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