private void notifyListeners(File file) {
// listeners is a synchronized list - no need to sync here
for (FileWatcherListener listener : listeners) {
try {
listener.fileChanged(file);
} catch (Exception e) {
logger.info(
"Discarding exception " + e.getLocalizedMessage() + " thrown by FileWatcherListener");
}
}
}
public void run() {
// now that thread is running, check that directory exists
// doing this test here allows it to be created subsequent to the file watcher construction
if (!dir.exists()) {
throw new RuntimeException("FileWatcher directory path does not exist[" + dir + "]");
}
for (FileWatcherListener listener : listeners) {
listener.startedWatching(dir);
}
// record time we started polling
long startPollTime = System.currentTimeMillis();
for (; ; ) {
logger.debug("starting directory poll {}", dir);
// has an external thread requested that this one be stopped?
if (stopHasBeenRequested()) {
logger.info("stopping file watcher thread");
break;
}
// scan directory for files or directories we are interested in
File[] files =
dir.listFiles(
new FileFilter() {
public boolean accept(File file) {
boolean isDir = file.isDirectory();
if (watchDirs != isDir) return false;
return file.getName().matches(nameRegexp);
}
});
// find directory entries that have been changed since previous poll
// note: given that even the retrieval of the last modified time can consume time
// (let alone any actions in the notifications), it is not safe to just compare the
// current last modified time of each file against a single time for the end of the
// previous poll - instead we maintain a record of the previous modification time
// for any file which has been modified during the lifetime of this poller
// then compare the current last modified time against that
for (File file : files) {
logger.debug("found " + file.getName());
// find previous known last modified time for file
Long prevModifiedTime = prevModifiedTimeByFile.get(file);
if (prevModifiedTime == null) {
// we do not know about this file - this means that it had not previously
// been modified since we started polling so use start of polling as its
// previous modification time
prevModifiedTimeByFile.put(file, prevModifiedTime = startPollTime);
logger.debug("no previous modification time for file {}", file);
} else if ((System.currentTimeMillis() - prevModifiedTime) > MAX_TIME_SINCE_LAST_MODIFIED) {
// the last time this file was modified since we started up this poller
// was over (default) a day ago - we can't possibly get confused over a
// modification time that long ago so get rid of file from cache
prevModifiedTimeByFile.remove(file);
logger.debug("cache entry expired, ignoring file {}", file);
continue;
}
logger.debug("prevModifiedTime={} for file {}", prevModifiedTime, file);
long lastModifiedTime = file.lastModified();
logger.debug("lastModifiedTime={} for file {}", lastModifiedTime, file);
if (lastModifiedTime > prevModifiedTime) {
notifyFileChange(file);
prevModifiedTimeByFile.put(file, lastModifiedTime);
}
}
try {
Thread.sleep(pollingIntervalMillis);
} catch (InterruptedException exp) {
}
}
}