1 /*
2 * Copyright (c) 2000, 2015, 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
22 * or visit www.oracle.com if you need additional information or have any
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 import sun.misc.ManagedLocalsThread;
33 // These imports needed only as a workaround for a JavaDoc bug
34 import java.lang.Integer;
35 import java.lang.Long;
36 import java.lang.Float;
37 import java.lang.Double;
38
39 /**
40 * This class provides a skeletal implementation of the {@link Preferences}
41 * class, greatly easing the task of implementing it.
42 *
43 * <p><strong>This class is for {@code Preferences} implementers only.
44 * Normal users of the {@code Preferences} facility should have no need to
45 * consult this documentation. The {@link Preferences} documentation
46 * should suffice.</strong>
47 *
48 * <p>Implementors must override the nine abstract service-provider interface
49 * (SPI) methods: {@link #getSpi(String)}, {@link #putSpi(String,String)},
50 * {@link #removeSpi(String)}, {@link #childSpi(String)}, {@link
51 * #removeNodeSpi()}, {@link #keysSpi()}, {@link #childrenNamesSpi()}, {@link
52 * #syncSpi()} and {@link #flushSpi()}. All of the concrete methods specify
53 * precisely how they are implemented atop these SPI methods. The implementor
54 * may, at his discretion, override one or more of the concrete methods if the
55 * default implementation is unsatisfactory for any reason, such as
56 * performance.
57 *
58 * <p>The SPI methods fall into three groups concerning exception
59 * behavior. The {@code getSpi} method should never throw exceptions, but it
60 * doesn't really matter, as any exception thrown by this method will be
61 * intercepted by {@link #get(String,String)}, which will return the specified
62 * default value to the caller. The {@code removeNodeSpi, keysSpi,
63 * childrenNamesSpi, syncSpi} and {@code flushSpi} methods are specified
64 * to throw {@link BackingStoreException}, and the implementation is required
65 * to throw this checked exception if it is unable to perform the operation.
66 * The exception propagates outward, causing the corresponding API method
67 * to fail.
68 *
69 * <p>The remaining SPI methods {@link #putSpi(String,String)}, {@link
70 * #removeSpi(String)} and {@link #childSpi(String)} have more complicated
71 * exception behavior. They are not specified to throw
72 * {@code BackingStoreException}, as they can generally obey their contracts
73 * even if the backing store is unavailable. This is true because they return
74 * no information and their effects are not required to become permanent until
75 * a subsequent call to {@link Preferences#flush()} or
76 * {@link Preferences#sync()}. Generally speaking, these SPI methods should not
77 * throw exceptions. In some implementations, there may be circumstances
78 * under which these calls cannot even enqueue the requested operation for
79 * later processing. Even under these circumstances it is generally better to
80 * simply ignore the invocation and return, rather than throwing an
81 * exception. Under these circumstances, however, subsequently invoking
82 * {@code flush()} or {@code sync} would not imply that all previous
83 * operations had successfully been made permanent.
84 *
85 * <p>There is one circumstance under which {@code putSpi, removeSpi and
86 * childSpi} <i>should</i> throw an exception: if the caller lacks
87 * sufficient privileges on the underlying operating system to perform the
88 * requested operation. This will, for instance, occur on most systems
89 * if a non-privileged user attempts to modify system preferences.
90 * (The required privileges will vary from implementation to
91 * implementation. On some implementations, they are the right to modify the
92 * contents of some directory in the file system; on others they are the right
93 * to modify contents of some key in a registry.) Under any of these
94 * circumstances, it would generally be undesirable to let the program
95 * continue executing as if these operations would become permanent at a later
96 * time. While implementations are not required to throw an exception under
97 * these circumstances, they are encouraged to do so. A {@link
98 * SecurityException} would be appropriate.
99 *
100 * <p>Most of the SPI methods require the implementation to read or write
101 * information at a preferences node. The implementor should beware of the
102 * fact that another VM may have concurrently deleted this node from the
103 * backing store. It is the implementation's responsibility to recreate the
104 * node if it has been deleted.
105 *
106 * <p>Implementation note: In Sun's default {@code Preferences}
107 * implementations, the user's identity is inherited from the underlying
108 * operating system and does not change for the lifetime of the virtual
109 * machine. It is recognized that server-side {@code Preferences}
110 * implementations may have the user identity change from request to request,
111 * implicitly passed to {@code Preferences} methods via the use of a
112 * static {@link ThreadLocal} instance. Authors of such implementations are
113 * <i>strongly</i> encouraged to determine the user at the time preferences
114 * are accessed (for example by the {@link #get(String,String)} or {@link
115 * #put(String,String)} method) rather than permanently associating a user
116 * with each {@code Preferences} instance. The latter behavior conflicts
117 * with normal {@code Preferences} usage and would lead to great confusion.
118 *
119 * @author Josh Bloch
120 * @see Preferences
121 * @since 1.4
122 */
123 public abstract class AbstractPreferences extends Preferences {
124 /**
125 * The code point U+0000, assigned to the null control character, is the
126 * only character encoded in Unicode and ISO/IEC 10646 that is always
127 * invalid in any XML 1.0 and 1.1 document.
128 */
129 static final int CODE_POINT_U0000 = '\u0000';
130
131 /**
132 * Our name relative to parent.
133 */
134 private final String name;
135
136 /**
137 * Our absolute path name.
138 */
139 private final String absolutePath;
140
141 /**
142 * Our parent node.
143 */
144 final AbstractPreferences parent;
145
146 /**
147 * Our root node.
148 */
149 private final AbstractPreferences root; // Relative to this node
150
151 /**
152 * This field should be {@code true} if this node did not exist in the
153 * backing store prior to the creation of this object. The field
154 * is initialized to false, but may be set to true by a subclass
155 * constructor (and should not be modified thereafter). This field
156 * indicates whether a node change event should be fired when
157 * creation is complete.
158 */
159 protected boolean newNode = false;
160
161 /**
162 * All known unremoved children of this node. (This "cache" is consulted
163 * prior to calling childSpi() or getChild().
164 */
165 private Map<String, AbstractPreferences> kidCache = new HashMap<>();
166
167 /**
168 * This field is used to keep track of whether or not this node has
169 * been removed. Once it's set to true, it will never be reset to false.
170 */
171 private boolean removed = false;
172
173 /**
174 * Registered preference change listeners.
175 */
176 private PreferenceChangeListener[] prefListeners =
177 new PreferenceChangeListener[0];
178
179 /**
180 * Registered node change listeners.
181 */
182 private NodeChangeListener[] nodeListeners = new NodeChangeListener[0];
183
184 /**
185 * An object whose monitor is used to lock this node. This object
186 * is used in preference to the node itself to reduce the likelihood of
187 * intentional or unintentional denial of service due to a locked node.
188 * To avoid deadlock, a node is <i>never</i> locked by a thread that
189 * holds a lock on a descendant of that node.
190 */
191 protected final Object lock = new Object();
192
193 /**
194 * Creates a preference node with the specified parent and the specified
195 * name relative to its parent.
196 *
197 * @param parent the parent of this preference node, or null if this
198 * is the root.
199 * @param name the name of this preference node, relative to its parent,
200 * or {@code ""} if this is the root.
201 * @throws IllegalArgumentException if {@code name} contains a slash
202 * ({@code '/'}), or {@code parent} is {@code null} and
203 * name isn't {@code ""}.
204 */
205 protected AbstractPreferences(AbstractPreferences parent, String name) {
206 if (parent==null) {
207 if (!name.equals(""))
208 throw new IllegalArgumentException("Root name '"+name+
209 "' must be \"\"");
210 this.absolutePath = "/";
211 root = this;
212 } else {
213 if (name.indexOf('/') != -1)
214 throw new IllegalArgumentException("Name '" + name +
215 "' contains '/'");
216 if (name.equals(""))
217 throw new IllegalArgumentException("Illegal name: empty string");
218
219 root = parent.root;
220 absolutePath = (parent==root ? "/" + name
221 : parent.absolutePath() + "/" + name);
222 }
223 this.name = name;
224 this.parent = parent;
225 }
226
227 /**
228 * Implements the {@code put} method as per the specification in
229 * {@link Preferences#put(String,String)}.
