[VFS-54] [vfs][PATCH] External File Monitor (Todo List Item)

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed

Environment

Operating System: Linux
Platform: PC

• Bugzilla Id: 31547
• Assignee: Unassigned
• Reporter: Christopher Ottley
• Created: 05/Oct/04 21:09
• Updated: 25/Mar/08 07:52
• Resolved: 25/Mar/08 07:52

Description

========================
FileMonitor.java
========================
/*

• Copyright 2002, 2003,2004 The Apache Software Foundation.
  *
• Licensed 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.provider;

import org.apache.commons.vfs.FileSystemManager;
import org.apache.commons.vfs.FileObject;
import org.apache.commons.vfs.FileSystemException;
import org.apache.commons.vfs.FileName;
import org.apache.commons.vfs.FileListener;
import org.apache.commons.vfs.FileType;
import org.apache.commons.vfs.provider.AbstractFileSystem;

import java.util.HashMap;
import java.util.Map;
import java.util.Iterator;
import java.util.Stack;

/**

• Implementation Documentation
• ============================
  *
• The FileMonitor is a Thread based polling file system monitor with a 1 second
  delay.
  *
• Design:
• 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. If the file existed before the
  refresh and
• it no longer exists, a delete event is fired. If the file existed before the
  refresh
• and it still exists, check the last modified timestamp to see if that has
  changed.
• If it has, fire a change event (BUG no change event, fires a create event
  instead).
• 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.
• 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.
  *
• Known bugs:
• If the fileListener is changed during the course of the monitoring, the
  original listener
• will not be removed if the file associated with it is removed.
  *
  *
• Example usage:

try

{ FileSystemManager fsManager = VFS.getManager(); FileObject listendir = fsManager.resolveFile("/home/username/monitored/"); FileMonitor fm = new FileMonitor(); fm.setRecursive(true); fm.setFileListener(new CustomFileSystemListener()); fm.addFile(listendir); fm.start(); }

catch (FileSystemException fse)

{ fse.printStackTrace(); }

*

• where CustomFileSystemListener is a class that implements the FileListener
  interface.
  */

/**

• A polling FileMonitor implementation.
  *
• @author <a href="mailto:[e-mail]">Christopher Ottley</a>
• @version $Revision: 1.0 $ $Date: 2004/10/05 03:22:13 $
  */
  public class FileMonitor implements java.lang.Runnable {

/**

• 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;

/**

• A listener object that if set, is notified on file creation and deletion.
  */
  private FileListener listener = null;

public FileMonitor() {

}

/**

• Access method to get the recursive setting when adding files for monitoring.
  */
  public boolean recursive() { 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.
  */
  public FileListener fileListener() { return this.listener; }

/**

• Access method to set the current FileListener object notified when there
  are changes with the files added.
  */
  public void setFileListener(final FileListener newListener) { this.listener = newListener; }

/**

• Adds a file to be monitored.
  */
  public 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) {

}

}
}
}

/**

• 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 = null;
  try { parent = file.getParent(); }

  catch (FileSystemException fse) {

}
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.
  */
  public void queueRemoveFile(final FileObject file) { this.deleteStack.push(file); }

/**

• Queues a file for addition to be monitored.
  */
  public void queueAddFile(final FileObject file) { this.addStack.push(file); }

/**

• Starts monitoring the files that have been added.
  */
  public void start()
  Unknown macro: { if (this.monitorThread == null) { this.monitorThread = new Thread(this); 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() {
  while (this.shouldRun) {
  while (!this.deleteStack.empty()) { this.removeFile((FileObject)this.deleteStack.pop()); }

// For each entry in the map
Iterator i = this.monitorMap.keySet().iterator();

while ((i.hasNext()) && (this.shouldRun))

{ ((FileMonitorAgent)this.monitorMap.get((FileName)i.next())).check(); }

while (!this.addStack.empty())

{ this.addFile((FileObject)this.addStack.pop()); }

try

{ Thread.sleep(1000); }

catch(Exception e) {

}
}

this.shouldRun = true;
}

/**

• File monitor agent.
  */
  private class FileMonitorAgent {

private FileObject file;
private boolean exists;
private long timestamp;
private FileMonitor fm;
private Map children = null;

public FileMonitorAgent(FileMonitor 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; }

}

public void resetChildrenList() {
try {
if (this.file.getType() == FileType.FOLDER) {
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
  */
  public void refresh() {
  // TODO: Check to see if there's a better way to do this

try

{ this.exists = this.file.exists(); ((AbstractFileSystem)this.file.getFileSystem()).removeFileFromCache(this.file.getName()); FileSystemManager fsManager = this.file.getFileSystem().getFileSystemManager(); this.file = fsManager.resolveFile(this.file.getName().getPath()); }

catch (FileSystemException fse)

{ fse.printStackTrace(); }
}


/**
* Recursively fires create events for all children if recursive descent is
* enabled. Otherwise the create event is only fired for the initial
FileObject.
*/
public void fireAllCreate(FileObject child) {
// Add listener so that it can be triggered
if (this.fm.fileListener() != null) { child.getFileSystem().addListener(child, this.fm.fileListener()); }

((AbstractFileSystem)child.getFileSystem()).fireFileCreated(child);

// Remove it because a listener is added in the queueAddFile
if (this.fm.fileListener() != null) { child.getFileSystem().removeListener(child, this.fm.fileListener()); }

this.fm.queueAddFile(child); // Add

try {

if (this.fm.recursive()) {
if (child.getType() == FileType.FOLDER) {
FileObject[] newChildren = child.getChildren();
for (int i=0; i<newChildren.length; i++) { fireAllCreate(newChildren[i]); }
}
}

} catch (FileSystemException fse) { fse.printStackTrace(); }

}

/**

• Only checks for new children. If children are removed, they'll
  eventually be checked.
  */
  public void checkForNewChildren() {
  try {
  if (this.file.getType() == FileType.FOLDER) {
  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)

{ fse.printStackTrace(); }
}

public 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.
// TODO - Figure out what to do if the original file listener used
was changed.
if (this.fm.fileListener() != null) { this.file.getFileSystem().removeListener(this.file, this.fm.fileListener()); }

// 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
// TODO - Add fireFileChanged method to AbstractFileSystem?
// TODO - Add fileChanged(FileChangeEvent event) to FileListener
interface?
// I can't find a way to specify solely a change event, so fire a
create event instead

// 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() != FileType.FOLDER) { ((AbstractFileSystem)this.file.getFileSystem()).fireFileCreated(this.file); }
}

}

this.checkForNewChildren();

} catch(FileSystemException fse) { fse.printStackTrace(); }

}

}

}