001/* 002 * This library is part of OpenCms - 003 * the Open Source Content Management System 004 * 005 * Copyright (c) Alkacon Software GmbH & Co. KG (http://www.alkacon.com) 006 * 007 * This library is free software; you can redistribute it and/or 008 * modify it under the terms of the GNU Lesser General Public 009 * License as published by the Free Software Foundation; either 010 * version 2.1 of the License, or (at your option) any later version. 011 * 012 * This library is distributed in the hope that it will be useful, 013 * but WITHOUT ANY WARRANTY; without even the implied warranty of 014 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 015 * Lesser General Public License for more details. 016 * 017 * For further information about Alkacon Software, please see the 018 * company website: http://www.alkacon.com 019 * 020 * For further information about OpenCms, please see the 021 * project website: http://www.opencms.org 022 * 023 * You should have received a copy of the GNU Lesser General Public 024 * License along with this library; if not, write to the Free Software 025 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA 026 */ 027 028package org.opencms.gwt.client.validation; 029 030import java.util.LinkedList; 031 032/** 033 * This is a helper class for scheduling form validations.<p> 034 * 035 * Since validations can be asynchronous, it would be possible for a validation to start while another one 036 * is still waiting for a response from the server if it were ran directly. This might result in an inconsistent state 037 * of the form fields being validated. To prevent this, validation controllers use this class to schedule validations, 038 * and call this class again after they're finished to execute the next validation.<p> 039 * 040 * The result of this is that a validation will only start after all unfinished validations which have been scheduled 041 * before it have finished running.<p> 042 * 043 * @since 8.0.0 044 */ 045public class CmsValidationScheduler { 046 047 /** The singleton instance of this class. */ 048 private static CmsValidationScheduler instance = new CmsValidationScheduler(); 049 050 /** The queue of validations which still need to be run. */ 051 private LinkedList<CmsValidationController> m_actions = new LinkedList<CmsValidationController>(); 052 053 /** A flag which indicates whether there is no validation currently running. */ 054 private boolean m_idle = true; 055 056 /** 057 * Hidden default constructor.<p> 058 */ 059 protected CmsValidationScheduler() { 060 061 // do nothing 062 } 063 064 /** 065 * Returns the singleton instance of the validation scheduler.<p> 066 * 067 * @return the validation scheduler 068 */ 069 public static CmsValidationScheduler get() { 070 071 return instance; 072 } 073 074 /** 075 * This method should be called by the validation controller when it has finished running.<p> 076 * 077 * It will execute the next validation if there is one.<p> 078 */ 079 public void executeNext() { 080 081 if (!m_idle) { 082 if (m_actions.isEmpty()) { 083 m_idle = true; 084 } else { 085 CmsValidationController action = m_actions.removeFirst(); 086 action.internalStartValidation(); 087 } 088 } else { 089 assert false; // this shouldn't happen 090 } 091 } 092 093 /** 094 * This schedules a new validation to be run after all currently scheduled or running validations have finished.<p> 095 * 096 * If there are no validations running, the validation will be started immediately.<p> 097 * 098 * @param action the validation to be scheduled 099 */ 100 public void schedule(CmsValidationController action) { 101 102 if (m_idle) { 103 m_idle = false; 104 action.internalStartValidation(); 105 } else { 106 m_actions.add(action); 107 } 108 } 109}