| AbstractPreferences.java |
1 /*
2 * %W% %E%
3 *
4 * Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved.
5 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6 */
7
8 package java.util.prefs;
9
10 import java.util.*;
11 import java.io.*;
12 import java.security.AccessController;
13 import java.security.PrivilegedAction;
14 // These imports needed only as a workaround for a JavaDoc bug
15 import java.lang.Integer;
16 import java.lang.Long;
17 import java.lang.Float;
18 import java.lang.Double;
19
20 /**
21 * This class provides a skeletal implementation of the {@link Preferences}
22 * class, greatly easing the task of implementing it.
23 *
24 * <p><strong>This class is for <tt>Preferences</tt> implementers only.
25 * Normal users of the <tt>Preferences</tt> facility should have no need to
26 * consult this documentation. The {@link Preferences} documentation
27 * should suffice.</strong>
28 *
29 * <p>Implementors must override the nine abstract service-provider interface
30 * (SPI) methods: {@link #getSpi(String)}, {@link #putSpi(String,String)},
31 * {@link #removeSpi(String)}, {@link #childSpi(String)}, {@link
32 * #removeNodeSpi()}, {@link #keysSpi()}, {@link #childrenNamesSpi()}, {@link
33 * #syncSpi()} and {@link #flushSpi()}. All of the concrete methods specify
34 * precisely how they are implemented atop these SPI methods. The implementor
35 * may, at his discretion, override one or more of the concrete methods if the
36 * default implementation is unsatisfactory for any reason, such as
37 * performance.
38 *
39 * <p>The SPI methods fall into three groups concerning exception
40 * behavior. The <tt>getSpi</tt> method should never throw exceptions, but it
41 * doesn't really matter, as any exception thrown by this method will be
42 * intercepted by {@link #get(String,String)}, which will return the specified
43 * default value to the caller. The <tt>removeNodeSpi, keysSpi,
44 * childrenNamesSpi, syncSpi</tt> and <tt>flushSpi</tt> methods are specified
45 * to throw {@link BackingStoreException}, and the implementation is required
46 * to throw this checked exception if it is unable to perform the operation.
47 * The exception propagates outward, causing the corresponding API method
48 * to fail.
49 *
50 * <p>The remaining SPI methods {@link #putSpi(String,String)}, {@link
51 * #removeSpi(String)} and {@link #childSpi(String)} have more complicated
52 * exception behavior. They are not specified to throw
53 * <tt>BackingStoreException</tt>, as they can generally obey their contracts
54 * even if the backing store is unavailable. This is true because they return
55 * no information and their effects are not required to become permanent until
56 * a subsequent call to {@link Preferences#flush()} or
57 * {@link Preferences#sync()}. Generally speaking, these SPI methods should not
58 * throw exceptions. In some implementations, there may be circumstances
59 * under which these calls cannot even enqueue the requested operation for
60 * later processing. Even under these circumstances it is generally better to
61 * simply ignore the invocation and return, rather than throwing an
62 * exception. Under these circumstances, however, all subsequent invocations
63 * of <tt>flush()</tt> and <tt>sync</tt> should return <tt>false</tt>, as
64 * returning <tt>true</tt> would imply that all previous operations had
65 * successfully been made permanent.
66 *
67 * <p>There is one circumstance under which <tt>putSpi, removeSpi and
68 * childSpi</tt> <i>should</i> throw an exception: if the caller lacks
69 * sufficient privileges on the underlying operating system to perform the
70 * requested operation. This will, for instance, occur on most systems
71 * if a non-privileged user attempts to modify system preferences.
72 * (The required privileges will vary from implementation to
73 * implementation. On some implementations, they are the right to modify the
74 * contents of some directory in the file system; on others they are the right
75 * to modify contents of some key in a registry.) Under any of these
76 * circumstances, it would generally be undesirable to let the program
77 * continue executing as if these operations would become permanent at a later
78 * time. While implementations are not required to throw an exception under
79 * these circumstances, they are encouraged to do so. A {@link
80 * SecurityException} would be appropriate.
81 *
82 * <p>Most of the SPI methods require the implementation to read or write
83 * information at a preferences node. The implementor should beware of the
84 * fact that another VM may have concurrently deleted this node from the
85 * backing store. It is the implementation's responsibility to recreate the
86 * node if it has been deleted.