230 *
231 * <p>This implementation checks that the key and value are legal,
232 * obtains this preference node's lock, checks that the node
233 * has not been removed, invokes {@link #putSpi(String,String)}, and if
234 * there are any preference change listeners, enqueues a notification
235 * event for processing by the event dispatch thread.
236 *
237 * @param key key with which the specified value is to be associated.
238 * @param value value to be associated with the specified key.
239 * @throws NullPointerException if key or value is {@code null}.
240 * @throws IllegalArgumentException if {@code key.length()} exceeds
241 * {@code MAX_KEY_LENGTH} or if {@code value.length} exceeds
242 * {@code MAX_VALUE_LENGTH}.
243 * @throws IllegalArgumentException if either key or value contain
244 * the null control character, code point U+0000.
245 * @throws IllegalStateException if this node (or an ancestor) has been
246 * removed with the {@link #removeNode()} method.
247 */
248 public void put(String key, String value) {
249 if (key==null || value==null)
250 throw new NullPointerException();
251 if (key.length() > MAX_KEY_LENGTH)
252 throw new IllegalArgumentException("Key too long: "+key);
253 if (value.length() > MAX_VALUE_LENGTH)
254 throw new IllegalArgumentException("Value too long: "+value);
255 if (key.indexOf(CODE_POINT_U0000) != -1)
256 throw new IllegalArgumentException("Key contains code point U+0000");
257 if (value.indexOf(CODE_POINT_U0000) != -1)
258 throw new IllegalArgumentException("Value contains code point U+0000");
259
260 synchronized(lock) {
261 if (removed)
262 throw new IllegalStateException("Node has been removed.");
263
264 putSpi(key, value);
265 enqueuePreferenceChangeEvent(key, value);
266 }
267 }
268
269 /**
270 * Implements the {@code get} method as per the specification in
271 * {@link Preferences#get(String,String)}.
272 *
273 * <p>This implementation first checks to see if {@code key} is
274 * {@code null} throwing a {@code NullPointerException} if this is
275 * the case. Then it obtains this preference node's lock,
276 * checks that the node has not been removed, invokes {@link
277 * #getSpi(String)}, and returns the result, unless the {@code getSpi}
278 * invocation returns {@code null} or throws an exception, in which case
279 * this invocation returns {@code def}.
280 *
281 * @param key key whose associated value is to be returned.
282 * @param def the value to be returned in the event that this
283 * preference node has no value associated with {@code key}.
284 * @return the value associated with {@code key}, or {@code def}
285 * if no value is associated with {@code key}.
286 * @throws IllegalStateException if this node (or an ancestor) has been
287 * removed with the {@link #removeNode()} method.
288 * @throws NullPointerException if key is {@code null}. (A
289 * {@code null} default <i>is</i> permitted.)
290 * @throws IllegalArgumentException if key contains the null control
291 * character, code point U+0000.
292 */
293 public String get(String key, String def) {
294 if (key==null)
295 throw new NullPointerException("Null key");
296 if (key.indexOf(CODE_POINT_U0000) != -1)
297 throw new IllegalArgumentException("Key contains code point U+0000");
298 synchronized(lock) {
299 if (removed)
300 throw new IllegalStateException("Node has been removed.");
301
302 String result = null;
303 try {
304 result = getSpi(key);
305 } catch (Exception e) {
306 // Ignoring exception causes default to be returned
307 }
308 return (result==null ? def : result);
309 }
310 }
311
312 /**
313 * Implements the {@code remove(String)} method as per the specification
314 * in {@link Preferences#remove(String)}.
315 *
316 * <p>This implementation obtains this preference node's lock,
317 * checks that the node has not been removed, invokes
318 * {@link #removeSpi(String)} and if there are any preference
319 * change listeners, enqueues a notification event for processing by the
320 * event dispatch thread.
321 *
322 * @param key key whose mapping is to be removed from the preference node.
323 * @throws IllegalStateException if this node (or an ancestor) has been
324 * removed with the {@link #removeNode()} method.
325 * @throws IllegalArgumentException if key contains the null control
326 * character, code point U+0000.
327 * @throws NullPointerException {@inheritDoc}.
328 */
329 public void remove(String key) {
330 Objects.requireNonNull(key, "Specified key cannot be null");
331 if (key.indexOf(CODE_POINT_U0000) != -1)
332 throw new IllegalArgumentException("Key contains code point U+0000");
333 synchronized(lock) {
334 if (removed)
335 throw new IllegalStateException("Node has been removed.");
336
337 removeSpi(key);
338 enqueuePreferenceChangeEvent(key, null);
339 }
340 }
341
342 /**
343 * Implements the {@code clear} method as per the specification in
344 * {@link Preferences#clear()}.
345 *
346 * <p>This implementation obtains this preference node's lock,
347 * invokes {@link #keys()} to obtain an array of keys, and
348 * iterates over the array invoking {@link #remove(String)} on each key.
349 *
350 * @throws BackingStoreException if this operation cannot be completed
351 * due to a failure in the backing store, or inability to
352 * communicate with it.
353 * @throws IllegalStateException if this node (or an ancestor) has been
354 * removed with the {@link #removeNode()} method.
355 */
356 public void clear() throws BackingStoreException {
357 synchronized(lock) {
358 for (String key : keys())
359 remove(key);
360 }
361 }
362
363 /**
364 * Implements the {@code putInt} method as per the specification in
365 * {@link Preferences#putInt(String,int)}.
366 *
367 * <p>This implementation translates {@code value} to a string with
368 * {@link Integer#toString(int)} and invokes {@link #put(String,String)}
369 * on the result.
370 *
371 * @param key key with which the string form of value is to be associated.
372 * @param value value whose string form is to be associated with key.
373 * @throws NullPointerException if key is {@code null}.
374 * @throws IllegalArgumentException if {@code key.length()} exceeds
375 * {@code MAX_KEY_LENGTH}.
376 * @throws IllegalArgumentException if key contains
377 * the null control character, code point U+0000.
378 * @throws IllegalStateException if this node (or an ancestor) has been
379 * removed with the {@link #removeNode()} method.
380 */
381 public void putInt(String key, int value) {
382 put(key, Integer.toString(value));
383 }
384
385 /**
386 * Implements the {@code getInt} method as per the specification in
387 * {@link Preferences#getInt(String,int)}.
388 *
389 * <p>This implementation invokes {@link #get(String,String) get(key,
390 * null)}. If the return value is non-null, the implementation
391 * attempts to translate it to an {@code int} with
392 * {@link Integer#parseInt(String)}. If the attempt succeeds, the return
393 * value is returned by this method. Otherwise, {@code def} is returned.
394 *
395 * @param key key whose associated value is to be returned as an int.
396 * @param def the value to be returned in the event that this
397 * preference node has no value associated with {@code key}
398 * or the associated value cannot be interpreted as an int.
399 * @return the int value represented by the string associated with
400 * {@code key} in this preference node, or {@code def} if the
401 * associated value does not exist or cannot be interpreted as
402 * an int.
403 * @throws IllegalStateException if this node (or an ancestor) has been
404 * removed with the {@link #removeNode()} method.
405 * @throws NullPointerException if {@code key} is {@code null}.
406 * @throws IllegalArgumentException if key contains the null control
407 * character, code point U+0000.
408 */
409 public int getInt(String key, int def) {
410 int result = def;
411 try {
412 String value = get(key, null);
413 if (value != null)
414 result = Integer.parseInt(value);
415 } catch (NumberFormatException e) {
416 // Ignoring exception causes specified default to be returned
417 }
418
419 return result;
420 }
421
422 /**
423 * Implements the {@code putLong} method as per the specification in
424 * {@link Preferences#putLong(String,long)}.
425 *
426 * <p>This implementation translates {@code value} to a string with
427 * {@link Long#toString(long)} and invokes {@link #put(String,String)}
428 * on the result.
