Working on the PluginRegistry class, it became apparent that when a
LoggerRepository/Hierarchy is shutdown, the PluginRegistry should be
informed so that it can cleanly shutdown and remove any plugins associated
with that Repository/Hierarchy. After looking at the problem, it was
confirmed that the best way to achieve this would be for the PluginRegistry
to register a HierarchyEventListener interface with each
LoggerRepository/Hierarchy it contains plugins for. Unfortunately, the
existing HierarchyEventListener interface only contains 2 methods, related
to appenders being added/removed.
So, I have taken a crack at extending the interface to be more generic and
support current and future expansion without affecting the method signature
of the interface. However, I don't know what the best course of action is
regarding the currently defined methods. They should be deprecated...but
the calling code in Hierarchy is going to need to be intelligent enough to
look for the deprecated methods and call those over the handleHierarchyEvent
method? Advice on this point would be appreciated.
Here is the proposed interface:
package org.apache.log4j.spi;
import java.util.Map;
import org.apache.log4j.*;
/**
Listen to events occuring within a {@link
org.apache.log4j.Hierarchy Hierarchy}.
@author Ceki Gülcü
@author Mark Womack
@since 1.2
*/
public interface HierarchyEventListener {
// defined event types
/** Hierarchy startup. Event data is empty. */
public static final int EVENT_HIERARCHY_STARTUP = 0;
/** Hierarchy shutdown. Event data is empty. */
public static final int EVENT_HIERARCHY_SHUTDOWN = 1;
/** Appender added to hierarchy. Event data contains APPENDER and
LOGGER. */
public static final int EVENT_APPENDER_ADDED = 2;
/** Appender removed from hierarchy. Event data contains APPENDER
and LOGGER. */
public static final int EVENT_APPENDER_REMOVED = 3;
// defined data keys for events
public static final String DATA_APPENDER = "appender";
public static final String DATA_LOGGER = "logger";
/**
@deprecated
Called when an appender is added a category.
Use handleHierarchyEvent instead as of v1.3. */
public void addAppenderEvent(Category cat, Appender appender);
/**
@deprecated
Called when an appender is removed from a category.
Use handleHierarchyEvent instead as of v1.3. */
public void removeAppenderEvent(Category cat, Appender appender);
/**
Called when events occur in the hierarchy. See the EVENT_* constants for
a list of supported hierarchy event type. Each event type documents the
set of event data sent for that event. Depending on the event type, the
set of event data varies. */
public void handleHierarchyEvent(int eventType, Hierarchy hierarchy,
Map eventData);
}
I chose to break out the event info (type, hierarchy, data) into parameters
to avoid creating an event object, but we could encapsulate the info into a
HierarchyEvent if desired. I want to get this squared away so that I can
continue with the plugin work.
-Mark
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