1 /*
2 * Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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23 * questions.
24 */
25
26 package java.util.prefs;
27
28 import java.util.*;
29 import java.io.*;
30 import java.security.AccessController;
31 import java.security.PrivilegedAction;
32 // These imports needed only as a workaround for a JavaDoc bug
33 import java.lang.Integer;
34 import java.lang.Long;
35 import java.lang.Float;
36 import java.lang.Double;
37
38 /**
39 * This class provides a skeletal implementation of the {@link Preferences}
40 * class, greatly easing the task of implementing it.
41 *
42 * <p><strong>This class is for {@code Preferences} implementers only.
43 * Normal users of the {@code Preferences} facility should have no need to
44 * consult this documentation. The {@link Preferences} documentation
45 * should suffice.</strong>
46 *
47 * <p>Implementors must override the nine abstract service-provider interface
48 * (SPI) methods: {@link #getSpi(String)}, {@link #putSpi(String,String)},
49 * {@link #removeSpi(String)}, {@link #childSpi(String)}, {@link
50 * #removeNodeSpi()}, {@link #keysSpi()}, {@link #childrenNamesSpi()}, {@link
51 * #syncSpi()} and {@link #flushSpi()}. All of the concrete methods specify
52 * precisely how they are implemented atop these SPI methods. The implementor
53 * may, at his discretion, override one or more of the concrete methods if the
54 * default implementation is unsatisfactory for any reason, such as
55 * performance.
56 *
57 * <p>The SPI methods fall into three groups concerning exception
58 * behavior. The {@code getSpi} method should never throw exceptions, but it
59 * doesn't really matter, as any exception thrown by this method will be
60 * intercepted by {@link #get(String,String)}, which will return the specified
61 * default value to the caller. The {@code removeNodeSpi, keysSpi,
62 * childrenNamesSpi, syncSpi} and {@code flushSpi} methods are specified
63 * to throw {@link BackingStoreException}, and the implementation is required
64 * to throw this checked exception if it is unable to perform the operation.
65 * The exception propagates outward, causing the corresponding API method
66 * to fail.
67 *
68 * <p>The remaining SPI methods {@link #putSpi(String,String)}, {@link
69 * #removeSpi(String)} and {@link #childSpi(String)} have more complicated
70 * exception behavior. They are not specified to throw
71 * {@code BackingStoreException}, as they can generally obey their contracts
72 * even if the backing store is unavailable. This is true because they return
73 * no information and their effects are not required to become permanent until
74 * a subsequent call to {@link Preferences#flush()} or
75 * {@link Preferences#sync()}. Generally speaking, these SPI methods should not
76 * throw exceptions. In some implementations, there may be circumstances
77 * under which these calls cannot even enqueue the requested operation for
78 * later processing. Even under these circumstances it is generally better to
79 * simply ignore the invocation and return, rather than throwing an
80 * exception. Under these circumstances, however, subsequently invoking
81 * {@code flush()} or {@code sync} would not imply that all previous
82 * operations had successfully been made permanent.
83 *
84 * <p>There is one circumstance under which {@code putSpi, removeSpi and
85 * childSpi} <i>should</i> throw an exception: if the caller lacks
86 * sufficient privileges on the underlying operating system to perform the
87 * requested operation. This will, for instance, occur on most systems
88 * if a non-privileged user attempts to modify system preferences.
89 * (The required privileges will vary from implementation to
90 * implementation. On some implementations, they are the right to modify the
91 * contents of some directory in the file system; on others they are the right
92 * to modify contents of some key in a registry.) Under any of these
93 * circumstances, it would generally be undesirable to let the program
94 * continue executing as if these operations would become permanent at a later
95 * time. While implementations are not required to throw an exception under
96 * these circumstances, they are encouraged to do so. A {@link
97 * SecurityException} would be appropriate.
98 *
99 * <p>Most of the SPI methods require the implementation to read or write
100 * information at a preferences node. The implementor should beware of the
101 * fact that another VM may have concurrently deleted this node from the
102 * backing store. It is the implementation's responsibility to recreate the
103 * node if it has been deleted.
104 *
105 * <p>Implementation note: In Sun's default {@code Preferences}
106 * implementations, the user's identity is inherited from the underlying
107 * operating system and does not change for the lifetime of the virtual
108 * machine. It is recognized that server-side {@code Preferences}
109 * implementations may have the user identity change from request to request,
110 * implicitly passed to {@code Preferences} methods via the use of a
111 * static {@link ThreadLocal} instance. Authors of such implementations are
112 * <i>strongly</i> encouraged to determine the user at the time preferences
113 * are accessed (for example by the {@link #get(String,String)} or {@link
114 * #put(String,String)} method) rather than permanently associating a user
115 * with each {@code Preferences} instance. The latter behavior conflicts
116 * with normal {@code Preferences} usage and would lead to great confusion.
117 *
118 * @author Josh Bloch
119 * @see Preferences
120 * @since 1.4
121 */
122 public abstract class AbstractPreferences extends Preferences {
123 /**
124 * The code point U+0000, assigned to the null control character, is the
125 * only character encoded in Unicode and ISO/IEC 10646 that is always
126 * invalid in any XML 1.0 and 1.1 document.
127 */
128 static final int CODE_POINT_U0000 = '\u0000';
129
130 /**
131 * Our name relative to parent.
132 */
133 private final String name;
134
135 /**
136 * Our absolute path name.
137 */
138 private final String absolutePath;
139
140 /**
141 * Our parent node.
142 */
143 final AbstractPreferences parent;
144
145 /**
146 * Our root node.
147 */
148 private final AbstractPreferences root; // Relative to this node
149
150 /**
151 * This field should be {@code true} if this node did not exist in the
152 * backing store prior to the creation of this object. The field
153 * is initialized to false, but may be set to true by a subclass
154 * constructor (and should not be modified thereafter). This field
155 * indicates whether a node change event should be fired when
156 * creation is complete.
157 */
158 protected boolean newNode = false;
159
160 /**
161 * All known unremoved children of this node. (This "cache" is consulted
162 * prior to calling childSpi() or getChild().
163 */
164 private Map<String, AbstractPreferences> kidCache = new HashMap<>();
165
166 /**
167 * This field is used to keep track of whether or not this node has
168 * been removed. Once it's set to true, it will never be reset to false.
169 */
170 private boolean removed = false;
171
172 /**
173 * Registered preference change listeners.
174 */
175 private PreferenceChangeListener[] prefListeners =
176 new PreferenceChangeListener[0];
177
178 /**
179 * Registered node change listeners.
180 */
181 private NodeChangeListener[] nodeListeners = new NodeChangeListener[0];
182
183 /**
184 * An object whose monitor is used to lock this node. This object
185 * is used in preference to the node itself to reduce the likelihood of
186 * intentional or unintentional denial of service due to a locked node.
187 * To avoid deadlock, a node is <i>never</i> locked by a thread that
188 * holds a lock on a descendant of that node.
189 */
190 protected final Object lock = new Object();
191
192 /**
193 * Creates a preference node with the specified parent and the specified
194 * name relative to its parent.
195 *
196 * @param parent the parent of this preference node, or null if this
197 * is the root.
198 * @param name the name of this preference node, relative to its parent,
199 * or {@code ""} if this is the root.
200 * @throws IllegalArgumentException if {@code name} contains a slash
201 * ({@code '/'}), or {@code parent} is {@code null} and
202 * name isn't {@code ""}.
203 */
204 protected AbstractPreferences(AbstractPreferences parent, String name) {
205 if (parent==null) {
206 if (!name.isEmpty())
207 throw new IllegalArgumentException("Root name '"+name+
208 "' must be \"\"");
209 this.absolutePath = "/";
210 root = this;
211 } else {
212 if (name.indexOf('/') != -1)
213 throw new IllegalArgumentException("Name '" + name +
214 "' contains '/'");
215 if (name.isEmpty())
216 throw new IllegalArgumentException("Illegal name: empty string");
217
218 root = parent.root;
219 absolutePath = (parent==root ? "/" + name
220 : parent.absolutePath() + "/" + name);
221 }
222 this.name = name;
223 this.parent = parent;
224 }
225
226 /**
227 * Implements the {@code put} method as per the specification in
228 * {@link Preferences#put(String,String)}.