429 *
430 * @param key key with which the string form of value is to be associated.
431 * @param value value whose string form is to be associated with key.
432 * @throws NullPointerException if key is {@code null}.
433 * @throws IllegalArgumentException if {@code key.length()} exceeds
434 * {@code MAX_KEY_LENGTH}.
435 * @throws IllegalArgumentException if key contains
436 * the null control character, code point U+0000.
437 * @throws IllegalStateException if this node (or an ancestor) has been
438 * removed with the {@link #removeNode()} method.
439 */
440 public void putLong(String key, long value) {
441 put(key, Long.toString(value));
442 }
443
444 /**
445 * Implements the {@code getLong} method as per the specification in
446 * {@link Preferences#getLong(String,long)}.
447 *
448 * <p>This implementation invokes {@link #get(String,String) get(key,
449 * null)}. If the return value is non-null, the implementation
450 * attempts to translate it to a {@code long} with
451 * {@link Long#parseLong(String)}. If the attempt succeeds, the return
452 * value is returned by this method. Otherwise, {@code def} is returned.
453 *
454 * @param key key whose associated value is to be returned as a long.
455 * @param def the value to be returned in the event that this
456 * preference node has no value associated with {@code key}
457 * or the associated value cannot be interpreted as a long.
458 * @return the long value represented by the string associated with
459 * {@code key} in this preference node, or {@code def} if the
460 * associated value does not exist or cannot be interpreted as
461 * a long.
462 * @throws IllegalStateException if this node (or an ancestor) has been
463 * removed with the {@link #removeNode()} method.
464 * @throws NullPointerException if {@code key} is {@code null}.
465 * @throws IllegalArgumentException if key contains the null control
466 * character, code point U+0000.
467 */
468 public long getLong(String key, long def) {
469 long result = def;
470 try {
471 String value = get(key, null);
472 if (value != null)
473 result = Long.parseLong(value);
474 } catch (NumberFormatException e) {
475 // Ignoring exception causes specified default to be returned
476 }
477
478 return result;
479 }
480
481 /**
482 * Implements the {@code putBoolean} method as per the specification in
483 * {@link Preferences#putBoolean(String,boolean)}.
484 *
485 * <p>This implementation translates {@code value} to a string with
486 * {@link String#valueOf(boolean)} and invokes {@link #put(String,String)}
487 * on the result.
488 *
489 * @param key key with which the string form of value is to be associated.
490 * @param value value whose string form is to be associated with key.
491 * @throws NullPointerException if key is {@code null}.
492 * @throws IllegalArgumentException if {@code key.length()} exceeds
493 * {@code MAX_KEY_LENGTH}.
494 * @throws IllegalArgumentException if key contains
495 * the null control character, code point U+0000.
496 * @throws IllegalStateException if this node (or an ancestor) has been
497 * removed with the {@link #removeNode()} method.
498 */
499 public void putBoolean(String key, boolean value) {
500 put(key, String.valueOf(value));
501 }
502
503 /**
504 * Implements the {@code getBoolean} method as per the specification in
505 * {@link Preferences#getBoolean(String,boolean)}.
506 *
507 * <p>This implementation invokes {@link #get(String,String) get(key,
508 * null)}. If the return value is non-null, it is compared with
509 * {@code "true"} using {@link String#equalsIgnoreCase(String)}. If the
510 * comparison returns {@code true}, this invocation returns
511 * {@code true}. Otherwise, the original return value is compared with
512 * {@code "false"}, again using {@link String#equalsIgnoreCase(String)}.
513 * If the comparison returns {@code true}, this invocation returns
514 * {@code false}. Otherwise, this invocation returns {@code def}.
515 *
516 * @param key key whose associated value is to be returned as a boolean.
517 * @param def the value to be returned in the event that this
518 * preference node has no value associated with {@code key}
519 * or the associated value cannot be interpreted as a boolean.
520 * @return the boolean value represented by the string associated with
521 * {@code key} in this preference node, or {@code def} if the
522 * associated value does not exist or cannot be interpreted as
523 * a boolean.
524 * @throws IllegalStateException if this node (or an ancestor) has been
525 * removed with the {@link #removeNode()} method.
526 * @throws NullPointerException if {@code key} is {@code null}.
527 * @throws IllegalArgumentException if key contains the null control
528 * character, code point U+0000.
529 */
530 public boolean getBoolean(String key, boolean def) {
531 boolean result = def;
532 String value = get(key, null);
533 if (value != null) {
534 if (value.equalsIgnoreCase("true"))
535 result = true;
536 else if (value.equalsIgnoreCase("false"))
537 result = false;
538 }
539
540 return result;
541 }
542
543 /**
544 * Implements the {@code putFloat} method as per the specification in
545 * {@link Preferences#putFloat(String,float)}.
546 *
547 * <p>This implementation translates {@code value} to a string with
548 * {@link Float#toString(float)} and invokes {@link #put(String,String)}
549 * on the result.
550 *
551 * @param key key with which the string form of value is to be associated.
552 * @param value value whose string form is to be associated with key.
553 * @throws NullPointerException if key is {@code null}.
554 * @throws IllegalArgumentException if {@code key.length()} exceeds
555 * {@code MAX_KEY_LENGTH}.
556 * @throws IllegalArgumentException if key contains
557 * the null control character, code point U+0000.
558 * @throws IllegalStateException if this node (or an ancestor) has been
559 * removed with the {@link #removeNode()} method.
560 */
561 public void putFloat(String key, float value) {
562 put(key, Float.toString(value));
563 }
564
565 /**
566 * Implements the {@code getFloat} method as per the specification in
567 * {@link Preferences#getFloat(String,float)}.
568 *
569 * <p>This implementation invokes {@link #get(String,String) get(key,
570 * null)}. If the return value is non-null, the implementation
571 * attempts to translate it to an {@code float} with
572 * {@link Float#parseFloat(String)}. If the attempt succeeds, the return
573 * value is returned by this method. Otherwise, {@code def} is returned.
574 *
575 * @param key key whose associated value is to be returned as a float.
576 * @param def the value to be returned in the event that this
577 * preference node has no value associated with {@code key}
578 * or the associated value cannot be interpreted as a float.
579 * @return the float value represented by the string associated with
580 * {@code key} in this preference node, or {@code def} if the
581 * associated value does not exist or cannot be interpreted as
582 * a float.
583 * @throws IllegalStateException if this node (or an ancestor) has been
584 * removed with the {@link #removeNode()} method.
585 * @throws NullPointerException if {@code key} is {@code null}.
586 * @throws IllegalArgumentException if key contains the null control
587 * character, code point U+0000.
588 */
589 public float getFloat(String key, float def) {
590 float result = def;
591 try {
592 String value = get(key, null);
593 if (value != null)
594 result = Float.parseFloat(value);
595 } catch (NumberFormatException e) {
596 // Ignoring exception causes specified default to be returned
597 }
598
599 return result;
600 }
601
602 /**
603 * Implements the {@code putDouble} method as per the specification in
604 * {@link Preferences#putDouble(String,double)}.
605 *
606 * <p>This implementation translates {@code value} to a string with
607 * {@link Double#toString(double)} and invokes {@link #put(String,String)}
608 * on the result.
609 *
610 * @param key key with which the string form of value is to be associated.
611 * @param value value whose string form is to be associated with key.
612 * @throws NullPointerException if key is {@code null}.
613 * @throws IllegalArgumentException if {@code key.length()} exceeds
614 * {@code MAX_KEY_LENGTH}.
615 * @throws IllegalArgumentException if key contains
616 * the null control character, code point U+0000.
617 * @throws IllegalStateException if this node (or an ancestor) has been
618 * removed with the {@link #removeNode()} method.
619 */
620 public void putDouble(String key, double value) {
621 put(key, Double.toString(value));
622 }
623
624 /**
625 * Implements the {@code getDouble} method as per the specification in
626 * {@link Preferences#getDouble(String,double)}.