87 *
88 * <p>Implementation note: In Sun's default <tt>Preferences</tt>
89 * implementations, the user's identity is inherited from the underlying
90 * operating system and does not change for the lifetime of the virtual
91 * machine. It is recognized that server-side <tt>Preferences</tt>
92 * implementations may have the user identity change from request to request,
93 * implicitly passed to <tt>Preferences</tt> methods via the use of a
94 * static {@link ThreadLocal} instance. Authors of such implementations are
95 * <i>strongly</i> encouraged to determine the user at the time preferences
96 * are accessed (for example by the {@link #get(String,String)} or {@link
97 * #put(String,String)} method) rather than permanently associating a user
98 * with each <tt>Preferences</tt> instance. The latter behavior conflicts
99 * with normal <tt>Preferences</tt> usage and would lead to great confusion.
100 *
101 * @author Josh Bloch
102 * @version %I%, %G%
103 * @see Preferences
104 * @since 1.4
105 */
106 public abstract class AbstractPreferences extends Preferences {
107 /**
108 * Our name relative to parent.
109 */
110 private final String name;
111
112 /**
113 * Our absolute path name.
114 */
115 private final String absolutePath;
116
117 /**
118 * Our parent node.
119 */
120 final AbstractPreferences parent;
121
122 /**
123 * Our root node.
124 */
125 private final AbstractPreferences root; // Relative to this node
126
127 /**
128 * This field should be <tt>true</tt> if this node did not exist in the
129 * backing store prior to the creation of this object. The field
130 * is initialized to false, but may be set to true by a subclass
131 * constructor (and should not be modified thereafter). This field
132 * indicates whether a node change event should be fired when
133 * creation is complete.
134 */
135 protected boolean newNode = false;
136
137 /**
138 * All known unremoved children of this node. (This "cache" is consulted
139 * prior to calling childSpi() or getChild().
140 */
141 private Map kidCache = new HashMap();
142
143 /**
144 * This field is used to keep track of whether or not this node has
145 * been removed. Once it's set to true, it will never be reset to false.
146 */
147 private boolean removed = false;
148
149 /**
150 * Registered preference change listeners.
151 */
152 private PreferenceChangeListener[] prefListeners =
153 new PreferenceChangeListener[0];
154
155 /**
156 * Registered node change listeners.
157 */
158 private NodeChangeListener[] nodeListeners = new NodeChangeListener[0];
159
160 /**
161 * An object whose monitor is used to lock this node. This object
162 * is used in preference to the node itself to reduce the likelihood of
163 * intentional or unintentional denial of service due to a locked node.
164 * To avoid deadlock, a node is <i>never</i> locked by a thread that
165 * holds a lock on a descendant of that node.
166 */
167 protected final Object lock = new Object();
168
169 /**
170 * Creates a preference node with the specified parent and the specified
171 * name relative to its parent.
172 *
173 * @param parent the parent of this preference node, or null if this
174 * is the root.
175 * @param name the name of this preference node, relative to its parent,
176 * or <tt>""</tt> if this is the root.
177 * @throws IllegalArgumentException if <tt>name</tt> contains a slash
178 * (<tt>'/'</tt>), or <tt>parent</tt> is <tt>null</tt> and
179 * name isn't <tt>""</tt>.
180 */
181 protected AbstractPreferences(AbstractPreferences parent, String name) {
182 if (parent==null) {
183 if (!name.equals(""))
184 throw new IllegalArgumentException("Root name '"+name+
185 "' must be \"\"");
186 this.absolutePath = "/";
187 root = this;
188 } else {
189 if (name.indexOf('/') != -1)
190 throw new IllegalArgumentException("Name '" + name +
191 "' contains '/'");
192 if (name.equals(""))
193 throw new IllegalArgumentException("Illegal name: empty string");
194
195 root = parent.root;
196 absolutePath = (parent==root ? "/" + name
197 : parent.absolutePath() + "/" + name);
198 }
199 this.name = name;
200 this.parent = parent;
201 }
202
203 /**
204 * Implements the <tt>put</tt> method as per the specification in
205 * {@link Preferences#put(String,String)}.
206 *
207 * <p>This implementation checks that the key and value are legal,
208 * obtains this preference node's lock, checks that the node
209 * has not been removed, invokes {@link #putSpi(String,String)}, and if
210 * there are any preference change listeners, enqueues a notification
211 * event for processing by the event dispatch thread.
212 *
213 * @param key key with which the specified value is to be associated.
214 * @param value value to be associated with the specified key.
215 * @throws NullPointerException if key or value is <tt>null</tt>.
216 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
217 * <tt>MAX_KEY_LENGTH</tt> or if <tt>value.length</tt> exceeds
218 * <tt>MAX_VALUE_LENGTH</tt>.
219 * @throws IllegalStateException if this node (or an ancestor) has been
220 * removed with the {@link #removeNode()} method.
