1 /*
2 * Copyright (c) 2000, 2010, 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 // 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 <tt>Preferences</tt> implementers only.
43 * Normal users of the <tt>Preferences</tt> 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 <tt>getSpi</tt> 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 <tt>removeNodeSpi, keysSpi,
62 * childrenNamesSpi, syncSpi</tt> and <tt>flushSpi</tt> 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 * <tt>BackingStoreException</tt>, 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, all subsequent invocations
81 * of <tt>flush()</tt> and <tt>sync</tt> should return <tt>false</tt>, as
82 * returning <tt>true</tt> would imply that all previous operations had
83 * successfully been made permanent.
84 *
85 * <p>There is one circumstance under which <tt>putSpi, removeSpi and
86 * childSpi</tt> <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 <tt>Preferences</tt>
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 <tt>Preferences</tt>
110 * implementations may have the user identity change from request to request,
111 * implicitly passed to <tt>Preferences</tt> 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 <tt>Preferences</tt> instance. The latter behavior conflicts
117 * with normal <tt>Preferences</tt> 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 * Our name relative to parent.
126 */
127 private final String name;
128
129 /**
130 * Our absolute path name.
131 */
132 private final String absolutePath;
133
134 /**
135 * Our parent node.
136 */
137 final AbstractPreferences parent;
138
139 /**
140 * Our root node.
141 */
142 private final AbstractPreferences root; // Relative to this node
143
144 /**
145 * This field should be <tt>true</tt> if this node did not exist in the
146 * backing store prior to the creation of this object. The field
147 * is initialized to false, but may be set to true by a subclass
148 * constructor (and should not be modified thereafter). This field
149 * indicates whether a node change event should be fired when
150 * creation is complete.
151 */
152 protected boolean newNode = false;
153
154 /**
155 * All known unremoved children of this node. (This "cache" is consulted
156 * prior to calling childSpi() or getChild().
157 */
158 private Map<String, AbstractPreferences> kidCache = new HashMap<>();
159
160 /**
161 * This field is used to keep track of whether or not this node has
162 * been removed. Once it's set to true, it will never be reset to false.
163 */
164 private boolean removed = false;
165
166 /**
167 * Registered preference change listeners.
168 */
169 private PreferenceChangeListener[] prefListeners =
170 new PreferenceChangeListener[0];
171
172 /**
173 * Registered node change listeners.
174 */
175 private NodeChangeListener[] nodeListeners = new NodeChangeListener[0];
176
177 /**
178 * An object whose monitor is used to lock this node. This object
179 * is used in preference to the node itself to reduce the likelihood of
180 * intentional or unintentional denial of service due to a locked node.
181 * To avoid deadlock, a node is <i>never</i> locked by a thread that
182 * holds a lock on a descendant of that node.
183 */
184 protected final Object lock = new Object();
185
186 /**
187 * Creates a preference node with the specified parent and the specified
188 * name relative to its parent.
189 *
190 * @param parent the parent of this preference node, or null if this
191 * is the root.
192 * @param name the name of this preference node, relative to its parent,
193 * or <tt>""</tt> if this is the root.
194 * @throws IllegalArgumentException if <tt>name</tt> contains a slash
195 * (<tt>'/'</tt>), or <tt>parent</tt> is <tt>null</tt> and
196 * name isn't <tt>""</tt>.
197 */
198 protected AbstractPreferences(AbstractPreferences parent, String name) {
199 if (parent==null) {
200 if (!name.equals(""))
201 throw new IllegalArgumentException("Root name '"+name+
202 "' must be \"\"");
203 this.absolutePath = "/";
204 root = this;
205 } else {
206 if (name.indexOf('/') != -1)
207 throw new IllegalArgumentException("Name '" + name +
208 "' contains '/'");
209 if (name.equals(""))
210 throw new IllegalArgumentException("Illegal name: empty string");
211
212 root = parent.root;
213 absolutePath = (parent==root ? "/" + name
214 : parent.absolutePath() + "/" + name);
215 }
216 this.name = name;
217 this.parent = parent;
218 }
219
220 /**
221 * Implements the <tt>put</tt> method as per the specification in
222 * {@link Preferences#put(String,String)}.
223 *
224 * <p>This implementation checks that the key and value are legal,
225 * obtains this preference node's lock, checks that the node
226 * has not been removed, invokes {@link #putSpi(String,String)}, and if
227 * there are any preference change listeners, enqueues a notification
228 * event for processing by the event dispatch thread.
229 *
230 * @param key key with which the specified value is to be associated.
231 * @param value value to be associated with the specified key.
232 * @throws NullPointerException if key or value is <tt>null</tt>.
233 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
234 * <tt>MAX_KEY_LENGTH</tt> or if <tt>value.length</tt> exceeds
235 * <tt>MAX_VALUE_LENGTH</tt>.
236 * @throws IllegalStateException if this node (or an ancestor) has been
237 * removed with the {@link #removeNode()} method.
238 */
239 public void put(String key, String value) {
240 if (key==null || value==null)
241 throw new NullPointerException();
242 if (key.length() > MAX_KEY_LENGTH)
243 throw new IllegalArgumentException("Key too long: "+key);
244 if (value.length() > MAX_VALUE_LENGTH)
245 throw new IllegalArgumentException("Value too long: "+value);
246
247 synchronized(lock) {
248 if (removed)
249 throw new IllegalStateException("Node has been removed.");
250
251 putSpi(key, value);
252 enqueuePreferenceChangeEvent(key, value);
253 }
254 }
255
256 /**
257 * Implements the <tt>get</tt> method as per the specification in
258 * {@link Preferences#get(String,String)}.
259 *
260 * <p>This implementation first checks to see if <tt>key</tt> is
261 * <tt>null</tt> throwing a <tt>NullPointerException</tt> if this is
262 * the case. Then it obtains this preference node's lock,
263 * checks that the node has not been removed, invokes {@link
264 * #getSpi(String)}, and returns the result, unless the <tt>getSpi</tt>
265 * invocation returns <tt>null</tt> or throws an exception, in which case
266 * this invocation returns <tt>def</tt>.
267 *
268 * @param key key whose associated value is to be returned.
269 * @param def the value to be returned in the event that this
270 * preference node has no value associated with <tt>key</tt>.
271 * @return the value associated with <tt>key</tt>, or <tt>def</tt>
272 * if no value is associated with <tt>key</tt>.
273 * @throws IllegalStateException if this node (or an ancestor) has been
274 * removed with the {@link #removeNode()} method.
275 * @throws NullPointerException if key is <tt>null</tt>. (A
276 * <tt>null</tt> default <i>is</i> permitted.)
277 */
278 public String get(String key, String def) {
279 if (key==null)
280 throw new NullPointerException("Null key");
281 synchronized(lock) {
282 if (removed)
283 throw new IllegalStateException("Node has been removed.");
284
285 String result = null;
286 try {
287 result = getSpi(key);
288 } catch (Exception e) {
289 // Ignoring exception causes default to be returned
290 }
291 return (result==null ? def : result);
292 }
293 }
294
295 /**
296 * Implements the <tt>remove(String)</tt> method as per the specification
297 * in {@link Preferences#remove(String)}.
298 *
299 * <p>This implementation obtains this preference node's lock,
300 * checks that the node has not been removed, invokes
301 * {@link #removeSpi(String)} and if there are any preference
302 * change listeners, enqueues a notification event for processing by the
303 * event dispatch thread.
