1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.io;
18
19 import java.io.File;
20 import java.io.FileFilter;
21 import java.io.IOException;
22 import java.util.Collection;
23
24 import org.apache.commons.io.filefilter.FileFilterUtils;
25 import org.apache.commons.io.filefilter.IOFileFilter;
26 import org.apache.commons.io.filefilter.TrueFileFilter;
27
28 /**
29 * Abstract class that walks through a directory hierarchy and provides
30 * subclasses with convenient hooks to add specific behaviour.
31 * <p>
32 * This class operates with a {@link FileFilter} and maximum depth to
33 * limit the files and direcories visited.
34 * Commons IO supplies many common filter implementations in the
35 * <a href="filefilter/package-summary.html"> filefilter</a> package.
36 * <p>
37 * The following sections describe:
38 * <ul>
39 * <li><a href="#example">1. Example Implementation</a> - example
40 * <code>FileCleaner</code> implementation.</li>
41 * <li><a href="#filter">2. Filter Example</a> - using
42 * {@link FileFilter}(s) with <code>DirectoryWalker</code>.</li>
43 * <li><a href="#cancel">3. Cancellation</a> - how to implement cancellation
44 * behaviour.</li>
45 * </ul>
46 *
47 * <a name="example"></a>
48 * <h3>1. Example Implementation</h3>
49 *
50 * There are many possible extensions, for example, to delete all
51 * files and '.svn' directories, and return a list of deleted files:
52 * <pre>
53 * public class FileCleaner extends DirectoryWalker {
54 *
55 * public FileCleaner() {
56 * super();
57 * }
58 *
59 * public List clean(File startDirectory) {
60 * List results = new ArrayList();
61 * walk(startDirectory, results);
62 * return results;
63 * }
64 *
65 * protected boolean handleDirectory(File directory, int depth, Collection results) {
66 * // delete svn directories and then skip
67 * if (".svn".equals(directory.getName())) {
68 * directory.delete();
69 * return false;
70 * } else {
71 * return true;
72 * }
73 *
74 * }
75 *
76 * protected void handleFile(File file, int depth, Collection results) {
77 * // delete file and add to list of deleted
78 * file.delete();
79 * results.add(file);
80 * }
81 * }
82 * </pre>
83 *
84 * <a name="filter"></a>
85 * <h3>2. Filter Example</h3>
86 *
87 * Choosing which directories and files to process can be a key aspect
88 * of using this class. This information can be setup in three ways,
89 * via three different constructors.
90 * <p>
91 * The first option is to visit all directories and files.
92 * This is achieved via the no-args constructor.
93 * <p>
94 * The second constructor option is to supply a single {@link FileFilter}
95 * that describes the files and directories to visit. Care must be taken
96 * with this option as the same filter is used for both directories
97 * and files.
98 * <p>
99 * For example, if you wanted all directories which are not hidden
100 * and files which end in ".txt":
101 * <pre>
102 * public class FooDirectoryWalker extends DirectoryWalker {
103 * public FooDirectoryWalker(FileFilter filter) {
104 * super(filter, -1);
105 * }
106 * }
107 *
108 * // Build up the filters and create the walker
109 * // Create a filter for Non-hidden directories
110 * IOFileFilter fooDirFilter =
111 * FileFilterUtils.andFileFilter(FileFilterUtils.directoryFileFilter,
112 * HiddenFileFilter.VISIBLE);
113 *
114 * // Create a filter for Files ending in ".txt"
115 * IOFileFilter fooFileFilter =
116 * FileFilterUtils.andFileFilter(FileFilterUtils.fileFileFilter,
117 * FileFilterUtils.suffixFileFilter(".txt"));
118 *
119 * // Combine the directory and file filters using an OR condition
120 * java.io.FileFilter fooFilter =
121 * FileFilterUtils.orFileFilter(fooDirFilter, fooFileFilter);
122 *
123 * // Use the filter to construct a DirectoryWalker implementation
124 * FooDirectoryWalker walker = new FooDirectoryWalker(fooFilter);
125 * </pre>
126 * <p>
127 * The third constructor option is to specify separate filters, one for
128 * directories and one for files. These are combined internally to form
129 * the correct <code>FileFilter</code>, something which is very easy to
130 * get wrong when attempted manually, particularly when trying to
131 * express constructs like 'any file in directories named docs'.