221 */
222 public void put(String key, String value) {
223 if (key==null || value==null)
224 throw new NullPointerException();
225 if (key.length() > MAX_KEY_LENGTH)
226 throw new IllegalArgumentException("Key too long: "+key);
227 if (value.length() > MAX_VALUE_LENGTH)
228 throw new IllegalArgumentException("Value too long: "+value);
229
230 synchronized(lock) {
231 if (removed)
232 throw new IllegalStateException("Node has been removed.");
233
234 putSpi(key, value);
235 enqueuePreferenceChangeEvent(key, value);
236 }
237 }
238
239 /**
240 * Implements the <tt>get</tt> method as per the specification in
241 * {@link Preferences#get(String,String)}.
242 *
243 * <p>This implementation first checks to see if <tt>key</tt> is
244 * <tt>null</tt> throwing a <tt>NullPointerException</tt> if this is
245 * the case. Then it obtains this preference node's lock,
246 * checks that the node has not been removed, invokes {@link
247 * #getSpi(String)}, and returns the result, unless the <tt>getSpi</tt>
248 * invocation returns <tt>null</tt> or throws an exception, in which case
249 * this invocation returns <tt>def</tt>.
250 *
251 * @param key key whose associated value is to be returned.
252 * @param def the value to be returned in the event that this
253 * preference node has no value associated with <tt>key</tt>.
254 * @return the value associated with <tt>key</tt>, or <tt>def</tt>
255 * if no value is associated with <tt>key</tt>.
256 * @throws IllegalStateException if this node (or an ancestor) has been
257 * removed with the {@link #removeNode()} method.
258 * @throws NullPointerException if key is <tt>null</tt>. (A
259 * <tt>null</tt> default <i>is</i> permitted.)
260 */
261 public String get(String key, String def) {
262 if (key==null)
263 throw new NullPointerException("Null key");
264 synchronized(lock) {
265 if (removed)
266 throw new IllegalStateException("Node has been removed.");
267
268 String result = null;
269 try {
270 result = getSpi(key);
271 } catch (Exception e) {
272 // Ignoring exception causes default to be returned
273 }
274 return (result==null ? def : result);
275 }
276 }
277
278 /**
279 * Implements the <tt>remove(String)</tt> method as per the specification
280 * in {@link Preferences#remove(String)}.
281 *
282 * <p>This implementation obtains this preference node's lock,
283 * checks that the node has not been removed, invokes
284 * {@link #removeSpi(String)} and if there are any preference
285 * change listeners, enqueues a notification event for processing by the
286 * event dispatch thread.
287 *
288 * @param key key whose mapping is to be removed from the preference node.
289 * @throws IllegalStateException if this node (or an ancestor) has been
290 * removed with the {@link #removeNode()} method.
291 */
292 public void remove(String key) {
293 synchronized(lock) {
294 if (removed)
295 throw new IllegalStateException("Node has been removed.");
296
297 removeSpi(key);
298 enqueuePreferenceChangeEvent(key, null);
299 }
300 }
301
302 /**
303 * Implements the <tt>clear</tt> method as per the specification in
304 * {@link Preferences#clear()}.
305 *
306 * <p>This implementation obtains this preference node's lock,
307 * invokes {@link #keys()} to obtain an array of keys, and
308 * iterates over the array invoking {@link #remove(String)} on each key.
309 *
310 * @throws BackingStoreException if this operation cannot be completed
311 * due to a failure in the backing store, or inability to
312 * communicate with it.
313 * @throws IllegalStateException if this node (or an ancestor) has been
314 * removed with the {@link #removeNode()} method.
315 */
316 public void clear() throws BackingStoreException {
317 synchronized(lock) {
318 String[] keys = keys();
319 for (int i=0; i<keys.length; i++)
320 remove(keys[i]);
321 }
322 }
323
324 /**
325 * Implements the <tt>putInt</tt> method as per the specification in
326 * {@link Preferences#putInt(String,int)}.
327 *
328 * <p>This implementation translates <tt>value</tt> to a string with
329 * {@link Integer#toString(int)} and invokes {@link #put(String,String)}
330 * on the result.
331 *
332 * @param key key with which the string form of value is to be associated.
333 * @param value value whose string form is to be associated with key.
334 * @throws NullPointerException if key is <tt>null</tt>.
335 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
336 * <tt>MAX_KEY_LENGTH</tt>.
337 * @throws IllegalStateException if this node (or an ancestor) has been
338 * removed with the {@link #removeNode()} method.
339 */
340 public void putInt(String key, int value) {
341 put(key, Integer.toString(value));
342 }
343
344 /**
345 * Implements the <tt>getInt</tt> method as per the specification in
346 * {@link Preferences#getInt(String,int)}.