627 *
628 * <p>This implementation invokes {@link #get(String,String) get(key,
629 * null)}. If the return value is non-null, the implementation
630 * attempts to translate it to an {@code double} with
631 * {@link Double#parseDouble(String)}. If the attempt succeeds, the return
632 * value is returned by this method. Otherwise, {@code def} is returned.
633 *
634 * @param key key whose associated value is to be returned as a double.
635 * @param def the value to be returned in the event that this
636 * preference node has no value associated with {@code key}
637 * or the associated value cannot be interpreted as a double.
638 * @return the double value represented by the string associated with
639 * {@code key} in this preference node, or {@code def} if the
640 * associated value does not exist or cannot be interpreted as
641 * a double.
642 * @throws IllegalStateException if this node (or an ancestor) has been
643 * removed with the {@link #removeNode()} method.
644 * @throws NullPointerException if {@code key} is {@code null}.
645 * @throws IllegalArgumentException if key contains the null control
646 * character, code point U+0000.
647 */
648 public double getDouble(String key, double def) {
649 double result = def;
650 try {
651 String value = get(key, null);
652 if (value != null)
653 result = Double.parseDouble(value);
654 } catch (NumberFormatException e) {
655 // Ignoring exception causes specified default to be returned
656 }
657
658 return result;
659 }
660
661 /**
662 * Implements the {@code putByteArray} method as per the specification in
663 * {@link Preferences#putByteArray(String,byte[])}.
664 *
665 * @param key key with which the string form of value is to be associated.
666 * @param value value whose string form is to be associated with key.
667 * @throws NullPointerException if key or value is {@code null}.
668 * @throws IllegalArgumentException if key.length() exceeds MAX_KEY_LENGTH
669 * or if value.length exceeds MAX_VALUE_LENGTH*3/4.
670 * @throws IllegalArgumentException if key contains
671 * the null control character, code point U+0000.
672 * @throws IllegalStateException if this node (or an ancestor) has been
673 * removed with the {@link #removeNode()} method.
674 */
675 public void putByteArray(String key, byte[] value) {
676 put(key, Base64.byteArrayToBase64(value));
677 }
678
679 /**
680 * Implements the {@code getByteArray} method as per the specification in
681 * {@link Preferences#getByteArray(String,byte[])}.
682 *
683 * @param key key whose associated value is to be returned as a byte array.
684 * @param def the value to be returned in the event that this
685 * preference node has no value associated with {@code key}
686 * or the associated value cannot be interpreted as a byte array.
687 * @return the byte array value represented by the string associated with
688 * {@code key} in this preference node, or {@code def} if the
689 * associated value does not exist or cannot be interpreted as
690 * a byte array.
691 * @throws IllegalStateException if this node (or an ancestor) has been
692 * removed with the {@link #removeNode()} method.
693 * @throws NullPointerException if {@code key} is {@code null}. (A
694 * {@code null} value for {@code def} <i>is</i> permitted.)
695 * @throws IllegalArgumentException if key contains the null control
696 * character, code point U+0000.
697 */
698 public byte[] getByteArray(String key, byte[] def) {
699 byte[] result = def;
700 String value = get(key, null);
701 try {
702 if (value != null)
703 result = Base64.base64ToByteArray(value);
704 }
705 catch (RuntimeException e) {
706 // Ignoring exception causes specified default to be returned
707 }
708
709 return result;
710 }
711
712 /**
713 * Implements the {@code keys} method as per the specification in
714 * {@link Preferences#keys()}.
715 *
716 * <p>This implementation obtains this preference node's lock, checks that
717 * the node has not been removed and invokes {@link #keysSpi()}.
718 *
719 * @return an array of the keys that have an associated value in this
720 * preference node.
721 * @throws BackingStoreException if this operation cannot be completed
722 * due to a failure in the backing store, or inability to
723 * communicate with it.
724 * @throws IllegalStateException if this node (or an ancestor) has been
725 * removed with the {@link #removeNode()} method.
726 */
727 public String[] keys() throws BackingStoreException {
728 synchronized(lock) {
729 if (removed)
730 throw new IllegalStateException("Node has been removed.");
731
732 return keysSpi();
733 }
734 }
735
736 /**
737 * Implements the {@code children} method as per the specification in
738 * {@link Preferences#childrenNames()}.
739 *
740 * <p>This implementation obtains this preference node's lock, checks that
741 * the node has not been removed, constructs a {@code TreeSet} initialized
742 * to the names of children already cached (the children in this node's
743 * "child-cache"), invokes {@link #childrenNamesSpi()}, and adds all of the
744 * returned child-names into the set. The elements of the tree set are
745 * dumped into a {@code String} array using the {@code toArray} method,
746 * and this array is returned.
747 *
748 * @return the names of the children of this preference node.
749 * @throws BackingStoreException if this operation cannot be completed
750 * due to a failure in the backing store, or inability to
751 * communicate with it.
752 * @throws IllegalStateException if this node (or an ancestor) has been
753 * removed with the {@link #removeNode()} method.
754 * @see #cachedChildren()
755 */
756 public String[] childrenNames() throws BackingStoreException {
757 synchronized(lock) {
758 if (removed)
759 throw new IllegalStateException("Node has been removed.");
760
761 Set<String> s = new TreeSet<>(kidCache.keySet());
762 for (String kid : childrenNamesSpi())
763 s.add(kid);
764 return s.toArray(EMPTY_STRING_ARRAY);
765 }
766 }
767
768 private static final String[] EMPTY_STRING_ARRAY = new String[0];
769
770 /**
771 * Returns all known unremoved children of this node.
772 *
773 * @return all known unremoved children of this node.
774 */
775 protected final AbstractPreferences[] cachedChildren() {
776 return kidCache.values().toArray(EMPTY_ABSTRACT_PREFS_ARRAY);
777 }
778
779 private static final AbstractPreferences[] EMPTY_ABSTRACT_PREFS_ARRAY
780 = new AbstractPreferences[0];
781
782 /**
783 * Implements the {@code parent} method as per the specification in
784 * {@link Preferences#parent()}.
785 *
786 * <p>This implementation obtains this preference node's lock, checks that
787 * the node has not been removed and returns the parent value that was
788 * passed to this node's constructor.
789 *
790 * @return the parent of this preference node.
791 * @throws IllegalStateException if this node (or an ancestor) has been
792 * removed with the {@link #removeNode()} method.
793 */
794 public Preferences parent() {
795 synchronized(lock) {
796 if (removed)
797 throw new IllegalStateException("Node has been removed.");
798
799 return parent;
800 }
801 }
802
803 /**
804 * Implements the {@code node} method as per the specification in
805 * {@link Preferences#node(String)}.
806 *
807 * <p>This implementation obtains this preference node's lock and checks
808 * that the node has not been removed. If {@code path} is {@code ""},
809 * this node is returned; if {@code path} is {@code "/"}, this node's
810 * root is returned. If the first character in {@code path} is
811 * not {@code '/'}, the implementation breaks {@code path} into
812 * tokens and recursively traverses the path from this node to the
813 * named node, "consuming" a name and a slash from {@code path} at
814 * each step of the traversal. At each step, the current node is locked
815 * and the node's child-cache is checked for the named node. If it is
816 * not found, the name is checked to make sure its length does not
817 * exceed {@code MAX_NAME_LENGTH}. Then the {@link #childSpi(String)}
818 * method is invoked, and the result stored in this node's child-cache.
819 * If the newly created {@code Preferences} object's {@link #newNode}
820 * field is {@code true} and there are any node change listeners,
821 * a notification event is enqueued for processing by the event dispatch
822 * thread.
823 *
824 * <p>When there are no more tokens, the last value found in the
825 * child-cache or returned by {@code childSpi} is returned by this
826 * method. If during the traversal, two {@code "/"} tokens occur
827 * consecutively, or the final token is {@code "/"} (rather than a name),
828 * an appropriate {@code IllegalArgumentException} is thrown.
