/*
* Copyright (C) NetStruxr, Inc. All rights reserved.
*
* This software is published under the terms of the NetStruxr
* Public Software License version 0.5, a copy of which has been
* included with this distribution in the LICENSE.NPL file. */
package er.extensions.foundation;
import java.io.File;
import java.io.IOException;
import java.util.Enumeration;
import org.apache.log4j.Logger;
import com.webobjects.appserver.WOApplication;
import com.webobjects.foundation.NSMutableDictionary;
import com.webobjects.foundation.NSMutableSet;
import com.webobjects.foundation.NSNotification;
import com.webobjects.foundation.NSNotificationCenter;
import com.webobjects.foundation.NSSelector;
import er.extensions.appserver.ERXApplication;
import er.extensions.eof.ERXConstant;
/**
* The file notification center is only used in development systems. It provides a nice repository about
* files and their last modified dates. So instead of every dynamic spot having to keep track of
* the files' dates, register and check at the end of every request-response loop, instead you
* can just add an observer to this center and be notified when the file changes. Files' last modification
* dates are checked at the end of every request-response loop.
*
* <p>It should be noted that the current version of the file notification center will retain a
* reference to each registered observer. This is not ideal and will be corrected in the
* future.</p>
*/
public class ERXFileNotificationCenter {
/** Logging support */
public static final Logger log = Logger.getLogger(ERXFileNotificationCenter.class);
/** Contains the name of the notification that is posted when a file changes. */
public static final String FileDidChange = "FileDidChange";
/** holds a reference to the default file notification center */
private static ERXFileNotificationCenter _defaultCenter;
/**
* @return the singleton instance of file notification center
*/
public static ERXFileNotificationCenter defaultCenter() {
if (_defaultCenter == null)
_defaultCenter = new ERXFileNotificationCenter();
return _defaultCenter;
}
/** In seconds. 0 means we will not regularly check files. */
private static int checkFilesPeriod() {
return ERXProperties.intForKeyWithDefault("er.extensions.ERXFileNotificationCenter.CheckFilesPeriod", 0);
}
/** collections of observers by file path */
private NSMutableDictionary _observersByFilePath = new NSMutableDictionary();
/** cache for last modified dates of files by file path */
private NSMutableDictionary _lastModifiedByFilePath = new NSMutableDictionary();
/** flag to tell if caching is enabled, set in the object constructor */
private boolean developmentMode;
/** The last time we checked files. We only check if !WOCachingEnabled or if there is a CheckFilesPeriod set */
private long lastCheckMillis = System.currentTimeMillis();
private boolean symlinkSupport;
/**
* Default constructor. If you are in development mode
* then this object will register for the notification
* {@link com.webobjects.appserver.WOApplication#ApplicationWillDispatchRequestNotification}
* which will enable it to check if files have changed at the end of every request-response
* loop. If WOCaching is enabled then this object will not register for anything and will generate
* warning messages if observers are registered with caching enabled.
*/
public ERXFileNotificationCenter() {
developmentMode = ERXApplication.isDevelopmentModeSafe();
if (developmentMode || checkFilesPeriod() > 0) {
ERXRetainer.retain(this);
log.debug("Caching disabled. Registering for notification: " + WOApplication.ApplicationWillDispatchRequestNotification);
NSNotificationCenter.defaultCenter().addObserver(this, new NSSelector("checkIfFilesHaveChanged", ERXConstant.NotificationClassArray), WOApplication.ApplicationWillDispatchRequestNotification, null);
}
// MS: In case we are touching properties before they're fully materialized or messed up from a failed reload, lets use System.props here
symlinkSupport = Boolean.valueOf(System.getProperty("ERXFileNotificationCenter.symlinkSupport", "true"));
}
/**
* When the file notification center is garbage collected it removes itself
* as an observer from the
* {@link com.webobjects.foundation.NSNotificationCenter NSNotificationCenter}.
* Not doing this will cause exceptions.
*/
@Override
public void finalize() throws Throwable {
NSNotificationCenter.defaultCenter().removeObserver(this);
super.finalize();
}
/**
* Used to register file observers for a particular file.
* @param observer object to be notified when a file changes
* @param selector selector to be invoked on the observer when
* the file changes.
* @param filePath location of the file
*/
public void addObserver(Object observer, NSSelector selector, String filePath) {
if (filePath == null)
throw new RuntimeException("Attempting to register observer for null filePath.");
addObserver(observer, selector, new File(filePath));
}
/**
* Used to register file observers for a particular file.
* @param observer object to be notified when a file changes
* @param selector selector to be invoked on the observer when
* the file changes.
* @param file file to watch for changes
*/
public void addObserver(Object observer, NSSelector selector, File file) {
if (file == null)
throw new RuntimeException("Attempting to register a null file.");
if (observer == null)
throw new RuntimeException("Attempting to register null observer for file: " + file);
if (selector == null)
throw new RuntimeException("Attempting to register null selector for file: " + file);
if (!developmentMode && checkFilesPeriod() == 0) {
log.info("Registering an observer when file checking is disabled (WOCaching must be " +
"disabled or the er.extensions.ERXFileNotificationCenter.CheckFilesPeriod " +
"property must be set). This observer will not ever by default be called: " + file);
}
String filePath = cacheKeyForFile(file);
if (log.isDebugEnabled())
log.debug("Registering Observer for file at path: " + filePath);
// Register last modified date.
registerLastModifiedDateForFile(file);
// FIXME: This retains the observer. This is not ideal. With the 1.3 JDK we can use a ReferenceQueue to maintain weak references.