347 *
348 * <p>This implementation invokes {@link #get(String,String) <tt>get(key,
349 * null)</tt>}. If the return value is non-null, the implementation
350 * attempts to translate it to an <tt>int</tt> with
351 * {@link Integer#parseInt(String)}. If the attempt succeeds, the return
352 * value is returned by this method. Otherwise, <tt>def</tt> is returned.
353 *
354 * @param key key whose associated value is to be returned as an int.
355 * @param def the value to be returned in the event that this
356 * preference node has no value associated with <tt>key</tt>
357 * or the associated value cannot be interpreted as an int.
358 * @return the int value represented by the string associated with
359 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
360 * associated value does not exist or cannot be interpreted as
361 * an int.
362 * @throws IllegalStateException if this node (or an ancestor) has been
363 * removed with the {@link #removeNode()} method.
364 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
365 */
366 public int getInt(String key, int def) {
367 int result = def;
368 try {
369 String value = get(key, null);
370 if (value != null)
371 result = Integer.parseInt(value);
372 } catch (NumberFormatException e) {
373 // Ignoring exception causes specified default to be returned
374 }
375
376 return result;
377 }
378
379 /**
380 * Implements the <tt>putLong</tt> method as per the specification in
381 * {@link Preferences#putLong(String,long)}.
382 *
383 * <p>This implementation translates <tt>value</tt> to a string with
384 * {@link Long#toString(long)} and invokes {@link #put(String,String)}
385 * on the result.
386 *
387 * @param key key with which the string form of value is to be associated.
388 * @param value value whose string form is to be associated with key.
389 * @throws NullPointerException if key is <tt>null</tt>.
390 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
391 * <tt>MAX_KEY_LENGTH</tt>.
392 * @throws IllegalStateException if this node (or an ancestor) has been
393 * removed with the {@link #removeNode()} method.
394 */
395 public void putLong(String key, long value) {
396 put(key, Long.toString(value));
397 }
398
399 /**
400 * Implements the <tt>getLong</tt> method as per the specification in
401 * {@link Preferences#getLong(String,long)}.
402 *
403 * <p>This implementation invokes {@link #get(String,String) <tt>get(key,
404 * null)</tt>}. If the return value is non-null, the implementation
405 * attempts to translate it to a <tt>long</tt> with
406 * {@link Long#parseLong(String)}. If the attempt succeeds, the return
407 * value is returned by this method. Otherwise, <tt>def</tt> is returned.
408 *
409 * @param key key whose associated value is to be returned as a long.
410 * @param def the value to be returned in the event that this
411 * preference node has no value associated with <tt>key</tt>
412 * or the associated value cannot be interpreted as a long.
413 * @return the long value represented by the string associated with
414 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
415 * associated value does not exist or cannot be interpreted as
416 * a long.
417 * @throws IllegalStateException if this node (or an ancestor) has been
418 * removed with the {@link #removeNode()} method.
419 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
420 */
421 public long getLong(String key, long def) {
422 long result = def;
423 try {
424 String value = get(key, null);
425 if (value != null)
426 result = Long.parseLong(value);
427 } catch (NumberFormatException e) {
428 // Ignoring exception causes specified default to be returned
429 }
430
431 return result;
432 }
433
434 /**
435 * Implements the <tt>putBoolean</tt> method as per the specification in
436 * {@link Preferences#putBoolean(String,boolean)}.
437 *
438 * <p>This implementation translates <tt>value</tt> to a string with
439 * {@link String#valueOf(boolean)} and invokes {@link #put(String,String)}
440 * on the result.
441 *
442 * @param key key with which the string form of value is to be associated.
443 * @param value value whose string form is to be associated with key.
444 * @throws NullPointerException if key is <tt>null</tt>.
445 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
446 * <tt>MAX_KEY_LENGTH</tt>.
447 * @throws IllegalStateException if this node (or an ancestor) has been
448 * removed with the {@link #removeNode()} method.
449 */
450 public void putBoolean(String key, boolean value) {
451 put(key, String.valueOf(value));
452 }
453
454 /**
455 * Implements the <tt>getBoolean</tt> method as per the specification in
456 * {@link Preferences#getBoolean(String,boolean)}.
457 *
458 * <p>This implementation invokes {@link #get(String,String) <tt>get(key,
459 * null)</tt>}. If the return value is non-null, it is compared with
460 * <tt>"true"</tt> using {@link String#equalsIgnoreCase(String)}. If the
461 * comparison returns <tt>true</tt>, this invocation returns
462 * <tt>true</tt>. Otherwise, the original return value is compared with
463 * <tt>"false"</tt>, again using {@link String#equalsIgnoreCase(String)}.
464 * If the comparison returns <tt>true</tt>, this invocation returns
465 * <tt>false</tt>. Otherwise, this invocation returns <tt>def</tt>.