132 * <p>
133 * For example, if you wanted all directories which are not hidden
134 * and files which end in ".txt":
135 * <pre>
136 * public class FooDirectoryWalker extends DirectoryWalker {
137 * public FooDirectoryWalker(IOFileFilter dirFilter, IOFileFilter fileFilter) {
138 * super(dirFilter, fileFilter, -1);
139 * }
140 * }
141 *
142 * // Use the filters to construct the walker
143 * FooDirectoryWalker walker = new FooDirectoryWalker(
144 * HiddenFileFilter.VISIBLE,
145 * FileFilterUtils.suffixFileFilter(".txt"),
146 * );
147 * </pre>
148 * This is much simpler than the previous example, and is why it is the preferred
149 * option for filtering.
150 *
151 * <a name="cancel"></a>
152 * <h3>3. Cancellation</h3>
153 *
154 * The DirectoryWalker contains some of the logic required for cancel processing.
155 * Subclasses must complete the implementation.
156 * <p>
157 * What <code>DirectoryWalker</code> does provide for cancellation is:
158 * <ul>
159 * <li>{@link CancelException} which can be thrown in any of the
160 * <i>lifecycle</i> methods to stop processing.</li>
161 * <li>The <code>walk()</code> method traps thrown {@link CancelException}
162 * and calls the <code>handleCancelled()</code> method, providing
163 * a place for custom cancel processing.</li>
164 * </ul>
165 * <p>
166 * Implementations need to provide:
167 * <ul>
168 * <li>The decision logic on whether to cancel processing or not.</li>
169 * <li>Constructing and throwing a {@link CancelException}.</li>
170 * <li>Custom cancel processing in the <code>handleCancelled()</code> method.
171 * </ul>
172 * <p>
173 * Two possible scenarios are envisaged for cancellation:
174 * <ul>
175 * <li><a href="#external">3.1 External / Mult-threaded</a> - cancellation being
176 * decided/initiated by an external process.</li>
177 * <li><a href="#internal">3.2 Internal</a> - cancellation being decided/initiated
178 * from within a DirectoryWalker implementation.</li>
179 * </ul>
180 * <p>
181 * The following sections provide example implementations for these two different
182 * scenarios.
183 *
184 * <a name="external"></a>
185 * <h4>3.1 External / Multi-threaded</h4>
186 *
187 * This example provides a public <code>cancel()</code> method that can be
188 * called by another thread to stop the processing. A typical example use-case
189 * would be a cancel button on a GUI. Calling this method sets a
190 * <a href="http://java.sun.com/docs/books/jls/second_edition/html/classes.doc.html#36930">
191 * volatile</a> flag to ensure it will work properly in a multi-threaded environment.
192 * The flag is returned by the <code>handleIsCancelled()</code> method, which
193 * will cause the walk to stop immediately. The <code>handleCancelled()</code>
194 * method will be the next, and last, callback method received once cancellation
195 * has occurred.
196 *
197 * <pre>
198 * public class FooDirectoryWalker extends DirectoryWalker {
199 *
200 * private volatile boolean cancelled = false;
201 *
202 * public void cancel() {
203 * cancelled = true;
204 * }
205 *
206 * private void handleIsCancelled(File file, int depth, Collection results) {
207 * return cancelled;
208 * }
209 *
210 * protected void handleCancelled(File startDirectory, Collection results, CancelException cancel) {
211 * // implement processing required when a cancellation occurs
212 * }
213 * }
214 * </pre>
215 *
216 * <a name="internal"></a>
217 * <h4>3.2 Internal</h4>
218 *
219 * This shows an example of how internal cancellation processing could be implemented.
220 * <b>Note</b> the decision logic and throwing a {@link CancelException} could be implemented
221 * in any of the <i>lifecycle</i> methods.
222 *
223 * <pre>
224 * public class BarDirectoryWalker extends DirectoryWalker {
225 *
226 * protected boolean handleDirectory(File directory, int depth, Collection results) throws IOException {
227 * // cancel if hidden directory
228 * if (directory.isHidden()) {
229 * throw new CancelException(file, depth);
230 * }
231 * return true;
232 * }
233 *
234 * protected void handleFile(File file, int depth, Collection results) throws IOException {
235 * // cancel if read-only file
236 * if (!file.canWrite()) {
237 * throw new CancelException(file, depth);
238 * }
239 * results.add(file);
240 * }
241 *
242 * protected void handleCancelled(File startDirectory, Collection results, CancelException cancel) {
243 * // implement processing required when a cancellation occurs
244 * }
245 * }
246 * </pre>
247 *
248 * @since Commons IO 1.3
249 * @version $Revision: 424748 $
250 */
251 public abstract class DirectoryWalker {
252
253 /**
254 * The file filter to use to filter files and directories.
