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 * @throws NullPointerException {@inheritDoc}.
309 */
310 public void remove(String key) {
311 Objects.requireNonNull(key, "Specified key cannot be null");
312 synchronized(lock) {
313 if (removed)
314 throw new IllegalStateException("Node has been removed.");
315
316 removeSpi(key);
317 enqueuePreferenceChangeEvent(key, null);
318 }
319 }
320
321 /**
322 * Implements the <tt>clear</tt> method as per the specification in
323 * {@link Preferences#clear()}.
324 *
325 * <p>This implementation obtains this preference node's lock,
326 * invokes {@link #keys()} to obtain an array of keys, and
327 * iterates over the array invoking {@link #remove(String)} on each key.
328 *
329 * @throws BackingStoreException if this operation cannot be completed
330 * due to a failure in the backing store, or inability to
331 * communicate with it.
332 * @throws IllegalStateException if this node (or an ancestor) has been
333 * removed with the {@link #removeNode()} method.
334 */
335 public void clear() throws BackingStoreException {
336 synchronized(lock) {
337 String[] keys = keys();
338 for (int i=0; i<keys.length; i++)
339 remove(keys[i]);
340 }
341 }
342
343 /**
344 * Implements the <tt>putInt</tt> method as per the specification in
345 * {@link Preferences#putInt(String,int)}.
346 *
347 * <p>This implementation translates <tt>value</tt> to a string with
348 * {@link Integer#toString(int)} and invokes {@link #put(String,String)}
349 * on the result.
350 *
351 * @param key key with which the string form of value is to be associated.
352 * @param value value whose string form is to be associated with key.
353 * @throws NullPointerException if key is <tt>null</tt>.
354 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
355 * <tt>MAX_KEY_LENGTH</tt>.
356 * @throws IllegalStateException if this node (or an ancestor) has been
357 * removed with the {@link #removeNode()} method.
358 */
359 public void putInt(String key, int value) {
360 put(key, Integer.toString(value));
361 }
362
363 /**
364 * Implements the <tt>getInt</tt> method as per the specification in
365 * {@link Preferences#getInt(String,int)}.
366 *
367 * <p>This implementation invokes {@link #get(String,String) <tt>get(key,
368 * null)</tt>}. If the return value is non-null, the implementation
369 * attempts to translate it to an <tt>int</tt> with
370 * {@link Integer#parseInt(String)}. If the attempt succeeds, the return
371 * value is returned by this method. Otherwise, <tt>def</tt> is returned.
372 *
373 * @param key key whose associated value is to be returned as an int.
374 * @param def the value to be returned in the event that this
375 * preference node has no value associated with <tt>key</tt>
376 * or the associated value cannot be interpreted as an int.
377 * @return the int value represented by the string associated with
378 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
379 * associated value does not exist or cannot be interpreted as
380 * an int.
381 * @throws IllegalStateException if this node (or an ancestor) has been
382 * removed with the {@link #removeNode()} method.
383 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
384 */
385 public int getInt(String key, int def) {
386 int result = def;
387 try {
388 String value = get(key, null);
389 if (value != null)
390 result = Integer.parseInt(value);
391 } catch (NumberFormatException e) {
392 // Ignoring exception causes specified default to be returned
393 }
394
395 return result;
396 }
397
398 /**
399 * Implements the <tt>putLong</tt> method as per the specification in
400 * {@link Preferences#putLong(String,long)}.
401 *
402 * <p>This implementation translates <tt>value</tt> to a string with
403 * {@link Long#toString(long)} and invokes {@link #put(String,String)}
404 * on the result.
405 *
406 * @param key key with which the string form of value is to be associated.
407 * @param value value whose string form is to be associated with key.
408 * @throws NullPointerException if key is <tt>null</tt>.
409 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
410 * <tt>MAX_KEY_LENGTH</tt>.
411 * @throws IllegalStateException if this node (or an ancestor) has been
412 * removed with the {@link #removeNode()} method.
413 */
414 public void putLong(String key, long value) {
415 put(key, Long.toString(value));
416 }
417
418 /**
419 * Implements the <tt>getLong</tt> method as per the specification in
420 * {@link Preferences#getLong(String,long)}.
421 *
422 * <p>This implementation invokes {@link #get(String,String) <tt>get(key,
423 * null)</tt>}. If the return value is non-null, the implementation
424 * attempts to translate it to a <tt>long</tt> with
425 * {@link Long#parseLong(String)}. If the attempt succeeds, the return
426 * value is returned by this method. Otherwise, <tt>def</tt> is returned.
427 *
428 * @param key key whose associated value is to be returned as a long.
429 * @param def the value to be returned in the event that this
430 * preference node has no value associated with <tt>key</tt>
431 * or the associated value cannot be interpreted as a long.
432 * @return the long value represented by the string associated with
433 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
434 * associated value does not exist or cannot be interpreted as
435 * a long.
436 * @throws IllegalStateException if this node (or an ancestor) has been
437 * removed with the {@link #removeNode()} method.
438 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
439 */
440 public long getLong(String key, long def) {
441 long result = def;
442 try {
443 String value = get(key, null);
444 if (value != null)
445 result = Long.parseLong(value);
446 } catch (NumberFormatException e) {
447 // Ignoring exception causes specified default to be returned
448 }
449
450 return result;
451 }
452
453 /**
454 * Implements the <tt>putBoolean</tt> method as per the specification in
455 * {@link Preferences#putBoolean(String,boolean)}.
456 *
457 * <p>This implementation translates <tt>value</tt> to a string with
458 * {@link String#valueOf(boolean)} and invokes {@link #put(String,String)}
459 * on the result.
460 *
461 * @param key key with which the string form of value is to be associated.
462 * @param value value whose string form is to be associated with key.
463 * @throws NullPointerException if key is <tt>null</tt>.
464 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
465 * <tt>MAX_KEY_LENGTH</tt>.
466 * @throws IllegalStateException if this node (or an ancestor) has been
467 * removed with the {@link #removeNode()} method.
468 */
469 public void putBoolean(String key, boolean value) {
470 put(key, String.valueOf(value));
471 }
472
473 /**
474 * Implements the <tt>getBoolean</tt> method as per the specification in
475 * {@link Preferences#getBoolean(String,boolean)}.