466 *
467 * @param key key whose associated value is to be returned as a boolean.
468 * @param def the value to be returned in the event that this
469 * preference node has no value associated with <tt>key</tt>
470 * or the associated value cannot be interpreted as a boolean.
471 * @return the boolean value represented by the string associated with
472 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
473 * associated value does not exist or cannot be interpreted as
474 * a boolean.
475 * @throws IllegalStateException if this node (or an ancestor) has been
476 * removed with the {@link #removeNode()} method.
477 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
478 */
479 public boolean getBoolean(String key, boolean def) {
480 boolean result = def;
481 String value = get(key, null);
482 if (value != null) {
483 if (value.equalsIgnoreCase("true"))
484 result = true;
485 else if (value.equalsIgnoreCase("false"))
486 result = false;
487 }
488
489 return result;
490 }
491
492 /**
493 * Implements the <tt>putFloat</tt> method as per the specification in
494 * {@link Preferences#putFloat(String,float)}.
495 *
496 * <p>This implementation translates <tt>value</tt> to a string with
497 * {@link Float#toString(float)} and invokes {@link #put(String,String)}
498 * on the result.
499 *
500 * @param key key with which the string form of value is to be associated.
501 * @param value value whose string form is to be associated with key.
502 * @throws NullPointerException if key is <tt>null</tt>.
503 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
504 * <tt>MAX_KEY_LENGTH</tt>.
505 * @throws IllegalStateException if this node (or an ancestor) has been
506 * removed with the {@link #removeNode()} method.
507 */
508 public void putFloat(String key, float value) {
509 put(key, Float.toString(value));
510 }
511
512 /**
513 * Implements the <tt>getFloat</tt> method as per the specification in
514 * {@link Preferences#getFloat(String,float)}.
515 *
516 * <p>This implementation invokes {@link #get(String,String) <tt>get(key,
517 * null)</tt>}. If the return value is non-null, the implementation
518 * attempts to translate it to an <tt>float</tt> with
519 * {@link Float#parseFloat(String)}. If the attempt succeeds, the return
520 * value is returned by this method. Otherwise, <tt>def</tt> is returned.
521 *
522 * @param key key whose associated value is to be returned as a float.
523 * @param def the value to be returned in the event that this
524 * preference node has no value associated with <tt>key</tt>
525 * or the associated value cannot be interpreted as a float.
526 * @return the float value represented by the string associated with
527 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
528 * associated value does not exist or cannot be interpreted as
529 * a float.
530 * @throws IllegalStateException if this node (or an ancestor) has been
531 * removed with the {@link #removeNode()} method.
532 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
533 */
534 public float getFloat(String key, float def) {
535 float result = def;
536 try {
537 String value = get(key, null);
538 if (value != null)
539 result = Float.parseFloat(value);
540 } catch (NumberFormatException e) {
541 // Ignoring exception causes specified default to be returned
542 }
543
544 return result;
545 }
546
547 /**
548 * Implements the <tt>putDouble</tt> method as per the specification in
549 * {@link Preferences#putDouble(String,double)}.
550 *
551 * <p>This implementation translates <tt>value</tt> to a string with
552 * {@link Double#toString(double)} and invokes {@link #put(String,String)}
553 * on the result.
554 *
555 * @param key key with which the string form of value is to be associated.
556 * @param value value whose string form is to be associated with key.
557 * @throws NullPointerException if key is <tt>null</tt>.
558 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
559 * <tt>MAX_KEY_LENGTH</tt>.
560 * @throws IllegalStateException if this node (or an ancestor) has been
561 * removed with the {@link #removeNode()} method.
562 */
563 public void putDouble(String key, double value) {
564 put(key, Double.toString(value));
565 }
566
567 /**
568 * Implements the <tt>getDouble</tt> method as per the specification in
569 * {@link Preferences#getDouble(String,double)}.
570 *
571 * <p>This implementation invokes {@link #get(String,String) <tt>get(key,
572 * null)</tt>}. If the return value is non-null, the implementation
573 * attempts to translate it to an <tt>double</tt> with
574 * {@link Double#parseDouble(String)}. If the attempt succeeds, the return
575 * value is returned by this method. Otherwise, <tt>def</tt> is returned.
576 *
577 * @param key key whose associated value is to be returned as a double.
578 * @param def the value to be returned in the event that this
579 * preference node has no value associated with <tt>key</tt>
580 * or the associated value cannot be interpreted as a double.
581 * @return the double value represented by the string associated with
582 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
583 * associated value does not exist or cannot be interpreted as
584 * a double.
585 * @throws IllegalStateException if this node (or an ancestor) has been
586 * removed with the {@link #removeNode()} method.