304 *
305 * @param key key whose mapping is to be removed from the preference node.
306 * @throws IllegalStateException if this node (or an ancestor) has been
307 * removed with the {@link #removeNode()} method.
308 */
309 public void remove(String key) {
310 Objects.requireNonNull(key, "Specified key cannot be null");
311 synchronized(lock) {
312 if (removed)
313 throw new IllegalStateException("Node has been removed.");
314
315 removeSpi(key);
316 enqueuePreferenceChangeEvent(key, null);
317 }
318 }
319
320 /**
321 * Implements the <tt>clear</tt> method as per the specification in
322 * {@link Preferences#clear()}.
323 *
324 * <p>This implementation obtains this preference node's lock,
325 * invokes {@link #keys()} to obtain an array of keys, and
326 * iterates over the array invoking {@link #remove(String)} on each key.
327 *
328 * @throws BackingStoreException if this operation cannot be completed
329 * due to a failure in the backing store, or inability to
330 * communicate with it.
331 * @throws IllegalStateException if this node (or an ancestor) has been
332 * removed with the {@link #removeNode()} method.
333 */
334 public void clear() throws BackingStoreException {
335 synchronized(lock) {
336 String[] keys = keys();
337 for (int i=0; i<keys.length; i++)
338 remove(keys[i]);
339 }
340 }
341
342 /**
343 * Implements the <tt>putInt</tt> method as per the specification in
344 * {@link Preferences#putInt(String,int)}.
345 *
346 * <p>This implementation translates <tt>value</tt> to a string with
347 * {@link Integer#toString(int)} and invokes {@link #put(String,String)}
348 * on the result.
349 *
350 * @param key key with which the string form of value is to be associated.
351 * @param value value whose string form is to be associated with key.
352 * @throws NullPointerException if key is <tt>null</tt>.
353 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
354 * <tt>MAX_KEY_LENGTH</tt>.
355 * @throws IllegalStateException if this node (or an ancestor) has been
356 * removed with the {@link #removeNode()} method.
357 */
358 public void putInt(String key, int value) {
359 put(key, Integer.toString(value));
360 }
361
362 /**
363 * Implements the <tt>getInt</tt> method as per the specification in
364 * {@link Preferences#getInt(String,int)}.
365 *
366 * <p>This implementation invokes {@link #get(String,String) <tt>get(key,
367 * null)</tt>}. If the return value is non-null, the implementation
368 * attempts to translate it to an <tt>int</tt> with
369 * {@link Integer#parseInt(String)}. If the attempt succeeds, the return
370 * value is returned by this method. Otherwise, <tt>def</tt> is returned.
371 *
372 * @param key key whose associated value is to be returned as an int.
373 * @param def the value to be returned in the event that this
374 * preference node has no value associated with <tt>key</tt>
375 * or the associated value cannot be interpreted as an int.
376 * @return the int value represented by the string associated with
377 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
378 * associated value does not exist or cannot be interpreted as
379 * an int.
380 * @throws IllegalStateException if this node (or an ancestor) has been
381 * removed with the {@link #removeNode()} method.
382 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
383 */
384 public int getInt(String key, int def) {
385 int result = def;
386 try {
387 String value = get(key, null);
388 if (value != null)
389 result = Integer.parseInt(value);
390 } catch (NumberFormatException e) {
391 // Ignoring exception causes specified default to be returned
392 }
393
394 return result;
395 }
396
397 /**
398 * Implements the <tt>putLong</tt> method as per the specification in
399 * {@link Preferences#putLong(String,long)}.
400 *
401 * <p>This implementation translates <tt>value</tt> to a string with
402 * {@link Long#toString(long)} and invokes {@link #put(String,String)}
403 * on the result.
404 *
405 * @param key key with which the string form of value is to be associated.
406 * @param value value whose string form is to be associated with key.
407 * @throws NullPointerException if key is <tt>null</tt>.
408 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
409 * <tt>MAX_KEY_LENGTH</tt>.
410 * @throws IllegalStateException if this node (or an ancestor) has been
411 * removed with the {@link #removeNode()} method.
412 */
413 public void putLong(String key, long value) {
414 put(key, Long.toString(value));
415 }
416
417 /**
418 * Implements the <tt>getLong</tt> method as per the specification in
419 * {@link Preferences#getLong(String,long)}.
420 *
421 * <p>This implementation invokes {@link #get(String,String) <tt>get(key,
422 * null)</tt>}. If the return value is non-null, the implementation
423 * attempts to translate it to a <tt>long</tt> with
424 * {@link Long#parseLong(String)}. If the attempt succeeds, the return
425 * value is returned by this method. Otherwise, <tt>def</tt> is returned.
426 *
427 * @param key key whose associated value is to be returned as a long.
428 * @param def the value to be returned in the event that this
429 * preference node has no value associated with <tt>key</tt>
430 * or the associated value cannot be interpreted as a long.
431 * @return the long value represented by the string associated with
432 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
433 * associated value does not exist or cannot be interpreted as
434 * a long.
435 * @throws IllegalStateException if this node (or an ancestor) has been
436 * removed with the {@link #removeNode()} method.
437 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
438 */
439 public long getLong(String key, long def) {
440 long result = def;
441 try {
442 String value = get(key, null);
443 if (value != null)
444 result = Long.parseLong(value);
445 } catch (NumberFormatException e) {
446 // Ignoring exception causes specified default to be returned
447 }
448
449 return result;
450 }
451
452 /**
453 * Implements the <tt>putBoolean</tt> method as per the specification in
454 * {@link Preferences#putBoolean(String,boolean)}.
455 *
456 * <p>This implementation translates <tt>value</tt> to a string with
457 * {@link String#valueOf(boolean)} and invokes {@link #put(String,String)}
458 * on the result.
459 *
460 * @param key key with which the string form of value is to be associated.
461 * @param value value whose string form is to be associated with key.
462 * @throws NullPointerException if key is <tt>null</tt>.
463 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
464 * <tt>MAX_KEY_LENGTH</tt>.
465 * @throws IllegalStateException if this node (or an ancestor) has been
466 * removed with the {@link #removeNode()} method.
467 */
468 public void putBoolean(String key, boolean value) {
469 put(key, String.valueOf(value));
470 }
471
472 /**
473 * Implements the <tt>getBoolean</tt> method as per the specification in
474 * {@link Preferences#getBoolean(String,boolean)}.
475 *
476 * <p>This implementation invokes {@link #get(String,String) <tt>get(key,
477 * null)</tt>}. If the return value is non-null, it is compared with
478 * <tt>"true"</tt> using {@link String#equalsIgnoreCase(String)}. If the
479 * comparison returns <tt>true</tt>, this invocation returns
480 * <tt>true</tt>. Otherwise, the original return value is compared with
481 * <tt>"false"</tt>, again using {@link String#equalsIgnoreCase(String)}.
482 * If the comparison returns <tt>true</tt>, this invocation returns
483 * <tt>false</tt>. Otherwise, this invocation returns <tt>def</tt>.
484 *
485 * @param key key whose associated value is to be returned as a boolean.
486 * @param def the value to be returned in the event that this
487 * preference node has no value associated with <tt>key</tt>
488 * or the associated value cannot be interpreted as a boolean.
