Java WatchService 意外停止工作

Question

我有一个递归监视服务，用于在应用程序处于运行时监视目录。出于未知原因，监视服务似乎在大约一天后停止工作。那时我可以将一个新文件添加到受监视的目录并且不会得到任何日志语句并且我的观察者也不会收到通知。

我认为 Spring 可能会破坏 bean，所以我在 class 的 @pre-destroy 部分添加了一条日志语句，但该日志语句在watchservice 停止工作，所以看起来 bean 仍然存在，只是没有按预期运行。 class如下

import com.sun.nio.file.SensitivityWatchEventModifier;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Service;

import java.io.File;
import java.io.IOException;
import java.nio.file.*;
import java.nio.file.attribute.BasicFileAttributes;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.function.Consumer;

import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;

import static java.nio.file.StandardWatchEventKinds.ENTRY_CREATE;
import static java.nio.file.StandardWatchEventKinds.ENTRY_DELETE;

@Service
public class DirectoryMonitor {

private static final Logger logger = LoggerFactory.getLogger(DirectoryMonitor.class);
private WatchService watcher;
private ExecutorService executor;
private List<DirectoryMonitorObserver> observerList = new ArrayList<>();
private final Map<WatchKey, Path> keys = new HashMap<>();

public void addObserver(DirectoryMonitorObserver observer){
    observerList.add(observer);
}

private void notifyObservers(){
    observerList.forEach(DirectoryMonitorObserver::directoryModified);
}

@PostConstruct
public void init() throws IOException {
    watcher = FileSystems.getDefault().newWatchService();
    executor = Executors.newSingleThreadExecutor();
}

@PreDestroy
public void cleanup() {
    try {
        logger.info("Stopping directory monitor");
        watcher.close();
    } catch (IOException e) {
        logger.error("Error closing watcher service", e);
    }
    executor.shutdown();
}

@SuppressWarnings("unchecked")
public void startRecursiveWatcher(String pathToMonitor) {
    logger.info("Starting Recursive Watcher");

    Consumer<Path> register = p -> {
        if (!p.toFile().exists() || !p.toFile().isDirectory())
            throw new RuntimeException("folder " + p + " does not exist or is not a directory");

        try {
            Files.walkFileTree(p, new SimpleFileVisitor<Path>() {
                @Override
                public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException {
                    logger.info("registering " + dir + " in watcher service");
                    WatchKey watchKey = dir.register(watcher, new WatchEvent.Kind[]{ENTRY_CREATE, ENTRY_DELETE}, SensitivityWatchEventModifier.HIGH);
                    keys.put(watchKey, dir);
                    return FileVisitResult.CONTINUE;
                }
            });
        } catch (IOException e) {
            throw new RuntimeException("Error registering path " + p);
        }
    };

    register.accept(Paths.get(pathToMonitor));

    executor.submit(() -> {
        while (true) {
            final WatchKey key;
            try {
                key = watcher.take();
            } catch (InterruptedException ex) {
                logger.error(ex.toString());
                continue;
            }

            final Path dir = keys.get(key);

            key.pollEvents().stream()
                    .map(e -> ((WatchEvent<Path>) e).context())
                    .forEach(p -> {
                        final Path absPath = dir.resolve(p);
                        if (absPath.toFile().isDirectory()) {
                            register.accept(absPath);
                        } else {
                            final File f = absPath.toFile();
                            logger.info("Detected new file " + f.getAbsolutePath());
                        }
                    });

            notifyObservers();
            key.reset();
        }
    });
}

}

这是我创建监视器 bean 的地方..

@Component
public class MovieInfoFacade {
    @Value("${media.path}")
    private String mediaPath;
    private MovieInfoControl movieInfoControl;
    private DirectoryMonitor directoryMonitor;
    private FileListProvider fileListProvider;

@Autowired
public MovieInfoFacade(MovieInfoControl movieInfoControl, DirectoryMonitor directoryMonitor, FileListProvider fileListProvider){
    this.movieInfoControl = movieInfoControl;
    this.directoryMonitor = directoryMonitor;
    this.fileListProvider = fileListProvider;
}

@PostConstruct
public void startDirectoryMonitor(){
    if(!mediaPath.equalsIgnoreCase("none")) {
        directoryMonitor.addObserver(fileListProvider);
        directoryMonitor.startRecursiveWatcher(mediaPath);
    }
}

public int loadMovieListLength(String directoryPath){
    return fileListProvider.listFiles(directoryPath).length;
}

public List<MovieInfo> loadMovieList(MovieSearchCriteria searchCriteria) {
    List<File> files = Arrays.asList(fileListProvider.listFiles(searchCriteria.getPath()));

    return files.parallelStream()
            .sorted()
            .skip(searchCriteria.getPage() * searchCriteria.getItemsPerPage())
            .limit(searchCriteria.getItemsPerPage())
            .map(file -> movieInfoControl.loadMovieInfoFromCache(file.getAbsolutePath()))
            .collect(Collectors.toList());
}

public MovieInfo loadSingleMovie(String filePath) {
    return movieInfoControl.loadMovieInfoFromCache(filePath);
}

}

Answer 1

看来错误是在我的异常处理中。删除 throw 语句（并用日志替换它们）后，我没有遇到任何问题。

Java WatchService 意外停止工作

Java WatchService unexpectedly stops working

java

spring

java-8

watchservice