The Spring Framework

org.springframework.context.event
Class AbstractApplicationEventMulticaster

java.lang.Object
  extended by org.springframework.context.event.AbstractApplicationEventMulticaster
All Implemented Interfaces:
ApplicationEventMulticaster
Direct Known Subclasses:
SimpleApplicationEventMulticaster

public abstract class AbstractApplicationEventMulticaster
extends Object
implements ApplicationEventMulticaster

Abstract implementation of the ApplicationEventMulticaster interface, providing the basic listener registration facility.

Doesn't permit multiple instances of the same listener by default, as it keeps listeners in a linked Set. The collection class used to hold ApplicationListener objects can be overridden through the "collectionClass" bean property.

Note that this class doesn't try to do anything clever to ensure thread safety if listeners are added or removed at runtime. A technique such as Copy-on-Write (Lea:137) could be used to ensure this, but the assumption in the basic version of the class is that listeners will be added at application configuration time and not added or removed as the application runs.

A custom collection class must be specified to allow for thread-safe runtime registration of listeners. A good candidate for this is Doug Lea's java.util.concurrent.CopyOnWriteArraySet or its non-JDK predecessor, EDU.oswego.cs.dl.util.concurrent.CopyOnWriteArraySet (or the respective CopyOnWriteArrayList version, allowing for registering the same listener multiple times). Those classes provide a thread-safe Iterator, optimized for read-mostly usage - matching this use case nicely.

Implementing ApplicationEventMulticaster's actual ApplicationEventMulticaster.multicastEvent(org.springframework.context.ApplicationEvent) method is left to subclasses. SimpleApplicationEventMulticaster simply multicasts all events to all registered listeners, invoking them in the calling thread. Alternative implementations could be more sophisticated in those respects.

Since:
1.2.3
Author:
Juergen Hoeller
See Also:
setCollectionClass(java.lang.Class), getApplicationListeners(), SimpleApplicationEventMulticaster

Constructor Summary
AbstractApplicationEventMulticaster()
           
 
Method Summary
 void addApplicationListener(ApplicationListener listener)
          Add a listener to be notified of all events.
protected  Collection getApplicationListeners()
          Return the current Collection of ApplicationListeners.
 void removeAllListeners()
          Remove all listeners registered with this multicaster.
 void removeApplicationListener(ApplicationListener listener)
          Remove a listener from the notification list.
 void setCollectionClass(Class collectionClass)
          Specify the collection class to use.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 
Methods inherited from interface org.springframework.context.event.ApplicationEventMulticaster
multicastEvent
 

Constructor Detail

AbstractApplicationEventMulticaster

public AbstractApplicationEventMulticaster()
Method Detail

setCollectionClass

public void setCollectionClass(Class collectionClass)
Specify the collection class to use. Can be populated with a fully qualified class name when defined in a Spring application context.

Default is a linked HashSet, keeping the registration order. If no linked Set implementation is available, a plain HashSet will be used as fallback (not keeping the registration order).

Note that a Set class specified will not permit multiple instances of the same listener, while a List class will allow for registering the same listener multiple times.

Consider Doug Lea's java.util.concurrent.CopyOnWriteArraySet or its JDK 1.4 backport, edu.emory.mathcs.backport.java.util.concurrent.CopyOnWriteArraySet (or the respective CopyOnWriteArrayList version). Those classes provide a thread-safe Iterator, optimized for read-mostly usage - matching this use case nicely.

See Also:
CollectionFactory.createLinkedSetIfPossible(int), CopyOnWriteArraySet, CopyOnWriteArraySet

addApplicationListener

public void addApplicationListener(ApplicationListener listener)
Description copied from interface: ApplicationEventMulticaster
Add a listener to be notified of all events.

Specified by:
addApplicationListener in interface ApplicationEventMulticaster
Parameters:
listener - the listener to add

removeApplicationListener

public void removeApplicationListener(ApplicationListener listener)
Description copied from interface: ApplicationEventMulticaster
Remove a listener from the notification list.

Specified by:
removeApplicationListener in interface ApplicationEventMulticaster
Parameters:
listener - the listener to remove

removeAllListeners

public void removeAllListeners()
Description copied from interface: ApplicationEventMulticaster
Remove all listeners registered with this multicaster. It will perform no action on event notification until more listeners are registered.

Specified by:
removeAllListeners in interface ApplicationEventMulticaster

getApplicationListeners

protected Collection getApplicationListeners()
Return the current Collection of ApplicationListeners.

Note that this is the raw Collection of ApplicationListeners, potentially modified when new listeners get registered or existing ones get removed. This Collection is not a snapshot copy.

Returns:
a Collection of ApplicationListeners
See Also:
ApplicationListener

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