476 *
477 * <p>This implementation invokes {@link #get(String,String) <tt>get(key,
478 * null)</tt>}. If the return value is non-null, it is compared with
479 * <tt>"true"</tt> using {@link String#equalsIgnoreCase(String)}. If the
480 * comparison returns <tt>true</tt>, this invocation returns
481 * <tt>true</tt>. Otherwise, the original return value is compared with
482 * <tt>"false"</tt>, again using {@link String#equalsIgnoreCase(String)}.
483 * If the comparison returns <tt>true</tt>, this invocation returns
484 * <tt>false</tt>. Otherwise, this invocation returns <tt>def</tt>.
485 *
486 * @param key key whose associated value is to be returned as a boolean.
487 * @param def the value to be returned in the event that this
488 * preference node has no value associated with <tt>key</tt>
489 * or the associated value cannot be interpreted as a boolean.
490 * @return the boolean value represented by the string associated with
491 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
492 * associated value does not exist or cannot be interpreted as
493 * a boolean.
494 * @throws IllegalStateException if this node (or an ancestor) has been
495 * removed with the {@link #removeNode()} method.
496 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
497 */
498 public boolean getBoolean(String key, boolean def) {
499 boolean result = def;
500 String value = get(key, null);
501 if (value != null) {
502 if (value.equalsIgnoreCase("true"))
503 result = true;
504 else if (value.equalsIgnoreCase("false"))
505 result = false;
506 }
507
508 return result;
509 }
510
511 /**
512 * Implements the <tt>putFloat</tt> method as per the specification in
513 * {@link Preferences#putFloat(String,float)}.
514 *
515 * <p>This implementation translates <tt>value</tt> to a string with
516 * {@link Float#toString(float)} and invokes {@link #put(String,String)}
517 * on the result.
518 *
519 * @param key key with which the string form of value is to be associated.
520 * @param value value whose string form is to be associated with key.
521 * @throws NullPointerException if key is <tt>null</tt>.
522 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
523 * <tt>MAX_KEY_LENGTH</tt>.
524 * @throws IllegalStateException if this node (or an ancestor) has been
525 * removed with the {@link #removeNode()} method.
526 */
527 public void putFloat(String key, float value) {
528 put(key, Float.toString(value));
529 }
530
531 /**
532 * Implements the <tt>getFloat</tt> method as per the specification in
533 * {@link Preferences#getFloat(String,float)}.
534 *
535 * <p>This implementation invokes {@link #get(String,String) <tt>get(key,
536 * null)</tt>}. If the return value is non-null, the implementation
537 * attempts to translate it to an <tt>float</tt> with
538 * {@link Float#parseFloat(String)}. If the attempt succeeds, the return
539 * value is returned by this method. Otherwise, <tt>def</tt> is returned.
540 *
541 * @param key key whose associated value is to be returned as a float.
542 * @param def the value to be returned in the event that this
543 * preference node has no value associated with <tt>key</tt>
544 * or the associated value cannot be interpreted as a float.
545 * @return the float value represented by the string associated with
546 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
547 * associated value does not exist or cannot be interpreted as
548 * a float.
549 * @throws IllegalStateException if this node (or an ancestor) has been
550 * removed with the {@link #removeNode()} method.
551 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
552 */
553 public float getFloat(String key, float def) {
554 float result = def;
555 try {
556 String value = get(key, null);
557 if (value != null)
558 result = Float.parseFloat(value);
559 } catch (NumberFormatException e) {
560 // Ignoring exception causes specified default to be returned
561 }
562
563 return result;
564 }
565
566 /**
567 * Implements the <tt>putDouble</tt> method as per the specification in
568 * {@link Preferences#putDouble(String,double)}.
569 *
570 * <p>This implementation translates <tt>value</tt> to a string with
571 * {@link Double#toString(double)} and invokes {@link #put(String,String)}
572 * on the result.
573 *
574 * @param key key with which the string form of value is to be associated.
575 * @param value value whose string form is to be associated with key.
576 * @throws NullPointerException if key is <tt>null</tt>.
577 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
578 * <tt>MAX_KEY_LENGTH</tt>.
579 * @throws IllegalStateException if this node (or an ancestor) has been
580 * removed with the {@link #removeNode()} method.
581 */
582 public void putDouble(String key, double value) {
583 put(key, Double.toString(value));
584 }
585
586 /**
587 * Implements the <tt>getDouble</tt> method as per the specification in
588 * {@link Preferences#getDouble(String,double)}.
589 *
590 * <p>This implementation invokes {@link #get(String,String) <tt>get(key,
591 * null)</tt>}. If the return value is non-null, the implementation
592 * attempts to translate it to an <tt>double</tt> with
593 * {@link Double#parseDouble(String)}. If the attempt succeeds, the return
594 * value is returned by this method. Otherwise, <tt>def</tt> is returned.
595 *
596 * @param key key whose associated value is to be returned as a double.
597 * @param def the value to be returned in the event that this
598 * preference node has no value associated with <tt>key</tt>
599 * or the associated value cannot be interpreted as a double.
600 * @return the double value represented by the string associated with
601 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
602 * associated value does not exist or cannot be interpreted as
603 * a double.
604 * @throws IllegalStateException if this node (or an ancestor) has been
605 * removed with the {@link #removeNode()} method.
606 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
607 */
608 public double getDouble(String key, double def) {
609 double result = def;
610 try {
611 String value = get(key, null);
612 if (value != null)
613 result = Double.parseDouble(value);
614 } catch (NumberFormatException e) {
615 // Ignoring exception causes specified default to be returned
616 }
617
618 return result;
619 }
620
621 /**
622 * Implements the <tt>putByteArray</tt> method as per the specification in
623 * {@link Preferences#putByteArray(String,byte[])}.
624 *
625 * @param key key with which the string form of value is to be associated.
626 * @param value value whose string form is to be associated with key.
627 * @throws NullPointerException if key or value is <tt>null</tt>.
628 * @throws IllegalArgumentException if key.length() exceeds MAX_KEY_LENGTH
629 * or if value.length exceeds MAX_VALUE_LENGTH*3/4.
630 * @throws IllegalStateException if this node (or an ancestor) has been
631 * removed with the {@link #removeNode()} method.
632 */
633 public void putByteArray(String key, byte[] value) {
634 put(key, Base64.byteArrayToBase64(value));
635 }
636
637 /**
638 * Implements the <tt>getByteArray</tt> method as per the specification in
639 * {@link Preferences#getByteArray(String,byte[])}.