229 *
230 * <p>This implementation checks that the key and value are legal,
231 * obtains this preference node's lock, checks that the node
232 * has not been removed, invokes {@link #putSpi(String,String)}, and if
233 * there are any preference change listeners, enqueues a notification
234 * event for processing by the event dispatch thread.
235 *
236 * @param key key with which the specified value is to be associated.
237 * @param value value to be associated with the specified key.
238 * @throws NullPointerException if key or value is {@code null}.
239 * @throws IllegalArgumentException if {@code key.length()} exceeds
240 * {@code MAX_KEY_LENGTH} or if {@code value.length} exceeds
241 * {@code MAX_VALUE_LENGTH}.
242 * @throws IllegalArgumentException if either key or value contain
243 * the null control character, code point U+0000.
244 * @throws IllegalStateException if this node (or an ancestor) has been
245 * removed with the {@link #removeNode()} method.
246 */
247 public void put(String key, String value) {
248 if (key==null || value==null)
249 throw new NullPointerException();
250 if (key.length() > MAX_KEY_LENGTH)
251 throw new IllegalArgumentException("Key too long: "+key);
252 if (value.length() > MAX_VALUE_LENGTH)
253 throw new IllegalArgumentException("Value too long: "+value);
254 if (key.indexOf(CODE_POINT_U0000) != -1)
255 throw new IllegalArgumentException("Key contains code point U+0000");
256 if (value.indexOf(CODE_POINT_U0000) != -1)
257 throw new IllegalArgumentException("Value contains code point U+0000");
258
259 synchronized(lock) {
260 if (removed)
261 throw new IllegalStateException("Node has been removed.");
262
263 putSpi(key, value);
264 enqueuePreferenceChangeEvent(key, value);
265 }
266 }
267
268 /**
269 * Implements the {@code get} method as per the specification in
270 * {@link Preferences#get(String,String)}.
271 *
272 * <p>This implementation first checks to see if {@code key} is
273 * {@code null} throwing a {@code NullPointerException} if this is
274 * the case. Then it obtains this preference node's lock,
275 * checks that the node has not been removed, invokes {@link
276 * #getSpi(String)}, and returns the result, unless the {@code getSpi}
277 * invocation returns {@code null} or throws an exception, in which case
278 * this invocation returns {@code def}.
279 *
280 * @param key key whose associated value is to be returned.
281 * @param def the value to be returned in the event that this
282 * preference node has no value associated with {@code key}.
283 * @return the value associated with {@code key}, or {@code def}
284 * if no value is associated with {@code key}.
285 * @throws IllegalStateException if this node (or an ancestor) has been
286 * removed with the {@link #removeNode()} method.
287 * @throws NullPointerException if key is {@code null}. (A
288 * {@code null} default <i>is</i> permitted.)
289 * @throws IllegalArgumentException if key contains the null control
290 * character, code point U+0000.
291 */
292 public String get(String key, String def) {
293 if (key==null)
294 throw new NullPointerException("Null key");
295 if (key.indexOf(CODE_POINT_U0000) != -1)
296 throw new IllegalArgumentException("Key contains code point U+0000");
297 synchronized(lock) {
298 if (removed)
299 throw new IllegalStateException("Node has been removed.");
300
301 String result = null;
302 try {
303 result = getSpi(key);
304 } catch (Exception e) {
305 // Ignoring exception causes default to be returned
306 }
307 return (result==null ? def : result);
308 }
309 }
310
311 /**
312 * Implements the {@code remove(String)} method as per the specification
313 * in {@link Preferences#remove(String)}.
314 *
315 * <p>This implementation obtains this preference node's lock,
316 * checks that the node has not been removed, invokes
317 * {@link #removeSpi(String)} and if there are any preference
318 * change listeners, enqueues a notification event for processing by the
319 * event dispatch thread.
320 *
321 * @param key key whose mapping is to be removed from the preference node.
322 * @throws IllegalStateException if this node (or an ancestor) has been
323 * removed with the {@link #removeNode()} method.
324 * @throws IllegalArgumentException if key contains the null control
325 * character, code point U+0000.
326 * @throws NullPointerException {@inheritDoc}.
327 */
328 public void remove(String key) {
329 Objects.requireNonNull(key, "Specified key cannot be null");
330 if (key.indexOf(CODE_POINT_U0000) != -1)
331 throw new IllegalArgumentException("Key contains code point U+0000");
332 synchronized(lock) {
333 if (removed)
334 throw new IllegalStateException("Node has been removed.");
335
336 removeSpi(key);
337 enqueuePreferenceChangeEvent(key, null);
338 }
339 }
340
341 /**
342 * Implements the {@code clear} method as per the specification in
343 * {@link Preferences#clear()}.
344 *
345 * <p>This implementation obtains this preference node's lock,
346 * invokes {@link #keys()} to obtain an array of keys, and
347 * iterates over the array invoking {@link #remove(String)} on each key.
348 *
349 * @throws BackingStoreException if this operation cannot be completed
350 * due to a failure in the backing store, or inability to
351 * communicate with it.
352 * @throws IllegalStateException if this node (or an ancestor) has been
353 * removed with the {@link #removeNode()} method.
354 */
355 public void clear() throws BackingStoreException {
356 synchronized(lock) {
357 for (String key : keys())
358 remove(key);
359 }
360 }
361
362 /**
363 * Implements the {@code putInt} method as per the specification in
364 * {@link Preferences#putInt(String,int)}.
365 *
366 * <p>This implementation translates {@code value} to a string with
367 * {@link Integer#toString(int)} and invokes {@link #put(String,String)}
368 * on the result.
369 *
370 * @param key key with which the string form of value is to be associated.
371 * @param value value whose string form is to be associated with key.
372 * @throws NullPointerException if key is {@code null}.
373 * @throws IllegalArgumentException if {@code key.length()} exceeds
374 * {@code MAX_KEY_LENGTH}.
375 * @throws IllegalArgumentException if key contains
376 * the null control character, code point U+0000.
377 * @throws IllegalStateException if this node (or an ancestor) has been
378 * removed with the {@link #removeNode()} method.
379 */
380 public void putInt(String key, int value) {
381 put(key, Integer.toString(value));
382 }
383
384 /**
385 * Implements the {@code getInt} method as per the specification in
386 * {@link Preferences#getInt(String,int)}.
387 *
388 * <p>This implementation invokes {@link #get(String,String) get(key,
389 * null)}. If the return value is non-null, the implementation
390 * attempts to translate it to an {@code int} with
391 * {@link Integer#parseInt(String)}. If the attempt succeeds, the return
392 * value is returned by this method. Otherwise, {@code def} is returned.
393 *
394 * @param key key whose associated value is to be returned as an int.
395 * @param def the value to be returned in the event that this
396 * preference node has no value associated with {@code key}
397 * or the associated value cannot be interpreted as an int.
398 * @return the int value represented by the string associated with
399 * {@code key} in this preference node, or {@code def} if the
400 * associated value does not exist or cannot be interpreted as
401 * an int.
402 * @throws IllegalStateException if this node (or an ancestor) has been
403 * removed with the {@link #removeNode()} method.
404 * @throws NullPointerException if {@code key} is {@code null}.
405 * @throws IllegalArgumentException if key contains the null control
406 * character, code point U+0000.
407 */
408 public int getInt(String key, int def) {
409 int result = def;
410 try {
411 String value = get(key, null);
412 if (value != null)
413 result = Integer.parseInt(value);
414 } catch (NumberFormatException e) {
415 // Ignoring exception causes specified default to be returned
416 }
417
418 return result;
419 }
420
421 /**
422 * Implements the {@code putLong} method as per the specification in
423 * {@link Preferences#putLong(String,long)}.
424 *
425 * <p>This implementation translates {@code value} to a string with
426 * {@link Long#toString(long)} and invokes {@link #put(String,String)}
427 * on the result.