489 * @return the boolean value represented by the string associated with
490 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
491 * associated value does not exist or cannot be interpreted as
492 * a boolean.
493 * @throws IllegalStateException if this node (or an ancestor) has been
494 * removed with the {@link #removeNode()} method.
495 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
496 */
497 public boolean getBoolean(String key, boolean def) {
498 boolean result = def;
499 String value = get(key, null);
500 if (value != null) {
501 if (value.equalsIgnoreCase("true"))
502 result = true;
503 else if (value.equalsIgnoreCase("false"))
504 result = false;
505 }
506
507 return result;
508 }
509
510 /**
511 * Implements the <tt>putFloat</tt> method as per the specification in
512 * {@link Preferences#putFloat(String,float)}.
513 *
514 * <p>This implementation translates <tt>value</tt> to a string with
515 * {@link Float#toString(float)} and invokes {@link #put(String,String)}
516 * on the result.
517 *
518 * @param key key with which the string form of value is to be associated.
519 * @param value value whose string form is to be associated with key.
520 * @throws NullPointerException if key is <tt>null</tt>.
521 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
522 * <tt>MAX_KEY_LENGTH</tt>.
523 * @throws IllegalStateException if this node (or an ancestor) has been
524 * removed with the {@link #removeNode()} method.
525 */
526 public void putFloat(String key, float value) {
527 put(key, Float.toString(value));
528 }
529
530 /**
531 * Implements the <tt>getFloat</tt> method as per the specification in
532 * {@link Preferences#getFloat(String,float)}.
533 *
534 * <p>This implementation invokes {@link #get(String,String) <tt>get(key,
535 * null)</tt>}. If the return value is non-null, the implementation
536 * attempts to translate it to an <tt>float</tt> with
537 * {@link Float#parseFloat(String)}. If the attempt succeeds, the return
538 * value is returned by this method. Otherwise, <tt>def</tt> is returned.
539 *
540 * @param key key whose associated value is to be returned as a float.
541 * @param def the value to be returned in the event that this
542 * preference node has no value associated with <tt>key</tt>
543 * or the associated value cannot be interpreted as a float.
544 * @return the float value represented by the string associated with
545 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
546 * associated value does not exist or cannot be interpreted as
547 * a float.
548 * @throws IllegalStateException if this node (or an ancestor) has been
549 * removed with the {@link #removeNode()} method.
550 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
551 */
552 public float getFloat(String key, float def) {
553 float result = def;
554 try {
555 String value = get(key, null);
556 if (value != null)
557 result = Float.parseFloat(value);
558 } catch (NumberFormatException e) {
559 // Ignoring exception causes specified default to be returned
560 }
561
562 return result;
563 }
564
565 /**
566 * Implements the <tt>putDouble</tt> method as per the specification in
567 * {@link Preferences#putDouble(String,double)}.
568 *
569 * <p>This implementation translates <tt>value</tt> to a string with
570 * {@link Double#toString(double)} and invokes {@link #put(String,String)}
571 * on the result.
572 *
573 * @param key key with which the string form of value is to be associated.
574 * @param value value whose string form is to be associated with key.
575 * @throws NullPointerException if key is <tt>null</tt>.
576 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
577 * <tt>MAX_KEY_LENGTH</tt>.
578 * @throws IllegalStateException if this node (or an ancestor) has been
579 * removed with the {@link #removeNode()} method.
580 */
581 public void putDouble(String key, double value) {
582 put(key, Double.toString(value));
583 }
584
585 /**
586 * Implements the <tt>getDouble</tt> method as per the specification in
587 * {@link Preferences#getDouble(String,double)}.
588 *
589 * <p>This implementation invokes {@link #get(String,String) <tt>get(key,
590 * null)</tt>}. If the return value is non-null, the implementation
591 * attempts to translate it to an <tt>double</tt> with
592 * {@link Double#parseDouble(String)}. If the attempt succeeds, the return
593 * value is returned by this method. Otherwise, <tt>def</tt> is returned.
594 *
595 * @param key key whose associated value is to be returned as a double.
596 * @param def the value to be returned in the event that this
597 * preference node has no value associated with <tt>key</tt>
598 * or the associated value cannot be interpreted as a double.
599 * @return the double value represented by the string associated with
600 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
601 * associated value does not exist or cannot be interpreted as
602 * a double.
603 * @throws IllegalStateException if this node (or an ancestor) has been
604 * removed with the {@link #removeNode()} method.
605 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
606 */
607 public double getDouble(String key, double def) {
608 double result = def;
609 try {
610 String value = get(key, null);
611 if (value != null)
612 result = Double.parseDouble(value);
613 } catch (NumberFormatException e) {
614 // Ignoring exception causes specified default to be returned
615 }
616
617 return result;
618 }
619
620 /**
621 * Implements the <tt>putByteArray</tt> method as per the specification in
622 * {@link Preferences#putByteArray(String,byte[])}.
623 *
624 * @param key key with which the string form of value is to be associated.
625 * @param value value whose string form is to be associated with key.
626 * @throws NullPointerException if key or value is <tt>null</tt>.
627 * @throws IllegalArgumentException if key.length() exceeds MAX_KEY_LENGTH
628 * or if value.length exceeds MAX_VALUE_LENGTH*3/4.
629 * @throws IllegalStateException if this node (or an ancestor) has been
630 * removed with the {@link #removeNode()} method.
631 */
632 public void putByteArray(String key, byte[] value) {
633 put(key, Base64.byteArrayToBase64(value));
634 }
635
636 /**
637 * Implements the <tt>getByteArray</tt> method as per the specification in
638 * {@link Preferences#getByteArray(String,byte[])}.
639 *
640 * @param key key whose associated value is to be returned as a byte array.
641 * @param def the value to be returned in the event that this
642 * preference node has no value associated with <tt>key</tt>
643 * or the associated value cannot be interpreted as a byte array.
644 * @return the byte array value represented by the string associated with
645 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
646 * associated value does not exist or cannot be interpreted as
647 * a byte array.
648 * @throws IllegalStateException if this node (or an ancestor) has been
649 * removed with the {@link #removeNode()} method.
650 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>. (A
651 * <tt>null</tt> value for <tt>def</tt> <i>is</i> permitted.)
652 */
653 public byte[] getByteArray(String key, byte[] def) {
654 byte[] result = def;
655 String value = get(key, null);
656 try {
657 if (value != null)
658 result = Base64.base64ToByteArray(value);
659 }
660 catch (RuntimeException e) {
661 // Ignoring exception causes specified default to be returned
662 }
663
664 return result;
665 }
666
667 /**
668 * Implements the <tt>keys</tt> method as per the specification in
669 * {@link Preferences#keys()}.
670 *
671 * <p>This implementation obtains this preference node's lock, checks that
672 * the node has not been removed and invokes {@link #keysSpi()}.
673 *
674 * @return an array of the keys that have an associated value in this
675 * preference node.
676 * @throws BackingStoreException if this operation cannot be completed
677 * due to a failure in the backing store, or inability to
678 * communicate with it.
679 * @throws IllegalStateException if this node (or an ancestor) has been
680 * removed with the {@link #removeNode()} method.
