Package org.apache.cayenne.event

Class EventBridge

java.lang.Object
org.apache.cayenne.event.EventBridge
All Implemented Interfaces:
EventListener
Direct Known Subclasses:
NoopEventBridge
public abstract class EventBridge extends Object implements EventListener

An object that passes events between a local EventManager and some other event dispatch mechanism. The most common example is sending local events to remote JVMs and receiving remote events dispatched by those VMs. EventBridge makes possible to connect a network of regular EventManagers in a single "virtual" distributed EventManager.

EventBridge encapsulates a transport agreed upon by all paries (such as JMS) and maintains an array of "local" subjects to communicate with local EventManager, and a single "remote" subject - to use for "external" communications that are transport-specific.

Subclasses that require special setup to listen for external events should implement startupExternal() method accordingly.

This class is an example of "bridge" design pattern, hence the name.

Since:
1.1

  • Field Details

  • Constructor Details

    • EventBridge

      public EventBridge(EventSubject localSubject, String externalSubject)
      Creates an EventBridge with a single local subject.

    • EventBridge

      public EventBridge(Collection<EventSubject> localSubjects, String externalSubject)
      Creates an EventBridge with multiple local subjects and a single external subject.
      Since:
      1.2

  • Method Details

    • convertToExternalSubject

      public static String convertToExternalSubject(EventSubject localSubject)
      A utility method that performs consistent translation from an EventSubject to a String that can be used by external transport as subject for distributed communications. Substitutes all chars that can be incorrectly interpreted by whoever (JNDI, ...?).

    • getExternalSubject

      public String getExternalSubject()
      Returns a String subject used to post distributed events.

    • isRunning

      public boolean isRunning()
      Returns true if this bridge is active.
      Since:
      1.2

    • getLocalSubjects

      public Collection<EventSubject> getLocalSubjects()
      Returns a Collection of local EventSubjects.
      Since:
      1.2

    • getEventManager

      public EventManager getEventManager()
      Returns local EventManager used by the bridge. Returned value will be null before the bridge is started and after it is shutdown.
      Since:
      1.2

    • getExternalEventSource

      public Object getExternalEventSource()
      Returns an object used as a source of local events posted in response to remote events. If externalEventSource wasn't setup during bridge startup (or if the bridge is not started), returns this object.
      Since:
      1.2

    • receivesLocalEvents

      public boolean receivesLocalEvents()
      Returns true if the bridge is configured to receive local events from its internal EventManager.

    • receivesExternalEvents

      public boolean receivesExternalEvents()
      Returns true if the bridge is configured to receive external events.

    • startup

      public void startup(EventManager eventManager, int mode) throws Exception
      Starts EventBridge in the specified mode and locally listening to all event sources that post on a preconfigured subject. Remote events reposted locally will have this EventBridge as their source.
      Parameters:
      eventManager - EventManager used to send and receive local events.
      mode - One of the possible modes of operation - RECEIVE_EXTERNAL, RECEIVE_LOCAL, RECEIVE_LOCAL_EXTERNAL.
      Throws:
      Exception

    • startup

      public void startup(EventManager eventManager, int mode, Object localEventSource) throws Exception
      Starts EventBridge in the specified mode and locally listening to a specified event source. Remote events reposted locally will have this EventBridge as their source.
      Parameters:
      eventManager - EventManager used to send and receive local events.
      mode - One of the possible modes of operation - RECEIVE_EXTERNAL, RECEIVE_LOCAL, RECEIVE_LOCAL_EXTERNAL.
      localEventSource - If not null, only events originating from localEventSource object will be processed by this bridge.
      Throws:
      Exception

    • startup

      public void startup(EventManager eventManager, int mode, Object localEventSource, Object remoteEventSource) throws Exception
      Starts EventBridge in the specified mode.
      Parameters:
      eventManager - EventManager used to send and receive local events.
      mode - One of the possible modes of operation - RECEIVE_EXTERNAL, RECEIVE_LOCAL, RECEIVE_LOCAL_EXTERNAL.
      localEventSource - If not null, only events originating from localEventSource object will be processed by this bridge.
      remoteEventSource - If not null, remoteEventSource object will be used as standby source of local events posted by this EventBridge in response to remote events.
      Throws:
      Exception
      Since:
      1.2

    • startupExternal

      protected abstract void startupExternal() throws Exception
      Starts an external interface of the EventBridge.
      Throws:
      Exception

    • shutdown

      public void shutdown() throws Exception
      Stops listening for events on both local and external interfaces.
      Throws:
      Exception

    • shutdownExternal

      protected abstract void shutdownExternal() throws Exception
      Shuts down the external interface of the EventBridge, cleaning up and releasing any resources used to communicate external events.
      Throws:
      Exception

    • onExternalEvent

      protected void onExternalEvent(CayenneEvent event)
      Helper method intended to be called explicitly by subclasses to asynchronously post an event obtained from a remote source. Subclasses do not have to use this method, but they probably should for consistency.

    • sendExternalEvent

      protected abstract void sendExternalEvent(CayenneEvent localEvent) throws Exception
      Sends a Cayenne event over the transport supported by this bridge.
      Throws:
      Exception