Class EventBridge
- java.lang.Object
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- org.apache.cayenne.event.EventBridge
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- 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
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Field Summary
Fields Modifier and Type Field Description protected EventManager
eventManager
protected Object
externalEventSource
protected String
externalSubject
protected Collection<EventSubject>
localSubjects
protected int
mode
static int
RECEIVE_EXTERNAL
static int
RECEIVE_LOCAL
static int
RECEIVE_LOCAL_EXTERNAL
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Constructor Summary
Constructors Constructor Description EventBridge(Collection<EventSubject> localSubjects, String externalSubject)
Creates an EventBridge with multiple local subjects and a single external subject.EventBridge(EventSubject localSubject, String externalSubject)
Creates an EventBridge with a single local subject.
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Method Summary
All Methods Static Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description 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.EventManager
getEventManager()
Returns local EventManager used by the bridge.Object
getExternalEventSource()
Returns an object used as a source of local events posted in response to remote events.String
getExternalSubject()
Returns a String subject used to post distributed events.Collection<EventSubject>
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.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, Object localEventSource)
Starts EventBridge in the specified mode and locally listening to a specified event source.void
startup(EventManager eventManager, int mode, Object localEventSource, Object remoteEventSource)
Starts EventBridge in the specified mode.protected abstract void
startupExternal()
Starts an external interface of the EventBridge.
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Field Detail
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RECEIVE_LOCAL
public static final int RECEIVE_LOCAL
- See Also:
- Constant Field Values
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RECEIVE_EXTERNAL
public static final int RECEIVE_EXTERNAL
- See Also:
- Constant Field Values
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RECEIVE_LOCAL_EXTERNAL
public static final int RECEIVE_LOCAL_EXTERNAL
- See Also:
- Constant Field Values
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externalSubject
protected String externalSubject
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localSubjects
protected Collection<EventSubject> localSubjects
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eventManager
protected EventManager eventManager
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mode
protected int mode
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externalEventSource
protected Object externalEventSource
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Constructor Detail
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EventBridge
public EventBridge(EventSubject localSubject, String externalSubject)
Creates an EventBridge with a single local subject.
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EventBridge
public EventBridge(Collection<EventSubject> localSubjects, String externalSubject)
Creates an EventBridge with multiple local subjects and a single external subject.- Since:
- 1.2
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Method Detail
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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, ...?).
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getExternalSubject
public String getExternalSubject()
Returns a String subject used to post distributed events.
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isRunning
public boolean isRunning()
Returns true if this bridge is active.- Since:
- 1.2
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getLocalSubjects
public Collection<EventSubject> getLocalSubjects()
Returns a Collection of local EventSubjects.- Since:
- 1.2
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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
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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
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receivesLocalEvents
public boolean receivesLocalEvents()
Returns true if the bridge is configured to receive local events from its internal EventManager.
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receivesExternalEvents
public boolean receivesExternalEvents()
Returns true if the bridge is configured to receive external events.
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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
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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
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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
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startupExternal
protected abstract void startupExternal() throws Exception
Starts an external interface of the EventBridge.- Throws:
Exception
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shutdown
public void shutdown() throws Exception
Stops listening for events on both local and external interfaces.- Throws:
Exception
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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
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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.
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sendExternalEvent
protected abstract void sendExternalEvent(CayenneEvent localEvent) throws Exception
Sends a Cayenne event over the transport supported by this bridge.- Throws:
Exception
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