255 */
256 private final FileFilter filter;
257 /**
258 * The limit on the directory depth to walk.
259 */
260 private final int depthLimit;
261
262 /**
263 * Construct an instance with no filtering and unlimited <i>depth</i>.
264 */
265 protected DirectoryWalker() {
266 this(null, -1);
267 }
268
269 /**
270 * Construct an instance with a filter and limit the <i>depth</i> navigated to.
271 * <p>
272 * The filter controls which files and directories will be navigated to as
273 * part of the walk. The {@link FileFilterUtils} class is useful for combining
274 * various filters together. A <code>null</code> filter means that no
275 * filtering should occur and all files and directories will be visited.
276 *
277 * @param filter the filter to apply, null means visit all files
278 * @param depthLimit controls how <i>deep</i> the hierarchy is
279 * navigated to (less than 0 means unlimited)
280 */
281 protected DirectoryWalker(FileFilter filter, int depthLimit) {
282 this.filter = filter;
283 this.depthLimit = depthLimit;
284 }
285
286 /**
287 * Construct an instance with a directory and a file filter and an optional
288 * limit on the <i>depth</i> navigated to.
289 * <p>
290 * The filters control which files and directories will be navigated to as part
291 * of the walk. This constructor uses {@link FileFilterUtils#makeDirectoryOnly(IOFileFilter)}
292 * and {@link FileFilterUtils#makeFileOnly(IOFileFilter)} internally to combine the filters.
293 * A <code>null</code> filter means that no filtering should occur.
294 *
295 * @param directoryFilter the filter to apply to directories, null means visit all directories
296 * @param fileFilter the filter to apply to files, null means visit all files
297 * @param depthLimit controls how <i>deep</i> the hierarchy is
298 * navigated to (less than 0 means unlimited)
299 */
300 protected DirectoryWalker(IOFileFilter directoryFilter, IOFileFilter fileFilter, int depthLimit) {
301 if (directoryFilter == null && fileFilter == null) {
302 this.filter = null;
303 } else {
304 directoryFilter = (directoryFilter != null ? directoryFilter : TrueFileFilter.TRUE);
305 fileFilter = (fileFilter != null ? fileFilter : TrueFileFilter.TRUE);
306 directoryFilter = FileFilterUtils.makeDirectoryOnly(directoryFilter);
307 fileFilter = FileFilterUtils.makeFileOnly(fileFilter);
308 this.filter = FileFilterUtils.orFileFilter(directoryFilter, fileFilter);
309 }
310 this.depthLimit = depthLimit;
311 }
312
313 //-----------------------------------------------------------------------
314 /**
315 * Internal method that walks the directory hierarchy in a depth-first manner.
316 * <p>
317 * Users of this class do not need to call this method. This method will
318 * be called automatically by another (public) method on the specific subclass.
319 * <p>
320 * Writers of subclasses should call this method to start the directory walk.
321 * Once called, this method will emit events as it walks the hierarchy.
322 * The event methods have the prefix <code>handle</code>.
323 *
324 * @param startDirectory the directory to start from, not null
325 * @param results the collection of result objects, may be updated
326 * @throws NullPointerException if the start directory is null
327 * @throws IOException if an I/O Error occurs
328 */
329 protected final void walk(File startDirectory, Collection results) throws IOException {
330 if (startDirectory == null) {
331 throw new NullPointerException("Start Directory is null");
332 }
333 try {
334 handleStart(startDirectory, results);
335 walk(startDirectory, 0, results);
336 handleEnd(results);
337 } catch(CancelException cancel) {
338 handleCancelled(startDirectory, results, cancel);
339 }
340 }
341
342 /**
343 * Main recursive method to examine the directory hierarchy.
