename.

If the Java Runtime Environment supports permissions, the Framework will ensure that the bundle has the java.io.FilePermission with actions read,write,delete for all files (recursively) in the persistent storage area provided for the context bundle.

Parameters:

filename - A relative name to the file to be accessed.

Returns:

A File object that represents the requested file or null if the platform does not have file system support.

Throws:

IllegalStateException - If this BundleContext is no longer valid.

createFilter

Filter createFilter(String filter)
                    throws InvalidSyntaxException

Creates a Filter object. This Filter object may be used to match a ServiceReference object or a Dictionary object.

If the filter cannot be parsed, an InvalidSyntaxException will be thrown with a human readable message where the filter became unparsable.

Parameters:

filter - The filter string.

Returns:

A Filter object encapsulating the filter string.

Throws:

InvalidSyntaxException - If filter contains an invalid filter string that cannot be parsed.

NullPointerException - If filter is null.

IllegalStateException - If this BundleContext is no longer valid.

Since:

1.1

See Also:

"Framework specification for a description of the filter string syntax.", FrameworkUtil.createFilter(String)