681 */
682 public String[] keys() throws BackingStoreException {
683 synchronized(lock) {
684 if (removed)
685 throw new IllegalStateException("Node has been removed.");
686
687 return keysSpi();
688 }
689 }
690
691 /**
692 * Implements the <tt>children</tt> method as per the specification in
693 * {@link Preferences#childrenNames()}.
694 *
695 * <p>This implementation obtains this preference node's lock, checks that
696 * the node has not been removed, constructs a <tt>TreeSet</tt> initialized
697 * to the names of children already cached (the children in this node's
698 * "child-cache"), invokes {@link #childrenNamesSpi()}, and adds all of the
699 * returned child-names into the set. The elements of the tree set are
700 * dumped into a <tt>String</tt> array using the <tt>toArray</tt> method,
701 * and this array is returned.
702 *
703 * @return the names of the children of this preference node.
704 * @throws BackingStoreException if this operation cannot be completed
705 * due to a failure in the backing store, or inability to
706 * communicate with it.
707 * @throws IllegalStateException if this node (or an ancestor) has been
708 * removed with the {@link #removeNode()} method.
709 * @see #cachedChildren()
710 */
711 public String[] childrenNames() throws BackingStoreException {
712 synchronized(lock) {
713 if (removed)
714 throw new IllegalStateException("Node has been removed.");
715
716 Set<String> s = new TreeSet<>(kidCache.keySet());
717 for (String kid : childrenNamesSpi())
718 s.add(kid);
719 return s.toArray(EMPTY_STRING_ARRAY);
720 }
721 }
722
723 private static final String[] EMPTY_STRING_ARRAY = new String[0];
724
725 /**
726 * Returns all known unremoved children of this node.
727 *
728 * @return all known unremoved children of this node.
729 */
730 protected final AbstractPreferences[] cachedChildren() {
731 return kidCache.values().toArray(EMPTY_ABSTRACT_PREFS_ARRAY);
732 }
733
734 private static final AbstractPreferences[] EMPTY_ABSTRACT_PREFS_ARRAY
735 = new AbstractPreferences[0];
736
737 /**
738 * Implements the <tt>parent</tt> method as per the specification in
739 * {@link Preferences#parent()}.
740 *
741 * <p>This implementation obtains this preference node's lock, checks that
742 * the node has not been removed and returns the parent value that was
743 * passed to this node's constructor.
744 *
745 * @return the parent of this preference node.
746 * @throws IllegalStateException if this node (or an ancestor) has been
747 * removed with the {@link #removeNode()} method.
748 */
749 public Preferences parent() {
750 synchronized(lock) {
751 if (removed)
752 throw new IllegalStateException("Node has been removed.");
753
754 return parent;
755 }
756 }
757
758 /**
759 * Implements the <tt>node</tt> method as per the specification in
760 * {@link Preferences#node(String)}.
761 *
762 * <p>This implementation obtains this preference node's lock and checks
763 * that the node has not been removed. If <tt>path</tt> is <tt>""</tt>,
764 * this node is returned; if <tt>path</tt> is <tt>"/"</tt>, this node's
765 * root is returned. If the first character in <tt>path</tt> is
766 * not <tt>'/'</tt>, the implementation breaks <tt>path</tt> into
767 * tokens and recursively traverses the path from this node to the
768 * named node, "consuming" a name and a slash from <tt>path</tt> at
769 * each step of the traversal. At each step, the current node is locked
770 * and the node's child-cache is checked for the named node. If it is
771 * not found, the name is checked to make sure its length does not
772 * exceed <tt>MAX_NAME_LENGTH</tt>. Then the {@link #childSpi(String)}
773 * method is invoked, and the result stored in this node's child-cache.
774 * If the newly created <tt>Preferences</tt> object's {@link #newNode}
775 * field is <tt>true</tt> and there are any node change listeners,
776 * a notification event is enqueued for processing by the event dispatch
777 * thread.
778 *
779 * <p>When there are no more tokens, the last value found in the
780 * child-cache or returned by <tt>childSpi</tt> is returned by this
781 * method. If during the traversal, two <tt>"/"</tt> tokens occur
782 * consecutively, or the final token is <tt>"/"</tt> (rather than a name),
783 * an appropriate <tt>IllegalArgumentException</tt> is thrown.
784 *
785 * <p> If the first character of <tt>path</tt> is <tt>'/'</tt>
786 * (indicating an absolute path name) this preference node's
787 * lock is dropped prior to breaking <tt>path</tt> into tokens, and
788 * this method recursively traverses the path starting from the root
789 * (rather than starting from this node). The traversal is otherwise
790 * identical to the one described for relative path names. Dropping
791 * the lock on this node prior to commencing the traversal at the root
792 * node is essential to avoid the possibility of deadlock, as per the
793 * {@link #lock locking invariant}.
794 *
795 * @param path the path name of the preference node to return.
796 * @return the specified preference node.
797 * @throws IllegalArgumentException if the path name is invalid (i.e.,
798 * it contains multiple consecutive slash characters, or ends
799 * with a slash character and is more than one character long).
800 * @throws IllegalStateException if this node (or an ancestor) has been
801 * removed with the {@link #removeNode()} method.
802 */
803 public Preferences node(String path) {
804 synchronized(lock) {
805 if (removed)
806 throw new IllegalStateException("Node has been removed.");
807 if (path.equals(""))
808 return this;
809 if (path.equals("/"))
810 return root;
811 if (path.charAt(0) != '/')
812 return node(new StringTokenizer(path, "/", true));
813 }
814
815 // Absolute path. Note that we've dropped our lock to avoid deadlock
816 return root.node(new StringTokenizer(path.substring(1), "/", true));
817 }
818
819 /**
820 * tokenizer contains <name> {'/' <name>}*
821 */
822 private Preferences node(StringTokenizer path) {
823 String token = path.nextToken();
824 if (token.equals("/")) // Check for consecutive slashes
825 throw new IllegalArgumentException("Consecutive slashes in path");
826 synchronized(lock) {
827 AbstractPreferences child = kidCache.get(token);
828 if (child == null) {
829 if (token.length() > MAX_NAME_LENGTH)
830 throw new IllegalArgumentException(
831 "Node name " + token + " too long");
832 child = childSpi(token);
833 if (child.newNode)
834 enqueueNodeAddedEvent(child);
835 kidCache.put(token, child);
836 }
837 if (!path.hasMoreTokens())
838 return child;
839 path.nextToken(); // Consume slash
840 if (!path.hasMoreTokens())
841 throw new IllegalArgumentException("Path ends with slash");
842 return child.node(path);
843 }
844 }
845
846 /**
847 * Implements the <tt>nodeExists</tt> method as per the specification in
848 * {@link Preferences#nodeExists(String)}.
849 *
850 * <p>This implementation is very similar to {@link #node(String)},
851 * except that {@link #getChild(String)} is used instead of {@link
852 * #childSpi(String)}.
853 *
854 * @param path the path name of the node whose existence is to be checked.
855 * @return true if the specified node exists.
856 * @throws BackingStoreException if this operation cannot be completed
857 * due to a failure in the backing store, or inability to
858 * communicate with it.
859 * @throws IllegalArgumentException if the path name is invalid (i.e.,
860 * it contains multiple consecutive slash characters, or ends
861 * with a slash character and is more than one character long).
862 * @throws IllegalStateException if this node (or an ancestor) has been
863 * removed with the {@link #removeNode()} method and
864 * <tt>pathname</tt> is not the empty string (<tt>""</tt>).
