Package org.onehippo.cms7.services

Class WhiteboardServiceRegistry<T>

  • Type Parameters:
    T - service object implementation type
    Direct Known Subclasses:
    HippoEventListenerRegistry, HippoWebappContextRegistry
    public abstract class WhiteboardServiceRegistry<T>
extends Object
    WhiteboardServiceRegistry<T> is an abstract base class for implementing and using the Whiteboard Patternfor decoupled lookup/wiring of multiple service objects by a common (base) type, which can be a class or interface.

    This WhiteboardServiceRegistry base class supports (un)registering service objects, and ServiceTrackers to retrieve those currently registered as well as be notified on future (un)registrations. Currently registered service object holders also can be retrieved through getEntries().

    All service objects registered through a WhiteboardServiceRegistry implementation need to be an instanceof of a common class or interface type T.

    For example with the following (complete) HippoEventListenerRegistry implementation, using implementation type Object, effectively all possible service objects can be registered: 

    
     public final class HippoEventListenerRegistry extends WhiteboardServiceRegistry<Object> {

         private static final HippoEventListenerRegistry INSTANCE = new HippoEventListenerRegistry();

         private HippoEventListenerRegistry() {}

         public static HippoEventListenerRegistry get() { return INSTANCE; }
     }

    For a typical usage of a WhiteboardServiceRegistry see the javadoc for the HippoEventListenerRegistry and HippoEventBus service interface.

    A more restricted variation is the PersistedHippoEventListenerRegistry in the hippo-repository-api module which is restricted to registering service objects implementing the PersistedHippoEventListener interface.

    For each registered service object a ServiceHolder is created and passed on to the ServiceTracker(s) (if any), which is just holding the service object itself together with the context classloader used to register the object. The serviceRegistered * and serviceUnregistered callback methods * provided by the service tracker will be invoked using the context classloader of the service tracker.

    When one or more service objects (only) should be exposed through a common service interface (and optionally additional interfaces), use the WhiteboardProxiedServiceRegistry<T> base class instead, or the HippoServiceRegistry for singleton service registration and lookup, like for the HippoEventBus service.

    • Constructor Detail

      • WhiteboardServiceRegistry

        public WhiteboardServiceRegistry()

    • Method Detail

      • register

        public void register​(T serviceObject)
              throws HippoServiceException
        Register a service object of type <T>
        Parameters:
        serviceObject - the service object
        Throws:
        HippoServiceException - when the service object was already registered

      • unregister

        public boolean unregister​(T serviceObject)
        Unregister a previously registered service object
        Parameters:
        serviceObject - the service object
        Returns:
        true if the service object was registered before and now removed, false otherwise

      • removeTracker

        public boolean removeTracker​(ServiceTracker<T> tracker)
        Remove a previously added ServiceObjectTracker<T>.
        Parameters:
        tracker - the tracker
        Returns:
        true if the tracker was added before and now removed, false otherwise

      • size

        public int size()
        Returns:
        the number of services registered