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本文主要研究一下canal的ApplicationConfigMonitor
ApplicationConfigMonitor
canal-1.1.4/client-adapter/launcher/src/main/java/com/alibaba/otter/canal/adapter/launcher/monitor/ApplicationConfigMonitor.java
@Component
public class ApplicationConfigMonitor {
private static final Logger logger = LoggerFactory.getLogger(ApplicationConfigMonitor.class);
@Resource
private ContextRefresher contextRefresher;
@Resource
private CanalAdapterService canalAdapterService;
private FileAlterationMonitor fileMonitor;
@PostConstruct
public void init() {
File confDir = Util.getConfDirPath();
try {
FileAlterationObserver observer = new FileAlterationObserver(confDir,
FileFilterUtils.and(FileFilterUtils.fileFileFilter(),
FileFilterUtils.prefixFileFilter("application"),
FileFilterUtils.suffixFileFilter("yml")));
FileListener listener = new FileListener();
observer.addListener(listener);
fileMonitor = new FileAlterationMonitor(3000, observer);
fileMonitor.start();
} catch (Exception e) {
logger.error(e.getMessage(), e);
}
}
@PreDestroy
public void destroy() {
try {
fileMonitor.stop();
} catch (Exception e) {
logger.error(e.getMessage(), e);
}
}
private class FileListener extends FileAlterationListenerAdaptor {
@Override
public void onFileChange(File file) {
super.onFileChange(file);
try {
// 检查yml格式
new Yaml().loadAs(new InputStreamReader(new FileInputStream(file), StandardCharsets.UTF_8), Map.class);
canalAdapterService.destroy();
// refresh context
contextRefresher.refresh();
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
// ignore
}
canalAdapterService.init();
logger.info("## adapter application config reloaded.");
} catch (Exception e) {
logger.error(e.getMessage(), e);
}
}
}
}
- ApplicationConfigMonitor在PostConstruct的时候创建FileAlterationObserver，添加FileListener，然后使用FileAlterationObserver创建FileAlterationMonitor，然后执行其start方法；在PreDestroy的时候执行fileMonitor.stop()；FileListener继承了FileAlterationListenerAdaptor，其onFileChange方法会检查yml格式，执行canalAdapterService.destroy()、contextRefresher.refresh()、canalAdapterService.init()
FileAlterationMonitor
commons-io-2.4-sources.jar!/org/apache/commons/io/monitor/FileAlterationMonitor.java
public final class FileAlterationMonitor implements Runnable {
private final long interval;
private final List<FileAlterationObserver> observers = new CopyOnWriteArrayList<FileAlterationObserver>();
private Thread thread = null;
private ThreadFactory threadFactory;
private volatile boolean running = false;
public FileAlterationMonitor() {
this(10000);
}
public FileAlterationMonitor(long interval) {
this.interval = interval;
}
public FileAlterationMonitor(long interval, FileAlterationObserver... observers) {
this(interval);
if (observers != null) {
for (FileAlterationObserver observer : observers) {
addObserver(observer);
}
}
}
//......
public synchronized void start() throws Exception {
if (running) {
throw new IllegalStateException("Monitor is already running");
}
for (FileAlterationObserver observer : observers) {
observer.initialize();
}
running = true;
if (threadFactory != null) {
thread = threadFactory.newThread(this);
} else {
thread = new Thread(this);
}
thread.start();
}
/**
* Stop monitoring.
*
* @throws Exception if an error occurs initializing the observer
*/
public synchronized void stop() throws Exception {
stop(interval);
}
/**
* Stop monitoring.
*
* @param stopInterval the amount of time in milliseconds to wait for the thread to finish.
* A value of zero will wait until the thread is finished (see {@link Thread#join(long)}).
* @throws Exception if an error occurs initializing the observer
* @since 2.1
*/
public synchronized void stop(long stopInterval) throws Exception {
if (running == false) {
throw new IllegalStateException("Monitor is not running");
}
running = false;
try {
thread.join(stopInterval);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
for (FileAlterationObserver observer : observers) {
observer.destroy();
}
}
public void run() {
while (running) {
for (FileAlterationObserver observer : observers) {
observer.checkAndNotify();
}
if (!running) {
break;
}
try {
Thread.sleep(interval);
} catch (final InterruptedException ignored) {
}
}
}
}
- FileAlterationMonitor的start方法会使用自己的runnable创建Thread，然后执行thread.start()；其stop方法则执行thread.join(stopInterval)，然后遍历observers，执行observer.destroy()；其run方法则遍历observers，执行observer.checkAndNotify()
FileAlterationObserver
commons-io-2.4-sources.jar!/org/apache/commons/io/monitor/FileAlterationObserver.java
public class FileAlterationObserver implements Serializable {
private final List<FileAlterationListener> listeners = new CopyOnWriteArrayList<FileAlterationListener>();
private final FileEntry rootEntry;
private final FileFilter fileFilter;
private final Comparator<File> comparator;
//......
public void checkAndNotify() {
/* fire onStart() */
for (FileAlterationListener listener : listeners) {
listener.onStart(this);
}
/* fire directory/file events */
File rootFile = rootEntry.getFile();
if (rootFile.exists()) {
checkAndNotify(rootEntry, rootEntry.getChildren(), listFiles(rootFile));
} else if (rootEntry.isExists()) {
checkAndNotify(rootEntry, rootEntry.getChildren(), FileUtils.EMPTY_FILE_ARRAY);
} else {
// Didn't exist and still doesn't
}
/* fire onStop() */
for (FileAlterationListener listener : listeners) {
listener.onStop(this);
}
}
private void checkAndNotify(FileEntry parent, FileEntry[] previous, File[] files) {
int c = 0;
FileEntry[] current = files.length > 0 ? new FileEntry[files.length] : FileEntry.EMPTY_ENTRIES;
for (FileEntry entry : previous) {
while (c < files.length && comparator.compare(entry.getFile(), files[c]) > 0) {
current[c] = createFileEntry(parent, files[c]);
doCreate(current[c]);
c++;
}
if (c < files.length && comparator.compare(entry.getFile(), files[c]) == 0) {
doMatch(entry, files[c]);
checkAndNotify(entry, entry.getChildren(), listFiles(files[c]));
current[c] = entry;
c++;
} else {
checkAndNotify(entry, entry.getChildren(), FileUtils.EMPTY_FILE_ARRAY);
doDelete(entry);
}
}
for (; c < files.length; c++) {
current[c] = createFileEntry(parent, files[c]);
doCreate(current[c]);
}
parent.setChildren(current);
}
//......
}
- FileAlterationObserver的checkAndNotify方法会遍历之前的FileEntry，然后使用NameFileComparator递归遍历对比文件变化，分别触发doCreate、doMatch、doDelete，他们会回调FileAlterationListener的对应方法
小结
ApplicationConfigMonitor在PostConstruct的时候创建FileAlterationObserver，添加FileListener，然后使用FileAlterationObserver创建FileAlterationMonitor，然后执行其start方法；在PreDestroy的时候执行fileMonitor.stop()；FileListener继承了FileAlterationListenerAdaptor，其onFileChange方法会检查yml格式，执行canalAdapterService.destroy()、contextRefresher.refresh()、canalAdapterService.init()
doc
来源：oschina
链接：https://my.oschina.net/go4it/blog/3218578