Java tutorial
// Copyright 2006 Chibacon /* * * Artistic License * * Preamble * * The intent of this document is to state the conditions under which a * Package may be copied, such that the Copyright Holder maintains some * semblance of artistic control over the development of the package, * while giving the users of the package the right to use and distribute * the Package in a more-or-less customary fashion, plus the right to make * reasonable modifications. * * Definitions: * * "Package" refers to the collection of files distributed by the * Copyright Holder, and derivatives of that collection of files created * through textual modification. * * "Standard Version" refers to such a Package if it has not been * modified, or has been modified in accordance with the wishes of the * Copyright Holder. * * "Copyright Holder" is whoever is named in the copyright or copyrights * for the package. * * "You" is you, if you're thinking about copying or distributing this Package. * * "Reasonable copying fee" is whatever you can justify on the basis of * media cost, duplication charges, time of people involved, and so * on. 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THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF * MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE. * */ package org.chiba.xml.xforms.core; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import java.lang.reflect.InvocationTargetException; import java.util.LinkedList; /** * The update sequencer provides a means to defer any further update while an * update is running. This is needed to perform nested updates in a sequential * manner, e.g. during <code>xforms-refresh</code> when any actions like * <code>xf:setvalue</code> happen which in turn cause another * <code>xforms-refresh</code>. * * @author Ulrich Nicolas Lissé * @version $Id: UpdateSequencer.java,v 1.1 2009/02/17 09:00:53 civilis Exp $ */ class UpdateSequencer { private static Log LOGGER = LogFactory.getLog(UpdateSequencer.class); private Model model; private boolean updateRunning; private LinkedList updateSequence; /** * Creates an update sequencer for the specified model. * * @param model the model to be updated. */ public UpdateSequencer(Model model) { this.model = model; this.updateRunning = false; this.updateSequence = new LinkedList(); } /** * Checks wether the specified update method needs to be sequenced. * <p/> * If no update is running yet, this method returns <code>true</code>. The * handler now assumes that an update is running. * <p/> * If an update is running already, this method returns <code>false</code>. * The handler supposes the model not to perform the update. The update * method name is added to the sequence of updates to be deferred further. * * @param method the update method. * @return <code>true</code> if the method has to be performed by the model * immediately, otherwise <code>false</code>. */ public boolean sequence(String method) { if (this.updateRunning) { if (LOGGER.isDebugEnabled()) { LOGGER.debug("sequencing " + method); } this.updateSequence.addLast(method); return true; } this.updateRunning = true; return false; } /** * Performs the next deferred update if any. * <p/> * The update method name is removed from the sequence of updates to be * deferred further. * * @return <code>true</code> if an deferred update has been performed, * otherwise <code>false</code>. * @throws Exception if any error occurred during the update. */ public boolean perform() throws Exception { this.updateRunning = false; if (this.updateSequence.size() > 0) { String name = this.updateSequence.removeFirst().toString(); if (LOGGER.isDebugEnabled()) { LOGGER.debug("performing sequenced " + name); } try { this.model.getClass().getDeclaredMethod(name, (Class[]) null).invoke(this.model, (Object[]) null); } catch (InvocationTargetException e) { throw new Exception(e.getTargetException()); } return true; } return false; } /** * Resets the update sequencer for reuse. */ public void reset() { if (LOGGER.isDebugEnabled()) { LOGGER.debug("reset"); } this.updateRunning = false; this.updateSequence.clear(); } }