829 *
830 * <p> If the first character of {@code path} is {@code '/'}
831 * (indicating an absolute path name) this preference node's
832 * lock is dropped prior to breaking {@code path} into tokens, and
833 * this method recursively traverses the path starting from the root
834 * (rather than starting from this node). The traversal is otherwise
835 * identical to the one described for relative path names. Dropping
836 * the lock on this node prior to commencing the traversal at the root
837 * node is essential to avoid the possibility of deadlock, as per the
838 * {@link #lock locking invariant}.
839 *
840 * @param path the path name of the preference node to return.
841 * @return the specified preference node.
842 * @throws IllegalArgumentException if the path name is invalid (i.e.,
843 * it contains multiple consecutive slash characters, or ends
844 * with a slash character and is more than one character long).
845 * @throws IllegalStateException if this node (or an ancestor) has been
846 * removed with the {@link #removeNode()} method.
847 */
848 public Preferences node(String path) {
849 synchronized(lock) {
850 if (removed)
851 throw new IllegalStateException("Node has been removed.");
852 if (path.equals(""))
853 return this;
854 if (path.equals("/"))
855 return root;
856 if (path.charAt(0) != '/')
857 return node(new StringTokenizer(path, "/", true));
858 }
859
860 // Absolute path. Note that we've dropped our lock to avoid deadlock
861 return root.node(new StringTokenizer(path.substring(1), "/", true));
862 }
863
864 /**
865 * tokenizer contains <name> {'/' <name>}*
866 */
867 private Preferences node(StringTokenizer path) {
868 String token = path.nextToken();
869 if (token.equals("/")) // Check for consecutive slashes
870 throw new IllegalArgumentException("Consecutive slashes in path");
871 synchronized(lock) {
872 AbstractPreferences child = kidCache.get(token);
873 if (child == null) {
874 if (token.length() > MAX_NAME_LENGTH)
875 throw new IllegalArgumentException(
876 "Node name " + token + " too long");
877 child = childSpi(token);
878 if (child.newNode)
879 enqueueNodeAddedEvent(child);
880 kidCache.put(token, child);
881 }
882 if (!path.hasMoreTokens())
883 return child;
884 path.nextToken(); // Consume slash
885 if (!path.hasMoreTokens())
886 throw new IllegalArgumentException("Path ends with slash");
887 return child.node(path);
888 }
889 }
890
891 /**
892 * Implements the {@code nodeExists} method as per the specification in
893 * {@link Preferences#nodeExists(String)}.
894 *
895 * <p>This implementation is very similar to {@link #node(String)},
896 * except that {@link #getChild(String)} is used instead of {@link
897 * #childSpi(String)}.
898 *
899 * @param path the path name of the node whose existence is to be checked.
900 * @return true if the specified node exists.
901 * @throws BackingStoreException if this operation cannot be completed
902 * due to a failure in the backing store, or inability to
903 * communicate with it.
904 * @throws IllegalArgumentException if the path name is invalid (i.e.,
905 * it contains multiple consecutive slash characters, or ends
906 * with a slash character and is more than one character long).
907 * @throws IllegalStateException if this node (or an ancestor) has been
908 * removed with the {@link #removeNode()} method and
909 * {@code pathname} is not the empty string ({@code ""}).
910 */
911 public boolean nodeExists(String path)
912 throws BackingStoreException
913 {
914 synchronized(lock) {
915 if (path.equals(""))
916 return !removed;
917 if (removed)
918 throw new IllegalStateException("Node has been removed.");
919 if (path.equals("/"))
920 return true;
921 if (path.charAt(0) != '/')
922 return nodeExists(new StringTokenizer(path, "/", true));
923 }
924
925 // Absolute path. Note that we've dropped our lock to avoid deadlock
926 return root.nodeExists(new StringTokenizer(path.substring(1), "/",
927 true));
928 }
929
930 /**
931 * tokenizer contains <name> {'/' <name>}*
932 */
933 private boolean nodeExists(StringTokenizer path)
934 throws BackingStoreException
935 {
936 String token = path.nextToken();
937 if (token.equals("/")) // Check for consecutive slashes
938 throw new IllegalArgumentException("Consecutive slashes in path");
939 synchronized(lock) {
940 AbstractPreferences child = kidCache.get(token);
941 if (child == null)
942 child = getChild(token);
943 if (child==null)
944 return false;
945 if (!path.hasMoreTokens())
946 return true;
947 path.nextToken(); // Consume slash
948 if (!path.hasMoreTokens())
949 throw new IllegalArgumentException("Path ends with slash");
950 return child.nodeExists(path);
951 }
952 }
953
954 /**
955
956 * Implements the {@code removeNode()} method as per the specification in
957 * {@link Preferences#removeNode()}.
958 *
959 * <p>This implementation checks to see that this node is the root; if so,
960 * it throws an appropriate exception. Then, it locks this node's parent,
961 * and calls a recursive helper method that traverses the subtree rooted at
962 * this node. The recursive method locks the node on which it was called,
963 * checks that it has not already been removed, and then ensures that all
964 * of its children are cached: The {@link #childrenNamesSpi()} method is
965 * invoked and each returned child name is checked for containment in the
966 * child-cache. If a child is not already cached, the {@link
967 * #childSpi(String)} method is invoked to create a {@code Preferences}
968 * instance for it, and this instance is put into the child-cache. Then
969 * the helper method calls itself recursively on each node contained in its
970 * child-cache. Next, it invokes {@link #removeNodeSpi()}, marks itself
971 * as removed, and removes itself from its parent's child-cache. Finally,
972 * if there are any node change listeners, it enqueues a notification
973 * event for processing by the event dispatch thread.
974 *
975 * <p>Note that the helper method is always invoked with all ancestors up
976 * to the "closest non-removed ancestor" locked.
977 *
978 * @throws IllegalStateException if this node (or an ancestor) has already
979 * been removed with the {@link #removeNode()} method.
980 * @throws UnsupportedOperationException if this method is invoked on
981 * the root node.
982 * @throws BackingStoreException if this operation cannot be completed
983 * due to a failure in the backing store, or inability to
984 * communicate with it.
985 */
986 public void removeNode() throws BackingStoreException {
987 if (this==root)
988 throw new UnsupportedOperationException("Can't remove the root!");
989 synchronized(parent.lock) {
990 removeNode2();
991 parent.kidCache.remove(name);
992 }
993 }
994
995 /*
996 * Called with locks on all nodes on path from parent of "removal root"
997 * to this (including the former but excluding the latter).
998 */
999 private void removeNode2() throws BackingStoreException {
1000 synchronized(lock) {
1001 if (removed)
1002 throw new IllegalStateException("Node already removed.");
1003
1004 // Ensure that all children are cached
1005 String[] kidNames = childrenNamesSpi();
1006 for (String kidName : kidNames)
1007 if (!kidCache.containsKey(kidName))
1008 kidCache.put(kidName, childSpi(kidName));
1009
1010 // Recursively remove all cached children
1011 for (Iterator<AbstractPreferences> i = kidCache.values().iterator();
1012 i.hasNext();) {
1013 try {
1014 i.next().removeNode2();
1015 i.remove();
1016 } catch (BackingStoreException x) { }
1017 }
1018
1019 // Now we have no descendants - it's time to die!
1020 removeNodeSpi();
1021 removed = true;
1022 parent.enqueueNodeRemovedEvent(this);
1023 }
1024 }
1025
1026 /**
1027 * Implements the {@code name} method as per the specification in
1028 * {@link Preferences#name()}.
1029 *
1030 * <p>This implementation merely returns the name that was
1031 * passed to this node's constructor.
1032 *
1033 * @return this preference node's name, relative to its parent.
1034 */
1035 public String name() {
1036 return name;
1037 }
1038
1039 /**
1040 * Implements the {@code absolutePath} method as per the specification in
1041 * {@link Preferences#absolutePath()}.
1042 *
1043 * <p>This implementation merely returns the absolute path name that
1044 * was computed at the time that this node was constructed (based on
1045 * the name that was passed to this node's constructor, and the names
1046 * that were passed to this node's ancestors' constructors).
