监视服务获取文件句柄

时间:2016-05-13 05:41:36

标签: java watchservice

我在我的应用程序中使用java watch服务来获取任何文件更改的通知。

但问题是监视服务保存父目录的文件句柄。 对于例如如果我的层次结构是

F
-F1
 -F2

当我在F,F1和F2上注册观看服务时。然后,如果我尝试重命名或删除父文件夹F,则会出现另一个程序即监视服务打开的文件消息。

我发现此处提到此问题http://bugs.java.com/bugdatabase/view_bug.do;jsessionid=76a42b61021a94ffffffffa049f7587fd4149?bug_id=6972833

还尝试过File_Tree修饰符来规避这个问题,但它没有帮助。可能我没有正确使用File_Tree修饰符。

以下是我正在测试的示例代码。请检查我的代码中FILE_TREE修饰符的用法是否正确。

/**
 * Example to watch a directory (or tree) for changes to files.
 * This code is direct copy from https://docs.oracle.com/javase/tutorial/essential/io/examples/WatchDir.java
 */

public class FileWatcher {

    private final WatchService watcher;
    private final Map<WatchKey,Path> keys;
    private final boolean recursive;
    private boolean trace = false;

    @SuppressWarnings("unchecked")
    static <T> WatchEvent<T> cast(WatchEvent<?> event) {
        return (WatchEvent<T>)event;
    }

    /**
     * Register the given directory with the WatchService
     */
    private void register(Path dir) throws IOException {
        WatchKey key = dir.register(watcher, new WatchEvent.Kind[] { ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY, OVERFLOW },com.sun.nio.file.ExtendedWatchEventModifier.FILE_TREE);
        if (trace) {
            Path prev = keys.get(key);
            if (prev == null) {
                System.out.format("register: %s\n", dir);
            } else {
                if (!dir.equals(prev)) {
                    System.out.format("update: %s -> %s\n", prev, dir);
                }
            }
        }
        keys.put(key, dir);
    }

    /**
     * Register the given directory, and all its sub-directories, with the
     * WatchService.
     */
    private void registerAll(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
                    {
                register(dir);
                return FileVisitResult.CONTINUE;
                    }
        });
    }

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

        if (recursive) {
            System.out.format("Scanning %s ...\n", dir);
            registerAll(dir);
            System.out.println("Done.");
        } else {
            register(dir);
        }

        // enable trace after initial registration
        this.trace = true;
    }

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

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

            Path dir = keys.get(key);
            if (dir == null) {
                System.err.println("WatchKey not recognized!!");
                continue;
            }

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

                // TBD - provide example of how OVERFLOW event is handled
                if (kind == OVERFLOW) {
                    continue;
                }

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

                // print out event
                System.out.format("%s: %s\n", event.kind().name(), child);

                // if directory is created, and watching recursively, then
                // register it and its sub-directories
                if (recursive && kind == ENTRY_CREATE) {
                    try {
                        if (Files.isDirectory(child, NOFOLLOW_LINKS)) {
                            registerAll(child);
                        }
                    } catch (IOException x) {
                        // ignore to keep sample readbale
                    }
                }
            }

            // 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;
                }
            }
        }
    }

    static void usage() {
        System.err.println("usage: java WatchDir [-r] dir");
        System.exit(-1);
    }

    public static void main(String[] args) throws IOException {
        // parse arguments
        if (args.length == 0 || args.length > 2) {
            usage();
        }
        boolean recursive = false;
        int dirArg = 0;
        if (args[0].equals("-r")) {
            if (args.length < 2) {
                usage();
            }
            recursive = false;
            dirArg++;
        }

        // register directory and process its events
        Path dir = Paths.get(args[dirArg]);
        new FileWatcher(dir, recursive).processEvents();
    }
}

1 个答案:

答案 0 :(得分:0)

在文档中挖了一点,找到了自己修复的方法。

使用File_Tree修饰符,将为所有文件夹/目录分配一个键。所以我们需要使用一个密钥。 因此,我尝试使用相同的根路径重新注册,然后在监视目录下的每个新项目创建时重用该键。