NSMutableSet observerSet = (NSMutableSet)_observersByFilePath.objectForKey(filePath);
if (observerSet == null) {
observerSet = new NSMutableSet();
_observersByFilePath.setObjectForKey(observerSet, filePath);
}
observerSet.addObject(new _ObserverSelectorHolder(observer, selector));
}
/**
* Returns the path that should be used as the cache key for the given file. This
* will return the absolute path of the file (specifically NOT the canonical path)
* so that we make sure to lookup files using their original sym links rather than
* resolving them at registration time.
*
* @param file the file to lookup a cache key for
* @return the absolute path of the file
*/
protected String cacheKeyForFile(File file) {
return file.getAbsolutePath();
}
/**
* Returns the value to cache to detect changes to this file. Currently this returns
* the lastModified date of the canonicalized version of this file, meaning that we
* compare the lastModified of the target of symlinks.
*
* @param file the file to lookup a cache value for
* @return a value representing the current version of this file
*/
protected Object cacheValueForFile(File file) {
if (symlinkSupport) {
try {
// MS: We want to compute the last modified time on the destination of a (possibly)
// symlinked file. On OS X, the lastModified of the sym link itself matches the
// lastModified of the referenced file, but I didn't want to presume that behavior.
File canonicalizedFile = file.getCanonicalFile();
return canonicalizedFile.getPath() + ":" + Long.valueOf(canonicalizedFile.lastModified());
}
catch (IOException e) {
// MS: return a zero to match the previous semantics from calling file.lastModified() on a missing file.
ERXFileNotificationCenter.log.warn("Failed to determine the lastModified time on '" + file + "': " + e.getMessage());
return Long.valueOf(0);
}
}
return Long.valueOf(file.lastModified());
}
/**
* Records the last modified date of the file for future comparison.
* @param file file to record the last modified date
*/
public void registerLastModifiedDateForFile(File file) {
if (file != null) {
// Note that if the file doesn't exist, it will be registered with a 0
// lastModified time by virtue of the semantics of File.lastModified.
_lastModifiedByFilePath.setObjectForKey(cacheValueForFile(file), cacheKeyForFile(file));
}
}
/**
* Compares the last modified date of the file with the last recorded modification date.
* @param file file to compare last modified date.
* @return if the file has changed since the last time the <code>lastModified</code> value
* was recorded.
*/
public boolean hasFileChanged(File file) {
if (file == null)
throw new RuntimeException("Attempting to check if a null file has been changed");
Object previousCacheValue = _lastModifiedByFilePath.objectForKey(cacheKeyForFile(file));
return previousCacheValue == null || !previousCacheValue.equals(cacheValueForFile(file));
}
/**
* Only used internally. Notifies all of the observers who have been registered for the
* given file.
* @param file file that has changed
*/
protected void fileHasChanged(File file) {
NSMutableSet observers = (NSMutableSet)_observersByFilePath.objectForKey(cacheKeyForFile(file));
if (observers == null)
log.warn("Unable to find observers for file: " + file);
else {
NSNotification notification = new NSNotification(FileDidChange, file);
for (Enumeration e = observers.objectEnumerator(); e.hasMoreElements();) {
_ObserverSelectorHolder holder = (_ObserverSelectorHolder)e.nextElement();
try {
holder.selector.invoke(holder.observer, notification);
} catch (Exception ex) {
log.error("Catching exception when invoking method on observer: " + ex.toString()+" - "+ERXUtilities.stackTrace(ex));
}
}
registerLastModifiedDateForFile(file);
}
}
/**
* Notified by the NSNotificationCenter at the end of every request-response
* loop. It is here that all of the currently watched files are checked to
* see if they have any changes.
* @param n NSNotification notification posted from the NSNotificationCenter.
*/
public void checkIfFilesHaveChanged(NSNotification n) {
int checkPeriod = checkFilesPeriod();
if (!developmentMode && (checkPeriod == 0 || System.currentTimeMillis() - lastCheckMillis < 1000 * checkPeriod)) {
return;
}
lastCheckMillis = System.currentTimeMillis();
if (log.isDebugEnabled()) log.debug("Checking if files have changed");
for (Enumeration e = _lastModifiedByFilePath.keyEnumerator(); e.hasMoreElements();) {
File file = new File((String)e.nextElement());
if (file.exists() && hasFileChanged(file)) {
fileHasChanged(file);
}
}
}
/**
* Simple observer-selector holder class.
*/
public static class _ObserverSelectorHolder {
/** Observing object */
// FIXME: Should be a weak reference
public Object observer;
/** Selector to call on observer */
public NSSelector selector;
/** Constructs a holder given an observer and a selector */
public _ObserverSelectorHolder(Object obs, NSSelector sel) {
observer = obs;
selector = sel;
}
@Override
public int hashCode() {
return (observer == null ? 1 : observer.hashCode()) * (selector == null ? 1 : selector.hashCode());
}
/**
* Overridden to return true if the object being compared has the same observer-selector pair.
* @param osh object to be compared
* @return result of comparison
*/
@Override
public boolean equals(Object osh) {
return osh != null && osh instanceof _ObserverSelectorHolder && ((_ObserverSelectorHolder)osh).selector.equals(selector) &&
((_ObserverSelectorHolder)osh).observer.equals(observer);
}
}
}