428 *
429 * @param key key with which the string form of value is to be associated.
430 * @param value value whose string form is to be associated with key.
431 * @throws NullPointerException if key is {@code null}.
432 * @throws IllegalArgumentException if {@code key.length()} exceeds
433 * {@code MAX_KEY_LENGTH}.
434 * @throws IllegalArgumentException if key contains
435 * the null control character, code point U+0000.
436 * @throws IllegalStateException if this node (or an ancestor) has been
437 * removed with the {@link #removeNode()} method.
438 */
439 public void putLong(String key, long value) {
440 put(key, Long.toString(value));
441 }
442
443 /**
444 * Implements the {@code getLong} method as per the specification in
445 * {@link Preferences#getLong(String,long)}.
446 *
447 * <p>This implementation invokes {@link #get(String,String) get(key,
448 * null)}. If the return value is non-null, the implementation
449 * attempts to translate it to a {@code long} with
450 * {@link Long#parseLong(String)}. If the attempt succeeds, the return
451 * value is returned by this method. Otherwise, {@code def} is returned.
452 *
453 * @param key key whose associated value is to be returned as a long.
454 * @param def the value to be returned in the event that this
455 * preference node has no value associated with {@code key}
456 * or the associated value cannot be interpreted as a long.
457 * @return the long value represented by the string associated with
458 * {@code key} in this preference node, or {@code def} if the
459 * associated value does not exist or cannot be interpreted as
460 * a long.
461 * @throws IllegalStateException if this node (or an ancestor) has been
462 * removed with the {@link #removeNode()} method.
463 * @throws NullPointerException if {@code key} is {@code null}.
464 * @throws IllegalArgumentException if key contains the null control
465 * character, code point U+0000.
466 */
467 public long getLong(String key, long def) {
468 long result = def;
469 try {
470 String value = get(key, null);
471 if (value != null)
472 result = Long.parseLong(value);
473 } catch (NumberFormatException e) {
474 // Ignoring exception causes specified default to be returned
475 }
476
477 return result;
478 }
479
480 /**
481 * Implements the {@code putBoolean} method as per the specification in
482 * {@link Preferences#putBoolean(String,boolean)}.
483 *
484 * <p>This implementation translates {@code value} to a string with
485 * {@link String#valueOf(boolean)} and invokes {@link #put(String,String)}
486 * on the result.
487 *
488 * @param key key with which the string form of value is to be associated.
489 * @param value value whose string form is to be associated with key.
490 * @throws NullPointerException if key is {@code null}.
491 * @throws IllegalArgumentException if {@code key.length()} exceeds
492 * {@code MAX_KEY_LENGTH}.
493 * @throws IllegalArgumentException if key contains
494 * the null control character, code point U+0000.
495 * @throws IllegalStateException if this node (or an ancestor) has been
496 * removed with the {@link #removeNode()} method.
497 */
498 public void putBoolean(String key, boolean value) {
499 put(key, String.valueOf(value));
500 }
501
502 /**
503 * Implements the {@code getBoolean} method as per the specification in
504 * {@link Preferences#getBoolean(String,boolean)}.
505 *
506 * <p>This implementation invokes {@link #get(String,String) get(key,
507 * null)}. If the return value is non-null, it is compared with
508 * {@code "true"} using {@link String#equalsIgnoreCase(String)}. If the
509 * comparison returns {@code true}, this invocation returns
510 * {@code true}. Otherwise, the original return value is compared with
511 * {@code "false"}, again using {@link String#equalsIgnoreCase(String)}.
512 * If the comparison returns {@code true}, this invocation returns
513 * {@code false}. Otherwise, this invocation returns {@code def}.
514 *
515 * @param key key whose associated value is to be returned as a boolean.
516 * @param def the value to be returned in the event that this
517 * preference node has no value associated with {@code key}
518 * or the associated value cannot be interpreted as a boolean.
519 * @return the boolean value represented by the string associated with
520 * {@code key} in this preference node, or {@code def} if the
521 * associated value does not exist or cannot be interpreted as
522 * a boolean.
523 * @throws IllegalStateException if this node (or an ancestor) has been
524 * removed with the {@link #removeNode()} method.
525 * @throws NullPointerException if {@code key} is {@code null}.
526 * @throws IllegalArgumentException if key contains the null control
527 * character, code point U+0000.
528 */
529 public boolean getBoolean(String key, boolean def) {
530 boolean result = def;
531 String value = get(key, null);
532 if (value != null) {
533 if (value.equalsIgnoreCase("true"))
534 result = true;
535 else if (value.equalsIgnoreCase("false"))
536 result = false;
537 }
538
539 return result;
540 }
541
542 /**
543 * Implements the {@code putFloat} method as per the specification in
544 * {@link Preferences#putFloat(String,float)}.
545 *
546 * <p>This implementation translates {@code value} to a string with
547 * {@link Float#toString(float)} and invokes {@link #put(String,String)}
548 * on the result.
549 *
550 * @param key key with which the string form of value is to be associated.
551 * @param value value whose string form is to be associated with key.
552 * @throws NullPointerException if key is {@code null}.
553 * @throws IllegalArgumentException if {@code key.length()} exceeds
554 * {@code MAX_KEY_LENGTH}.
555 * @throws IllegalArgumentException if key contains
556 * the null control character, code point U+0000.
557 * @throws IllegalStateException if this node (or an ancestor) has been
558 * removed with the {@link #removeNode()} method.
559 */
560 public void putFloat(String key, float value) {
561 put(key, Float.toString(value));
562 }
563
564 /**
565 * Implements the {@code getFloat} method as per the specification in
566 * {@link Preferences#getFloat(String,float)}.
567 *
568 * <p>This implementation invokes {@link #get(String,String) get(key,
569 * null)}. If the return value is non-null, the implementation
570 * attempts to translate it to an {@code float} with
571 * {@link Float#parseFloat(String)}. If the attempt succeeds, the return
572 * value is returned by this method. Otherwise, {@code def} is returned.
573 *
574 * @param key key whose associated value is to be returned as a float.
575 * @param def the value to be returned in the event that this
576 * preference node has no value associated with {@code key}
577 * or the associated value cannot be interpreted as a float.
578 * @return the float value represented by the string associated with
579 * {@code key} in this preference node, or {@code def} if the
580 * associated value does not exist or cannot be interpreted as
581 * a float.
582 * @throws IllegalStateException if this node (or an ancestor) has been
583 * removed with the {@link #removeNode()} method.
584 * @throws NullPointerException if {@code key} is {@code null}.
585 * @throws IllegalArgumentException if key contains the null control
586 * character, code point U+0000.
587 */
588 public float getFloat(String key, float def) {
589 float result = def;
590 try {
591 String value = get(key, null);
592 if (value != null)
593 result = Float.parseFloat(value);
594 } catch (NumberFormatException e) {
595 // Ignoring exception causes specified default to be returned
596 }
597
598 return result;
599 }
600
601 /**
602 * Implements the {@code putDouble} method as per the specification in
603 * {@link Preferences#putDouble(String,double)}.
604 *
605 * <p>This implementation translates {@code value} to a string with
606 * {@link Double#toString(double)} and invokes {@link #put(String,String)}
607 * on the result.
608 *
609 * @param key key with which the string form of value is to be associated.
610 * @param value value whose string form is to be associated with key.
611 * @throws NullPointerException if key is {@code null}.
612 * @throws IllegalArgumentException if {@code key.length()} exceeds
613 * {@code MAX_KEY_LENGTH}.
614 * @throws IllegalArgumentException if key contains
615 * the null control character, code point U+0000.
616 * @throws IllegalStateException if this node (or an ancestor) has been
617 * removed with the {@link #removeNode()} method.
618 */
619 public void putDouble(String key, double value) {
620 put(key, Double.toString(value));
621 }
622
623 /**
624 * Implements the {@code getDouble} method as per the specification in
625 * {@link Preferences#getDouble(String,double)}.