865 */
866 public boolean nodeExists(String path)
867 throws BackingStoreException
868 {
869 synchronized(lock) {
870 if (path.equals(""))
871 return !removed;
872 if (removed)
873 throw new IllegalStateException("Node has been removed.");
874 if (path.equals("/"))
875 return true;
876 if (path.charAt(0) != '/')
877 return nodeExists(new StringTokenizer(path, "/", true));
878 }
879
880 // Absolute path. Note that we've dropped our lock to avoid deadlock
881 return root.nodeExists(new StringTokenizer(path.substring(1), "/",
882 true));
883 }
884
885 /**
886 * tokenizer contains <name> {'/' <name>}*
887 */
888 private boolean nodeExists(StringTokenizer path)
889 throws BackingStoreException
890 {
891 String token = path.nextToken();
892 if (token.equals("/")) // Check for consecutive slashes
893 throw new IllegalArgumentException("Consecutive slashes in path");
894 synchronized(lock) {
895 AbstractPreferences child = kidCache.get(token);
896 if (child == null)
897 child = getChild(token);
898 if (child==null)
899 return false;
900 if (!path.hasMoreTokens())
901 return true;
902 path.nextToken(); // Consume slash
903 if (!path.hasMoreTokens())
904 throw new IllegalArgumentException("Path ends with slash");
905 return child.nodeExists(path);
906 }
907 }
908
909 /**
910
911 * Implements the <tt>removeNode()</tt> method as per the specification in
912 * {@link Preferences#removeNode()}.
913 *
914 * <p>This implementation checks to see that this node is the root; if so,
915 * it throws an appropriate exception. Then, it locks this node's parent,
916 * and calls a recursive helper method that traverses the subtree rooted at
917 * this node. The recursive method locks the node on which it was called,
918 * checks that it has not already been removed, and then ensures that all
919 * of its children are cached: The {@link #childrenNamesSpi()} method is
920 * invoked and each returned child name is checked for containment in the
921 * child-cache. If a child is not already cached, the {@link
922 * #childSpi(String)} method is invoked to create a <tt>Preferences</tt>
923 * instance for it, and this instance is put into the child-cache. Then
924 * the helper method calls itself recursively on each node contained in its
925 * child-cache. Next, it invokes {@link #removeNodeSpi()}, marks itself
926 * as removed, and removes itself from its parent's child-cache. Finally,
927 * if there are any node change listeners, it enqueues a notification
928 * event for processing by the event dispatch thread.
929 *
930 * <p>Note that the helper method is always invoked with all ancestors up
931 * to the "closest non-removed ancestor" locked.
932 *
933 * @throws IllegalStateException if this node (or an ancestor) has already
934 * been removed with the {@link #removeNode()} method.
935 * @throws UnsupportedOperationException if this method is invoked on
936 * the root node.
937 * @throws BackingStoreException if this operation cannot be completed
938 * due to a failure in the backing store, or inability to
939 * communicate with it.
940 */
941 public void removeNode() throws BackingStoreException {
942 if (this==root)
943 throw new UnsupportedOperationException("Can't remove the root!");
944 synchronized(parent.lock) {
945 removeNode2();
946 parent.kidCache.remove(name);
947 }
948 }
949
950 /*
951 * Called with locks on all nodes on path from parent of "removal root"
952 * to this (including the former but excluding the latter).
953 */
954 private void removeNode2() throws BackingStoreException {
955 synchronized(lock) {
956 if (removed)
957 throw new IllegalStateException("Node already removed.");
958
959 // Ensure that all children are cached
960 String[] kidNames = childrenNamesSpi();
961 for (int i=0; i<kidNames.length; i++)
962 if (!kidCache.containsKey(kidNames[i]))
963 kidCache.put(kidNames[i], childSpi(kidNames[i]));
964
965 // Recursively remove all cached children
966 for (Iterator<AbstractPreferences> i = kidCache.values().iterator();
967 i.hasNext();) {
968 try {
969 i.next().removeNode2();
970 i.remove();
971 } catch (BackingStoreException x) { }
972 }
973
974 // Now we have no descendants - it's time to die!
975 removeNodeSpi();
976 removed = true;
977 parent.enqueueNodeRemovedEvent(this);
978 }
979 }
980
981 /**
982 * Implements the <tt>name</tt> method as per the specification in
983 * {@link Preferences#name()}.
984 *
985 * <p>This implementation merely returns the name that was
986 * passed to this node's constructor.
987 *
988 * @return this preference node's name, relative to its parent.
989 */
990 public String name() {
991 return name;
992 }
993
994 /**
995 * Implements the <tt>absolutePath</tt> method as per the specification in
996 * {@link Preferences#absolutePath()}.
997 *
998 * <p>This implementation merely returns the absolute path name that
999 * was computed at the time that this node was constructed (based on
1000 * the name that was passed to this node's constructor, and the names
1001 * that were passed to this node's ancestors' constructors).
1002 *
1003 * @return this preference node's absolute path name.
1004 */
1005 public String absolutePath() {
1006 return absolutePath;
1007 }
1008
1009 /**
1010 * Implements the <tt>isUserNode</tt> method as per the specification in
1011 * {@link Preferences#isUserNode()}.
1012 *
1013 * <p>This implementation compares this node's root node (which is stored
1014 * in a private field) with the value returned by
1015 * {@link Preferences#userRoot()}. If the two object references are
1016 * identical, this method returns true.
1017 *
1018 * @return <tt>true</tt> if this preference node is in the user
1019 * preference tree, <tt>false</tt> if it's in the system
1020 * preference tree.
