Java Reference
In-Depth Information
■
int
or
Integer
—Receives the reason why the component is being deactivated,
where the value is one of the following reasons:
◆
0—Unspecified.
1—The component was disabled.
◆
2—A reference became unsatisfied.
◆
3—A configuration was changed.
◆
4—A configuration was deleted.
◆
5—The component was disposed.
◆
6—The bundle was stopped.
◆
Of these arguments, you know little yet about
ComponentContext
. What is its purpose?
USING THE COMPONENTCONTEXT
The Declarative Services framework creates a unique
ComponentContext
object for
each component it activates. This object plays a role for components similar to the
role the
BundleContext
object plays for bundles—it provides access to execution envi-
ronment facilities. The
ComponentContext
interface is as follows:
public interface ComponentContext {
public Dictionary getProperties();
public Object locateService(String name);
public Object locateService(String name, ServiceReference reference);
public Object[] locateServices(String name);
public BundleContext getBundleContext();
public Bundle getUsingBundle();
public ComponentInstance getComponentInstance();
public void enableComponent(String name);
public void disableComponent(String name);
public ServiceReference getServiceReference();
}
The
getProperties()
method allows a component to access its configuration proper-
ties. The methods for locating services provide an alternative approach to service
injection for using services; this alternative strategy is discussed in the “Lookup strat-
egy” sidebar. The
getBundleContext()
method provides access to the containing bun-
dle's
BundleContext
object. The
getUsingBundle()
method is related to component
factories, which we'll discuss later.
The
getComponentInstance()
,
enableComponent()
, and
disableComponent()
methods provide a component with a way to programmatically control the compo-
nent lifecycle; we'll discuss them further in the next section. Finally, the
getService-
Reference()
method allows a component to access the
ServiceReference
of this
component if it provides a service.
In the general case, whether or not a component is satisfied is dictated by whether
or not its service dependencies are satisfied. But this isn't the only type of dependency
considered by Declarative Services; another situation is where a component is depen-
dent on its configuration properties.