344 *
345 * @param directory the directory to examine, not null
346 * @param depth the directory level (starting directory = 0)
347 * @param results the collection of result objects, may be updated
348 * @throws IOException if an I/O Error occurs
349 */
350 private void walk(File directory, int depth, Collection results) throws IOException {
351 checkIfCancelled(directory, depth, results);
352 if (handleDirectory(directory, depth, results)) {
353 handleDirectoryStart(directory, depth, results);
354 int childDepth = depth + 1;
355 if (depthLimit < 0 || childDepth <= depthLimit) {
356 checkIfCancelled(directory, depth, results);
357 File[] childFiles = (filter == null ? directory.listFiles() : directory.listFiles(filter));
358 if (childFiles == null) {
359 handleRestricted(directory, childDepth, results);
360 } else {
361 for (int i = 0; i < childFiles.length; i++) {
362 File childFile = childFiles[i];
363 if (childFile.isDirectory()) {
364 walk(childFile, childDepth, results);
365 } else {
366 checkIfCancelled(childFile, childDepth, results);
367 handleFile(childFile, childDepth, results);
368 checkIfCancelled(childFile, childDepth, results);
369 }
370 }
371 }
372 }
373 handleDirectoryEnd(directory, depth, results);
374 }
375 checkIfCancelled(directory, depth, results);
376 }
377
378 //-----------------------------------------------------------------------
379 /**
380 * Checks whether the walk has been cancelled by calling {@link #handleIsCancelled},
381 * throwing a <code>CancelException</code> if it has.
382 * <p>
383 * Writers of subclasses should not normally call this method as it is called
384 * automatically by the walk of the tree. However, sometimes a single method,
385 * typically {@link #handleFile}, may take a long time to run. In that case,
386 * you may wish to check for cancellation by calling this method.
387 *
388 * @param file the current file being processed
389 * @param depth the current file level (starting directory = 0)
390 * @param results the collection of result objects, may be updated
391 * @throws IOException if an I/O Error occurs
392 */
393 protected final void checkIfCancelled(File file, int depth, Collection results) throws IOException {
394 if (handleIsCancelled(file, depth, results)) {
395 throw new CancelException(file, depth);
396 }
397 }
398
399 /**
400 * Overridable callback method invoked to determine if the entire walk
401 * operation should be immediately cancelled.
402 * <p>
403 * This method should be implemented by those subclasses that want to
404 * provide a public <code>cancel()</code> method available from another
405 * thread. The design pattern for the subclass should be as follows:
406 * <pre>
407 * public class FooDirectoryWalker extends DirectoryWalker {
408 * private volatile boolean cancelled = false;
409 *
410 * public void cancel() {
411 * cancelled = true;
412 * }
413 * private void handleIsCancelled(File file, int depth, Collection results) {
414 * return cancelled;
415 * }
416 * protected void handleCancelled(File startDirectory,
417 * Collection results, CancelException cancel) {
418 * // implement processing required when a cancellation occurs
419 * }
420 * }
421 * </pre>
422 * <p>
423 * If this method returns true, then the directory walk is immediately
424 * cancelled. The next callback method will be {@link #handleCancelled}.
425 * <p>
426 * This implementation returns false.
427 *
428 * @param file the file or directory being processed
429 * @param depth the current directory level (starting directory = 0)
430 * @param results the collection of result objects, may be updated
431 * @return true if the walk has been cancelled
432 * @throws IOException if an I/O Error occurs
433 */
434 protected boolean handleIsCancelled(
435 File file, int depth, Collection results) throws IOException {
436 // do nothing - overridable by subclass
437 return false; // not cancelled
438 }
439
440 /**
441 * Overridable callback method invoked when the operation is cancelled.
442 * The file being processed when the cancellation occurred can be
443 * obtained from the exception.
444 * <p>
445 * This implementation just re-throws the {@link CancelException}.
446 *
447 * @param startDirectory the directory that the walk started from
448 * @param results the collection of result objects, may be updated
449 * @param cancel the exception throw to cancel further processing
450 * containing details at the point of cancellation.
451 * @throws IOException if an I/O Error occurs
452 */
453 protected void handleCancelled(File startDirectory, Collection results,
454 CancelException cancel) throws IOException {
455 // re-throw exception - overridable by subclass
456 throw cancel;
457 }
458
459 //-----------------------------------------------------------------------
460 /**
461 * Overridable callback method invoked at the start of processing.
462 * <p>
463 * This implementation does nothing.
464 *
465 * @param startDirectory the directory to start from
466 * @param results the collection of result objects, may be updated
467 * @throws IOException if an I/O Error occurs
468 */
469 protected void handleStart(File startDirectory, Collection results) throws IOException {
470 // do nothing - overridable by subclass
471 }
472
473 /**
474 * Overridable callback method invoked to determine if a directory should be processed.
475 * <p>
476 * This method returns a boolean to indicate if the directory should be examined or not.
