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/*
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* Angkor Web Framework
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*
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* Distributable under LGPL license.
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* See terms of license at gnu.org.
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*/
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package com.tirsen.angkor.event;
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import com.tirsen.angkor.Application;
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import com.tirsen.angkor.Debug;
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import com.tirsen.angkor.Multicaster;
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import org.apache.log4j.Category;
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import java.lang.reflect.InvocationTargetException;
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import java.lang.reflect.Method;
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import java.util.ArrayList;
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import java.util.EventListener;
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import java.util.EventObject;
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import java.util.Iterator;
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import java.util.LinkedList;
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import java.util.List;
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/**
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* The EventQueue is used to schedule the sending of events until just before the render-phase.
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* This is to ensure that all models have been updated before event-processing.
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* Q: with the new model with separated smaller components there are several parse and render-phases
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* this means that the events will only be queued up for each component. This might prove to be acceptable
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* though.
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* A: This is resolved for the following reason, during the render phase components are registered for parsing
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* when the request returns the ApplicationFilter starts the parse phase which ends with the RenderContext resetting
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* the list of registered parsing components, when the RenderContext is ready with this the ApplicationFilter
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* passes the request to the FilterChain. This means that all components from the previous request are parsed before
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* the jsps or components are rendered.
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* Q: In what order are events sent?
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* A: Events can not be ordered in the same sense as in a Swing application when it comes to a web application.
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* Therefor some kind of guessing needs to be applied to in what order events are to be processed. A pre-defined
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* ordering of events are applied. This could be: ViewLinkEvent, <all other event types>, ActionEvent.
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* @author $Author: tirsen $
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* @version $Revision: 1.4 $
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* <BR>
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* $Id: EventQueue.java,v 1.4 2002/10/13 13:37:26 tirsen Exp $
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*/
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public class EventQueue
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{
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private static final Category logger = Debug.getCategory();
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private List queue = new LinkedList();
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private boolean postponeEvents = true;
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public static class QueuedEvent
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{
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private Class listenerInterface;
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private EventListener target;
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private EventObject event;
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private String method;
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public QueuedEvent(Class listenerInterface, EventListener target, EventObject event, String method)
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{
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this.listenerInterface = listenerInterface;
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this.target = target;
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this.event = event;
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this.method = method;
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}
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public void send(Application application) throws Exception
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{
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logger.debug("sending event " + event + " to " + target);
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logger.debug("calling method " + method);
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Method m = listenerInterface.getMethod(method, new Class[]{event.getClass()});
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try
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{
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m.invoke(target, new Object[]{event});
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}
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catch (InvocationTargetException e)
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{
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Multicaster.throwRealException(e);
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}
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}
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public EventObject getEvent()
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{
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return event;
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}
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}
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/**
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* Currently does not queue up events to be sent later on. Rather they are sent immediately.
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* TODO: queue up events.
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* Note that further events can of course be sent while sending events.
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*/
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public void postEvent(Class listenerInterface, EventListener target, EventObject event, String method)
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{
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QueuedEvent queuedEvent = new QueuedEvent(listenerInterface, target, event, method);
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if (postponeEvents)
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{
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queue.add(queuedEvent);
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}
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else
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{
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try
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{
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queuedEvent.send(Application.getApplication());
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}
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catch (Exception e)
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{
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Application.getApplication().handleError(e);
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}
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}
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}
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public void setPostponeEvents(boolean postponeEvents)
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{
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this.postponeEvents = postponeEvents;
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}
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/**
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* Sends the events and clears the event queue.
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*/
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public void processEvents(Application application) throws Exception
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{
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for (Iterator iterator = iterateEvents(); iterator.hasNext();)
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{
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QueuedEvent event = (QueuedEvent) iterator.next();
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event.send(application);
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0
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if (application != null && application.getError() != null) break;
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}
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3
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reset();
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}
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/**
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* Returns a thread safe iterator over the current events. Events can be added while
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* using this iterator but they will not be added to this iterator. To process the events
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* posted while processing these events another iterator must be added.
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*/
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public Iterator iterateEvents()
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{
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return new ArrayList(queue).iterator();
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}
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public void reset()
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{
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queue.clear();
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}
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}
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