JDK7之Java Watch Service API监控文件变化

秒速五厘米 2022-08-07 03:46 166阅读 0赞

[示例代码][Link 1]

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    import java.nio.file.*;
    import static java.nio.file.StandardWatchEventKinds.*;
    import static java.nio.file.LinkOption.*;
    import java.nio.file.attribute.*;
    import java.io.*;
    import java.util.*;
    
    /**
     * Example to watch a directory (or tree) for changes to files.
     */
    
    public class WatchDir {
    
        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, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
            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
         */
        WatchDir(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 = true;
                dirArg++;
            }
    
            // register directory and process its events
            Path dir = Paths.get(args[dirArg]);
            new WatchDir(dir, recursive).processEvents();
        }
    }

[Link 1]: http://docs.oracle.com/javase/tutorial/essential/io/examples/WatchDir.java