org.apache.cayenne.event
Class EventBridge

java.lang.Object
  org.apache.cayenne.event.EventBridge

All Implemented Interfaces:

java.util.EventListener

Direct Known Subclasses:

JavaGroupsBridge, JMSBridge, XMPPBridge

public abstract class EventBridge
extends java.lang.Object
implements java.util.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

Author:

Andrus Adamchik

Field Summary

protected EventManager	eventManager
protected java.lang.Object	externalEventSource
protected java.lang.String	externalSubject
protected java.util.Collection	localSubjects
protected int	mode
static int	RECEIVE_EXTERNAL
static int	RECEIVE_LOCAL
static int	RECEIVE_LOCAL_EXTERNAL
static java.lang.String	VM_ID Deprecated. unused since 1.2
static java.lang.String	VM_ID_PROPERRTY Deprecated. unused since 1.2

Constructor Summary

EventBridge(java.util.Collection localSubjects, java.lang.String externalSubject)
Creates an EventBridge with multiple local subjects and a single external subject.

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

Method Summary

static java.lang.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.
EventManager	getEventManager() Returns local EventManager used by the bridge.
java.lang.Object	getExternalEventSource() Returns an object used as a source of local events posted in response to remote events.
java.lang.String	getExternalSubject() Returns a String subject used to post distributed events.
EventSubject	getLocalSubject() Deprecated. since 1.2 EventBridge supports multiple local subjects, so use 'getLocalSubjects()' instead. This method returns the first subject from the subject array for backwards compatibility.
java.util.Collection	getLocalSubjects() Returns a Collection of local EventSubjects.
boolean	isRunning() Returns true if this bridge is active.
protected void	onExternalEvent(CayenneEvent event) Helper method intended to be called explicitly by subclasses to asynchronously post an event obtained from a remote source.
void	onLocalEvent(CayenneEvent event) Deprecated. Unused since 1.2, as event dispatch is done via internal listeners.
boolean	receivesExternalEvents() Returns true if the bridge is configured to receive external events.
boolean	receivesLocalEvents() Returns true if the bridge is configured to receive local events from its internal EventManager.
protected abstract void	sendExternalEvent(CayenneEvent localEvent) Sends a Cayenne event over the transport supported by this bridge.
void	shutdown() Stops listening for events on both local and external interfaces.
protected abstract void	shutdownExternal() Shuts down the external interface of the EventBridge, cleaning up and releasing any resources used to communicate external events.
void	startup(EventManager eventManager, int mode) Starts EventBridge in the specified mode and locally listening to all event sources that post on a preconfigured subject.
void	startup(EventManager eventManager, int mode, java.lang.Object localEventSource) Starts EventBridge in the specified mode and locally listening to a specified event source.
void	startup(EventManager eventManager, int mode, java.lang.Object localEventSource, java.lang.Object remoteEventSource) Starts EventBridge in the specified mode.
protected abstract void	startupExternal() Starts an external interface of the EventBridge.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

VM_ID

public static final java.lang.String VM_ID

Deprecated. unused since 1.2

VM_ID_PROPERRTY

public static final java.lang.String VM_ID_PROPERRTY

Deprecated. unused since 1.2

See Also:

Constant Field Values

RECEIVE_LOCAL

public static final int RECEIVE_LOCAL

See Also:

Constant Field Values

RECEIVE_EXTERNAL

public static final int RECEIVE_EXTERNAL

See Also:

Constant Field Values

RECEIVE_LOCAL_EXTERNAL

public static final int RECEIVE_LOCAL_EXTERNAL

See Also:

Constant Field Values

externalSubject

protected java.lang.String externalSubject

localSubjects

protected java.util.Collection localSubjects

eventManager

protected EventManager eventManager

mode

protected int mode

externalEventSource

protected java.lang.Object externalEventSource

Constructor Detail

EventBridge

public EventBridge(EventSubject localSubject,
                   java.lang.String externalSubject)

Creates an EventBridge with a single local subject.

EventBridge

public EventBridge(java.util.Collection localSubjects,
                   java.lang.String externalSubject)

Creates an EventBridge with multiple local subjects and a single external subject.

Since:

1.2

Method Detail

convertToExternalSubject

public static java.lang.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 java.lang.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

getLocalSubject

public EventSubject getLocalSubject()

Deprecated. since 1.2 EventBridge supports multiple local subjects, so use 'getLocalSubjects()' instead. This method returns the first subject from the subject array for backwards compatibility.

Returns a subject used for events within the local JVM.

getLocalSubjects

public java.util.Collection 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 java.lang.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 java.lang.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:

java.lang.Exception

startup

public void startup(EventManager eventManager,
                    int mode,
                    java.lang.Object localEventSource)
             throws java.lang.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:

java.lang.Exception

startup

public void startup(EventManager eventManager,
                    int mode,
                    java.lang.Object localEventSource,
                    java.lang.Object remoteEventSource)
             throws java.lang.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:

java.lang.Exception

Since:

1.2

startupExternal

protected abstract void startupExternal()
                                 throws java.lang.Exception

Starts an external interface of the EventBridge.

Throws:

java.lang.Exception

shutdown

public void shutdown()
              throws java.lang.Exception

Stops listening for events on both local and external interfaces.

Throws:

java.lang.Exception

shutdownExternal

protected abstract void shutdownExternal()
                                  throws java.lang.Exception

Shuts down the external interface of the EventBridge, cleaning up and releasing any resources used to communicate external events.

Throws:

java.lang.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.

onLocalEvent

public void onLocalEvent(CayenneEvent event)
                  throws java.lang.Exception

Deprecated. Unused since 1.2, as event dispatch is done via internal listeners.

Invoked by local EventManager when a local event of interest occurred. Internally delegates to "sendExternalEvent" abstract method.

Throws:

java.lang.Exception

sendExternalEvent

protected abstract void sendExternalEvent(CayenneEvent localEvent)
                                   throws java.lang.Exception

Sends a Cayenne event over the transport supported by this bridge.

Throws:

java.lang.Exception