587 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
588 */
589 public double getDouble(String key, double def) {
590 double result = def;
591 try {
592 String value = get(key, null);
593 if (value != null)
594 result = Double.parseDouble(value);
595 } catch (NumberFormatException e) {
596 // Ignoring exception causes specified default to be returned
597 }
598
599 return result;
600 }
601
602 /**
603 * Implements the <tt>putByteArray</tt> method as per the specification in
604 * {@link Preferences#putByteArray(String,byte[])}.
605 *
606 * @param key key with which the string form of value is to be associated.
607 * @param value value whose string form is to be associated with key.
608 * @throws NullPointerException if key or value is <tt>null</tt>.
609 * @throws IllegalArgumentException if key.length() exceeds MAX_KEY_LENGTH
610 * or if value.length exceeds MAX_VALUE_LENGTH*3/4.
611 * @throws IllegalStateException if this node (or an ancestor) has been
612 * removed with the {@link #removeNode()} method.
613 */
614 public void putByteArray(String key, byte[] value) {
615 put(key, Base64.byteArrayToBase64(value));
616 }
617
618 /**
619 * Implements the <tt>getByteArray</tt> method as per the specification in
620 * {@link Preferences#getByteArray(String,byte[])}.
621 *
622 * @param key key whose associated value is to be returned as a byte array.
623 * @param def the value to be returned in the event that this
624 * preference node has no value associated with <tt>key</tt>
625 * or the associated value cannot be interpreted as a byte array.
626 * @return the byte array value represented by the string associated with
627 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
628 * associated value does not exist or cannot be interpreted as
629 * a byte array.
630 * @throws IllegalStateException if this node (or an ancestor) has been
631 * removed with the {@link #removeNode()} method.
632 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>. (A
633 * <tt>null</tt> value for <tt>def</tt> <i>is</i> permitted.)
634 */
635 public byte[] getByteArray(String key, byte[] def) {
636 byte[] result = def;
637 String value = get(key, null);
638 try {
639 if (value != null)
640 result = Base64.base64ToByteArray(value);
641 }
642 catch (RuntimeException e) {
643 // Ignoring exception causes specified default to be returned
644 }
645
646 return result;
647 }
648
649 /**
650 * Implements the <tt>keys</tt> method as per the specification in
651 * {@link Preferences#keys()}.
652 *
653 * <p>This implementation obtains this preference node's lock, checks that
654 * the node has not been removed and invokes {@link #keysSpi()}.
655 *
656 * @return an array of the keys that have an associated value in this
657 * preference node.
658 * @throws BackingStoreException if this operation cannot be completed
659 * due to a failure in the backing store, or inability to
660 * communicate with it.
661 * @throws IllegalStateException if this node (or an ancestor) has been
662 * removed with the {@link #removeNode()} method.
663 */
664 public String[] keys() throws BackingStoreException {
665 synchronized(lock) {
666 if (removed)
667 throw new IllegalStateException("Node has been removed.");
668
669 return keysSpi();
670 }
671 }
672
673 /**
674 * Implements the <tt>children</tt> method as per the specification in
675 * {@link Preferences#childrenNames()}.
676 *
677 * <p>This implementation obtains this preference node's lock, checks that
678 * the node has not been removed, constructs a <tt>TreeSet</tt> initialized
679 * to the names of children already cached (the children in this node's
680 * "child-cache"), invokes {@link #childrenNamesSpi()}, and adds all of the
681 * returned child-names into the set. The elements of the tree set are
682 * dumped into a <tt>String</tt> array using the <tt>toArray</tt> method,
683 * and this array is returned.
684 *
685 * @return the names of the children of this preference node.
686 * @throws BackingStoreException if this operation cannot be completed
687 * due to a failure in the backing store, or inability to
688 * communicate with it.
689 * @throws IllegalStateException if this node (or an ancestor) has been
690 * removed with the {@link #removeNode()} method.
691 * @see #cachedChildren()
692 */
693 public String[] childrenNames() throws BackingStoreException {
694 synchronized(lock) {
695 if (removed)
696 throw new IllegalStateException("Node has been removed.");
697
698 Set s = new TreeSet(kidCache.keySet());
699 String[] kids = childrenNamesSpi();
700 for(int i=0; i<kids.length; i++)
701 s.add(kids[i]);
702 return (String[]) s.toArray(EMPTY_STRING_ARRAY);
703 }
704 }
705
706 private static final String[] EMPTY_STRING_ARRAY = new String[0];
707
708 /**
709 * Returns all known unremoved children of this node.
710 *
711 * @return all known unremoved children of this node.
712 */
713 protected final AbstractPreferences[] cachedChildren() {
714 return (AbstractPreferences[]) kidCache.values().
