chore(watch_dir): initial commit
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# Overview
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This project shows how to watch a folder.
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# Links
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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xmlns="http://maven.apache.org/POM/4.0.0"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<name>watch_dir</name>
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<description>description</description>
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<url>https://swingbe.de</url>
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<groupId>org.swingbe.de</groupId>
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<artifactId>watch_dir</artifactId>
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<version>0.0.1</version>
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<packaging>jar</packaging>
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<licenses>
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<license>
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<name>GNU General Public License</name>
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<url>https://www.gnu.org/licenses/gpl-3.0.txt</url>
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</license>
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</licenses>
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<scm>
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<url>https://github.com/Software-Ingenieur-Begerad/sandbox-java</url>
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</scm>
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<properties>
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<!-- Other properties -->
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<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
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</properties>
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<build>
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<plugins>
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-compiler-plugin</artifactId>
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<version>3.8.1</version>
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<configuration>
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<!-- Target Java versions -->
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<release>11</release>
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</configuration>
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</plugin>
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-shade-plugin</artifactId>
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<version>3.2.1</version>
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<executions>
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<execution>
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<phase>package</phase>
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<goals>
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<goal>shade</goal>
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</goals>
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<configuration>
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<filters>
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<filter>
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<!-- exclude signatures from merged JAR to avoid invalid signature messages -->
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<artifact>*:*</artifact>
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<excludes>
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<exclude>META-INF/*.SF</exclude>
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<exclude>META-INF/*.DSA</exclude>
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<exclude>META-INF/*.RSA</exclude>
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</excludes>
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</filter>
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</filters>
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<!-- The shaded JAR will not be the main artifact for the project, it will be attached
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for deployment in the way source and docs are. -->
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<shadedArtifactAttached>true
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</shadedArtifactAttached>
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<shadedClassifierName>shaded</shadedClassifierName>
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<transformers>
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<transformer
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implementation="org.apache.maven.plugins.shade.resource.ServicesResourceTransformer"/>
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<transformer
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implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
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<manifestEntries>
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<Main-Class>de.swingbe.watch_dir.Main
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</Main-Class>
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</manifestEntries>
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</transformer>
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</transformers>
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</configuration>
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</execution>
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</executions>
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</plugin>
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</plugins>
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</build>
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</project>
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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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