Class ServiceCaller<S>
- Type Parameters:
S
- the service type for this caller
ServiceCaller
provides functional methods for invoking OSGi services
in two different ways
- Single invocations which happen only once or very rarely. In this case, maintaining a cache of the service is not worth the overhead.
- Multiple invocations that happen often and rapidly. In this case, maintaining a cache of the service is worth the overhead.
For single invocations of a service the static method
callOnce(Class, Class, Consumer)
can be used. This
method will wrap a call to the consumer of the service with the necessary
OSGi service registry calls to ensure the service exists and will do the
proper get and release service operations surround the calls to the service.
By wrapping a call around the service we can ensure that it is correctly
released after use.
Single invocation example:
ServiceCaller.callOnce(MyClass.class, ILog.class, (logger) -> logger.info("All systems go!"));
Note that it is generally more efficient to use a long-running service
utility, such as ServiceTracker
or declarative services, but there
are cases where a single one-shot lookup is preferable, especially if the
service is not required after use. Examples might include logging unlikely
conditions or processing debug options that are only read once.
This allows boilerplate code to be reduced at call sites, which would otherwise have to do something like:
Bundle bundle = FrameworkUtil.getBundle(BadExample.class); BundleContext context = bundle == null ? null : bundle.getBundleContext(); ServiceReference<Service> reference = context == null ? null : context.getServiceReference(serviceType); try { Service service = reference == null ? null : context.getService(reference); if (service != null) consumer.accept(service); } finally { context.ungetService(reference); }
For cases where a service is used much more often a ServiceCaller
instance can be used to cache and track the available service. This may be
useful for cases that cannot use declarative services and that want to avoid
using something like a ServiceTracker
that does not easily allow for
lazy instantiation of the service instance. For example, if logging is used
more often then something like the following could be used:
static final ServiceCaller<ILog> log = new ServiceCaller(MyClass.class, ILog.class); static void info(String msg) { log.call(logger -> logger.info(msg)); }
Note that this class is intended for simple service usage patterns only. More
advanced cases should use other mechanisms such as the ServiceTracker
or declarative services.
- Since:
- 3.13
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Constructor Summary
ConstructorDescriptionServiceCaller
(Class<?> caller, Class<S> serviceType) Creates aServiceCaller
instance for invoking an OSGi service many times with a consumer function.ServiceCaller
(Class<?> caller, Class<S> serviceType, String filter) Creates aServiceCaller
instance for invoking an OSGi service many times with a consumer function. -
Method Summary
Modifier and TypeMethodDescriptionboolean
Calls an OSGi service by dynamically looking it up and passing it to the given consumer.static <S> boolean
AscallOnce(Class, Class, Consumer)
with an additional OSGi filter.static <S> boolean
Calls an OSGi service by dynamically looking it up and passing it to the given consumer.current()
Return the currently available service.void
unget()
Releases the cached service object, if it exists.
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Constructor Details
-
ServiceCaller
Creates aServiceCaller
instance for invoking an OSGi service many times with a consumer function.- Parameters:
caller
- a class from the bundle that will consume the serviceserviceType
- the OSGi service type to look up- Throws:
NullPointerException
- if any of the parameters arenull
IllegalStateException
- if the bundle associated with the caller class cannot be determined
-
ServiceCaller
Creates aServiceCaller
instance for invoking an OSGi service many times with a consumer function.- Parameters:
caller
- a class from the bundle that will consume the serviceserviceType
- the OSGi service type to look upfilter
- the service filter used to look up the service. May benull
.- Throws:
NullPointerException
- if any of the parameters arenull
IllegalStateException
- if the bundle associated with the caller class cannot be determined
-
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Method Details
-
callOnce
Calls an OSGi service by dynamically looking it up and passing it to the given consumer.If not running under OSGi, the caller bundle is not active or the service is not available, return false. If the service is found, call the service and return true.
Any runtime exception thrown by the consumer is rethrown by this method. If the consumer throws a checked exception, it can be propagated using a sneakyThrow inside a try/catch block:
callOnce(MyClass.class, Callable.class, (callable) -> { try { callable.call(); } catch (Exception e) { sneakyThrow(e); } }); ... @SuppressWarnings("unchecked") static <E extends Throwable> void sneakyThrow(Throwable e) throws E { throw (E) e; }
- Type Parameters:
S
- the OSGi service type to look up- Parameters:
caller
- a class from the bundle that will use serviceserviceType
- the OSGi service type to look upconsumer
- the consumer of the OSGi service- Returns:
- true if the OSGi service was located and called successfully, false otherwise
- Throws:
NullPointerException
- if any of the parameters arenull
IllegalStateException
- if the bundle associated with the caller class cannot be determined
-
callOnce
public static <S> boolean callOnce(Class<?> caller, Class<S> serviceType, String filter, Consumer<S> consumer) AscallOnce(Class, Class, Consumer)
with an additional OSGi filter.- Type Parameters:
S
- the OSGi service type to look up- Parameters:
caller
- a class from the bundle that will use serviceserviceType
- the OSGi service type to look upconsumer
- the consumer of the OSGi servicefilter
- an OSGi filter to restrict the services found- Returns:
- true if the OSGi service was located and called successfully, false otherwise
- Throws:
NullPointerException
- if any of the parameters arenull
IllegalStateException
- if the bundle associated with the caller class cannot be determined
-
call
Calls an OSGi service by dynamically looking it up and passing it to the given consumer. If not running under OSGi, the caller bundle is not active or the service is not available, return false. Any runtime exception thrown by the consumer is rethrown by this method. (For handling checked exceptions, seecallOnce(Class, Class, Consumer)
for a solution.) Subsequent calls to this method will attempt to reuse the previously acquired service instance until one of the following occurs:- The
unget()
method is called. - The service is unregistered.
- The service properties change such that this
ServiceCaller
filter no longer matches. - The caller bundle is stopped.
- The service rankings have changed.
- Parameters:
consumer
- the consumer of the OSGi service- Returns:
- true if the OSGi service was located and called successfully, false otherwise
- The
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current
Return the currently available service.- Returns:
- the currently available service or empty if the service cannot be found.
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unget
public void unget()Releases the cached service object, if it exists. Another invocation ofcall(Consumer)
will lazily get the service instance again and cache the new instance if found.
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