1021 */
1022 public boolean isUserNode() {
1023 return AccessController.doPrivileged(
1024 new PrivilegedAction<Boolean>() {
1025 public Boolean run() {
1026 return root == Preferences.userRoot();
1027 }
1028 }).booleanValue();
1029 }
1030
1031 public void addPreferenceChangeListener(PreferenceChangeListener pcl) {
1032 if (pcl==null)
1033 throw new NullPointerException("Change listener is null.");
1034 synchronized(lock) {
1035 if (removed)
1036 throw new IllegalStateException("Node has been removed.");
1037
1038 // Copy-on-write
1039 PreferenceChangeListener[] old = prefListeners;
1040 prefListeners = new PreferenceChangeListener[old.length + 1];
1041 System.arraycopy(old, 0, prefListeners, 0, old.length);
1042 prefListeners[old.length] = pcl;
1043 }
1044 startEventDispatchThreadIfNecessary();
1045 }
1046
1047 public void removePreferenceChangeListener(PreferenceChangeListener pcl) {
1048 synchronized(lock) {
1049 if (removed)
1050 throw new IllegalStateException("Node has been removed.");
1051 if ((prefListeners == null) || (prefListeners.length == 0))
1052 throw new IllegalArgumentException("Listener not registered.");
1053
1054 // Copy-on-write
1055 PreferenceChangeListener[] newPl =
1056 new PreferenceChangeListener[prefListeners.length - 1];
1057 int i = 0;
1058 while (i < newPl.length && prefListeners[i] != pcl)
1059 newPl[i] = prefListeners[i++];
1060
1061 if (i == newPl.length && prefListeners[i] != pcl)
1062 throw new IllegalArgumentException("Listener not registered.");
1063 while (i < newPl.length)
1064 newPl[i] = prefListeners[++i];
1065 prefListeners = newPl;
1066 }
1067 }
1068
1069 public void addNodeChangeListener(NodeChangeListener ncl) {
1070 if (ncl==null)
1071 throw new NullPointerException("Change listener is null.");
1072 synchronized(lock) {
1073 if (removed)
1074 throw new IllegalStateException("Node has been removed.");
1075
1076 // Copy-on-write
1077 if (nodeListeners == null) {
1078 nodeListeners = new NodeChangeListener[1];
1079 nodeListeners[0] = ncl;
1080 } else {
1081 NodeChangeListener[] old = nodeListeners;
1082 nodeListeners = new NodeChangeListener[old.length + 1];
1083 System.arraycopy(old, 0, nodeListeners, 0, old.length);
1084 nodeListeners[old.length] = ncl;
1085 }
1086 }
1087 startEventDispatchThreadIfNecessary();
1088 }
1089
1090 public void removeNodeChangeListener(NodeChangeListener ncl) {
1091 synchronized(lock) {
1092 if (removed)
1093 throw new IllegalStateException("Node has been removed.");
1094 if ((nodeListeners == null) || (nodeListeners.length == 0))
1095 throw new IllegalArgumentException("Listener not registered.");
1096
1097 // Copy-on-write
1098 int i = 0;
1099 while (i < nodeListeners.length && nodeListeners[i] != ncl)
1100 i++;
1101 if (i == nodeListeners.length)
1102 throw new IllegalArgumentException("Listener not registered.");
1103 NodeChangeListener[] newNl =
1104 new NodeChangeListener[nodeListeners.length - 1];
1105 if (i != 0)
1106 System.arraycopy(nodeListeners, 0, newNl, 0, i);
1107 if (i != newNl.length)
1108 System.arraycopy(nodeListeners, i + 1,
1109 newNl, i, newNl.length - i);
1110 nodeListeners = newNl;
1111 }
1112 }
1113
1114 // "SPI" METHODS
1115
1116 /**
1117 * Put the given key-value association into this preference node. It is
1118 * guaranteed that <tt>key</tt> and <tt>value</tt> are non-null and of
1119 * legal length. Also, it is guaranteed that this node has not been
1120 * removed. (The implementor needn't check for any of these things.)
1121 *
1122 * <p>This method is invoked with the lock on this node held.
1123 */
1124 protected abstract void putSpi(String key, String value);
1125
1126 /**
1127 * Return the value associated with the specified key at this preference
1128 * node, or <tt>null</tt> if there is no association for this key, or the
1129 * association cannot be determined at this time. It is guaranteed that
1130 * <tt>key</tt> is non-null. Also, it is guaranteed that this node has
1131 * not been removed. (The implementor needn't check for either of these
1132 * things.)
1133 *
1134 * <p> Generally speaking, this method should not throw an exception
1135 * under any circumstances. If, however, if it does throw an exception,
1136 * the exception will be intercepted and treated as a <tt>null</tt>
1137 * return value.
1138 *
1139 * <p>This method is invoked with the lock on this node held.
1140 *
1141 * @return the value associated with the specified key at this preference
1142 * node, or <tt>null</tt> if there is no association for this
1143 * key, or the association cannot be determined at this time.
1144 */
1145 protected abstract String getSpi(String key);
1146
1147 /**
1148 * Remove the association (if any) for the specified key at this
1149 * preference node. It is guaranteed that <tt>key</tt> is non-null.
1150 * Also, it is guaranteed that this node has not been removed.
1151 * (The implementor needn't check for either of these things.)
1152 *
1153 * <p>This method is invoked with the lock on this node held.
1154 */
1155 protected abstract void removeSpi(String key);
1156
1157 /**
1158 * Removes this preference node, invalidating it and any preferences that
1159 * it contains. The named child will have no descendants at the time this
1160 * invocation is made (i.e., the {@link Preferences#removeNode()} method
1161 * invokes this method repeatedly in a bottom-up fashion, removing each of
1162 * a node's descendants before removing the node itself).
1163 *
1164 * <p>This method is invoked with the lock held on this node and its
1165 * parent (and all ancestors that are being removed as a
1166 * result of a single invocation to {@link Preferences#removeNode()}).
1167 *
1168 * <p>The removal of a node needn't become persistent until the
1169 * <tt>flush</tt> method is invoked on this node (or an ancestor).
1170 *
1171 * <p>If this node throws a <tt>BackingStoreException</tt>, the exception
1172 * will propagate out beyond the enclosing {@link #removeNode()}
1173 * invocation.
1174 *
1175 * @throws BackingStoreException if this operation cannot be completed
1176 * due to a failure in the backing store, or inability to
1177 * communicate with it.
1178 */
1179 protected abstract void removeNodeSpi() throws BackingStoreException;
1180
1181 /**
1182 * Returns all of the keys that have an associated value in this
1183 * preference node. (The returned array will be of size zero if
1184 * this node has no preferences.) It is guaranteed that this node has not
1185 * been removed.
1186 *
1187 * <p>This method is invoked with the lock on this node held.
1188 *
1189 * <p>If this node throws a <tt>BackingStoreException</tt>, the exception
1190 * will propagate out beyond the enclosing {@link #keys()} invocation.
1191 *
1192 * @return an array of the keys that have an associated value in this
1193 * preference node.
1194 * @throws BackingStoreException if this operation cannot be completed
1195 * due to a failure in the backing store, or inability to
1196 * communicate with it.
1197 */
1198 protected abstract String[] keysSpi() throws BackingStoreException;
1199
1200 /**
1201 * Returns the names of the children of this preference node. (The
1202 * returned array will be of size zero if this node has no children.)
1203 * This method need not return the names of any nodes already cached,
1204 * but may do so without harm.
1205 *
1206 * <p>This method is invoked with the lock on this node held.
1207 *
1208 * <p>If this node throws a <tt>BackingStoreException</tt>, the exception
1209 * will propagate out beyond the enclosing {@link #childrenNames()}
1210 * invocation.
1211 *
1212 * @return an array containing the names of the children of this
1213 * preference node.
1214 * @throws BackingStoreException if this operation cannot be completed
1215 * due to a failure in the backing store, or inability to
1216 * communicate with it.
1217 */
1218 protected abstract String[] childrenNamesSpi()
1219 throws BackingStoreException;
1220
1221 /**
1222 * Returns the named child if it exists, or <tt>null</tt> if it does not.
1223 * It is guaranteed that <tt>nodeName</tt> is non-null, non-empty,
1224 * does not contain the slash character ('/'), and is no longer than
1225 * {@link #MAX_NAME_LENGTH} characters. Also, it is guaranteed
1226 * that this node has not been removed. (The implementor needn't check
1227 * for any of these things if he chooses to override this method.)
1228 *
1229 * <p>Finally, it is guaranteed that the named node has not been returned
1230 * by a previous invocation of this method or {@link #childSpi} after the
1231 * last time that it was removed. In other words, a cached value will
1232 * always be used in preference to invoking this method. (The implementor
1233 * needn't maintain his own cache of previously returned children if he
1234 * chooses to override this method.)