626 *
627 * <p>This implementation invokes {@link #get(String,String) get(key,
628 * null)}. If the return value is non-null, the implementation
629 * attempts to translate it to an {@code double} with
630 * {@link Double#parseDouble(String)}. If the attempt succeeds, the return
631 * value is returned by this method. Otherwise, {@code def} is returned.
632 *
633 * @param key key whose associated value is to be returned as a double.
634 * @param def the value to be returned in the event that this
635 * preference node has no value associated with {@code key}
636 * or the associated value cannot be interpreted as a double.
637 * @return the double value represented by the string associated with
638 * {@code key} in this preference node, or {@code def} if the
639 * associated value does not exist or cannot be interpreted as
640 * a double.
641 * @throws IllegalStateException if this node (or an ancestor) has been
642 * removed with the {@link #removeNode()} method.
643 * @throws NullPointerException if {@code key} is {@code null}.
644 * @throws IllegalArgumentException if key contains the null control
645 * character, code point U+0000.
646 */
647 public double getDouble(String key, double def) {
648 double result = def;
649 try {
650 String value = get(key, null);
651 if (value != null)
652 result = Double.parseDouble(value);
653 } catch (NumberFormatException e) {
654 // Ignoring exception causes specified default to be returned
655 }
656
657 return result;
658 }
659
660 /**
661 * Implements the {@code putByteArray} method as per the specification in
662 * {@link Preferences#putByteArray(String,byte[])}.
663 *
664 * @param key key with which the string form of value is to be associated.
665 * @param value value whose string form is to be associated with key.
666 * @throws NullPointerException if key or value is {@code null}.
667 * @throws IllegalArgumentException if key.length() exceeds MAX_KEY_LENGTH
668 * or if value.length exceeds MAX_VALUE_LENGTH*3/4.
669 * @throws IllegalArgumentException if key contains
670 * the null control character, code point U+0000.
671 * @throws IllegalStateException if this node (or an ancestor) has been
672 * removed with the {@link #removeNode()} method.
673 */
674 public void putByteArray(String key, byte[] value) {
675 put(key, Base64.byteArrayToBase64(value));
676 }
677
678 /**
679 * Implements the {@code getByteArray} method as per the specification in
680 * {@link Preferences#getByteArray(String,byte[])}.
681 *
682 * @param key key whose associated value is to be returned as a byte array.
683 * @param def the value to be returned in the event that this
684 * preference node has no value associated with {@code key}
685 * or the associated value cannot be interpreted as a byte array.
686 * @return the byte array value represented by the string associated with
687 * {@code key} in this preference node, or {@code def} if the
688 * associated value does not exist or cannot be interpreted as
689 * a byte array.
690 * @throws IllegalStateException if this node (or an ancestor) has been
691 * removed with the {@link #removeNode()} method.
692 * @throws NullPointerException if {@code key} is {@code null}. (A
693 * {@code null} value for {@code def} <i>is</i> permitted.)
694 * @throws IllegalArgumentException if key contains the null control
695 * character, code point U+0000.
696 */
697 public byte[] getByteArray(String key, byte[] def) {
698 byte[] result = def;
699 String value = get(key, null);
700 try {
701 if (value != null)
702 result = Base64.base64ToByteArray(value);
703 }
704 catch (RuntimeException e) {
705 // Ignoring exception causes specified default to be returned
706 }
707
708 return result;
709 }
710
711 /**
712 * Implements the {@code keys} method as per the specification in
713 * {@link Preferences#keys()}.
714 *
715 * <p>This implementation obtains this preference node's lock, checks that
716 * the node has not been removed and invokes {@link #keysSpi()}.
717 *
718 * @return an array of the keys that have an associated value in this
719 * preference node.
720 * @throws BackingStoreException if this operation cannot be completed
721 * due to a failure in the backing store, or inability to
722 * communicate with it.
723 * @throws IllegalStateException if this node (or an ancestor) has been
724 * removed with the {@link #removeNode()} method.
725 */
726 public String[] keys() throws BackingStoreException {
727 synchronized(lock) {
728 if (removed)
729 throw new IllegalStateException("Node has been removed.");
730
731 return keysSpi();
732 }
733 }
734
735 /**
736 * Implements the {@code children} method as per the specification in
737 * {@link Preferences#childrenNames()}.
738 *
739 * <p>This implementation obtains this preference node's lock, checks that
740 * the node has not been removed, constructs a {@code TreeSet} initialized
741 * to the names of children already cached (the children in this node's
742 * "child-cache"), invokes {@link #childrenNamesSpi()}, and adds all of the
743 * returned child-names into the set. The elements of the tree set are
744 * dumped into a {@code String} array using the {@code toArray} method,
745 * and this array is returned.
746 *
747 * @return the names of the children of this preference node.
748 * @throws BackingStoreException if this operation cannot be completed
749 * due to a failure in the backing store, or inability to
750 * communicate with it.
751 * @throws IllegalStateException if this node (or an ancestor) has been
752 * removed with the {@link #removeNode()} method.
753 * @see #cachedChildren()
754 */
755 public String[] childrenNames() throws BackingStoreException {
756 synchronized(lock) {
757 if (removed)
758 throw new IllegalStateException("Node has been removed.");
759
760 Set<String> s = new TreeSet<>(kidCache.keySet());
761 for (String kid : childrenNamesSpi())
762 s.add(kid);
763 return s.toArray(EMPTY_STRING_ARRAY);
764 }
765 }
766
767 private static final String[] EMPTY_STRING_ARRAY = new String[0];
768
769 /**
770 * Returns all known unremoved children of this node.
771 *
772 * @return all known unremoved children of this node.
773 */
774 protected final AbstractPreferences[] cachedChildren() {
775 return kidCache.values().toArray(EMPTY_ABSTRACT_PREFS_ARRAY);
776 }
777
778 private static final AbstractPreferences[] EMPTY_ABSTRACT_PREFS_ARRAY
779 = new AbstractPreferences[0];
780
781 /**
782 * Implements the {@code parent} method as per the specification in
783 * {@link Preferences#parent()}.
784 *
785 * <p>This implementation obtains this preference node's lock, checks that
786 * the node has not been removed and returns the parent value that was
787 * passed to this node's constructor.
788 *
789 * @return the parent of this preference node.
790 * @throws IllegalStateException if this node (or an ancestor) has been
791 * removed with the {@link #removeNode()} method.
792 */
793 public Preferences parent() {
794 synchronized(lock) {
795 if (removed)
796 throw new IllegalStateException("Node has been removed.");
797
798 return parent;
799 }
800 }
801
802 /**
803 * Implements the {@code node} method as per the specification in
804 * {@link Preferences#node(String)}.
805 *
806 * <p>This implementation obtains this preference node's lock and checks
807 * that the node has not been removed. If {@code path} is {@code ""},
808 * this node is returned; if {@code path} is {@code "/"}, this node's
809 * root is returned. If the first character in {@code path} is
810 * not {@code '/'}, the implementation breaks {@code path} into
811 * tokens and recursively traverses the path from this node to the
812 * named node, "consuming" a name and a slash from {@code path} at
813 * each step of the traversal. At each step, the current node is locked
814 * and the node's child-cache is checked for the named node. If it is
815 * not found, the name is checked to make sure its length does not
816 * exceed {@code MAX_NAME_LENGTH}. Then the {@link #childSpi(String)}
817 * method is invoked, and the result stored in this node's child-cache.
818 * If the newly created {@code Preferences} object's {@link #newNode}
819 * field is {@code true} and there are any node change listeners,
820 * a notification event is enqueued for processing by the event dispatch
821 * thread.
822 *
823 * <p>When there are no more tokens, the last value found in the
824 * child-cache or returned by {@code childSpi} is returned by this
825 * method. If during the traversal, two {@code "/"} tokens occur
826 * consecutively, or the final token is {@code "/"} (rather than a name),
827 * an appropriate {@code IllegalArgumentException} is thrown.
