WebListener empêche le lancement de l'application Web

Question

J'ai une application Web Vaadin qui est en cours de déploiement. mais quand j'ajouter un service de FolderWatcher en tant qu'auditeur en utilisant

@WebListener 

L'application ne parvient pas à déployer, mais il commence le fil si je désactive l'annotation @WebListener l'application ne se déploie.

classe veilleur dossier

public class FolderWatchService { 

private final WatchService watcher; 
private final Map<WatchKey, Path> keys; 
private static final Logger LOGGER = Logger.getLogger(FolderWatchService.class.getName()); 

/** 
* Creates a WatchService and registers the given directory 
*/ 
public FolderWatchService(Path dir) throws IOException { 
    this.watcher = FileSystems.getDefault().newWatchService(); 
    this.keys = new HashMap<WatchKey, Path>(); 

    walkAndRegisterDirectories(dir); 
} 

/** 
* Register the given directory with the WatchService; This function will be called by FileVisitor 
*/ 
private void registerDirectory(Path dir) throws IOException 
{ 
    WatchKey key = dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY); 
    keys.put(key, dir); 
} 

/** 
* Register the given directory, and all its sub-directories, with the WatchService. 
*/ 
private void walkAndRegisterDirectories(final Path start) throws IOException { 
    // register directory and sub-directories 
    Files.walkFileTree(start, new SimpleFileVisitor<Path>() { 
     @Override 
     public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException { 
      registerDirectory(dir); 
      return FileVisitResult.CONTINUE; 
     } 
    }); 
} 

/** 
* Process all events for keys queued to the watcher 
*/ 
public void processEvents() { 
    for (;;) { 

     // wait for key to be signaled 
     WatchKey key; 
     try { 
      key = watcher.take(); 
     } catch (InterruptedException x) { 
      return; 
     } 

     Path dir = keys.get(key); 
     if (dir == null) { 
      LOGGER.log(Level.FINE, "WatchKey not recognized!!", ""); 

      System.err.println("WatchKey not recognized!!"); 
      continue; 
     } 

     for (WatchEvent<?> event : key.pollEvents()) { 
      @SuppressWarnings("rawtypes") 
      WatchEvent.Kind kind = event.kind(); 

      // Context for directory entry event is the file name of entry 
      @SuppressWarnings("unchecked") 
      Path name = ((WatchEvent<Path>)event).context(); 
      Path child = dir.resolve(name); 


      String fileContent; 



      // if directory is created, and watching recursively, then register it and its sub-directories 
      if (kind == ENTRY_CREATE) { 
       System.out.println("File created"); 
       LOGGER.log(Level.FINER, "New File created", ""); 
       readFile(child.toString()); 
      } 
     } 

     // reset key and remove from set if directory no longer accessible 
     boolean valid = key.reset(); 
     if (!valid) { 
      keys.remove(key); 

      // all directories are inaccessible 
      if (keys.isEmpty()) { 
       break; 
      } 
     } 
    } 
} 
private static void readFile(String pathname){ 

    try { 
     File file = new File(pathname); 

     StringBuilder fileContents = new StringBuilder((int)file.length()); 
     Scanner scanner = new Scanner(file); 
     String lineSeparator = System.getProperty("line.separator"); 

     try { 
      while(scanner.hasNextLine()) { 
       fileContents.append(scanner.nextLine() + lineSeparator); 
      } 
      String fileContent = fileContents.toString(); 
      System.out.println("File name: "+FilenameUtils.getBaseName(pathname)); 
      LOGGER.log(Level.FINER, "File name: "+FilenameUtils.getBaseName(pathname), ""); 
      String title = "File Title: "+fileContent.substring(0, 64).trim().lastIndexOf(System.getProperty("line.separator"))+"..."; 

     } finally { 
      scanner.close(); 
     } 
    } catch (FileNotFoundException e) { 
     // TODO Auto-generated catch block 
     e.printStackTrace(); 
    } 