1047 *
1048 * @return this preference node's absolute path name.
1049 */
1050 public String absolutePath() {
1051 return absolutePath;
1052 }
1053
1054 /**
1055 * Implements the {@code isUserNode} method as per the specification in
1056 * {@link Preferences#isUserNode()}.
1057 *
1058 * <p>This implementation compares this node's root node (which is stored
1059 * in a private field) with the value returned by
1060 * {@link Preferences#userRoot()}. If the two object references are
1061 * identical, this method returns true.
1062 *
1063 * @return {@code true} if this preference node is in the user
1064 * preference tree, {@code false} if it's in the system
1065 * preference tree.
1066 */
1067 public boolean isUserNode() {
1068 return AccessController.doPrivileged(
1069 new PrivilegedAction<Boolean>() {
1070 public Boolean run() {
1071 return root == Preferences.userRoot();
1072 }
1073 }).booleanValue();
1074 }
1075
1076 public void addPreferenceChangeListener(PreferenceChangeListener pcl) {
1077 if (pcl==null)
1078 throw new NullPointerException("Change listener is null.");
1079 synchronized(lock) {
1080 if (removed)
1081 throw new IllegalStateException("Node has been removed.");
1082
1083 // Copy-on-write
1084 PreferenceChangeListener[] old = prefListeners;
1085 prefListeners = new PreferenceChangeListener[old.length + 1];
1086 System.arraycopy(old, 0, prefListeners, 0, old.length);
1087 prefListeners[old.length] = pcl;
1088 }
1089 startEventDispatchThreadIfNecessary();
1090 }
1091
1092 public void removePreferenceChangeListener(PreferenceChangeListener pcl) {
1093 synchronized(lock) {
1094 if (removed)
1095 throw new IllegalStateException("Node has been removed.");
1096 if ((prefListeners == null) || (prefListeners.length == 0))
1097 throw new IllegalArgumentException("Listener not registered.");
1098
1099 // Copy-on-write
1100 PreferenceChangeListener[] newPl =
1101 new PreferenceChangeListener[prefListeners.length - 1];
1102 int i = 0;
1103 while (i < newPl.length && prefListeners[i] != pcl)
1104 newPl[i] = prefListeners[i++];
1105
1106 if (i == newPl.length && prefListeners[i] != pcl)
1107 throw new IllegalArgumentException("Listener not registered.");
1108 while (i < newPl.length)
1109 newPl[i] = prefListeners[++i];
1110 prefListeners = newPl;
1111 }
1112 }
1113
1114 public void addNodeChangeListener(NodeChangeListener ncl) {
1115 if (ncl==null)
1116 throw new NullPointerException("Change listener is null.");
1117 synchronized(lock) {
1118 if (removed)
1119 throw new IllegalStateException("Node has been removed.");
1120
1121 // Copy-on-write
1122 if (nodeListeners == null) {
1123 nodeListeners = new NodeChangeListener[1];
1124 nodeListeners[0] = ncl;
1125 } else {
1126 NodeChangeListener[] old = nodeListeners;
1127 nodeListeners = new NodeChangeListener[old.length + 1];
1128 System.arraycopy(old, 0, nodeListeners, 0, old.length);
1129 nodeListeners[old.length] = ncl;
1130 }
1131 }
1132 startEventDispatchThreadIfNecessary();
1133 }
1134
1135 public void removeNodeChangeListener(NodeChangeListener ncl) {
1136 synchronized(lock) {
1137 if (removed)
1138 throw new IllegalStateException("Node has been removed.");
1139 if ((nodeListeners == null) || (nodeListeners.length == 0))
1140 throw new IllegalArgumentException("Listener not registered.");
1141
1142 // Copy-on-write
1143 int i = 0;
1144 while (i < nodeListeners.length && nodeListeners[i] != ncl)
1145 i++;
1146 if (i == nodeListeners.length)
1147 throw new IllegalArgumentException("Listener not registered.");
1148 NodeChangeListener[] newNl =
1149 new NodeChangeListener[nodeListeners.length - 1];
1150 if (i != 0)
1151 System.arraycopy(nodeListeners, 0, newNl, 0, i);
1152 if (i != newNl.length)
1153 System.arraycopy(nodeListeners, i + 1,
1154 newNl, i, newNl.length - i);
1155 nodeListeners = newNl;
1156 }
1157 }
1158
1159 // "SPI" METHODS
1160
1161 /**
1162 * Put the given key-value association into this preference node. It is
1163 * guaranteed that {@code key} and {@code value} are non-null and of
1164 * legal length. Also, it is guaranteed that this node has not been
1165 * removed. (The implementor needn't check for any of these things.)
1166 *
1167 * <p>This method is invoked with the lock on this node held.
1168 * @param key the key
1169 * @param value the value
1170 */
1171 protected abstract void putSpi(String key, String value);
1172
1173 /**
1174 * Return the value associated with the specified key at this preference
1175 * node, or {@code null} if there is no association for this key, or the
1176 * association cannot be determined at this time. It is guaranteed that
1177 * {@code key} is non-null. Also, it is guaranteed that this node has
1178 * not been removed. (The implementor needn't check for either of these
1179 * things.)
1180 *
1181 * <p> Generally speaking, this method should not throw an exception
1182 * under any circumstances. If, however, if it does throw an exception,
1183 * the exception will be intercepted and treated as a {@code null}
1184 * return value.
1185 *
1186 * <p>This method is invoked with the lock on this node held.
1187 *
1188 * @param key the key
1189 * @return the value associated with the specified key at this preference
1190 * node, or {@code null} if there is no association for this
1191 * key, or the association cannot be determined at this time.
1192 */
1193 protected abstract String getSpi(String key);
1194
1195 /**
1196 * Remove the association (if any) for the specified key at this
1197 * preference node. It is guaranteed that {@code key} is non-null.
1198 * Also, it is guaranteed that this node has not been removed.
1199 * (The implementor needn't check for either of these things.)
1200 *
1201 * <p>This method is invoked with the lock on this node held.
1202 * @param key the key
1203 */
1204 protected abstract void removeSpi(String key);
1205
1206 /**
1207 * Removes this preference node, invalidating it and any preferences that
1208 * it contains. The named child will have no descendants at the time this
1209 * invocation is made (i.e., the {@link Preferences#removeNode()} method
1210 * invokes this method repeatedly in a bottom-up fashion, removing each of
1211 * a node's descendants before removing the node itself).
1212 *
1213 * <p>This method is invoked with the lock held on this node and its
1214 * parent (and all ancestors that are being removed as a
1215 * result of a single invocation to {@link Preferences#removeNode()}).
1216 *
1217 * <p>The removal of a node needn't become persistent until the
1218 * {@code flush} method is invoked on this node (or an ancestor).
1219 *
1220 * <p>If this node throws a {@code BackingStoreException}, the exception
1221 * will propagate out beyond the enclosing {@link #removeNode()}
1222 * invocation.
1223 *
1224 * @throws BackingStoreException if this operation cannot be completed
1225 * due to a failure in the backing store, or inability to
1226 * communicate with it.
1227 */
1228 protected abstract void removeNodeSpi() throws BackingStoreException;
1229
1230 /**
1231 * Returns all of the keys that have an associated value in this
1232 * preference node. (The returned array will be of size zero if
1233 * this node has no preferences.) It is guaranteed that this node has not
1234 * been removed.
1235 *
1236 * <p>This method is invoked with the lock on this node held.
1237 *
1238 * <p>If this node throws a {@code BackingStoreException}, the exception
1239 * will propagate out beyond the enclosing {@link #keys()} invocation.
1240 *
1241 * @return an array of the keys that have an associated value in this
1242 * preference node.
1243 * @throws BackingStoreException if this operation cannot be completed
1244 * due to a failure in the backing store, or inability to
1245 * communicate with it.
1246 */
1247 protected abstract String[] keysSpi() throws BackingStoreException;
1248
1249 /**
1250 * Returns the names of the children of this preference node. (The
1251 * returned array will be of size zero if this node has no children.)
