@Override
public void run() {
for (Map.Entry<String, ConfigFileInfo> entry : watchedFileMap.entrySet()) {
String filePath = entry.getKey();
ConfigFileInfo configFileInfo = entry.getValue();
try {
File file = new File(filePath);
long lastModified = file.lastModified();
Preconditions.checkArgument(lastModified > 0L);
if (lastModified != configFileInfo.lastModifiedTimestampMillis) {
configFileInfo.lastModifiedTimestampMillis = lastModified;
ByteSource byteSource = Files.asByteSource(file);
HashCode newContentHash = byteSource.hash(HASH_FUNCTION);
if (!newContentHash.equals(configFileInfo.contentHash)) {
configFileInfo.contentHash = newContentHash;
LOG.info("File {} was modified at {}, notifying watchers.", filePath, lastModified);
byte[] newContents = byteSource.read();
for (Function<byte[], Void> watchers : configFileInfo.changeWatchers) {
try {
watchers.apply(newContents);
} catch (Exception e) {
LOG.error(
"Exception in watcher callback for {}, ignoring. New file contents were: {}",
filePath,
new String(newContents, Charsets.UTF_8),
e);
}
}
} else {
LOG.info(
"File {} was modified at {} but content hash is unchanged.",
filePath,
lastModified);
}
} else {
LOG.debug("File {} not modified since {}", filePath, lastModified);
}
} catch (Exception e) {
// We catch and log exceptions related to the update of any specific file, but
// move on so others aren't affected. Issues can happen for example if the watcher
// races with an external file replace operation; in that case, the next run should
// pick up the update.
// TODO: Consider adding a metric to track this so we can alert on failures.
LOG.error("Config update check failed for {}", filePath, e);
}
}
}
/**
* Adds a watch on the specified file. The file must exist, otherwise a FileNotFoundException is
* returned. If the file is deleted after a watch is established, the watcher will log errors but
* continue to monitor it, and resume watching if it is recreated.
*
* @param filePath path to the file to watch.
* @param onUpdate function to call when a change is detected to the file. The entire contents of
* the file will be passed in to the function. Note that onUpdate will be called once before
* this call completes, which facilities initial load of data. This callback is executed
* synchronously on the watcher thread - it is important that the function be non-blocking.
*/
public synchronized void addWatch(String filePath, Function<byte[], Void> onUpdate)
throws IOException {
MorePreconditions.checkNotBlank(filePath);
Preconditions.checkNotNull(onUpdate);
// Read the file and make the initial onUpdate call.
File file = new File(filePath);
ByteSource byteSource = Files.asByteSource(file);
onUpdate.apply(byteSource.read());
// Add the file to our map if it isn't already there, and register the new change watcher.
ConfigFileInfo configFileInfo = watchedFileMap.get(filePath);
if (configFileInfo == null) {
configFileInfo = new ConfigFileInfo(file.lastModified(), byteSource.hash(HASH_FUNCTION));
watchedFileMap.put(filePath, configFileInfo);
}
configFileInfo.changeWatchers.add(onUpdate);
}