640 *
641 * @param key key whose associated value is to be returned as a byte array.
642 * @param def the value to be returned in the event that this
643 * preference node has no value associated with <tt>key</tt>
644 * or the associated value cannot be interpreted as a byte array.
645 * @return the byte array value represented by the string associated with
646 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
647 * associated value does not exist or cannot be interpreted as
648 * a byte array.
649 * @throws IllegalStateException if this node (or an ancestor) has been
650 * removed with the {@link #removeNode()} method.
651 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>. (A
652 * <tt>null</tt> value for <tt>def</tt> <i>is</i> permitted.)
653 */
654 public byte[] getByteArray(String key, byte[] def) {
655 byte[] result = def;
656 String value = get(key, null);
657 try {
658 if (value != null)
659 result = Base64.base64ToByteArray(value);
660 }
661 catch (RuntimeException e) {
662 // Ignoring exception causes specified default to be returned
663 }
664
665 return result;
666 }
667
668 /**
669 * Implements the <tt>keys</tt> method as per the specification in
670 * {@link Preferences#keys()}.
671 *
672 * <p>This implementation obtains this preference node's lock, checks that
673 * the node has not been removed and invokes {@link #keysSpi()}.
674 *
675 * @return an array of the keys that have an associated value in this
676 * preference node.
677 * @throws BackingStoreException if this operation cannot be completed
678 * due to a failure in the backing store, or inability to
679 * communicate with it.
680 * @throws IllegalStateException if this node (or an ancestor) has been
681 * removed with the {@link #removeNode()} method.
682 */
683 public String[] keys() throws BackingStoreException {
684 synchronized(lock) {
685 if (removed)
686 throw new IllegalStateException("Node has been removed.");
687
688 return keysSpi();
689 }
690 }
691
692 /**
693 * Implements the <tt>children</tt> method as per the specification in
694 * {@link Preferences#childrenNames()}.
695 *
696 * <p>This implementation obtains this preference node's lock, checks that
697 * the node has not been removed, constructs a <tt>TreeSet</tt> initialized
698 * to the names of children already cached (the children in this node's
699 * "child-cache"), invokes {@link #childrenNamesSpi()}, and adds all of the
700 * returned child-names into the set. The elements of the tree set are
701 * dumped into a <tt>String</tt> array using the <tt>toArray</tt> method,
702 * and this array is returned.
703 *
704 * @return the names of the children of this preference node.
705 * @throws BackingStoreException if this operation cannot be completed
706 * due to a failure in the backing store, or inability to
707 * communicate with it.
708 * @throws IllegalStateException if this node (or an ancestor) has been
709 * removed with the {@link #removeNode()} method.
710 * @see #cachedChildren()
711 */
712 public String[] childrenNames() throws BackingStoreException {
713 synchronized(lock) {
714 if (removed)
715 throw new IllegalStateException("Node has been removed.");
716
717 Set<String> s = new TreeSet<>(kidCache.keySet());
718 for (String kid : childrenNamesSpi())
719 s.add(kid);
720 return s.toArray(EMPTY_STRING_ARRAY);
721 }
722 }
723
724 private static final String[] EMPTY_STRING_ARRAY = new String[0];
725
726 /**
727 * Returns all known unremoved children of this node.
728 *
729 * @return all known unremoved children of this node.
730 */
731 protected final AbstractPreferences[] cachedChildren() {
732 return kidCache.values().toArray(EMPTY_ABSTRACT_PREFS_ARRAY);
733 }
734
735 private static final AbstractPreferences[] EMPTY_ABSTRACT_PREFS_ARRAY
736 = new AbstractPreferences[0];
737
738 /**
739 * Implements the <tt>parent</tt> method as per the specification in
740 * {@link Preferences#parent()}.
741 *
742 * <p>This implementation obtains this preference node's lock, checks that
743 * the node has not been removed and returns the parent value that was
744 * passed to this node's constructor.
745 *
746 * @return the parent of this preference node.
747 * @throws IllegalStateException if this node (or an ancestor) has been
748 * removed with the {@link #removeNode()} method.
749 */
750 public Preferences parent() {
751 synchronized(lock) {
752 if (removed)
753 throw new IllegalStateException("Node has been removed.");
754
755 return parent;
756 }
757 }
758
759 /**
760 * Implements the <tt>node</tt> method as per the specification in
761 * {@link Preferences#node(String)}.
762 *
763 * <p>This implementation obtains this preference node's lock and checks
764 * that the node has not been removed. If <tt>path</tt> is <tt>""</tt>,
765 * this node is returned; if <tt>path</tt> is <tt>"/"</tt>, this node's
766 * root is returned. If the first character in <tt>path</tt> is
767 * not <tt>'/'</tt>, the implementation breaks <tt>path</tt> into
768 * tokens and recursively traverses the path from this node to the
769 * named node, "consuming" a name and a slash from <tt>path</tt> at
770 * each step of the traversal. At each step, the current node is locked
771 * and the node's child-cache is checked for the named node. If it is
772 * not found, the name is checked to make sure its length does not
773 * exceed <tt>MAX_NAME_LENGTH</tt>. Then the {@link #childSpi(String)}
774 * method is invoked, and the result stored in this node's child-cache.
775 * If the newly created <tt>Preferences</tt> object's {@link #newNode}
776 * field is <tt>true</tt> and there are any node change listeners,
777 * a notification event is enqueued for processing by the event dispatch
778 * thread.
779 *
780 * <p>When there are no more tokens, the last value found in the
781 * child-cache or returned by <tt>childSpi</tt> is returned by this
782 * method. If during the traversal, two <tt>"/"</tt> tokens occur
783 * consecutively, or the final token is <tt>"/"</tt> (rather than a name),
784 * an appropriate <tt>IllegalArgumentException</tt> is thrown.
785 *
786 * <p> If the first character of <tt>path</tt> is <tt>'/'</tt>
787 * (indicating an absolute path name) this preference node's
788 * lock is dropped prior to breaking <tt>path</tt> into tokens, and
789 * this method recursively traverses the path starting from the root
790 * (rather than starting from this node). The traversal is otherwise
791 * identical to the one described for relative path names. Dropping
792 * the lock on this node prior to commencing the traversal at the root
793 * node is essential to avoid the possibility of deadlock, as per the
794 * {@link #lock locking invariant}.
795 *
796 * @param path the path name of the preference node to return.
797 * @return the specified preference node.