828 *
829 * <p> If the first character of {@code path} is {@code '/'}
830 * (indicating an absolute path name) this preference node's
831 * lock is dropped prior to breaking {@code path} into tokens, and
832 * this method recursively traverses the path starting from the root
833 * (rather than starting from this node). The traversal is otherwise
834 * identical to the one described for relative path names. Dropping
835 * the lock on this node prior to commencing the traversal at the root
836 * node is essential to avoid the possibility of deadlock, as per the
837 * {@link #lock locking invariant}.
838 *
839 * @param path the path name of the preference node to return.
840 * @return the specified preference node.
841 * @throws IllegalArgumentException if the path name is invalid (i.e.,
842 * it contains multiple consecutive slash characters, or ends
843 * with a slash character and is more than one character long).
844 * @throws IllegalStateException if this node (or an ancestor) has been
845 * removed with the {@link #removeNode()} method.
846 */
847 public Preferences node(String path) {
848 synchronized(lock) {
849 if (removed)
850 throw new IllegalStateException("Node has been removed.");
851 if (path.isEmpty())
852 return this;
853 if (path.equals("/"))
854 return root;
855 if (path.charAt(0) != '/')
856 return node(new StringTokenizer(path, "/", true));
857 }
858
859 // Absolute path. Note that we've dropped our lock to avoid deadlock
860 return root.node(new StringTokenizer(path.substring(1), "/", true));
861 }
862
863 /**
864 * tokenizer contains <name> {'/' <name>}*
865 */
866 private Preferences node(StringTokenizer path) {
867 String token = path.nextToken();
868 if (token.equals("/")) // Check for consecutive slashes
869 throw new IllegalArgumentException("Consecutive slashes in path");
870 synchronized(lock) {
871 AbstractPreferences child = kidCache.get(token);
872 if (child == null) {
873 if (token.length() > MAX_NAME_LENGTH)
874 throw new IllegalArgumentException(
875 "Node name " + token + " too long");
876 child = childSpi(token);
877 if (child.newNode)
878 enqueueNodeAddedEvent(child);
879 kidCache.put(token, child);
880 }
881 if (!path.hasMoreTokens())
882 return child;
883 path.nextToken(); // Consume slash
884 if (!path.hasMoreTokens())
885 throw new IllegalArgumentException("Path ends with slash");
886 return child.node(path);
887 }
888 }
889
890 /**
891 * Implements the {@code nodeExists} method as per the specification in
892 * {@link Preferences#nodeExists(String)}.
893 *
894 * <p>This implementation is very similar to {@link #node(String)},
895 * except that {@link #getChild(String)} is used instead of {@link
896 * #childSpi(String)}.
897 *
898 * @param path the path name of the node whose existence is to be checked.
899 * @return true if the specified node exists.
900 * @throws BackingStoreException if this operation cannot be completed
901 * due to a failure in the backing store, or inability to
902 * communicate with it.
903 * @throws IllegalArgumentException if the path name is invalid (i.e.,
904 * it contains multiple consecutive slash characters, or ends
905 * with a slash character and is more than one character long).
906 * @throws IllegalStateException if this node (or an ancestor) has been
907 * removed with the {@link #removeNode()} method and
908 * {@code pathname} is not the empty string ({@code ""}).
909 */
910 public boolean nodeExists(String path)
911 throws BackingStoreException
912 {
913 synchronized(lock) {
914 if (path.isEmpty())
915 return !removed;
916 if (removed)
917 throw new IllegalStateException("Node has been removed.");
918 if (path.equals("/"))
919 return true;
920 if (path.charAt(0) != '/')
921 return nodeExists(new StringTokenizer(path, "/", true));
922 }
923
924 // Absolute path. Note that we've dropped our lock to avoid deadlock
925 return root.nodeExists(new StringTokenizer(path.substring(1), "/",
926 true));
927 }
928
929 /**
930 * tokenizer contains <name> {'/' <name>}*
931 */
932 private boolean nodeExists(StringTokenizer path)
933 throws BackingStoreException
934 {
935 String token = path.nextToken();
936 if (token.equals("/")) // Check for consecutive slashes
937 throw new IllegalArgumentException("Consecutive slashes in path");
938 synchronized(lock) {
939 AbstractPreferences child = kidCache.get(token);
940 if (child == null)
941 child = getChild(token);
942 if (child==null)
943 return false;
944 if (!path.hasMoreTokens())
945 return true;
946 path.nextToken(); // Consume slash
947 if (!path.hasMoreTokens())
948 throw new IllegalArgumentException("Path ends with slash");
949 return child.nodeExists(path);
950 }
951 }
952
953 /**
954
955 * Implements the {@code removeNode()} method as per the specification in
956 * {@link Preferences#removeNode()}.
957 *
958 * <p>This implementation checks to see that this node is the root; if so,
959 * it throws an appropriate exception. Then, it locks this node's parent,
960 * and calls a recursive helper method that traverses the subtree rooted at
961 * this node. The recursive method locks the node on which it was called,
962 * checks that it has not already been removed, and then ensures that all
963 * of its children are cached: The {@link #childrenNamesSpi()} method is
964 * invoked and each returned child name is checked for containment in the
965 * child-cache. If a child is not already cached, the {@link
966 * #childSpi(String)} method is invoked to create a {@code Preferences}
967 * instance for it, and this instance is put into the child-cache. Then
968 * the helper method calls itself recursively on each node contained in its
969 * child-cache. Next, it invokes {@link #removeNodeSpi()}, marks itself
970 * as removed, and removes itself from its parent's child-cache. Finally,
971 * if there are any node change listeners, it enqueues a notification
972 * event for processing by the event dispatch thread.
973 *
974 * <p>Note that the helper method is always invoked with all ancestors up
975 * to the "closest non-removed ancestor" locked.
976 *
977 * @throws IllegalStateException if this node (or an ancestor) has already
978 * been removed with the {@link #removeNode()} method.
979 * @throws UnsupportedOperationException if this method is invoked on
980 * the root node.
981 * @throws BackingStoreException if this operation cannot be completed
982 * due to a failure in the backing store, or inability to
983 * communicate with it.
984 */
985 public void removeNode() throws BackingStoreException {
986 if (this==root)
987 throw new UnsupportedOperationException("Can't remove the root!");
988 synchronized(parent.lock) {
989 removeNode2();
990 parent.kidCache.remove(name);
991 }
992 }
993
994 /*
995 * Called with locks on all nodes on path from parent of "removal root"
996 * to this (including the former but excluding the latter).
997 */
998 private void removeNode2() throws BackingStoreException {
999 synchronized(lock) {
1000 if (removed)
1001 throw new IllegalStateException("Node already removed.");
1002
1003 // Ensure that all children are cached
1004 String[] kidNames = childrenNamesSpi();
1005 for (String kidName : kidNames)
1006 if (!kidCache.containsKey(kidName))
1007 kidCache.put(kidName, childSpi(kidName));
1008
1009 // Recursively remove all cached children
1010 for (Iterator<AbstractPreferences> i = kidCache.values().iterator();
1011 i.hasNext();) {
1012 try {
1013 i.next().removeNode2();
1014 i.remove();
1015 } catch (BackingStoreException x) { }
1016 }
1017
1018 // Now we have no descendants - it's time to die!
1019 removeNodeSpi();
1020 removed = true;
1021 parent.enqueueNodeRemovedEvent(this);
1022 }
1023 }
1024
1025 /**
1026 * Implements the {@code name} method as per the specification in
1027 * {@link Preferences#name()}.
1028 *
1029 * <p>This implementation merely returns the name that was
1030 * passed to this node's constructor.
1031 *
1032 * @return this preference node's name, relative to its parent.
1033 */
1034 public String name() {
1035 return name;
1036 }
1037
1038 /**
1039 * Implements the {@code absolutePath} method as per the specification in
1040 * {@link Preferences#absolutePath()}.
1041 *
1042 * <p>This implementation merely returns the absolute path name that
1043 * was computed at the time that this node was constructed (based on
1044 * the name that was passed to this node's constructor, and the names
1045 * that were passed to this node's ancestors' constructors).
1046 *
1047 * @return this preference node's absolute path name.