715 toArray(EMPTY_ABSTRACT_PREFS_ARRAY);
716 }
717
718 private static final AbstractPreferences[] EMPTY_ABSTRACT_PREFS_ARRAY
719 = new AbstractPreferences[0];
720
721 /**
722 * Implements the <tt>parent</tt> method as per the specification in
723 * {@link Preferences#parent()}.
724 *
725 * <p>This implementation obtains this preference node's lock, checks that
726 * the node has not been removed and returns the parent value that was
727 * passed to this node's constructor.
728 *
729 * @return the parent of this preference node.
730 * @throws IllegalStateException if this node (or an ancestor) has been
731 * removed with the {@link #removeNode()} method.
732 */
733 public Preferences parent() {
734 synchronized(lock) {
735 if (removed)
736 throw new IllegalStateException("Node has been removed.");
737
738 return parent;
739 }
740 }
741
742 /**
743 * Implements the <tt>node</tt> method as per the specification in
744 * {@link Preferences#node(String)}.
745 *
746 * <p>This implementation obtains this preference node's lock and checks
747 * that the node has not been removed. If <tt>path</tt> is <tt>""</tt>,
748 * this node is returned; if <tt>path</tt> is <tt>"/"</tt>, this node's
749 * root is returned. If the first character in <tt>path</tt> is
750 * not <tt>'/'</tt>, the implementation breaks <tt>path</tt> into
751 * tokens and recursively traverses the path from this node to the
752 * named node, "consuming" a name and a slash from <tt>path</tt> at
753 * each step of the traversal. At each step, the current node is locked
754 * and the node's child-cache is checked for the named node. If it is
755 * not found, the name is checked to make sure its length does not
756 * exceed <tt>MAX_NAME_LENGTH</tt>. Then the {@link #childSpi(String)}
757 * method is invoked, and the result stored in this node's child-cache.
758 * If the newly created <tt>Preferences</tt> object's {@link #newNode}
759 * field is <tt>true</tt> and there are any node change listeners,
760 * a notification event is enqueued for processing by the event dispatch
761 * thread.
762 *
763 * <p>When there are no more tokens, the last value found in the
764 * child-cache or returned by <tt>childSpi</tt> is returned by this
765 * method. If during the traversal, two <tt>"/"</tt> tokens occur
766 * consecutively, or the final token is <tt>"/"</tt> (rather than a name),
767 * an appropriate <tt>IllegalArgumentException</tt> is thrown.
768 *
769 * <p> If the first character of <tt>path</tt> is <tt>'/'</tt>
770 * (indicating an absolute path name) this preference node's
771 * lock is dropped prior to breaking <tt>path</tt> into tokens, and
772 * this method recursively traverses the path starting from the root
773 * (rather than starting from this node). The traversal is otherwise
774 * identical to the one described for relative path names. Dropping
775 * the lock on this node prior to commencing the traversal at the root
776 * node is essential to avoid the possibility of deadlock, as per the
777 * {@link #lock locking invariant}.
778 *
779 * @param path the path name of the preference node to return.
780 * @return the specified preference node.
781 * @throws IllegalArgumentException if the path name is invalid (i.e.,
782 * it contains multiple consecutive slash characters, or ends
783 * with a slash character and is more than one character long).
784 * @throws IllegalStateException if this node (or an ancestor) has been
785 * removed with the {@link #removeNode()} method.
786 */
787 public Preferences node(String path) {
788 synchronized(lock) {
789 if (removed)
790 throw new IllegalStateException("Node has been removed.");
791 if (path.equals(""))
792 return this;
793 if (path.equals("/"))
794 return root;
795 if (path.charAt(0) != '/')
796 return node(new StringTokenizer(path, "/", true));
797 }
798
799 // Absolute path. Note that we've dropped our lock to avoid deadlock
800 return root.node(new StringTokenizer(path.substring(1), "/", true));
801 }
802
803 /**
804 * tokenizer contains <name> {'/' <name>}*
805 */
806 private Preferences node(StringTokenizer path) {
807 String token = path.nextToken();
808 if (token.equals("/")) // Check for consecutive slashes
809 throw new IllegalArgumentException("Consecutive slashes in path");
810 synchronized(lock) {
811 AbstractPreferences child=(AbstractPreferences)kidCache.get(token);
812 if (child == null) {
813 if (token.length() > MAX_NAME_LENGTH)
814 throw new IllegalArgumentException(
815 "Node name " + token + " too long");
816 child = childSpi(token);
817 if (child.newNode)
818 enqueueNodeAddedEvent(child);
819 kidCache.put(token, child);
820 }
821 if (!path.hasMoreTokens())
822 return child;
823 path.nextToken(); // Consume slash
824 if (!path.hasMoreTokens())
825 throw new IllegalArgumentException("Path ends with slash");
826 return child.node(path);
827 }
828 }
829
830 /**
831 * Implements the <tt>nodeExists</tt> method as per the specification in
832 * {@link Preferences#nodeExists(String)}.