798 * @throws IllegalArgumentException if the path name is invalid (i.e.,
799 * it contains multiple consecutive slash characters, or ends
800 * with a slash character and is more than one character long).
801 * @throws IllegalStateException if this node (or an ancestor) has been
802 * removed with the {@link #removeNode()} method.
803 */
804 public Preferences node(String path) {
805 synchronized(lock) {
806 if (removed)
807 throw new IllegalStateException("Node has been removed.");
808 if (path.equals(""))
809 return this;
810 if (path.equals("/"))
811 return root;
812 if (path.charAt(0) != '/')
813 return node(new StringTokenizer(path, "/", true));
814 }
815
816 // Absolute path. Note that we've dropped our lock to avoid deadlock
817 return root.node(new StringTokenizer(path.substring(1), "/", true));
818 }
819
820 /**
821 * tokenizer contains <name> {'/' <name>}*
822 */
823 private Preferences node(StringTokenizer path) {
824 String token = path.nextToken();
825 if (token.equals("/")) // Check for consecutive slashes
826 throw new IllegalArgumentException("Consecutive slashes in path");
827 synchronized(lock) {
828 AbstractPreferences child = kidCache.get(token);
829 if (child == null) {
830 if (token.length() > MAX_NAME_LENGTH)
831 throw new IllegalArgumentException(
832 "Node name " + token + " too long");
833 child = childSpi(token);
834 if (child.newNode)
835 enqueueNodeAddedEvent(child);
836 kidCache.put(token, child);
837 }
838 if (!path.hasMoreTokens())
839 return child;
840 path.nextToken(); // Consume slash
841 if (!path.hasMoreTokens())
842 throw new IllegalArgumentException("Path ends with slash");
843 return child.node(path);
844 }
845 }
846
847 /**
848 * Implements the <tt>nodeExists</tt> method as per the specification in
849 * {@link Preferences#nodeExists(String)}.
850 *
851 * <p>This implementation is very similar to {@link #node(String)},
852 * except that {@link #getChild(String)} is used instead of {@link
853 * #childSpi(String)}.
854 *
855 * @param path the path name of the node whose existence is to be checked.
856 * @return true if the specified node exists.
857 * @throws BackingStoreException if this operation cannot be completed
858 * due to a failure in the backing store, or inability to
859 * communicate with it.
860 * @throws IllegalArgumentException if the path name is invalid (i.e.,
861 * it contains multiple consecutive slash characters, or ends
862 * with a slash character and is more than one character long).
863 * @throws IllegalStateException if this node (or an ancestor) has been
864 * removed with the {@link #removeNode()} method and
865 * <tt>pathname</tt> is not the empty string (<tt>""</tt>).
866 */
867 public boolean nodeExists(String path)
868 throws BackingStoreException
869 {
870 synchronized(lock) {
871 if (path.equals(""))
872 return !removed;
873 if (removed)
874 throw new IllegalStateException("Node has been removed.");
875 if (path.equals("/"))
876 return true;
877 if (path.charAt(0) != '/')
878 return nodeExists(new StringTokenizer(path, "/", true));
879 }
880
881 // Absolute path. Note that we've dropped our lock to avoid deadlock
882 return root.nodeExists(new StringTokenizer(path.substring(1), "/",
883 true));
884 }
885
886 /**
887 * tokenizer contains <name> {'/' <name>}*
888 */
889 private boolean nodeExists(StringTokenizer path)
890 throws BackingStoreException
891 {
892 String token = path.nextToken();
893 if (token.equals("/")) // Check for consecutive slashes
894 throw new IllegalArgumentException("Consecutive slashes in path");
895 synchronized(lock) {
896 AbstractPreferences child = kidCache.get(token);
897 if (child == null)
898 child = getChild(token);
899 if (child==null)
900 return false;
901 if (!path.hasMoreTokens())
902 return true;
903 path.nextToken(); // Consume slash
904 if (!path.hasMoreTokens())
905 throw new IllegalArgumentException("Path ends with slash");
906 return child.nodeExists(path);
907 }
908 }
909
910 /**
911
912 * Implements the <tt>removeNode()</tt> method as per the specification in
913 * {@link Preferences#removeNode()}.
914 *
915 * <p>This implementation checks to see that this node is the root; if so,
916 * it throws an appropriate exception. Then, it locks this node's parent,
917 * and calls a recursive helper method that traverses the subtree rooted at
918 * this node. The recursive method locks the node on which it was called,
919 * checks that it has not already been removed, and then ensures that all
920 * of its children are cached: The {@link #childrenNamesSpi()} method is
921 * invoked and each returned child name is checked for containment in the
922 * child-cache. If a child is not already cached, the {@link
923 * #childSpi(String)} method is invoked to create a <tt>Preferences</tt>
924 * instance for it, and this instance is put into the child-cache. Then
925 * the helper method calls itself recursively on each node contained in its
926 * child-cache. Next, it invokes {@link #removeNodeSpi()}, marks itself
927 * as removed, and removes itself from its parent's child-cache. Finally,
928 * if there are any node change listeners, it enqueues a notification
929 * event for processing by the event dispatch thread.
930 *
931 * <p>Note that the helper method is always invoked with all ancestors up
932 * to the "closest non-removed ancestor" locked.
933 *
934 * @throws IllegalStateException if this node (or an ancestor) has already
935 * been removed with the {@link #removeNode()} method.
936 * @throws UnsupportedOperationException if this method is invoked on
937 * the root node.
938 * @throws BackingStoreException if this operation cannot be completed
939 * due to a failure in the backing store, or inability to
940 * communicate with it.
941 */
942 public void removeNode() throws BackingStoreException {
943 if (this==root)
944 throw new UnsupportedOperationException("Can't remove the root!");
945 synchronized(parent.lock) {
946 removeNode2();
947 parent.kidCache.remove(name);
948 }
949 }
950
951 /*
952 * Called with locks on all nodes on path from parent of "removal root"
953 * to this (including the former but excluding the latter).
954 */
955 private void removeNode2() throws BackingStoreException {
956 synchronized(lock) {
957 if (removed)
958 throw new IllegalStateException("Node already removed.");
959
960 // Ensure that all children are cached
961 String[] kidNames = childrenNamesSpi();
962 for (int i=0; i<kidNames.length; i++)
963 if (!kidCache.containsKey(kidNames[i]))
964 kidCache.put(kidNames[i], childSpi(kidNames[i]));
965
966 // Recursively remove all cached children
967 for (Iterator<AbstractPreferences> i = kidCache.values().iterator();
968 i.hasNext();) {
969 try {
970 i.next().removeNode2();
971 i.remove();
972 } catch (BackingStoreException x) { }
973 }
974
975 // Now we have no descendants - it's time to die!