1048 */
1049 public String absolutePath() {
1050 return absolutePath;
1051 }
1052
1053 /**
1054 * Implements the {@code isUserNode} method as per the specification in
1055 * {@link Preferences#isUserNode()}.
1056 *
1057 * <p>This implementation compares this node's root node (which is stored
1058 * in a private field) with the value returned by
1059 * {@link Preferences#userRoot()}. If the two object references are
1060 * identical, this method returns true.
1061 *
1062 * @return {@code true} if this preference node is in the user
1063 * preference tree, {@code false} if it's in the system
1064 * preference tree.
1065 */
1066 public boolean isUserNode() {
1067 return AccessController.doPrivileged(
1068 new PrivilegedAction<Boolean>() {
1069 public Boolean run() {
1070 return root == Preferences.userRoot();
1071 }
1072 }).booleanValue();
1073 }
1074
1075 public void addPreferenceChangeListener(PreferenceChangeListener pcl) {
1076 if (pcl==null)
1077 throw new NullPointerException("Change listener is null.");
1078 synchronized(lock) {
1079 if (removed)
1080 throw new IllegalStateException("Node has been removed.");
1081
1082 // Copy-on-write
1083 PreferenceChangeListener[] old = prefListeners;
1084 prefListeners = new PreferenceChangeListener[old.length + 1];
1085 System.arraycopy(old, 0, prefListeners, 0, old.length);
1086 prefListeners[old.length] = pcl;
1087 }
1088 startEventDispatchThreadIfNecessary();
1089 }
1090
1091 public void removePreferenceChangeListener(PreferenceChangeListener pcl) {
1092 synchronized(lock) {
1093 if (removed)
1094 throw new IllegalStateException("Node has been removed.");
1095 if ((prefListeners == null) || (prefListeners.length == 0))
1096 throw new IllegalArgumentException("Listener not registered.");
1097
1098 // Copy-on-write
1099 PreferenceChangeListener[] newPl =
1100 new PreferenceChangeListener[prefListeners.length - 1];
1101 int i = 0;
1102 while (i < newPl.length && prefListeners[i] != pcl)
1103 newPl[i] = prefListeners[i++];
1104
1105 if (i == newPl.length && prefListeners[i] != pcl)
1106 throw new IllegalArgumentException("Listener not registered.");
1107 while (i < newPl.length)
1108 newPl[i] = prefListeners[++i];
1109 prefListeners = newPl;
1110 }
1111 }
1112
1113 public void addNodeChangeListener(NodeChangeListener ncl) {
1114 if (ncl==null)
1115 throw new NullPointerException("Change listener is null.");
1116 synchronized(lock) {
1117 if (removed)
1118 throw new IllegalStateException("Node has been removed.");
1119
1120 // Copy-on-write
1121 if (nodeListeners == null) {
1122 nodeListeners = new NodeChangeListener[1];
1123 nodeListeners[0] = ncl;
1124 } else {
1125 NodeChangeListener[] old = nodeListeners;
1126 nodeListeners = new NodeChangeListener[old.length + 1];
1127 System.arraycopy(old, 0, nodeListeners, 0, old.length);
1128 nodeListeners[old.length] = ncl;
1129 }
1130 }
1131 startEventDispatchThreadIfNecessary();
1132 }
1133
1134 public void removeNodeChangeListener(NodeChangeListener ncl) {
1135 synchronized(lock) {
1136 if (removed)
1137 throw new IllegalStateException("Node has been removed.");
1138 if ((nodeListeners == null) || (nodeListeners.length == 0))
1139 throw new IllegalArgumentException("Listener not registered.");
1140
1141 // Copy-on-write
1142 int i = 0;
1143 while (i < nodeListeners.length && nodeListeners[i] != ncl)
1144 i++;
1145 if (i == nodeListeners.length)
1146 throw new IllegalArgumentException("Listener not registered.");
1147 NodeChangeListener[] newNl =
1148 new NodeChangeListener[nodeListeners.length - 1];
1149 if (i != 0)
1150 System.arraycopy(nodeListeners, 0, newNl, 0, i);
1151 if (i != newNl.length)
1152 System.arraycopy(nodeListeners, i + 1,
1153 newNl, i, newNl.length - i);
1154 nodeListeners = newNl;
1155 }
1156 }
1157
1158 // "SPI" METHODS
1159
1160 /**
1161 * Put the given key-value association into this preference node. It is
1162 * guaranteed that {@code key} and {@code value} are non-null and of
1163 * legal length. Also, it is guaranteed that this node has not been
1164 * removed. (The implementor needn't check for any of these things.)
1165 *
1166 * <p>This method is invoked with the lock on this node held.
1167 * @param key the key
1168 * @param value the value
1169 */
1170 protected abstract void putSpi(String key, String value);
1171
1172 /**
1173 * Return the value associated with the specified key at this preference
1174 * node, or {@code null} if there is no association for this key, or the
1175 * association cannot be determined at this time. It is guaranteed that
1176 * {@code key} is non-null. Also, it is guaranteed that this node has
1177 * not been removed. (The implementor needn't check for either of these
1178 * things.)
1179 *
1180 * <p> Generally speaking, this method should not throw an exception
1181 * under any circumstances. If, however, if it does throw an exception,
1182 * the exception will be intercepted and treated as a {@code null}
1183 * return value.
1184 *
1185 * <p>This method is invoked with the lock on this node held.
1186 *
1187 * @param key the key
1188 * @return the value associated with the specified key at this preference
1189 * node, or {@code null} if there is no association for this
1190 * key, or the association cannot be determined at this time.
1191 */
1192 protected abstract String getSpi(String key);
1193
1194 /**
1195 * Remove the association (if any) for the specified key at this
1196 * preference node. It is guaranteed that {@code key} is non-null.
1197 * Also, it is guaranteed that this node has not been removed.
1198 * (The implementor needn't check for either of these things.)
1199 *
1200 * <p>This method is invoked with the lock on this node held.
1201 * @param key the key
1202 */
1203 protected abstract void removeSpi(String key);
1204
1205 /**
1206 * Removes this preference node, invalidating it and any preferences that
1207 * it contains. The named child will have no descendants at the time this
1208 * invocation is made (i.e., the {@link Preferences#removeNode()} method
1209 * invokes this method repeatedly in a bottom-up fashion, removing each of
1210 * a node's descendants before removing the node itself).
1211 *
1212 * <p>This method is invoked with the lock held on this node and its
1213 * parent (and all ancestors that are being removed as a
1214 * result of a single invocation to {@link Preferences#removeNode()}).
1215 *
1216 * <p>The removal of a node needn't become persistent until the
1217 * {@code flush} method is invoked on this node (or an ancestor).
1218 *
1219 * <p>If this node throws a {@code BackingStoreException}, the exception
1220 * will propagate out beyond the enclosing {@link #removeNode()}
1221 * invocation.
1222 *
1223 * @throws BackingStoreException if this operation cannot be completed
1224 * due to a failure in the backing store, or inability to
1225 * communicate with it.
1226 */
1227 protected abstract void removeNodeSpi() throws BackingStoreException;
1228
1229 /**
1230 * Returns all of the keys that have an associated value in this
1231 * preference node. (The returned array will be of size zero if
1232 * this node has no preferences.) It is guaranteed that this node has not
1233 * been removed.
1234 *
1235 * <p>This method is invoked with the lock on this node held.
1236 *
1237 * <p>If this node throws a {@code BackingStoreException}, the exception
1238 * will propagate out beyond the enclosing {@link #keys()} invocation.
1239 *
1240 * @return an array of the keys that have an associated value in this
1241 * preference node.
1242 * @throws BackingStoreException if this operation cannot be completed
1243 * due to a failure in the backing store, or inability to
1244 * communicate with it.
1245 */
1246 protected abstract String[] keysSpi() throws BackingStoreException;
1247
1248 /**
1249 * Returns the names of the children of this preference node. (The
1250 * returned array will be of size zero if this node has no children.)
1251 * This method need not return the names of any nodes already cached,
1252 * but may do so without harm.
