001/* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017package org.apache.wicket.util.watch; 018 019import java.time.Duration; 020import java.time.Instant; 021import java.util.Set; 022import java.util.concurrent.ConcurrentHashMap; 023 024import org.apache.wicket.util.lang.Generics; 025import org.apache.wicket.util.listener.ChangeListenerSet; 026import org.apache.wicket.util.listener.IChangeListener; 027import org.apache.wicket.util.thread.ICode; 028import org.apache.wicket.util.thread.Task; 029import org.slf4j.Logger; 030import org.slf4j.LoggerFactory; 031 032 033/** 034 * Monitors one or more <code>IModifiable</code> objects, calling a {@link IChangeListener 035 * IChangeListener} when a given object's modification time changes. 036 * 037 * @author Jonathan Locke 038 * @since 1.2.6 039 */ 040public class ModificationWatcher implements IModificationWatcher 041{ 042 /** logger */ 043 private static final Logger log = LoggerFactory.getLogger(ModificationWatcher.class); 044 045 /** maps <code>IModifiable</code> objects to <code>Entry</code> objects */ 046 private final ConcurrentHashMap<IModifiable, Entry> modifiableToEntry = Generics.newConcurrentHashMap(); 047 048 /** the <code>Task</code> to run */ 049 private Task task; 050 051 /** 052 * Container class for holding modifiable entries to watch. 053 */ 054 protected static final class Entry 055 { 056 // The most recent lastModificationTime polled on the object 057 public Instant lastModifiedTime; 058 059 // The set of listeners to call when the modifiable changes 060 public final ChangeListenerSet<IModifiable> listeners = new ChangeListenerSet<>(); 061 062 // The modifiable thing 063 public IModifiable modifiable; 064 } 065 066 /** 067 * Default constructor for two-phase construction. 068 */ 069 public ModificationWatcher() 070 { 071 } 072 073 /** 074 * Constructor that accepts a <code>Duration</code> argument representing the poll frequency. 075 * 076 * @param pollFrequency 077 * how often to check on <code>IModifiable</code>s 078 */ 079 public ModificationWatcher(final Duration pollFrequency) 080 { 081 start(pollFrequency); 082 } 083 084 @Override 085 public final boolean add(final IModifiable modifiable, final IChangeListener<IModifiable> listener) 086 { 087 // Look up entry for modifiable 088 final Entry entry = modifiableToEntry.get(modifiable); 089 090 // Found it? 091 if (entry == null) 092 { 093 Instant lastModifiedTime = modifiable.lastModifiedTime(); 094 if (lastModifiedTime != null) 095 { 096 // Construct new entry 097 final Entry newEntry = new Entry(); 098 099 newEntry.modifiable = modifiable; 100 newEntry.lastModifiedTime = lastModifiedTime; 101 newEntry.listeners.add(listener); 102 103 // Put in map 104 modifiableToEntry.putIfAbsent(modifiable, newEntry); 105 } 106 else 107 { 108 // The IModifiable is not returning a valid lastModifiedTime 109 log.info("Cannot track modifications to resource '{}'", modifiable); 110 } 111 112 return true; 113 } 114 else 115 { 116 // Add listener to existing entry 117 return !entry.listeners.add(listener); 118 } 119 } 120 121 @Override 122 public IModifiable remove(final IModifiable modifiable) 123 { 124 final Entry entry = modifiableToEntry.remove(modifiable); 125 if (entry != null) 126 { 127 return entry.modifiable; 128 } 129 return null; 130 } 131 132 @Override 133 public void start(final Duration pollFrequency) 134 { 135 // Construct task with the given polling frequency 136 task = new Task("ModificationWatcher"); 137 138 task.run(pollFrequency, new ICode() 139 { 140 @Override 141 public void run(final Logger log) 142 { 143 checkModified(); 144 } 145 }); 146 } 147 148 /** 149 * Checks which IModifiables were modified and notifies their listeners 150 */ 151 protected void checkModified() 152 { 153 for (Entry entry : modifiableToEntry.values()) 154 { 155 // If the modifiable has been modified after the last known 156 // modification time 157 final Instant modifiableLastModified = entry.modifiable.lastModifiedTime(); 158 if ((modifiableLastModified != null) && 159 modifiableLastModified.isAfter(entry.lastModifiedTime)) 160 { 161 // Notify all listeners that the modifiable was modified 162 entry.listeners.notifyListeners(entry.modifiable); 163 164 // Update timestamp 165 entry.lastModifiedTime = modifiableLastModified; 166 } 167 } 168 } 169 170 @Override 171 public void destroy() 172 { 173 if (task != null) 174 { 175 // task.stop(); 176 task.interrupt(); 177 } 178 } 179 180 @Override 181 public final Set<IModifiable> getEntries() 182 { 183 return modifiableToEntry.keySet(); 184 } 185}