976 removeNodeSpi();
977 removed = true;
978 parent.enqueueNodeRemovedEvent(this);
979 }
980 }
981
982 /**
983 * Implements the <tt>name</tt> method as per the specification in
984 * {@link Preferences#name()}.
985 *
986 * <p>This implementation merely returns the name that was
987 * passed to this node's constructor.
988 *
989 * @return this preference node's name, relative to its parent.
990 */
991 public String name() {
992 return name;
993 }
994
995 /**
996 * Implements the <tt>absolutePath</tt> method as per the specification in
997 * {@link Preferences#absolutePath()}.
998 *
999 * <p>This implementation merely returns the absolute path name that
1000 * was computed at the time that this node was constructed (based on
1001 * the name that was passed to this node's constructor, and the names
1002 * that were passed to this node's ancestors' constructors).
1003 *
1004 * @return this preference node's absolute path name.
1005 */
1006 public String absolutePath() {
1007 return absolutePath;
1008 }
1009
1010 /**
1011 * Implements the <tt>isUserNode</tt> method as per the specification in
1012 * {@link Preferences#isUserNode()}.
1013 *
1014 * <p>This implementation compares this node's root node (which is stored
1015 * in a private field) with the value returned by
1016 * {@link Preferences#userRoot()}. If the two object references are
1017 * identical, this method returns true.
1018 *
1019 * @return <tt>true</tt> if this preference node is in the user
1020 * preference tree, <tt>false</tt> if it's in the system
1021 * preference tree.
1022 */
1023 public boolean isUserNode() {
1024 return AccessController.doPrivileged(
1025 new PrivilegedAction<Boolean>() {
1026 public Boolean run() {
1027 return root == Preferences.userRoot();
1028 }
1029 }).booleanValue();
1030 }
1031
1032 public void addPreferenceChangeListener(PreferenceChangeListener pcl) {
1033 if (pcl==null)
1034 throw new NullPointerException("Change listener is null.");
1035 synchronized(lock) {
1036 if (removed)
1037 throw new IllegalStateException("Node has been removed.");
1038
1039 // Copy-on-write
1040 PreferenceChangeListener[] old = prefListeners;
1041 prefListeners = new PreferenceChangeListener[old.length + 1];
1042 System.arraycopy(old, 0, prefListeners, 0, old.length);
1043 prefListeners[old.length] = pcl;
1044 }
1045 startEventDispatchThreadIfNecessary();
1046 }
1047
1048 public void removePreferenceChangeListener(PreferenceChangeListener pcl) {
1049 synchronized(lock) {
1050 if (removed)
1051 throw new IllegalStateException("Node has been removed.");
1052 if ((prefListeners == null) || (prefListeners.length == 0))
1053 throw new IllegalArgumentException("Listener not registered.");
1054
1055 // Copy-on-write
1056 PreferenceChangeListener[] newPl =
1057 new PreferenceChangeListener[prefListeners.length - 1];
1058 int i = 0;
1059 while (i < newPl.length && prefListeners[i] != pcl)
1060 newPl[i] = prefListeners[i++];
1061
1062 if (i == newPl.length && prefListeners[i] != pcl)
1063 throw new IllegalArgumentException("Listener not registered.");
1064 while (i < newPl.length)
1065 newPl[i] = prefListeners[++i];
1066 prefListeners = newPl;
1067 }
1068 }
1069
1070 public void addNodeChangeListener(NodeChangeListener ncl) {
1071 if (ncl==null)
1072 throw new NullPointerException("Change listener is null.");
1073 synchronized(lock) {
1074 if (removed)
1075 throw new IllegalStateException("Node has been removed.");
1076
1077 // Copy-on-write
1078 if (nodeListeners == null) {
1079 nodeListeners = new NodeChangeListener[1];
1080 nodeListeners[0] = ncl;
1081 } else {
1082 NodeChangeListener[] old = nodeListeners;
1083 nodeListeners = new NodeChangeListener[old.length + 1];
1084 System.arraycopy(old, 0, nodeListeners, 0, old.length);
1085 nodeListeners[old.length] = ncl;
1086 }
1087 }
1088 startEventDispatchThreadIfNecessary();
1089 }
1090
1091 public void removeNodeChangeListener(NodeChangeListener ncl) {
1092 synchronized(lock) {
1093 if (removed)
1094 throw new IllegalStateException("Node has been removed.");
1095 if ((nodeListeners == null) || (nodeListeners.length == 0))
1096 throw new IllegalArgumentException("Listener not registered.");
1097
1098 // Copy-on-write
1099 int i = 0;
1100 while (i < nodeListeners.length && nodeListeners[i] != ncl)
1101 i++;
1102 if (i == nodeListeners.length)
1103 throw new IllegalArgumentException("Listener not registered.");
1104 NodeChangeListener[] newNl =
1105 new NodeChangeListener[nodeListeners.length - 1];
1106 if (i != 0)
1107 System.arraycopy(nodeListeners, 0, newNl, 0, i);
1108 if (i != newNl.length)
1109 System.arraycopy(nodeListeners, i + 1,
1110 newNl, i, newNl.length - i);
1111 nodeListeners = newNl;
1112 }
1113 }
1114
1115 // "SPI" METHODS
1116
1117 /**
1118 * Put the given key-value association into this preference node. It is
1119 * guaranteed that <tt>key</tt> and <tt>value</tt> are non-null and of
1120 * legal length. Also, it is guaranteed that this node has not been
1121 * removed. (The implementor needn't check for any of these things.)
1122 *
1123 * <p>This method is invoked with the lock on this node held.
1124 */
1125 protected abstract void putSpi(String key, String value);
1126
1127 /**
1128 * Return the value associated with the specified key at this preference
1129 * node, or <tt>null</tt> if there is no association for this key, or the
1130 * association cannot be determined at this time. It is guaranteed that
1131 * <tt>key</tt> is non-null. Also, it is guaranteed that this node has
1132 * not been removed. (The implementor needn't check for either of these
1133 * things.)
