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