1235 *
1236 * <p>This implementation obtains this preference node's lock, invokes
1237 * {@link #childrenNames()} to get an array of the names of this node's
1238 * children, and iterates over the array comparing the name of each child
1239 * with the specified node name. If a child node has the correct name,
1240 * the {@link #childSpi(String)} method is invoked and the resulting
1241 * node is returned. If the iteration completes without finding the
1242 * specified name, <tt>null</tt> is returned.
1243 *
1244 * @param nodeName name of the child to be searched for.
1245 * @return the named child if it exists, or null if it does not.
1246 * @throws BackingStoreException if this operation cannot be completed
1247 * due to a failure in the backing store, or inability to
1248 * communicate with it.
1249 */
1250 protected AbstractPreferences getChild(String nodeName)
1251 throws BackingStoreException {
1252 synchronized(lock) {
1253 // assert kidCache.get(nodeName)==null;
1254 String[] kidNames = childrenNames();
1255 for (int i=0; i<kidNames.length; i++)
1256 if (kidNames[i].equals(nodeName))
1257 return childSpi(kidNames[i]);
1258 }
1259 return null;
1260 }
1261
1262 /**
1263 * Returns the named child of this preference node, creating it if it does
1264 * not already exist. It is guaranteed that <tt>name</tt> is non-null,
1265 * non-empty, does not contain the slash character ('/'), and is no longer
1266 * than {@link #MAX_NAME_LENGTH} characters. Also, it is guaranteed that
1267 * this node has not been removed. (The implementor needn't check for any
1268 * of these things.)
1269 *
1270 * <p>Finally, it is guaranteed that the named node has not been returned
1271 * by a previous invocation of this method or {@link #getChild(String)}
1272 * after the last time that it was removed. In other words, a cached
1273 * value will always be used in preference to invoking this method.
1274 * Subclasses need not maintain their own cache of previously returned
1275 * children.
1276 *
1277 * <p>The implementer must ensure that the returned node has not been
1278 * removed. If a like-named child of this node was previously removed, the
1279 * implementer must return a newly constructed <tt>AbstractPreferences</tt>
1280 * node; once removed, an <tt>AbstractPreferences</tt> node
1281 * cannot be "resuscitated."
1282 *
1283 * <p>If this method causes a node to be created, this node is not
1284 * guaranteed to be persistent until the <tt>flush</tt> method is
1285 * invoked on this node or one of its ancestors (or descendants).
1286 *
1287 * <p>This method is invoked with the lock on this node held.
1288 *
1289 * @param name The name of the child node to return, relative to
1290 * this preference node.
1291 * @return The named child node.
1292 */
1293 protected abstract AbstractPreferences childSpi(String name);
1294
1295 /**
1296 * Returns the absolute path name of this preferences node.
1297 */
1298 public String toString() {
1299 return (this.isUserNode() ? "User" : "System") +
1300 " Preference Node: " + this.absolutePath();
1301 }
1302
1303 /**
1304 * Implements the <tt>sync</tt> method as per the specification in
1305 * {@link Preferences#sync()}.
1306 *
1307 * <p>This implementation calls a recursive helper method that locks this
1308 * node, invokes syncSpi() on it, unlocks this node, and recursively
1309 * invokes this method on each "cached child." A cached child is a child
1310 * of this node that has been created in this VM and not subsequently
1311 * removed. In effect, this method does a depth first traversal of the
1312 * "cached subtree" rooted at this node, calling syncSpi() on each node in
1313 * the subTree while only that node is locked. Note that syncSpi() is
1314 * invoked top-down.
1315 *
1316 * @throws BackingStoreException if this operation cannot be completed
1317 * due to a failure in the backing store, or inability to
1318 * communicate with it.
1319 * @throws IllegalStateException if this node (or an ancestor) has been
1320 * removed with the {@link #removeNode()} method.
1321 * @see #flush()
1322 */
1323 public void sync() throws BackingStoreException {
1324 sync2();
1325 }
1326
1327 private void sync2() throws BackingStoreException {
1328 AbstractPreferences[] cachedKids;
1329
1330 synchronized(lock) {
1331 if (removed)
1332 throw new IllegalStateException("Node has been removed");
1333 syncSpi();
1334 cachedKids = cachedChildren();
1335 }
1336
1337 for (int i=0; i<cachedKids.length; i++)
1338 cachedKids[i].sync2();
1339 }
1340
1341 /**
1342 * This method is invoked with this node locked. The contract of this
1343 * method is to synchronize any cached preferences stored at this node
1344 * with any stored in the backing store. (It is perfectly possible that
1345 * this node does not exist on the backing store, either because it has
1346 * been deleted by another VM, or because it has not yet been created.)
1347 * Note that this method should <i>not</i> synchronize the preferences in
1348 * any subnodes of this node. If the backing store naturally syncs an
1349 * entire subtree at once, the implementer is encouraged to override
1350 * sync(), rather than merely overriding this method.
1351 *
1352 * <p>If this node throws a <tt>BackingStoreException</tt>, the exception
1353 * will propagate out beyond the enclosing {@link #sync()} invocation.
1354 *
1355 * @throws BackingStoreException if this operation cannot be completed
1356 * due to a failure in the backing store, or inability to
1357 * communicate with it.
1358 */
1359 protected abstract void syncSpi() throws BackingStoreException;
1360
1361 /**
1362 * Implements the <tt>flush</tt> method as per the specification in
1363 * {@link Preferences#flush()}.
1364 *
1365 * <p>This implementation calls a recursive helper method that locks this
1366 * node, invokes flushSpi() on it, unlocks this node, and recursively
1367 * invokes this method on each "cached child." A cached child is a child
1368 * of this node that has been created in this VM and not subsequently
1369 * removed. In effect, this method does a depth first traversal of the
1370 * "cached subtree" rooted at this node, calling flushSpi() on each node in
1371 * the subTree while only that node is locked. Note that flushSpi() is
1372 * invoked top-down.
1373 *
1374 * <p> If this method is invoked on a node that has been removed with
1375 * the {@link #removeNode()} method, flushSpi() is invoked on this node,
1376 * but not on others.
1377 *
1378 * @throws BackingStoreException if this operation cannot be completed
1379 * due to a failure in the backing store, or inability to
1380 * communicate with it.
1381 * @see #flush()
1382 */
1383 public void flush() throws BackingStoreException {
1384 flush2();
1385 }
1386
1387 private void flush2() throws BackingStoreException {
1388 AbstractPreferences[] cachedKids;
1389
1390 synchronized(lock) {
1391 flushSpi();
1392 if(removed)
1393 return;
1394 cachedKids = cachedChildren();
1395 }
1396
1397 for (int i = 0; i < cachedKids.length; i++)
1398 cachedKids[i].flush2();
1399 }
1400
1401 /**
1402 * This method is invoked with this node locked. The contract of this
1403 * method is to force any cached changes in the contents of this
1404 * preference node to the backing store, guaranteeing their persistence.
1405 * (It is perfectly possible that this node does not exist on the backing
1406 * store, either because it has been deleted by another VM, or because it
1407 * has not yet been created.) Note that this method should <i>not</i>
1408 * flush the preferences in any subnodes of this node. If the backing
1409 * store naturally flushes an entire subtree at once, the implementer is
1410 * encouraged to override flush(), rather than merely overriding this
1411 * method.
1412 *
1413 * <p>If this node throws a <tt>BackingStoreException</tt>, the exception
1414 * will propagate out beyond the enclosing {@link #flush()} invocation.