1134 *
1135 * <p> Generally speaking, this method should not throw an exception
1136 * under any circumstances. If, however, if it does throw an exception,
1137 * the exception will be intercepted and treated as a <tt>null</tt>
1138 * return value.
1139 *
1140 * <p>This method is invoked with the lock on this node held.
1141 *
1142 * @return the value associated with the specified key at this preference
1143 * node, or <tt>null</tt> if there is no association for this
1144 * key, or the association cannot be determined at this time.
1145 */
1146 protected abstract String getSpi(String key);
1147
1148 /**
1149 * Remove the association (if any) for the specified key at this
1150 * preference node. It is guaranteed that <tt>key</tt> is non-null.
1151 * Also, it is guaranteed that this node has not been removed.
1152 * (The implementor needn't check for either of these things.)
1153 *
1154 * <p>This method is invoked with the lock on this node held.
1155 */
1156 protected abstract void removeSpi(String key);
1157
1158 /**
1159 * Removes this preference node, invalidating it and any preferences that
1160 * it contains. The named child will have no descendants at the time this
1161 * invocation is made (i.e., the {@link Preferences#removeNode()} method
1162 * invokes this method repeatedly in a bottom-up fashion, removing each of
1163 * a node's descendants before removing the node itself).
1164 *
1165 * <p>This method is invoked with the lock held on this node and its
1166 * parent (and all ancestors that are being removed as a
1167 * result of a single invocation to {@link Preferences#removeNode()}).
1168 *
1169 * <p>The removal of a node needn't become persistent until the
1170 * <tt>flush</tt> method is invoked on this node (or an ancestor).
1171 *
1172 * <p>If this node throws a <tt>BackingStoreException</tt>, the exception
1173 * will propagate out beyond the enclosing {@link #removeNode()}
1174 * invocation.
1175 *
1176 * @throws BackingStoreException if this operation cannot be completed
1177 * due to a failure in the backing store, or inability to
1178 * communicate with it.
1179 */
1180 protected abstract void removeNodeSpi() throws BackingStoreException;
1181
1182 /**
1183 * Returns all of the keys that have an associated value in this
1184 * preference node. (The returned array will be of size zero if
1185 * this node has no preferences.) It is guaranteed that this node has not
1186 * been removed.
1187 *
1188 * <p>This method is invoked with the lock on this node held.
1189 *
1190 * <p>If this node throws a <tt>BackingStoreException</tt>, the exception
1191 * will propagate out beyond the enclosing {@link #keys()} invocation.
1192 *
1193 * @return an array of the keys that have an associated value in this
1194 * preference node.
1195 * @throws BackingStoreException if this operation cannot be completed
1196 * due to a failure in the backing store, or inability to
1197 * communicate with it.
1198 */
1199 protected abstract String[] keysSpi() throws BackingStoreException;
1200
1201 /**
1202 * Returns the names of the children of this preference node. (The
1203 * returned array will be of size zero if this node has no children.)
1204 * This method need not return the names of any nodes already cached,
1205 * but may do so without harm.
1206 *
1207 * <p>This method is invoked with the lock on this node held.
1208 *
1209 * <p>If this node throws a <tt>BackingStoreException</tt>, the exception
1210 * will propagate out beyond the enclosing {@link #childrenNames()}
1211 * invocation.
1212 *
1213 * @return an array containing the names of the children of this
1214 * preference node.
1215 * @throws BackingStoreException if this operation cannot be completed
1216 * due to a failure in the backing store, or inability to
1217 * communicate with it.
1218 */
1219 protected abstract String[] childrenNamesSpi()
1220 throws BackingStoreException;
1221
1222 /**
1223 * Returns the named child if it exists, or <tt>null</tt> if it does not.
1224 * It is guaranteed that <tt>nodeName</tt> is non-null, non-empty,
1225 * does not contain the slash character ('/'), and is no longer than
1226 * {@link #MAX_NAME_LENGTH} characters. Also, it is guaranteed
1227 * that this node has not been removed. (The implementor needn't check
1228 * for any of these things if he chooses to override this method.)
1229 *
1230 * <p>Finally, it is guaranteed that the named node has not been returned
1231 * by a previous invocation of this method or {@link #childSpi} after the
1232 * last time that it was removed. In other words, a cached value will
1233 * always be used in preference to invoking this method. (The implementor
1234 * needn't maintain his own cache of previously returned children if he
1235 * chooses to override this method.)
1236 *
1237 * <p>This implementation obtains this preference node's lock, invokes
1238 * {@link #childrenNames()} to get an array of the names of this node's
1239 * children, and iterates over the array comparing the name of each child
1240 * with the specified node name. If a child node has the correct name,
1241 * the {@link #childSpi(String)} method is invoked and the resulting
1242 * node is returned. If the iteration completes without finding the
1243 * specified name, <tt>null</tt> is returned.
1244 *
1245 * @param nodeName name of the child to be searched for.
1246 * @return the named child if it exists, or null if it does not.
1247 * @throws BackingStoreException if this operation cannot be completed
1248 * due to a failure in the backing store, or inability to
1249 * communicate with it.
1250 */
1251 protected AbstractPreferences getChild(String nodeName)
1252 throws BackingStoreException {
1253 synchronized(lock) {
1254 // assert kidCache.get(nodeName)==null;
1255 String[] kidNames = childrenNames();
1256 for (int i=0; i<kidNames.length; i++)
1257 if (kidNames[i].equals(nodeName))
1258 return childSpi(kidNames[i]);
1259 }
1260 return null;
1261 }
1262
1263 /**
1264 * Returns the named child of this preference node, creating it if it does
1265 * not already exist. It is guaranteed that <tt>name</tt> is non-null,
1266 * non-empty, does not contain the slash character ('/'), and is no longer
1267 * than {@link #MAX_NAME_LENGTH} characters. Also, it is guaranteed that
1268 * this node has not been removed. (The implementor needn't check for any
1269 * of these things.)
1270 *
1271 * <p>Finally, it is guaranteed that the named node has not been returned
1272 * by a previous invocation of this method or {@link #getChild(String)}
1273 * after the last time that it was removed. In other words, a cached
1274 * value will always be used in preference to invoking this method.
1275 * Subclasses need not maintain their own cache of previously returned
1276 * children.
1277 *
1278 * <p>The implementer must ensure that the returned node has not been
1279 * removed. If a like-named child of this node was previously removed, the
1280 * implementer must return a newly constructed <tt>AbstractPreferences</tt>
1281 * node; once removed, an <tt>AbstractPreferences</tt> node
1282 * cannot be "resuscitated."