477 * If you return false, the entire directory and any subdirectories will be skipped.
478 * Note that this functionality is in addition to the filtering by file filter.
479 * <p>
480 * This implementation does nothing and returns true.
481 *
482 * @param directory the current directory being processed
483 * @param depth the current directory level (starting directory = 0)
484 * @param results the collection of result objects, may be updated
485 * @return true to process this directory, false to skip this directory
486 * @throws IOException if an I/O Error occurs
487 */
488 protected boolean handleDirectory(File directory, int depth, Collection results) throws IOException {
489 // do nothing - overridable by subclass
490 return true; // process directory
491 }
492
493 /**
494 * Overridable callback method invoked at the start of processing each directory.
495 * <p>
496 * This implementation does nothing.
497 *
498 * @param directory the current directory being processed
499 * @param depth the current directory level (starting directory = 0)
500 * @param results the collection of result objects, may be updated
501 * @throws IOException if an I/O Error occurs
502 */
503 protected void handleDirectoryStart(File directory, int depth, Collection results) throws IOException {
504 // do nothing - overridable by subclass
505 }
506
507 /**
508 * Overridable callback method invoked for each (non-directory) file.
509 * <p>
510 * This implementation does nothing.
511 *
512 * @param file the current file being processed
513 * @param depth the current directory level (starting directory = 0)
514 * @param results the collection of result objects, may be updated
515 * @throws IOException if an I/O Error occurs
516 */
517 protected void handleFile(File file, int depth, Collection results) throws IOException {
518 // do nothing - overridable by subclass
519 }
520
521 /**
522 * Overridable callback method invoked for each restricted directory.
523 * <p>
524 * This implementation does nothing.
525 *
526 * @param directory the restricted directory
527 * @param depth the current directory level (starting directory = 0)
528 * @param results the collection of result objects, may be updated
529 * @throws IOException if an I/O Error occurs
530 */
531 protected void handleRestricted(File directory, int depth, Collection results) throws IOException {
532 // do nothing - overridable by subclass
533 }
534
535 /**
536 * Overridable callback method invoked at the end of processing each directory.
537 * <p>
538 * This implementation does nothing.
539 *
540 * @param directory the directory being processed
541 * @param depth the current directory level (starting directory = 0)
542 * @param results the collection of result objects, may be updated
543 * @throws IOException if an I/O Error occurs
544 */
545 protected void handleDirectoryEnd(File directory, int depth, Collection results) throws IOException {
546 // do nothing - overridable by subclass
547 }
548
549 /**
550 * Overridable callback method invoked at the end of processing.
551 * <p>
552 * This implementation does nothing.
553 *
554 * @param results the collection of result objects, may be updated
555 * @throws IOException if an I/O Error occurs
556 */
557 protected void handleEnd(Collection results) throws IOException {
558 // do nothing - overridable by subclass
559 }
560
561 //-----------------------------------------------------------------------
562 /**
563 * CancelException is thrown in DirectoryWalker to cancel the current
564 * processing.
565 */
566 public static class CancelException extends IOException {
567
568 /** Serialization id. */
569 private static final long serialVersionUID = 1347339620135041008L;
570
571 /** The file being processed when the exception was thrown. */
572 private File file;
573 /** The file depth when the exception was thrown. */
574 private int depth = -1;
575
576 /**
577 * Constructs a <code>CancelException</code> with
578 * the file and depth when cancellation occurred.
579 *
580 * @param file the file when the operation was cancelled, may be null
581 * @param depth the depth when the operation was cancelled, may be null
582 */
583 public CancelException(File file, int depth) {
584 this("Operation Cancelled", file, depth);
585 }
586
587 /**
588 * Constructs a <code>CancelException</code> with
589 * an appropriate message and the file and depth when
590 * cancellation occurred.
591 *
592 * @param message the detail message
593 * @param file the file when the operation was cancelled
594 * @param depth the depth when the operation was cancelled
595 */
596 public CancelException(String message, File file, int depth) {
597 super(message);
598 this.file = file;
599 this.depth = depth;
600 }
601
602 /**
603 * Return the file when the operation was cancelled.
604 *
605 * @return the file when the operation was cancelled
606 */
607 public File getFile() {
608 return file;
609 }
610
611 /**
612 * Return the depth when the operation was cancelled.
613 *
614 * @return the depth when the operation was cancelled
615 */
616 public int getDepth() {
617 return depth;
618 }
619 }
620 }