1252 * This method need not return the names of any nodes already cached,
1253 * but may do so without harm.
1254 *
1255 * <p>This method is invoked with the lock on this node held.
1256 *
1257 * <p>If this node throws a {@code BackingStoreException}, the exception
1258 * will propagate out beyond the enclosing {@link #childrenNames()}
1259 * invocation.
1260 *
1261 * @return an array containing the names of the children of this
1262 * preference node.
1263 * @throws BackingStoreException if this operation cannot be completed
1264 * due to a failure in the backing store, or inability to
1265 * communicate with it.
1266 */
1267 protected abstract String[] childrenNamesSpi()
1268 throws BackingStoreException;
1269
1270 /**
1271 * Returns the named child if it exists, or {@code null} if it does not.
1272 * It is guaranteed that {@code nodeName} is non-null, non-empty,
1273 * does not contain the slash character ('/'), and is no longer than
1274 * {@link #MAX_NAME_LENGTH} characters. Also, it is guaranteed
1275 * that this node has not been removed. (The implementor needn't check
1276 * for any of these things if he chooses to override this method.)
1277 *
1278 * <p>Finally, it is guaranteed that the named node has not been returned
1279 * by a previous invocation of this method or {@link #childSpi} after the
1280 * last time that it was removed. In other words, a cached value will
1281 * always be used in preference to invoking this method. (The implementor
1282 * needn't maintain his own cache of previously returned children if he
1283 * chooses to override this method.)
1284 *
1285 * <p>This implementation obtains this preference node's lock, invokes
1286 * {@link #childrenNames()} to get an array of the names of this node's
1287 * children, and iterates over the array comparing the name of each child
1288 * with the specified node name. If a child node has the correct name,
1289 * the {@link #childSpi(String)} method is invoked and the resulting
1290 * node is returned. If the iteration completes without finding the
1291 * specified name, {@code null} is returned.
1292 *
1293 * @param nodeName name of the child to be searched for.
1294 * @return the named child if it exists, or null if it does not.
1295 * @throws BackingStoreException if this operation cannot be completed
1296 * due to a failure in the backing store, or inability to
1297 * communicate with it.
1298 */
1299 protected AbstractPreferences getChild(String nodeName)
1300 throws BackingStoreException {
1301 synchronized(lock) {
1302 // assert kidCache.get(nodeName)==null;
1303 String[] kidNames = childrenNames();
1304 for (String kidName : kidNames)
1305 if (kidName.equals(nodeName))
1306 return childSpi(kidName);
1307 }
1308 return null;
1309 }
1310
1311 /**
1312 * Returns the named child of this preference node, creating it if it does
1313 * not already exist. It is guaranteed that {@code name} is non-null,
1314 * non-empty, does not contain the slash character ('/'), and is no longer
1315 * than {@link #MAX_NAME_LENGTH} characters. Also, it is guaranteed that
1316 * this node has not been removed. (The implementor needn't check for any
1317 * of these things.)
1318 *
1319 * <p>Finally, it is guaranteed that the named node has not been returned
1320 * by a previous invocation of this method or {@link #getChild(String)}
1321 * after the last time that it was removed. In other words, a cached
1322 * value will always be used in preference to invoking this method.
1323 * Subclasses need not maintain their own cache of previously returned
1324 * children.
1325 *
1326 * <p>The implementer must ensure that the returned node has not been
1327 * removed. If a like-named child of this node was previously removed, the
1328 * implementer must return a newly constructed {@code AbstractPreferences}
1329 * node; once removed, an {@code AbstractPreferences} node
1330 * cannot be "resuscitated."
1331 *
1332 * <p>If this method causes a node to be created, this node is not
1333 * guaranteed to be persistent until the {@code flush} method is
1334 * invoked on this node or one of its ancestors (or descendants).
1335 *
1336 * <p>This method is invoked with the lock on this node held.
1337 *
1338 * @param name The name of the child node to return, relative to
1339 * this preference node.
1340 * @return The named child node.
1341 */
1342 protected abstract AbstractPreferences childSpi(String name);
1343
1344 /**
1345 * Returns the absolute path name of this preferences node.
1346 */
1347 public String toString() {
1348 return (this.isUserNode() ? "User" : "System") +
1349 " Preference Node: " + this.absolutePath();
1350 }
1351
1352 /**
1353 * Implements the {@code sync} method as per the specification in
1354 * {@link Preferences#sync()}.
1355 *
1356 * <p>This implementation calls a recursive helper method that locks this
1357 * node, invokes syncSpi() on it, unlocks this node, and recursively
1358 * invokes this method on each "cached child." A cached child is a child
1359 * of this node that has been created in this VM and not subsequently
1360 * removed. In effect, this method does a depth first traversal of the
1361 * "cached subtree" rooted at this node, calling syncSpi() on each node in
1362 * the subTree while only that node is locked. Note that syncSpi() is
1363 * invoked top-down.
1364 *
1365 * @throws BackingStoreException if this operation cannot be completed
1366 * due to a failure in the backing store, or inability to
1367 * communicate with it.
1368 * @throws IllegalStateException if this node (or an ancestor) has been
1369 * removed with the {@link #removeNode()} method.
1370 * @see #flush()
1371 */
1372 public void sync() throws BackingStoreException {
1373 sync2();
1374 }
1375
1376 private void sync2() throws BackingStoreException {
1377 AbstractPreferences[] cachedKids;
1378
1379 synchronized(lock) {
1380 if (removed)
1381 throw new IllegalStateException("Node has been removed");
1382 syncSpi();
1383 cachedKids = cachedChildren();
1384 }
1385
1386 for (AbstractPreferences cachedKid : cachedKids)
1387 cachedKid.sync2();
1388 }
1389
1390 /**
1391 * This method is invoked with this node locked. The contract of this
1392 * method is to synchronize any cached preferences stored at this node
1393 * with any stored in the backing store. (It is perfectly possible that
1394 * this node does not exist on the backing store, either because it has
1395 * been deleted by another VM, or because it has not yet been created.)
1396 * Note that this method should <i>not</i> synchronize the preferences in
1397 * any subnodes of this node. If the backing store naturally syncs an
1398 * entire subtree at once, the implementer is encouraged to override
1399 * sync(), rather than merely overriding this method.
1400 *
1401 * <p>If this node throws a {@code BackingStoreException}, the exception
1402 * will propagate out beyond the enclosing {@link #sync()} invocation.
1403 *
1404 * @throws BackingStoreException if this operation cannot be completed
1405 * due to a failure in the backing store, or inability to
1406 * communicate with it.
1407 */
1408 protected abstract void syncSpi() throws BackingStoreException;
1409
1410 /**
1411 * Implements the {@code flush} method as per the specification in
1412 * {@link Preferences#flush()}.
1413 *
1414 * <p>This implementation calls a recursive helper method that locks this
1415 * node, invokes flushSpi() on it, unlocks this node, and recursively
1416 * invokes this method on each "cached child." A cached child is a child
1417 * of this node that has been created in this VM and not subsequently
1418 * removed. In effect, this method does a depth first traversal of the
1419 * "cached subtree" rooted at this node, calling flushSpi() on each node in
1420 * the subTree while only that node is locked. Note that flushSpi() is
1421 * invoked top-down.
1422 *
1423 * <p> If this method is invoked on a node that has been removed with
1424 * the {@link #removeNode()} method, flushSpi() is invoked on this node,
1425 * but not on others.
1426 *
1427 * @throws BackingStoreException if this operation cannot be completed
1428 * due to a failure in the backing store, or inability to
1429 * communicate with it.
1430 * @see #flush()
1431 */
1432 public void flush() throws BackingStoreException {
1433 flush2();
1434 }
1435
1436 private void flush2() throws BackingStoreException {
1437 AbstractPreferences[] cachedKids;
1438
1439 synchronized(lock) {
1440 flushSpi();
1441 if(removed)
1442 return;
1443 cachedKids = cachedChildren();
1444 }
1445
1446 for (AbstractPreferences cachedKid : cachedKids)
1447 cachedKid.flush2();
1448 }
1449
1450 /**
1451 * This method is invoked with this node locked. The contract of this
1452 * method is to force any cached changes in the contents of this
1453 * preference node to the backing store, guaranteeing their persistence.