1283 *
1284 * <p>If this method causes a node to be created, this node is not
1285 * guaranteed to be persistent until the <tt>flush</tt> method is
1286 * invoked on this node or one of its ancestors (or descendants).
1287 *
1288 * <p>This method is invoked with the lock on this node held.
1289 *
1290 * @param name The name of the child node to return, relative to
1291 * this preference node.
1292 * @return The named child node.
1293 */
1294 protected abstract AbstractPreferences childSpi(String name);
1295
1296 /**
1297 * Returns the absolute path name of this preferences node.
1298 */
1299 public String toString() {
1300 return (this.isUserNode() ? "User" : "System") +
1301 " Preference Node: " + this.absolutePath();
1302 }
1303
1304 /**
1305 * Implements the <tt>sync</tt> method as per the specification in
1306 * {@link Preferences#sync()}.
1307 *
1308 * <p>This implementation calls a recursive helper method that locks this
1309 * node, invokes syncSpi() on it, unlocks this node, and recursively
1310 * invokes this method on each "cached child." A cached child is a child
1311 * of this node that has been created in this VM and not subsequently
1312 * removed. In effect, this method does a depth first traversal of the
1313 * "cached subtree" rooted at this node, calling syncSpi() on each node in
1314 * the subTree while only that node is locked. Note that syncSpi() is
1315 * invoked top-down.
1316 *
1317 * @throws BackingStoreException if this operation cannot be completed
1318 * due to a failure in the backing store, or inability to
1319 * communicate with it.
1320 * @throws IllegalStateException if this node (or an ancestor) has been
1321 * removed with the {@link #removeNode()} method.
1322 * @see #flush()
1323 */
1324 public void sync() throws BackingStoreException {
1325 sync2();
1326 }
1327
1328 private void sync2() throws BackingStoreException {
1329 AbstractPreferences[] cachedKids;
1330
1331 synchronized(lock) {
1332 if (removed)
1333 throw new IllegalStateException("Node has been removed");
1334 syncSpi();
1335 cachedKids = cachedChildren();
1336 }
1337
1338 for (int i=0; i<cachedKids.length; i++)
1339 cachedKids[i].sync2();
1340 }
1341
1342 /**
1343 * This method is invoked with this node locked. The contract of this
1344 * method is to synchronize any cached preferences stored at this node
1345 * with any stored in the backing store. (It is perfectly possible that
1346 * this node does not exist on the backing store, either because it has
1347 * been deleted by another VM, or because it has not yet been created.)
1348 * Note that this method should <i>not</i> synchronize the preferences in
1349 * any subnodes of this node. If the backing store naturally syncs an
1350 * entire subtree at once, the implementer is encouraged to override
1351 * sync(), rather than merely overriding this method.
1352 *
1353 * <p>If this node throws a <tt>BackingStoreException</tt>, the exception
1354 * will propagate out beyond the enclosing {@link #sync()} invocation.
1355 *
1356 * @throws BackingStoreException if this operation cannot be completed
1357 * due to a failure in the backing store, or inability to
1358 * communicate with it.
1359 */
1360 protected abstract void syncSpi() throws BackingStoreException;
1361
1362 /**
1363 * Implements the <tt>flush</tt> method as per the specification in
1364 * {@link Preferences#flush()}.
1365 *
1366 * <p>This implementation calls a recursive helper method that locks this
1367 * node, invokes flushSpi() on it, unlocks this node, and recursively
1368 * invokes this method on each "cached child." A cached child is a child
1369 * of this node that has been created in this VM and not subsequently
1370 * removed. In effect, this method does a depth first traversal of the
1371 * "cached subtree" rooted at this node, calling flushSpi() on each node in
1372 * the subTree while only that node is locked. Note that flushSpi() is
1373 * invoked top-down.
1374 *
1375 * <p> If this method is invoked on a node that has been removed with
1376 * the {@link #removeNode()} method, flushSpi() is invoked on this node,
1377 * but not on others.
1378 *
1379 * @throws BackingStoreException if this operation cannot be completed
1380 * due to a failure in the backing store, or inability to
1381 * communicate with it.
1382 * @see #flush()
1383 */
1384 public void flush() throws BackingStoreException {
1385 flush2();
1386 }
1387
1388 private void flush2() throws BackingStoreException {
1389 AbstractPreferences[] cachedKids;
1390
1391 synchronized(lock) {
1392 flushSpi();
1393 if(removed)
1394 return;
1395 cachedKids = cachedChildren();
1396 }
1397
1398 for (int i = 0; i < cachedKids.length; i++)
1399 cachedKids[i].flush2();
1400 }
1401
1402 /**
1403 * This method is invoked with this node locked. The contract of this
1404 * method is to force any cached changes in the contents of this
1405 * preference node to the backing store, guaranteeing their persistence.
1406 * (It is perfectly possible that this node does not exist on the backing
1407 * store, either because it has been deleted by another VM, or because it
1408 * has not yet been created.) Note that this method should <i>not</i>
1409 * flush the preferences in any subnodes of this node. If the backing
1410 * store naturally flushes an entire subtree at once, the implementer is
1411 * encouraged to override flush(), rather than merely overriding this
1412 * method.
1413 *
1414 * <p>If this node throws a <tt>BackingStoreException</tt>, the exception
1415 * will propagate out beyond the enclosing {@link #flush()} invocation.
1416 *
1417 * @throws BackingStoreException if this operation cannot be completed
1418 * due to a failure in the backing store, or inability to
1419 * communicate with it.
1420 */
1421 protected abstract void flushSpi() throws BackingStoreException;
1422
1423 /**
1424 * Returns <tt>true</tt> iff this node (or an ancestor) has been
1425 * removed with the {@link #removeNode()} method. This method
1426 * locks this node prior to returning the contents of the private
1427 * field used to track this state.
1428 *
1429 * @return <tt>true</tt> iff this node (or an ancestor) has been
1430 * removed with the {@link #removeNode()} method.
1431 */
1432 protected boolean isRemoved() {
1433 synchronized(lock) {
1434 return removed;
1435 }
1436 }
1437
1438 /**
1439 * Queue of pending notification events. When a preference or node
1440 * change event for which there are one or more listeners occurs,
1441 * it is placed on this queue and the queue is notified. A background
1442 * thread waits on this queue and delivers the events. This decouples
1443 * event delivery from preference activity, greatly simplifying
1444 * locking and reducing opportunity for deadlock.
