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Class EventContext

Contains methods for registering/deregistering listeners to be notified of events fired when objects named in a context changes.

Target

The name parameter in the addNamingListener() methods is referred to as the target. The target along with the scope identify the object(s) that the listener is interested in. It is possible to register interest in a target that does not exist but there might be limitations in the extent to which this can be supported by the service provider and underlying protocol/service.

If a service only supports registration for existing targets an attempt to register for a nonexistent target results in a NameNotFoundException being thrown as early as possible preferably at the time addNamingListener() is called or if that is not possible the listener will receive the exception through the NamingExceptionEvent.

Also for service providers that only support registration for existing targets when the target that a listener has registered for is subsequently removed from the namespace the listener is notified via a NamingExceptionEvent (containing a NameNotFoundException).

An application can use the method targetMustExist() to check whether a EventContext supports registration of nonexistent targets.

Event Source

The EventContext instance on which you invoke the registration methods is the event source of the events that are (potentially) generated. The source is not necessarily the object named by the target. Only when the target is the empty name is the object named by the target the source. In other words the target along with the scope parameter are used to identify the object(s) that the listener is interested in but the event source is the EventContext instance with which the listener has registered.

For example suppose a listener makes the following registration:

 NamespaceChangeListener listener = ...; src.addNamingListener("x" SUBTREE_SCOPE listener); 
When an object named "x/y" is subsequently deleted the corresponding NamingEvent (evt) must contain:
 evt.getEventContext() == src evt.getOldBinding().getName().equals("x/y") 

Furthermore listener registration/deregistration is with the EventContext instance and not with the corresponding object in the namespace. If the program intends at some point to remove a listener then it needs to keep a reference to the EventContext instance on which it invoked addNamingListener() (just as it needs to keep a reference to the listener in order to remove it later). It cannot expect to do a lookup() and get another instance of a EventContext on which to perform the deregistration.

Lifetime of Registration

A registered listener becomes deregistered when: Until that point a EventContext instance that has outstanding listeners will continue to exist and be maintained by the service provider.

Listener Implementations

The registration/deregistration methods accept an instance of NamingListener. There are subinterfaces of NamingListener for different of event types of NamingEvent. For example the ObjectChangeListener interface is for the NamingEvent.OBJECT_CHANGED event type. To register interest in multiple event types the listener implementation should implement multiple NamingListener subinterfaces and use a single invocation of addNamingListener(). In addition to reducing the number of method calls and possibly the code size of the listeners this allows some service providers to optimize the registration.

Threading Issues

Like Context instances in general instances of EventContext are not guaranteed to be thread-safe. Care must be taken when multiple threads are accessing the same EventContext concurrently. See the package description for more information on threading issues. @author Rosanna Lee @author Scott Seligman @version 1.9 01/0212/0903 @since 1.3

Class EventDirContext

Contains methods for registering listeners to be notified of events fired when objects named in a directory context changes.

The methods in this interface support identification of objects by RFC 2254 search filters.

Using the search filter it is possible to register interest in objects that do not exist at the time of registration but later come into existence and satisfy the filter. However there might be limitations in the extent to which this can be supported by the service provider and underlying protocol/service. If the caller submits a filter that cannot be supported in this way addNamingListener() throws an InvalidSearchFilterException.

See EventContext for a description of event source and target and information about listener registration/deregistration that are also applicable to methods in this interface. See the package description for information on threading issues.

A SearchControls or array object passed as a parameter to any method is owned by the caller. The service provider will not modify the object or keep a reference to it. @author Rosanna Lee @author Scott Seligman @version 1.5 006 01/0212/0203 @since 1.3


Class NamespaceChangeListener

Specifies the methods that a listener interested in namespace changes must implement. Specifically the listener is interested in NamingEvents with event types of OBJECT_ADDED OBJECT_RENAMED or OBJECT_REMOVED.

Such a listener must:

  1. Implement this interface and its methods.
  2. Implement NamingListener.namingExceptionThrown() so that it will be notified of exceptions thrown while attempting to collect information about the events.
  3. Register with the source using the source's addNamingListener() method.
A listener that wants to be notified of OBJECT_CHANGED event types should also implement the ObjectChangeListener interface. @author Rosanna Lee @author Scott Seligman @version 1.4 005 01/0212/0203 @see NamingEvent @see ObjectChangeListener @see EventContext @see EventDirContext @since 1.3

Class NamingEvent

This class represents an event fired by a naming/directory service.

The NamingEvent's state consists of

Note that the event source is always the same EventContext instance that the listener has registered with. Furthermore the names of the bindings in the NamingEvent are always relative to that instance. For example suppose a listener makes the following registration:

 NamespaceChangeListener listener = ...; src.addNamingListener("x" SUBTREE_SCOPE listener); 
When an object named "x/y" is subsequently deleted the corresponding NamingEvent (evt) must contain:
 evt.getEventContext() == src evt.getOldBinding().getName().equals("x/y") 
Care must be taken when multiple threads are accessing the same EventContext concurrently. See the package description for more information on threading issues. @author Rosanna Lee @author Scott Seligman @version 1.8 01/0212/0903 @see NamingListener @see EventContext @since 1.3

Class NamingExceptionEvent

This class represents an event fired when the procedures/processes used to collect information for notifying listeners of NamingEvents threw a NamingException. This can happen for example if the server which the listener is using aborts subsequent to the addNamingListener() call. @author Rosanna Lee @author Scott Seligman @version 1.4 005 01/0212/0203 @see NamingListener#namingExceptionThrown @see EventContext @since 1.3

Class NamingListener

This interface is the root of listener interfaces that handle NamingEvents. It does not make sense for a listener to implement just this interface. A listener typically implements a subinterface of NamingListener such as ObjectChangeListener or NamespaceChangeListener.

This interface contains a single method namingExceptionThrown() that must be implemented so that the listener can be notified of exceptions that are thrown (by the service provider) while gathering information about the events that they're interested in. When this method is invoked the listener has been automatically deregistered from the EventContext with which it has registered.

For example suppose a listener implements ObjectChangeListener and registers with a EventContext. Then if the connection to the server is subsequently broken the listener will receive a NamingExceptionEvent and may take some corrective action such as notifying the user of the application. @author Rosanna Lee @author Scott Seligman @version 1.4 005 01/0212/0203 @see NamingEvent @see NamingExceptionEvent @see EventContext @see EventDirContext @since 1.3


Class ObjectChangeListener

Specifies the method that a listener of a NamingEvent with event type of OBJECT_CHANGED must implement.

An OBJECT_CHANGED event type is fired when (the contents of) an object has changed. This might mean that its attributes have been modified added or removed and/or that the object itself has been replaced. How the object has changed can be determined by examining the NamingEvent's old and new bindings.

A listener interested in OBJECT_CHANGED event types must:

  1. Implement this interface and its method (objectChanged())
  2. Implement NamingListener.namingExceptionThrown() so that it will be notified of exceptions thrown while attempting to collect information about the events.
  3. Register with the source using the source's addNamingListener() method.
A listener that wants to be notified of namespace change events should also implement the NamespaceChangeListener interface. @author Rosanna Lee @author Scott Seligman @version 1.4 005 01/0212/0203 @see NamingEvent @see NamespaceChangeListener @see EventContext @see EventDirContext @since 1.3