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This article mainly studies canal's 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 { // Check the yml format 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); } } } }
- The ApplicationConfigMonitor creates the FileAlterationObserver when PostConstruct, adds the FileListener, then creates the FileAlterationMonitor using FileAlterationObserver, and executes its start method; executes the fileMonitor.stop() when PreDestroy; the FileListener inherits the FileAlterationListenerAdaptor, and its onFileChange method checks the yml format to execute canal alterationObserverAdapterService.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) { } } } }
- The start method of FileAlterationMonitor creates a Thread using its own runnable, then executes thread.start(); its stop method executes thread.join(stopInterval), then traverses observers and executes observer.destroy(); its run method traverses observers and executes 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's checkAndNotify method traverses the previous FileEntry, then uses NameFileComparator to recursively traverse the changes in the comparison file, triggering doCreate, doMatch, doDelete, respectively, which calls back FileAlterationListener's corresponding method
Summary
The ApplicationConfigMonitor creates the FileAlterationObserver when PostConstruct, adds the FileListener, then creates the FileAlterationMonitor using FileAlterationObserver, and executes its start method; executes the fileMonitor.stop() when PreDestroy; the FileListener inherits the FileAlterationListenerAdaptor, and its onFileChange method checks the yml format to execute canal alterationObserverAdapterService.destroy(), contextRefresher.refresh(), canalAdapterService.init()