} 

} 

classe ContextLister

@WebListener 
public class ContextListener implements ServletContextListener { 

    @Override 
    public void contextDestroyed(ServletContextEvent arg0) { 
     System.out.println("#### Folder watcher service destroyed"); 

    } 

    @Override 
    public void contextInitialized(ServletContextEvent arg0) { 
     System.out.println("#### Folder watcher service initialized"); 
     Path dir = Paths.get(PropertiesCache.getInstance().getProperty("file_input_location")); 
      try { 
       new FolderWatchService(dir).processEvents(); 
       System.out.println("#### Folder watcher service started"); 
      } catch (IOException e) { 
       System.out.println("#### Folder watcher Problem"); 
       // TODO Auto-generated catch block 
       e.printStackTrace(); 
      } 

    } 
    } 

EDIT: Ajout ce qui est imprimé par les journaux

Jun 26, 2017 10:56:31 PM org.apache.catalina.core.AprLifecycleListener 
lifecycleEvent 
INFO: Loaded APR based Apache Tomcat Native library 1.2.12 using APR version 
1.5.2. 
Jun 26, 2017 10:56:31 PM org.apache.catalina.core.AprLifecycleListener 
lifecycleEvent 
INFO: APR capabilities: IPv6 [true], sendfile [true], accept filters 
[false], random [true]. 
Jun 26, 2017 10:56:31 PM org.apache.catalina.core.AprLifecycleListener 
lifecycleEvent 
INFO: APR/OpenSSL configuration: useAprConnector [false], useOpenSSL [true] 
Jun 26, 2017 10:56:31 PM org.apache.catalina.core.AprLifecycleListener 
initializeSSL 
INFO: OpenSSL successfully initialized (OpenSSL 1.0.2k 26 Jan 2017) 
Jun 26, 2017 10:56:31 PM org.apache.coyote.AbstractProtocol init 
INFO: Initializing ProtocolHandler ["http-nio-8080"] 
Jun 26, 2017 10:56:31 PM org.apache.tomcat.util.net.NioSelectorPool 
getSharedSelector 
INFO: Using a shared selector for servlet write/read 
Jun 26, 2017 10:56:31 PM org.apache.coyote.AbstractProtocol init 
INFO: Initializing ProtocolHandler ["ajp-nio-8009"] 
Jun 26, 2017 10:56:31 PM org.apache.tomcat.util.net.NioSelectorPool 
getSharedSelector 
INFO: Using a shared selector for servlet write/read 
Jun 26, 2017 10:56:31 PM org.apache.catalina.startup.Catalina load 
INFO: Initialization processed in 1392 ms 
Jun 26, 2017 10:56:31 PM org.apache.catalina.core.StandardService 
startInternal 
INFO: Starting service Catalina 
Jun 26, 2017 10:56:31 PM org.apache.catalina.core.StandardEngine 
startInternal 
INFO: Starting Servlet Engine: Apache Tomcat/8.5.12 
Jun 26, 2017 10:56:32 PM org.apache.catalina.util.SessionIdGeneratorBase 
createSecureRandom 
INFO: Creation of SecureRandom instance for session ID generation using 
[SHA1PRNG] took [126] milliseconds. 
Jun 26, 2017 10:56:40 PM org.apache.jasper.servlet.TldScanner scanJars 
INFO: At least one JAR was scanned for TLDs yet contained no TLDs. Enable 
debug logging for this logger for a complete list of JARs that were scanned 
but no TLDs were found in them. Skipping unneeded JARs during scanning can 
improve startup time and JSP compilation time. 
#### Folder watcher service initialized 

La dernière ligne est println ici de ContextLister, et applic

Qu'est-ce que je fais mal ici?

Answer 1

Il semble que l'implémentation de l'écouteur bloque à new FolderWatchService(dir).processEvents();. Vous devez exécuter le traitement des événements dans un autre thread (c'est-à-dire en utilisant un ExecutorService pour soumettre le travail processEvents et peut-être annuler/arrêter en contextDestroyed)