1415 *
1416 * @throws BackingStoreException if this operation cannot be completed
1417 * due to a failure in the backing store, or inability to
1418 * communicate with it.
1419 */
1420 protected abstract void flushSpi() throws BackingStoreException;
1421
1422 /**
1423 * Returns <tt>true</tt> iff this node (or an ancestor) has been
1424 * removed with the {@link #removeNode()} method. This method
1425 * locks this node prior to returning the contents of the private
1426 * field used to track this state.
1427 *
1428 * @return <tt>true</tt> iff this node (or an ancestor) has been
1429 * removed with the {@link #removeNode()} method.
1430 */
1431 protected boolean isRemoved() {
1432 synchronized(lock) {
1433 return removed;
1434 }
1435 }
1436
1437 /**
1438 * Queue of pending notification events. When a preference or node
1439 * change event for which there are one or more listeners occurs,
1440 * it is placed on this queue and the queue is notified. A background
1441 * thread waits on this queue and delivers the events. This decouples
1442 * event delivery from preference activity, greatly simplifying
1443 * locking and reducing opportunity for deadlock.
1444 */
1445 private static final List<EventObject> eventQueue = new LinkedList<>();
1446
1447 /**
1448 * These two classes are used to distinguish NodeChangeEvents on
1449 * eventQueue so the event dispatch thread knows whether to call
1450 * childAdded or childRemoved.
1451 */
1452 private class NodeAddedEvent extends NodeChangeEvent {
1453 private static final long serialVersionUID = -6743557530157328528L;
1454 NodeAddedEvent(Preferences parent, Preferences child) {
1455 super(parent, child);
1456 }
1457 }
1458 private class NodeRemovedEvent extends NodeChangeEvent {
1459 private static final long serialVersionUID = 8735497392918824837L;
1460 NodeRemovedEvent(Preferences parent, Preferences child) {
1461 super(parent, child);
1462 }
1463 }
1464
1465 /**
1466 * A single background thread ("the event notification thread") monitors
1467 * the event queue and delivers events that are placed on the queue.
1468 */
1469 private static class EventDispatchThread extends Thread {
1470 public void run() {
1471 while(true) {
1472 // Wait on eventQueue till an event is present
1473 EventObject event = null;
1474 synchronized(eventQueue) {
1475 try {
1476 while (eventQueue.isEmpty())
1477 eventQueue.wait();
1478 event = eventQueue.remove(0);
1479 } catch (InterruptedException e) {
1480 // XXX Log "Event dispatch thread interrupted. Exiting"
1481 return;
1482 }
1483 }
1484
1485 // Now we have event & hold no locks; deliver evt to listeners
1486 AbstractPreferences src=(AbstractPreferences)event.getSource();
1487 if (event instanceof PreferenceChangeEvent) {
1488 PreferenceChangeEvent pce = (PreferenceChangeEvent)event;
1489 PreferenceChangeListener[] listeners = src.prefListeners();
1490 for (int i=0; i<listeners.length; i++)
1491 listeners[i].preferenceChange(pce);
1492 } else {
1493 NodeChangeEvent nce = (NodeChangeEvent)event;
1494 NodeChangeListener[] listeners = src.nodeListeners();
1495 if (nce instanceof NodeAddedEvent) {
1496 for (int i=0; i<listeners.length; i++)
1497 listeners[i].childAdded(nce);
1498 } else {
1499 // assert nce instanceof NodeRemovedEvent;
1500 for (int i=0; i<listeners.length; i++)
1501 listeners[i].childRemoved(nce);
1502 }
1503 }
1504 }
1505 }
1506 }
1507
1508 private static Thread eventDispatchThread = null;
1509
1510 /**
1511 * This method starts the event dispatch thread the first time it
1512 * is called. The event dispatch thread will be started only
1513 * if someone registers a listener.
1514 */
1515 private static synchronized void startEventDispatchThreadIfNecessary() {
1516 if (eventDispatchThread == null) {
1517 // XXX Log "Starting event dispatch thread"
1518 eventDispatchThread = new EventDispatchThread();
1519 eventDispatchThread.setDaemon(true);
1520 eventDispatchThread.start();
1521 }
1522 }
1523
1524 /**
1525 * Return this node's preference/node change listeners. Even though
1526 * we're using a copy-on-write lists, we use synchronized accessors to
1527 * ensure information transmission from the writing thread to the
1528 * reading thread.
1529 */
1530 PreferenceChangeListener[] prefListeners() {
1531 synchronized(lock) {
1532 return prefListeners;
1533 }
1534 }
1535 NodeChangeListener[] nodeListeners() {
1536 synchronized(lock) {
1537 return nodeListeners;
1538 }
1539 }
1540
1541 /**
1542 * Enqueue a preference change event for delivery to registered
1543 * preference change listeners unless there are no registered
1544 * listeners. Invoked with this.lock held.
1545 */
1546 private void enqueuePreferenceChangeEvent(String key, String newValue) {
1547 if (prefListeners.length != 0) {
1548 synchronized(eventQueue) {
1549 eventQueue.add(new PreferenceChangeEvent(this, key, newValue));
1550 eventQueue.notify();
1551 }
1552 }
1553 }
1554
1555 /**
1556 * Enqueue a "node added" event for delivery to registered node change
1557 * listeners unless there are no registered listeners. Invoked with
1558 * this.lock held.
1559 */
1560 private void enqueueNodeAddedEvent(Preferences child) {
1561 if (nodeListeners.length != 0) {
1562 synchronized(eventQueue) {
1563 eventQueue.add(new NodeAddedEvent(this, child));
1564 eventQueue.notify();
1565 }
1566 }
1567 }
1568
1569 /**
1570 * Enqueue a "node removed" event for delivery to registered node change
1571 * listeners unless there are no registered listeners. Invoked with
1572 * this.lock held.
1573 */
1574 private void enqueueNodeRemovedEvent(Preferences child) {
1575 if (nodeListeners.length != 0) {
1576 synchronized(eventQueue) {
1577 eventQueue.add(new NodeRemovedEvent(this, child));
1578 eventQueue.notify();
1579 }
1580 }
1581 }
1582
1583 /**
1584 * Implements the <tt>exportNode</tt> method as per the specification in
1585 * {@link Preferences#exportNode(OutputStream)}.
1586 *
1587 * @param os the output stream on which to emit the XML document.
1588 * @throws IOException if writing to the specified output stream
1589 * results in an <tt>IOException</tt>.
1590 * @throws BackingStoreException if preference data cannot be read from
1591 * backing store.
1592 */
1593 public void exportNode(OutputStream os)
1594 throws IOException, BackingStoreException
1595 {
1596 XmlSupport.export(os, this, false);
1597 }
1598
1599 /**
1600 * Implements the <tt>exportSubtree</tt> method as per the specification in
1601 * {@link Preferences#exportSubtree(OutputStream)}.
1602 *
1603 * @param os the output stream on which to emit the XML document.
1604 * @throws IOException if writing to the specified output stream
1605 * results in an <tt>IOException</tt>.
1606 * @throws BackingStoreException if preference data cannot be read from
1607 * backing store.
1608 */
1609 public void exportSubtree(OutputStream os)
1610 throws IOException, BackingStoreException
1611 {
1612 XmlSupport.export(os, this, true);
1613 }
1614 }