1253 *
1254 * <p>This method is invoked with the lock on this node held.
1255 *
1256 * <p>If this node throws a {@code BackingStoreException}, the exception
1257 * will propagate out beyond the enclosing {@link #childrenNames()}
1258 * invocation.
1259 *
1260 * @return an array containing the names of the children of this
1261 * preference node.
1262 * @throws BackingStoreException if this operation cannot be completed
1263 * due to a failure in the backing store, or inability to
1264 * communicate with it.
1265 */
1266 protected abstract String[] childrenNamesSpi()
1267 throws BackingStoreException;
1268
1269 /**
1270 * Returns the named child if it exists, or {@code null} if it does not.
1271 * It is guaranteed that {@code nodeName} is non-null, non-empty,
1272 * does not contain the slash character ('/'), and is no longer than
1273 * {@link #MAX_NAME_LENGTH} characters. Also, it is guaranteed
1274 * that this node has not been removed. (The implementor needn't check
1275 * for any of these things if he chooses to override this method.)
1276 *
1277 * <p>Finally, it is guaranteed that the named node has not been returned
1278 * by a previous invocation of this method or {@link #childSpi} after the
1279 * last time that it was removed. In other words, a cached value will
1280 * always be used in preference to invoking this method. (The implementor
1281 * needn't maintain his own cache of previously returned children if he
1282 * chooses to override this method.)
1283 *
1284 * <p>This implementation obtains this preference node's lock, invokes
1285 * {@link #childrenNames()} to get an array of the names of this node's
1286 * children, and iterates over the array comparing the name of each child
1287 * with the specified node name. If a child node has the correct name,
1288 * the {@link #childSpi(String)} method is invoked and the resulting
1289 * node is returned. If the iteration completes without finding the
1290 * specified name, {@code null} is returned.
1291 *
1292 * @param nodeName name of the child to be searched for.
1293 * @return the named child if it exists, or null if it does not.
1294 * @throws BackingStoreException if this operation cannot be completed
1295 * due to a failure in the backing store, or inability to
1296 * communicate with it.
1297 */
1298 protected AbstractPreferences getChild(String nodeName)
1299 throws BackingStoreException {
1300 synchronized(lock) {
1301 // assert kidCache.get(nodeName)==null;
1302 String[] kidNames = childrenNames();
1303 for (String kidName : kidNames)
1304 if (kidName.equals(nodeName))
1305 return childSpi(kidName);
1306 }
1307 return null;
1308 }
1309
1310 /**
1311 * Returns the named child of this preference node, creating it if it does
1312 * not already exist. It is guaranteed that {@code name} is non-null,
1313 * non-empty, does not contain the slash character ('/'), and is no longer
1314 * than {@link #MAX_NAME_LENGTH} characters. Also, it is guaranteed that
1315 * this node has not been removed. (The implementor needn't check for any
1316 * of these things.)
1317 *
1318 * <p>Finally, it is guaranteed that the named node has not been returned
1319 * by a previous invocation of this method or {@link #getChild(String)}
1320 * after the last time that it was removed. In other words, a cached
1321 * value will always be used in preference to invoking this method.
1322 * Subclasses need not maintain their own cache of previously returned
1323 * children.
1324 *
1325 * <p>The implementer must ensure that the returned node has not been
1326 * removed. If a like-named child of this node was previously removed, the
1327 * implementer must return a newly constructed {@code AbstractPreferences}
1328 * node; once removed, an {@code AbstractPreferences} node
1329 * cannot be "resuscitated."
1330 *
1331 * <p>If this method causes a node to be created, this node is not
1332 * guaranteed to be persistent until the {@code flush} method is
1333 * invoked on this node or one of its ancestors (or descendants).
1334 *
1335 * <p>This method is invoked with the lock on this node held.
1336 *
1337 * @param name The name of the child node to return, relative to
1338 * this preference node.
1339 * @return The named child node.
1340 */
1341 protected abstract AbstractPreferences childSpi(String name);
1342
1343 /**
1344 * Returns the absolute path name of this preferences node.
1345 */
1346 public String toString() {
1347 return (this.isUserNode() ? "User" : "System") +
1348 " Preference Node: " + this.absolutePath();
1349 }
1350
1351 /**
1352 * Implements the {@code sync} method as per the specification in
1353 * {@link Preferences#sync()}.
1354 *
1355 * <p>This implementation calls a recursive helper method that locks this
1356 * node, invokes syncSpi() on it, unlocks this node, and recursively
1357 * invokes this method on each "cached child." A cached child is a child
1358 * of this node that has been created in this VM and not subsequently
1359 * removed. In effect, this method does a depth first traversal of the
1360 * "cached subtree" rooted at this node, calling syncSpi() on each node in
1361 * the subTree while only that node is locked. Note that syncSpi() is
1362 * invoked top-down.
1363 *
1364 * @throws BackingStoreException if this operation cannot be completed
1365 * due to a failure in the backing store, or inability to
1366 * communicate with it.
1367 * @throws IllegalStateException if this node (or an ancestor) has been
1368 * removed with the {@link #removeNode()} method.
1369 * @see #flush()
1370 */
1371 public void sync() throws BackingStoreException {
1372 sync2();
1373 }
1374
1375 private void sync2() throws BackingStoreException {
1376 AbstractPreferences[] cachedKids;
1377
1378 synchronized(lock) {
1379 if (removed)
1380 throw new IllegalStateException("Node has been removed");
1381 syncSpi();
1382 cachedKids = cachedChildren();
1383 }
1384
1385 for (AbstractPreferences cachedKid : cachedKids)
1386 cachedKid.sync2();
1387 }
1388
1389 /**
1390 * This method is invoked with this node locked. The contract of this
1391 * method is to synchronize any cached preferences stored at this node
1392 * with any stored in the backing store. (It is perfectly possible that
1393 * this node does not exist on the backing store, either because it has
1394 * been deleted by another VM, or because it has not yet been created.)
1395 * Note that this method should <i>not</i> synchronize the preferences in
1396 * any subnodes of this node. If the backing store naturally syncs an
1397 * entire subtree at once, the implementer is encouraged to override
1398 * sync(), rather than merely overriding this method.
1399 *
1400 * <p>If this node throws a {@code BackingStoreException}, the exception
1401 * will propagate out beyond the enclosing {@link #sync()} invocation.
1402 *
1403 * @throws BackingStoreException if this operation cannot be completed
1404 * due to a failure in the backing store, or inability to
1405 * communicate with it.
1406 */
1407 protected abstract void syncSpi() throws BackingStoreException;
1408
1409 /**
1410 * Implements the {@code flush} method as per the specification in
1411 * {@link Preferences#flush()}.
1412 *
1413 * <p>This implementation calls a recursive helper method that locks this
1414 * node, invokes flushSpi() on it, unlocks this node, and recursively
1415 * invokes this method on each "cached child." A cached child is a child
1416 * of this node that has been created in this VM and not subsequently
1417 * removed. In effect, this method does a depth first traversal of the
1418 * "cached subtree" rooted at this node, calling flushSpi() on each node in
1419 * the subTree while only that node is locked. Note that flushSpi() is
1420 * invoked top-down.
1421 *
1422 * <p> If this method is invoked on a node that has been removed with
1423 * the {@link #removeNode()} method, flushSpi() is invoked on this node,
1424 * but not on others.
1425 *
1426 * @throws BackingStoreException if this operation cannot be completed
1427 * due to a failure in the backing store, or inability to
1428 * communicate with it.
1429 * @see #flush()
1430 */
1431 public void flush() throws BackingStoreException {
1432 flush2();
1433 }
1434
1435 private void flush2() throws BackingStoreException {
1436 AbstractPreferences[] cachedKids;
1437
1438 synchronized(lock) {
1439 flushSpi();
1440 if(removed)
1441 return;
1442 cachedKids = cachedChildren();
1443 }
1444
1445 for (AbstractPreferences cachedKid : cachedKids)
1446 cachedKid.flush2();
1447 }
1448
1449 /**
1450 * This method is invoked with this node locked. The contract of this
1451 * method is to force any cached changes in the contents of this
1452 * preference node to the backing store, guaranteeing their persistence.