1454 * (It is perfectly possible that this node does not exist on the backing
1455 * store, either because it has been deleted by another VM, or because it
1456 * has not yet been created.) Note that this method should <i>not</i>
1457 * flush the preferences in any subnodes of this node. If the backing
1458 * store naturally flushes an entire subtree at once, the implementer is
1459 * encouraged to override flush(), rather than merely overriding this
1460 * method.
1461 *
1462 * <p>If this node throws a {@code BackingStoreException}, the exception
1463 * will propagate out beyond the enclosing {@link #flush()} invocation.
1464 *
1465 * @throws BackingStoreException if this operation cannot be completed
1466 * due to a failure in the backing store, or inability to
1467 * communicate with it.
1468 */
1469 protected abstract void flushSpi() throws BackingStoreException;
1470
1471 /**
1472 * Returns {@code true} iff this node (or an ancestor) has been
1473 * removed with the {@link #removeNode()} method. This method
1474 * locks this node prior to returning the contents of the private
1475 * field used to track this state.
1476 *
1477 * @return {@code true} iff this node (or an ancestor) has been
1478 * removed with the {@link #removeNode()} method.
1479 */
1480 protected boolean isRemoved() {
1481 synchronized(lock) {
1482 return removed;
1483 }
1484 }
1485
1486 /**
1487 * Queue of pending notification events. When a preference or node
1488 * change event for which there are one or more listeners occurs,
1489 * it is placed on this queue and the queue is notified. A background
1490 * thread waits on this queue and delivers the events. This decouples
1491 * event delivery from preference activity, greatly simplifying
1492 * locking and reducing opportunity for deadlock.
1493 */
1494 private static final List<EventObject> eventQueue = new LinkedList<>();
1495
1496 /**
1497 * These two classes are used to distinguish NodeChangeEvents on
1498 * eventQueue so the event dispatch thread knows whether to call
1499 * childAdded or childRemoved.
1500 */
1501 private class NodeAddedEvent extends NodeChangeEvent {
1502 private static final long serialVersionUID = -6743557530157328528L;
1503 NodeAddedEvent(Preferences parent, Preferences child) {
1504 super(parent, child);
1505 }
1506 }
1507 private class NodeRemovedEvent extends NodeChangeEvent {
1508 private static final long serialVersionUID = 8735497392918824837L;
1509 NodeRemovedEvent(Preferences parent, Preferences child) {
1510 super(parent, child);
1511 }
1512 }
1513
1514 /**
1515 * A single background thread ("the event notification thread") monitors
1516 * the event queue and delivers events that are placed on the queue.
1517 */
1518 private static class EventDispatchThread extends ManagedLocalsThread {
1519 public void run() {
1520 while(true) {
1521 // Wait on eventQueue till an event is present
1522 EventObject event = null;
1523 synchronized(eventQueue) {
1524 try {
1525 while (eventQueue.isEmpty())
1526 eventQueue.wait();
1527 event = eventQueue.remove(0);
1528 } catch (InterruptedException e) {
1529 // XXX Log "Event dispatch thread interrupted. Exiting"
1530 return;
1531 }
1532 }
1533
1534 // Now we have event & hold no locks; deliver evt to listeners
1535 AbstractPreferences src=(AbstractPreferences)event.getSource();
1536 if (event instanceof PreferenceChangeEvent) {
1537 PreferenceChangeEvent pce = (PreferenceChangeEvent)event;
1538 PreferenceChangeListener[] listeners = src.prefListeners();
1539 for (PreferenceChangeListener listener : listeners)
1540 listener.preferenceChange(pce);
1541 } else {
1542 NodeChangeEvent nce = (NodeChangeEvent)event;
1543 NodeChangeListener[] listeners = src.nodeListeners();
1544 if (nce instanceof NodeAddedEvent) {
1545 for (NodeChangeListener listener : listeners)
1546 listener.childAdded(nce);
1547 } else {
1548 // assert nce instanceof NodeRemovedEvent;
1549 for (NodeChangeListener listener : listeners)
1550 listener.childRemoved(nce);
1551 }
1552 }
1553 }
1554 }
1555 }
1556
1557 private static Thread eventDispatchThread = null;
1558
1559 /**
1560 * This method starts the event dispatch thread the first time it
1561 * is called. The event dispatch thread will be started only
1562 * if someone registers a listener.
1563 */
1564 private static synchronized void startEventDispatchThreadIfNecessary() {
1565 if (eventDispatchThread == null) {
1566 // XXX Log "Starting event dispatch thread"
1567 eventDispatchThread = new EventDispatchThread();
1568 eventDispatchThread.setDaemon(true);
1569 eventDispatchThread.start();
1570 }
1571 }
1572
1573 /**
1574 * Return this node's preference/node change listeners. Even though
1575 * we're using a copy-on-write lists, we use synchronized accessors to
1576 * ensure information transmission from the writing thread to the
1577 * reading thread.
1578 */
1579 PreferenceChangeListener[] prefListeners() {
1580 synchronized(lock) {
1581 return prefListeners;
1582 }
1583 }
1584 NodeChangeListener[] nodeListeners() {
1585 synchronized(lock) {
1586 return nodeListeners;
1587 }
1588 }
1589
1590 /**
1591 * Enqueue a preference change event for delivery to registered
1592 * preference change listeners unless there are no registered
1593 * listeners. Invoked with this.lock held.
1594 */
1595 private void enqueuePreferenceChangeEvent(String key, String newValue) {
1596 if (prefListeners.length != 0) {
1597 synchronized(eventQueue) {
1598 eventQueue.add(new PreferenceChangeEvent(this, key, newValue));
1599 eventQueue.notify();
1600 }
1601 }
1602 }
1603
1604 /**
1605 * Enqueue a "node added" event for delivery to registered node change
1606 * listeners unless there are no registered listeners. Invoked with
1607 * this.lock held.
1608 */
1609 private void enqueueNodeAddedEvent(Preferences child) {
1610 if (nodeListeners.length != 0) {
1611 synchronized(eventQueue) {
1612 eventQueue.add(new NodeAddedEvent(this, child));
1613 eventQueue.notify();
1614 }
1615 }
1616 }
1617
1618 /**
1619 * Enqueue a "node removed" event for delivery to registered node change
1620 * listeners unless there are no registered listeners. Invoked with
1621 * this.lock held.
1622 */
1623 private void enqueueNodeRemovedEvent(Preferences child) {
1624 if (nodeListeners.length != 0) {
1625 synchronized(eventQueue) {
1626 eventQueue.add(new NodeRemovedEvent(this, child));
1627 eventQueue.notify();
1628 }
1629 }
1630 }
1631
1632 /**
1633 * Implements the {@code exportNode} method as per the specification in
1634 * {@link Preferences#exportNode(OutputStream)}.
1635 *
1636 * @param os the output stream on which to emit the XML document.
1637 * @throws IOException if writing to the specified output stream
1638 * results in an {@code IOException}.
1639 * @throws BackingStoreException if preference data cannot be read from
1640 * backing store.
1641 */
1642 public void exportNode(OutputStream os)
1643 throws IOException, BackingStoreException
1644 {
1645 XmlSupport.export(os, this, false);
1646 }
1647
1648 /**
1649 * Implements the {@code exportSubtree} method as per the specification in
1650 * {@link Preferences#exportSubtree(OutputStream)}.
1651 *
1652 * @param os the output stream on which to emit the XML document.
1653 * @throws IOException if writing to the specified output stream
1654 * results in an {@code IOException}.
1655 * @throws BackingStoreException if preference data cannot be read from
1656 * backing store.
1657 */
1658 public void exportSubtree(OutputStream os)
1659 throws IOException, BackingStoreException
1660 {
1661 XmlSupport.export(os, this, true);
1662 }
1663 }