主要收获是

  1. 不再需要以递归的方式访问目录中的每个文件夹。
  2. 只要在根路径下创建新文件夹,就需要在同一路径上重新注册,因为每次只需要密钥
  3. 每次我注册整个路径时,我都不确定性能部分。我可能会做一些性能分析。
  4. 以下是我的代码的修改版本。如果代码不清楚,请告诉我

    package com.sap.mcm;  
    
    import static java.nio.file.StandardWatchEventKinds.ENTRY_CREATE;
    import static java.nio.file.StandardWatchEventKinds.ENTRY_DELETE;
    import static java.nio.file.StandardWatchEventKinds.ENTRY_MODIFY;
    import static java.nio.file.StandardWatchEventKinds.OVERFLOW;
    
    import java.io.IOException;
    import java.nio.file.FileSystems;
    import java.nio.file.FileVisitResult;
    import java.nio.file.Files;
    import java.nio.file.Path;
    import java.nio.file.Paths;
    import java.nio.file.SimpleFileVisitor;
    import java.nio.file.WatchEvent;
    import java.nio.file.WatchKey;
    import java.nio.file.WatchService;
    import java.nio.file.attribute.BasicFileAttributes;
    import java.util.HashMap;
    import java.util.Map;
    
    import com.sun.nio.file.ExtendedWatchEventModifier;
    
    /**
     * Example to watch a directory (or tree) for changes to files.
     * This code is direct copy from https://docs.oracle.com/javase/tutorial/essential/io/examples/WatchDir.java
     */
    public class FileWatcher {
    
        private final WatchService watcher;
        private final Map<WatchKey,Path> keys;
        private final boolean recursive;
        private boolean trace = true;
        private Path parentDir;
        private WatchKey key;
    
        @SuppressWarnings("unchecked")
        static <T> WatchEvent<T> cast(WatchEvent<?> event) {
            return (WatchEvent<T>)event;
        }
    
        /**
         * Register the given directory with the WatchService
         */
        private void register(Path dir) throws IOException {
            try {
                parentDir = dir;
                key = parentDir.register(watcher, new WatchEvent.Kind[] { ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY, OVERFLOW }, ExtendedWatchEventModifier.FILE_TREE);
            } catch (UnsupportedOperationException usoe) {
                usoe.printStackTrace();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    
        public void reregister() throws IOException {
            // WatchKey key = keys.get(path);
            key.cancel();
            register(parentDir);
        }
        /**
         * Register the given directory, and all its sub-directories, with the
         * WatchService.
         */
        private void registerAll(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 {
                    register(dir);
                    return FileVisitResult.CONTINUE;
                }
            });
        }
    
        /**
         * Creates a WatchService and registers the given directory
         */
        FileWatcher(Path dir, boolean recursive) throws IOException {
            this.watcher = FileSystems.getDefault().newWatchService();
            this.keys = new HashMap<WatchKey,Path>();
            this.recursive = recursive;
    
            if (recursive) {
                System.out.format("Scanning %s ...\n", dir);
                registerAll(dir);
                System.out.println("Done.");
            } else {
                register(dir);
            }
    
            // enable trace after initial registration
            this.trace = true;
        }
    
        /**
         * Process all events for keys queued to the watcher
         */
        void processEvents() {
            for (;;) {
    
                // wait for key to be signalled
                WatchKey key;
                try {
                    key = watcher.take();
                } catch (InterruptedException x) {
                    return;
                }
    
                // Path dir = keys.get(key);
                // if (dir == null) {
                // System.err.println("WatchKey not recognized!!");
                // continue;
                // }
                if (this.key != key) {
                    return;
                }
                for (WatchEvent<?> event: key.pollEvents()) {
                    WatchEvent.Kind kind = event.kind();
    
                    // TBD - provide example of how OVERFLOW event is handled
                    if (kind == OVERFLOW) {
                        continue;
                    }
    
                    // Context for directory entry event is the file name of entry
                    WatchEvent<Path> ev = cast(event);
                    ev.context();
    
                    // print out event
                    System.out.format("%s: %s \n", event.kind().name(), event.context());
    
                    // if directory is created, and watching recursively, then
                    // register it and its sub-directories
                    if (kind == ENTRY_CREATE) {
                        try {
                            // if (Files.isDirectory(child, NOFOLLOW_LINKS)) {
                            reregister();
                            // }
                        } catch (IOException x) {
                            // ignore to keep sample readbale
                        }
                    }
                }
    
                // reset key and remove from set if directory no longer accessible
                boolean valid = this.key.reset();
                if (!valid) {
                    keys.remove(key);
    
                    // all directories are inaccessible
                    if (keys.isEmpty()) {
                        break;
                    }
                }
            }
        }
    
        static void usage() {
            System.err.println("usage: java WatchDir [-r] dir");
            System.exit(-1);
        }
    
        public static void main(String[] args) throws IOException {
            // parse arguments
            if (args.length == 0 || args.length > 2) {
                usage();
            }
            boolean recursive = false;
            int dirArg = 0;
            if (args[0].equals("-r")) {
                if (args.length < 2) {
                    usage();
                }
                recursive = false;
                dirArg++;
            }
    
            // register directory and process its events
            Path dir = Paths.get(args[dirArg]);
            new FileWatcher(dir, recursive).processEvents();
        }
    }