Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.commons.vfs.impl; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.commons.vfs.FileListener; import org.apache.commons.vfs.FileMonitor; import org.apache.commons.vfs.FileName; import org.apache.commons.vfs.FileObject; import org.apache.commons.vfs.FileSystemException; import org.apache.commons.vfs.FileType; import org.apache.commons.vfs.provider.AbstractFileSystem; import java.util.HashMap; import java.util.Map; import java.util.Stack; /** * A polling {@link FileMonitor} implementation.<br /> * <br /> * The DefaultFileMonitor is a Thread based polling file system monitor with a 1 * second delay.<br /> * <br /> * <b>Design:</b> * <p/> * There is a Map of monitors known as FileMonitorAgents. With the thread running, * each FileMonitorAgent object is asked to "check" on the file it is * responsible for. * To do this check, the cache is cleared. * </p> * <ul> * <li>If the file existed before the refresh and it no longer exists, a delete * event is fired.</li> * <li>If the file existed before the refresh and it still exists, check the * last modified timestamp to see if that has changed.</li> * <li>If it has, fire a change event.</li> * </ul> * <p/> * With each file delete, the FileMonitorAgent of the parent is asked to * re-build its * list of children, so that they can be accurately checked when there are new * children.<br/> * New files are detected during each "check" as each file does a check for new * children. * If new children are found, create events are fired recursively if recursive * descent is * enabled. * </p> * <p/> * For performance reasons, added a delay that increases as the number of files * monitored * increases. The default is a delay of 1 second for every 1000 files processed. * </p> * <p/> * <br /><b>Example usage:</b><pre> * FileSystemManager fsManager = VFS.getManager(); * FileObject listendir = fsManager.resolveFile("/home/username/monitored/"); * <p/> * DefaultFileMonitor fm = new DefaultFileMonitor(new CustomFileListener()); * fm.setRecursive(true); * fm.addFile(listendir); * fm.start(); * </pre> * <i>(where CustomFileListener is a class that implements the FileListener * interface.)</i> * * @author <a href="mailto:xknight@users.sourceforge.net">Christopher Ottley</a> * @version $Revision$ $Date$ */ public class DefaultFileMonitor implements Runnable, FileMonitor { private final static Log log = LogFactory.getLog(DefaultFileMonitor.class); /** * Map from FileName to FileObject being monitored. */ private final Map monitorMap = new HashMap(); /** * The low priority thread used for checking the files being monitored. */ private Thread monitorThread; /** * File objects to be removed from the monitor map. */ private Stack deleteStack = new Stack(); /** * File objects to be added to the monitor map. */ private Stack addStack = new Stack(); /** * A flag used to determine if the monitor thread should be running. */ private boolean shouldRun = true; /** * A flag used to determine if adding files to be monitored should be recursive. */ private boolean recursive = false; /** * Set the delay between checks */ private long delay = 1000; /** * Set the number of files to check until a delay will be inserted */ private int checksPerRun = 1000; /** * A listener object that if set, is notified on file creation and deletion. */ private final FileListener listener; public DefaultFileMonitor(final FileListener listener) { this.listener = listener; } /** * Access method to get the recursive setting when adding files for monitoring. */ public boolean isRecursive() { return this.recursive; } /** * Access method to set the recursive setting when adding files for monitoring. */ public void setRecursive(final boolean newRecursive) { this.recursive = newRecursive; } /** * Access method to get the current FileListener object notified when there * are changes with the files added. */ FileListener getFileListener() { return this.listener; } /** * Adds a file to be monitored. */ public void addFile(final FileObject file) { _addFile(file); try { // add all direct children too if (file.getType().hasChildren()) { // Traverse the children final FileObject[] children = file.getChildren(); for (int i = 0; i < children.length; i++) { _addFile(children[i]); } } } catch (FileSystemException fse) { log.error(fse.getLocalizedMessage(), fse); } } /** * Adds a file to be monitored. */ private void _addFile(final FileObject file) { synchronized (this.monitorMap) { if (this.monitorMap.get(file.getName()) == null) { this.monitorMap.put(file.getName(), new FileMonitorAgent(this, file)); try { if (this.listener != null) { file.getFileSystem().addListener(file, this.listener); } if (file.getType().hasChildren() && this.recursive) { // Traverse the children final FileObject[] children = file.getChildren(); for (int i = 0; i < children.length; i++) { this.addFile(children[i]); // Add depth first } } } catch (FileSystemException fse) { log.error(fse.getLocalizedMessage(), fse); } } } } /** * Removes a file from being monitored. */ public void removeFile(final FileObject file) { synchronized (this.monitorMap) { FileName fn = file.getName(); if (this.monitorMap.get(fn) != null) { FileObject parent; try { parent = file.getParent(); } catch (FileSystemException fse) { parent = null; } this.monitorMap.remove(fn); if (parent != null) { // Not the root FileMonitorAgent parentAgent = (FileMonitorAgent) this.monitorMap.get(parent.getName()); if (parentAgent != null) { parentAgent.resetChildrenList(); } } } } } /** * Queues a file for removal from being monitored. */ protected void queueRemoveFile(final FileObject file) { this.deleteStack.push(file); } /** * Get the delay between runs */ public long getDelay() { return delay; } /** * Set the delay between runs */ public void setDelay(long delay) { if (delay > 0) { this.delay = delay; } else { this.delay = 1000; } } /** * get the number of files to check per run */ public int getChecksPerRun() { return checksPerRun; } /** * set the number of files to check per run. * a additional delay will be added if there are more files to check * * @param checksPerRun a value less than 1 will disable this feature */ public void setChecksPerRun(int checksPerRun) { this.checksPerRun = checksPerRun; } /** * Queues a file for addition to be monitored. */ protected void queueAddFile(final FileObject file) { this.addStack.push(file); } /** * Starts monitoring the files that have been added. */ public void start() { if (this.monitorThread == null) { this.monitorThread = new Thread(this); this.monitorThread.setDaemon(true); this.monitorThread.setPriority(Thread.MIN_PRIORITY); } this.monitorThread.start(); } /** * Stops monitoring the files that have been added. */ public void stop() { this.shouldRun = false; } /** * Asks the agent for each file being monitored to check its file for changes. */ public void run() { mainloop: while (!Thread.currentThread().isInterrupted() && this.shouldRun) { while (!this.deleteStack.empty()) { this.removeFile((FileObject) this.deleteStack.pop()); } // For each entry in the map Object fileNames[]; synchronized (this.monitorMap) { fileNames = this.monitorMap.keySet().toArray(); } for (int iterFileNames = 0; iterFileNames < fileNames.length; iterFileNames++) { FileName fileName = (FileName) fileNames[iterFileNames]; FileMonitorAgent agent; synchronized (this.monitorMap) { agent = (FileMonitorAgent) this.monitorMap.get(fileName); } if (agent != null) { agent.check(); } if (getChecksPerRun() > 0) { if ((iterFileNames % getChecksPerRun()) == 0) { try { Thread.sleep(getDelay()); } catch (InterruptedException e) { } } } if (Thread.currentThread().isInterrupted() || !this.shouldRun) { continue mainloop; } } while (!this.addStack.empty()) { this.addFile((FileObject) this.addStack.pop()); } try { Thread.sleep(getDelay()); } catch (InterruptedException e) { continue; } } this.shouldRun = true; } /** * File monitor agent. */ private static class FileMonitorAgent { private final FileObject file; private final DefaultFileMonitor fm; private boolean exists; private long timestamp; private Map children = null; private FileMonitorAgent(DefaultFileMonitor fm, FileObject file) { this.fm = fm; this.file = file; this.refresh(); this.resetChildrenList(); try { this.exists = this.file.exists(); } catch (FileSystemException fse) { this.exists = false; } try { this.timestamp = this.file.getContent().getLastModifiedTime(); } catch (FileSystemException fse) { this.timestamp = -1; } } private void resetChildrenList() { try { if (this.file.getType().hasChildren()) { this.children = new HashMap(); FileObject[] childrenList = this.file.getChildren(); for (int i = 0; i < childrenList.length; i++) { this.children.put(childrenList[i].getName(), new Object()); // null? } } } catch (FileSystemException fse) { this.children = null; } } /** * Clear the cache and re-request the file object */ private void refresh() { try { this.file.refresh(); } catch (FileSystemException fse) { log.error(fse.getLocalizedMessage(), fse); } } /** * Recursively fires create events for all children if recursive descent is * enabled. Otherwise the create event is only fired for the initial * FileObject. */ private void fireAllCreate(FileObject child) { // Add listener so that it can be triggered if (this.fm.getFileListener() != null) { child.getFileSystem().addListener(child, this.fm.getFileListener()); } ((AbstractFileSystem) child.getFileSystem()).fireFileCreated(child); // Remove it because a listener is added in the queueAddFile if (this.fm.getFileListener() != null) { child.getFileSystem().removeListener(child, this.fm.getFileListener()); } this.fm.queueAddFile(child); // Add try { if (this.fm.isRecursive()) { if (child.getType().hasChildren()) { FileObject[] newChildren = child.getChildren(); for (int i = 0; i < newChildren.length; i++) { fireAllCreate(newChildren[i]); } } } } catch (FileSystemException fse) { log.error(fse.getLocalizedMessage(), fse); } } /** * Only checks for new children. If children are removed, they'll * eventually be checked. */ private void checkForNewChildren() { try { if (this.file.getType().hasChildren()) { FileObject[] newChildren = this.file.getChildren(); if (this.children != null) { // See which new children are not listed in the current children map. Map newChildrenMap = new HashMap(); Stack missingChildren = new Stack(); for (int i = 0; i < newChildren.length; i++) { newChildrenMap.put(newChildren[i].getName(), new Object()); // null ? // If the child's not there if (!this.children.containsKey(newChildren[i].getName())) { missingChildren.push(newChildren[i]); } } this.children = newChildrenMap; // If there were missing children if (!missingChildren.empty()) { while (!missingChildren.empty()) { FileObject child = (FileObject) missingChildren.pop(); this.fireAllCreate(child); } } } else { // First set of children - Break out the cigars if (newChildren.length > 0) { this.children = new HashMap(); } for (int i = 0; i < newChildren.length; i++) { this.children.put(newChildren[i].getName(), new Object()); // null? this.fireAllCreate(newChildren[i]); } } } } catch (FileSystemException fse) { log.error(fse.getLocalizedMessage(), fse); } } private void check() { this.refresh(); try { // If the file existed and now doesn't if (this.exists && !this.file.exists()) { this.exists = this.file.exists(); this.timestamp = -1; // Fire delete event ((AbstractFileSystem) this.file.getFileSystem()).fireFileDeleted(this.file); // Remove listener in case file is re-created. Don't want to fire twice. if (this.fm.getFileListener() != null) { this.file.getFileSystem().removeListener(this.file, this.fm.getFileListener()); } // Remove from map this.fm.queueRemoveFile(this.file); } else if (this.exists && this.file.exists()) { // Check the timestamp to see if it has been modified if (this.timestamp != this.file.getContent().getLastModifiedTime()) { this.timestamp = this.file.getContent().getLastModifiedTime(); // Fire change event // Don't fire if it's a folder because new file children // and deleted files in a folder have their own event triggered. if (!this.file.getType().hasChildren()) { ((AbstractFileSystem) this.file.getFileSystem()).fireFileChanged(this.file); } } } this.checkForNewChildren(); } catch (FileSystemException fse) { log.error(fse.getLocalizedMessage(), fse); } } } }