1445 */
1446 private static final List<EventObject> eventQueue = new LinkedList<>();
1447
1448 /**
1449 * These two classes are used to distinguish NodeChangeEvents on
1450 * eventQueue so the event dispatch thread knows whether to call
1451 * childAdded or childRemoved.
1452 */
1453 private class NodeAddedEvent extends NodeChangeEvent {
1454 private static final long serialVersionUID = -6743557530157328528L;
1455 NodeAddedEvent(Preferences parent, Preferences child) {
1456 super(parent, child);
1457 }
1458 }
1459 private class NodeRemovedEvent extends NodeChangeEvent {
1460 private static final long serialVersionUID = 8735497392918824837L;
1461 NodeRemovedEvent(Preferences parent, Preferences child) {
1462 super(parent, child);
1463 }
1464 }
1465
1466 /**
1467 * A single background thread ("the event notification thread") monitors
1468 * the event queue and delivers events that are placed on the queue.
1469 */
1470 private static class EventDispatchThread extends Thread {
1471 public void run() {
1472 while(true) {
1473 // Wait on eventQueue till an event is present
1474 EventObject event = null;
1475 synchronized(eventQueue) {
1476 try {
1477 while (eventQueue.isEmpty())
1478 eventQueue.wait();
1479 event = eventQueue.remove(0);
1480 } catch (InterruptedException e) {
1481 // XXX Log "Event dispatch thread interrupted. Exiting"
1482 return;
1483 }
1484 }
1485
1486 // Now we have event & hold no locks; deliver evt to listeners
1487 AbstractPreferences src=(AbstractPreferences)event.getSource();
1488 if (event instanceof PreferenceChangeEvent) {
1489 PreferenceChangeEvent pce = (PreferenceChangeEvent)event;
1490 PreferenceChangeListener[] listeners = src.prefListeners();
1491 for (int i=0; i<listeners.length; i++)
1492 listeners[i].preferenceChange(pce);
1493 } else {
1494 NodeChangeEvent nce = (NodeChangeEvent)event;
1495 NodeChangeListener[] listeners = src.nodeListeners();
1496 if (nce instanceof NodeAddedEvent) {
1497 for (int i=0; i<listeners.length; i++)
1498 listeners[i].childAdded(nce);
1499 } else {
1500 // assert nce instanceof NodeRemovedEvent;
1501 for (int i=0; i<listeners.length; i++)
1502 listeners[i].childRemoved(nce);
1503 }
1504 }
1505 }
1506 }
1507 }
1508
1509 private static Thread eventDispatchThread = null;
1510
1511 /**
1512 * This method starts the event dispatch thread the first time it
1513 * is called. The event dispatch thread will be started only
1514 * if someone registers a listener.
1515 */
1516 private static synchronized void startEventDispatchThreadIfNecessary() {
1517 if (eventDispatchThread == null) {
1518 // XXX Log "Starting event dispatch thread"
1519 eventDispatchThread = new EventDispatchThread();
1520 eventDispatchThread.setDaemon(true);
1521 eventDispatchThread.start();
1522 }
1523 }
1524
1525 /**
1526 * Return this node's preference/node change listeners. Even though
1527 * we're using a copy-on-write lists, we use synchronized accessors to
1528 * ensure information transmission from the writing thread to the
1529 * reading thread.
1530 */
1531 PreferenceChangeListener[] prefListeners() {
1532 synchronized(lock) {
1533 return prefListeners;
1534 }
1535 }
1536 NodeChangeListener[] nodeListeners() {
1537 synchronized(lock) {
1538 return nodeListeners;
1539 }
1540 }
1541
1542 /**
1543 * Enqueue a preference change event for delivery to registered
1544 * preference change listeners unless there are no registered
1545 * listeners. Invoked with this.lock held.
1546 */
1547 private void enqueuePreferenceChangeEvent(String key, String newValue) {
1548 if (prefListeners.length != 0) {
1549 synchronized(eventQueue) {
1550 eventQueue.add(new PreferenceChangeEvent(this, key, newValue));
1551 eventQueue.notify();
1552 }
1553 }
1554 }
1555
1556 /**
1557 * Enqueue a "node added" event for delivery to registered node change
1558 * listeners unless there are no registered listeners. Invoked with
1559 * this.lock held.
1560 */
1561 private void enqueueNodeAddedEvent(Preferences child) {
1562 if (nodeListeners.length != 0) {
1563 synchronized(eventQueue) {
1564 eventQueue.add(new NodeAddedEvent(this, child));
1565 eventQueue.notify();
1566 }
1567 }
1568 }
1569
1570 /**
1571 * Enqueue a "node removed" event for delivery to registered node change
1572 * listeners unless there are no registered listeners. Invoked with
1573 * this.lock held.
1574 */
1575 private void enqueueNodeRemovedEvent(Preferences child) {
1576 if (nodeListeners.length != 0) {
1577 synchronized(eventQueue) {
1578 eventQueue.add(new NodeRemovedEvent(this, child));
1579 eventQueue.notify();
1580 }
1581 }
1582 }
1583
1584 /**
1585 * Implements the <tt>exportNode</tt> method as per the specification in
1586 * {@link Preferences#exportNode(OutputStream)}.
1587 *
1588 * @param os the output stream on which to emit the XML document.
1589 * @throws IOException if writing to the specified output stream
1590 * results in an <tt>IOException</tt>.
1591 * @throws BackingStoreException if preference data cannot be read from
1592 * backing store.
1593 */
1594 public void exportNode(OutputStream os)
1595 throws IOException, BackingStoreException
1596 {
1597 XmlSupport.export(os, this, false);
1598 }
1599
1600 /**
1601 * Implements the <tt>exportSubtree</tt> method as per the specification in
1602 * {@link Preferences#exportSubtree(OutputStream)}.
1603 *
1604 * @param os the output stream on which to emit the XML document.
1605 * @throws IOException if writing to the specified output stream
1606 * results in an <tt>IOException</tt>.
1607 * @throws BackingStoreException if preference data cannot be read from
1608 * backing store.
1609 */
1610 public void exportSubtree(OutputStream os)
1611 throws IOException, BackingStoreException
1612 {
1613 XmlSupport.export(os, this, true);
1614 }
1615 }