1453 * (It is perfectly possible that this node does not exist on the backing
1454 * store, either because it has been deleted by another VM, or because it
1455 * has not yet been created.) Note that this method should <i>not</i>
1456 * flush the preferences in any subnodes of this node. If the backing
1457 * store naturally flushes an entire subtree at once, the implementer is
1458 * encouraged to override flush(), rather than merely overriding this
1459 * method.
1460 *
1461 * <p>If this node throws a {@code BackingStoreException}, the exception
1462 * will propagate out beyond the enclosing {@link #flush()} invocation.
1463 *
1464 * @throws BackingStoreException if this operation cannot be completed
1465 * due to a failure in the backing store, or inability to
1466 * communicate with it.
1467 */
1468 protected abstract void flushSpi() throws BackingStoreException;
1469
1470 /**
1471 * Returns {@code true} iff this node (or an ancestor) has been
1472 * removed with the {@link #removeNode()} method. This method
1473 * locks this node prior to returning the contents of the private
1474 * field used to track this state.
1475 *
1476 * @return {@code true} iff this node (or an ancestor) has been
1477 * removed with the {@link #removeNode()} method.
1478 */
1479 protected boolean isRemoved() {
1480 synchronized(lock) {
1481 return removed;
1482 }
1483 }
1484
1485 /**
1486 * Queue of pending notification events. When a preference or node
1487 * change event for which there are one or more listeners occurs,
1488 * it is placed on this queue and the queue is notified. A background
1489 * thread waits on this queue and delivers the events. This decouples
1490 * event delivery from preference activity, greatly simplifying
1491 * locking and reducing opportunity for deadlock.
1492 */
1493 private static final List<EventObject> eventQueue = new LinkedList<>();
1494
1495 /**
1496 * These two classes are used to distinguish NodeChangeEvents on
1497 * eventQueue so the event dispatch thread knows whether to call
1498 * childAdded or childRemoved.
1499 */
1500 private class NodeAddedEvent extends NodeChangeEvent {
1501 private static final long serialVersionUID = -6743557530157328528L;
1502 NodeAddedEvent(Preferences parent, Preferences child) {
1503 super(parent, child);
1504 }
1505 }
1506 private class NodeRemovedEvent extends NodeChangeEvent {
1507 private static final long serialVersionUID = 8735497392918824837L;
1508 NodeRemovedEvent(Preferences parent, Preferences child) {
1509 super(parent, child);
1510 }
1511 }
1512
1513 /**
1514 * A single background thread ("the event notification thread") monitors
1515 * the event queue and delivers events that are placed on the queue.
1516 */
1517 private static class EventDispatchThread extends Thread {
1518 private EventDispatchThread() {
1519 super(null, null, "Event Dispatch Thread", 0, false);
1520 }
1521
1522 public void run() {
1523 while(true) {
1524 // Wait on eventQueue till an event is present
1525 EventObject event = null;
1526 synchronized(eventQueue) {
1527 try {
1528 while (eventQueue.isEmpty())
1529 eventQueue.wait();
1530 event = eventQueue.remove(0);
1531 } catch (InterruptedException e) {
1532 // XXX Log "Event dispatch thread interrupted. Exiting"
1533 return;
1534 }
1535 }
1536
1537 // Now we have event & hold no locks; deliver evt to listeners
1538 AbstractPreferences src=(AbstractPreferences)event.getSource();
1539 if (event instanceof PreferenceChangeEvent) {
1540 PreferenceChangeEvent pce = (PreferenceChangeEvent)event;
1541 PreferenceChangeListener[] listeners = src.prefListeners();
1542 for (PreferenceChangeListener listener : listeners)
1543 listener.preferenceChange(pce);
1544 } else {
1545 NodeChangeEvent nce = (NodeChangeEvent)event;
1546 NodeChangeListener[] listeners = src.nodeListeners();
1547 if (nce instanceof NodeAddedEvent) {
1548 for (NodeChangeListener listener : listeners)
1549 listener.childAdded(nce);
1550 } else {
1551 // assert nce instanceof NodeRemovedEvent;
1552 for (NodeChangeListener listener : listeners)
1553 listener.childRemoved(nce);
1554 }
1555 }
1556 }
1557 }
1558 }
1559
1560 private static Thread eventDispatchThread = null;
1561
1562 /**
1563 * This method starts the event dispatch thread the first time it
1564 * is called. The event dispatch thread will be started only
1565 * if someone registers a listener.
1566 */
1567 private static synchronized void startEventDispatchThreadIfNecessary() {
1568 if (eventDispatchThread == null) {
1569 // XXX Log "Starting event dispatch thread"
1570 eventDispatchThread = new EventDispatchThread();
1571 eventDispatchThread.setDaemon(true);
1572 eventDispatchThread.start();
1573 }
1574 }
1575
1576 /**
1577 * Return this node's preference/node change listeners. Even though
1578 * we're using a copy-on-write lists, we use synchronized accessors to
1579 * ensure information transmission from the writing thread to the
1580 * reading thread.
1581 */
1582 PreferenceChangeListener[] prefListeners() {
1583 synchronized(lock) {
1584 return prefListeners;
1585 }
1586 }
1587 NodeChangeListener[] nodeListeners() {
1588 synchronized(lock) {
1589 return nodeListeners;
1590 }
1591 }
1592
1593 /**
1594 * Enqueue a preference change event for delivery to registered
1595 * preference change listeners unless there are no registered
1596 * listeners. Invoked with this.lock held.
1597 */
1598 private void enqueuePreferenceChangeEvent(String key, String newValue) {
1599 if (prefListeners.length != 0) {
1600 synchronized(eventQueue) {
1601 eventQueue.add(new PreferenceChangeEvent(this, key, newValue));
1602 eventQueue.notify();
1603 }
1604 }
1605 }
1606
1607 /**
1608 * Enqueue a "node added" event for delivery to registered node change
1609 * listeners unless there are no registered listeners. Invoked with
1610 * this.lock held.
1611 */
1612 private void enqueueNodeAddedEvent(Preferences child) {
1613 if (nodeListeners.length != 0) {
1614 synchronized(eventQueue) {
1615 eventQueue.add(new NodeAddedEvent(this, child));
1616 eventQueue.notify();
1617 }
1618 }
1619 }
1620
1621 /**
1622 * Enqueue a "node removed" event for delivery to registered node change
1623 * listeners unless there are no registered listeners. Invoked with
1624 * this.lock held.
1625 */
1626 private void enqueueNodeRemovedEvent(Preferences child) {
1627 if (nodeListeners.length != 0) {
1628 synchronized(eventQueue) {
1629 eventQueue.add(new NodeRemovedEvent(this, child));
1630 eventQueue.notify();
1631 }
1632 }
1633 }
1634
1635 /**
1636 * Implements the {@code exportNode} method as per the specification in
1637 * {@link Preferences#exportNode(OutputStream)}.
1638 *
1639 * @param os the output stream on which to emit the XML document.
1640 * @throws IOException if writing to the specified output stream
1641 * results in an {@code IOException}.
1642 * @throws BackingStoreException if preference data cannot be read from
1643 * backing store.
1644 */
1645 public void exportNode(OutputStream os)
1646 throws IOException, BackingStoreException
1647 {
1648 XmlSupport.export(os, this, false);
1649 }
1650
1651 /**
1652 * Implements the {@code exportSubtree} method as per the specification in
1653 * {@link Preferences#exportSubtree(OutputStream)}.
1654 *
1655 * @param os the output stream on which to emit the XML document.
1656 * @throws IOException if writing to the specified output stream
1657 * results in an {@code IOException}.
1658 * @throws BackingStoreException if preference data cannot be read from
1659 * backing store.
1660 */
1661 public void exportSubtree(OutputStream os)
1662 throws IOException, BackingStoreException
1663 {
1664 XmlSupport.export(os, this, true);
1665 }
1666 }