1 /*
2 * Copyright (c) 2008, 2010, Oracle and/or its affiliates. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 *
8 * - Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 *
11 * - Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 *
15 * - Neither the name of Oracle nor the names of its
16 * contributors may be used to endorse or promote products derived
17 * from this software without specific prior written permission.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
20 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
21 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
23 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
24 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
25 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
26 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
27 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
28 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
29 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
30 */
31
32 import java.nio.file.*;
33 import static java.nio.file.StandardWatchEventKind.*;
34 import static java.nio.file.LinkOption.*;
35 import java.nio.file.attribute.*;
36 import java.io.*;
37 import java.util.*;
38
39 /**
40 * Example to watch a directory (or tree) for changes to files.
41 */
42
43 public class WatchDir {
44
45 private final WatchService watcher;
46 private final Map<WatchKey,Path> keys;
47 private final boolean recursive;
48 private boolean trace = false;
49
50 @SuppressWarnings("unchecked")
51 static <T> WatchEvent<T> cast(WatchEvent<?> event) {
52 return (WatchEvent<T>)event;
53 }
54
55 /**
56 * Register the given directory with the WatchService
57 */
58 private void register(Path dir) throws IOException {
59 WatchKey key = dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
60 if (trace) {
61 FileRef prev = keys.get(key);
62 if (prev == null) {
63 System.out.format("register: %s\n", dir);
64 } else {
65 if (!dir.equals(prev)) {
66 System.out.format("update: %s -> %s\n", prev, dir);
67 }
68 }
69 }
70 keys.put(key, dir);
71 }
72
73 /**
74 * Register the given directory, and all its sub-directories, with the
75 * WatchService.
76 */
77 private void registerAll(final Path start) throws IOException {
78 // register directory and sub-directories
79 Files.walkFileTree(start, new SimpleFileVisitor<Path>() {
80 @Override
81 public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs)
82 throws IOException
83 {
84 register(dir);
85 return FileVisitResult.CONTINUE;
86 }
87 });
88 }
89
90 /**
91 * Creates a WatchService and registers the given directory
92 */
93 WatchDir(Path dir, boolean recursive) throws IOException {
94 this.watcher = FileSystems.getDefault().newWatchService();
95 this.keys = new HashMap<WatchKey,Path>();
96 this.recursive = recursive;
97
98 if (recursive) {
99 System.out.format("Scanning %s ...\n", dir);
100 registerAll(dir);
101 System.out.println("Done.");
102 } else {
103 register(dir);
104 }
105
106 // enable trace after initial registration
107 this.trace = true;
108 }
109
110 /**
111 * Process all events for keys queued to the watcher
112 */
113 void processEvents() {
114 for (;;) {
115
116 // wait for key to be signalled
117 WatchKey key;
118 try {
119 key = watcher.take();
120 } catch (InterruptedException x) {
121 return;
122 }
123
124 Path dir = keys.get(key);
125 if (dir == null) {
126 System.err.println("WatchKey not recognized!!");
127 continue;
128 }
129
130 for (WatchEvent<?> event: key.pollEvents()) {
131 WatchEvent.Kind kind = event.kind();
132
133 // TBD - provide example of how OVERFLOW event is handled
134 if (kind == OVERFLOW) {
135 continue;
136 }
137
138 // Context for directory entry event is the file name of entry
139 WatchEvent<Path> ev = cast(event);
140 Path name = ev.context();
141 Path child = dir.resolve(name);
142
143 // print out event
144 System.out.format("%s: %s\n", event.kind().name(), child);
145
146 // if directory is created, and watching recursively, then
147 // register it and its sub-directories
148 if (recursive && (kind == ENTRY_CREATE)) {
149 try {
150 if (Attributes.readBasicFileAttributes(child, NOFOLLOW_LINKS).isDirectory()) {
151 registerAll(child);
152 }
153 } catch (IOException x) {
154 // ignore to keep sample readbale
155 }
156 }
157 }
158
159 // reset key and remove from set if directory no longer accessible
160 boolean valid = key.reset();
161 if (!valid) {
162 keys.remove(key);
163
164 // all directories are inaccessible
165 if (keys.isEmpty()) {
166 break;
167 }
168 }
169 }
170 }
171
172 static void usage() {
173 System.err.println("usage: java WatchDir [-r] dir");
174 System.exit(-1);
175 }
176
177 public static void main(String[] args) throws IOException {
178 // parse arguments
179 if (args.length == 0 || args.length > 2)
180 usage();
181 boolean recursive = false;
182 int dirArg = 0;
183 if (args[0].equals("-r")) {
184 if (args.length < 2)
185 usage();
186 recursive = true;
187 dirArg++;
188 }
189
190 // register directory and process its events
191 Path dir = Paths.get(args[dirArg]);
192 new WatchDir(dir, recursive).processEvents();
193 }
194 }