833 *
834 * <p>This implementation is very similar to {@link #node(String)},
835 * except that {@link #getChild(String)} is used instead of {@link
836 * #childSpi(String)}.
837 *
838 * @param path the path name of the node whose existence is to be checked.
839 * @return true if the specified node exists.
840 * @throws BackingStoreException if this operation cannot be completed
841 * due to a failure in the backing store, or inability to
842 * communicate with it.
843 * @throws IllegalArgumentException if the path name is invalid (i.e.,
844 * it contains multiple consecutive slash characters, or ends
845 * with a slash character and is more than one character long).
846 * @throws IllegalStateException if this node (or an ancestor) has been
847 * removed with the {@link #removeNode()} method and
848 * <tt>pathname</tt> is not the empty string (<tt>""</tt>).
849 */
850 public boolean nodeExists(String path)
851 throws BackingStoreException
852 {
853 synchronized(lock) {
854 if (path.equals(""))
855 return !removed;
856 if (removed)
857 throw new IllegalStateException("Node has been removed.");
858 if (path.equals("/"))
859 return true;
860 if (path.charAt(0) != '/')
861 return nodeExists(new StringTokenizer(path, "/", true));
862 }
863
864 // Absolute path. Note that we've dropped our lock to avoid deadlock
865 return root.nodeExists(new StringTokenizer(path.substring(1), "/",
866 true));
867 }
868
869 /**
870 * tokenizer contains <name> {'/' <name>}*
871 */
872 private boolean nodeExists(StringTokenizer path)
873 throws BackingStoreException
874 {
875 String token = path.nextToken();
876 if (token.equals("/")) // Check for consecutive slashes
877 throw new IllegalArgumentException("Consecutive slashes in path");
878 synchronized(lock) {
879 AbstractPreferences child=(AbstractPreferences)kidCache.get(token);
880 if (child == null)
881 child = getChild(token);
882 if (child==null)
883 return false;
884 if (!path.hasMoreTokens())
885 return true;
886 path.nextToken(); // Consume slash
887 if (!path.hasMoreTokens())
888 throw new IllegalArgumentException("Path ends with slash");
889 return child.nodeExists(path);
890 }
891 }
892
893 /**
894
895 * Implements the <tt>removeNode()</tt> method as per the specification in
896 * {@link Preferences#removeNode()}.
897 *
898 * <p>This implementation checks to see that this node is the root; if so,
899 * it throws an appropriate exception. Then, it locks this node's parent,
900 * and calls a recursive helper method that traverses the subtree rooted at
901 * this node. The recursive method locks the node on which it was called,
902 * checks that it has not already been removed, and then ensures that all
903 * of its children are cached: The {@link #childrenNamesSpi()} method is
904 * invoked and each returned child name is checked for containment in the
905 * child-cache. If a child is not already cached, the {@link
906 * #childSpi(String)} method is invoked to create a <tt>Preferences</tt>
907 * instance for it, and this instance is put into the child-cache. Then
908 * the helper method calls itself recursively on each node contained in its
909 * child-cache. Next, it invokes {@link #removeNodeSpi()}, marks itself
910 * as removed, and removes itself from its parent's child-cache. Finally,
911 * if there are any node change listeners, it enqueues a notification
912 * event for processing by the event dispatch thread.
913 *
914 * <p>Note that the helper method is always invoked with all ancestors up
915 * to the "closest non-removed ancestor" locked.
916 *
917 * @throws IllegalStateException if this node (or an ancestor) has already
918 * been removed with the {@link #removeNode()} method.
919 * @throws UnsupportedOperationException if this method is invoked on
920 * the root node.
921 * @throws BackingStoreException if this operation cannot be completed
922 * due to a failure in the backing store, or inability to
923 * communicate with it.
924 */
925 public void removeNode() throws BackingStoreException {
926 if (this==root)
927 throw new UnsupportedOperationException("Can't remove the root!");
928 synchronized(parent.lock) {
929 removeNode2();
930 parent.kidCache.remove(name);
931 }
932 }
933
934 /*
935 * Called with locks on all nodes on path from parent of "removal root"
936 * to this (including the former but excluding the latter).
937 */
938 private void removeNode2() throws BackingStoreException {
939 synchronized(lock) {
940 if (removed)
941 throw new IllegalStateException("Node already removed.");
942
943 // Ensure that all children are cached
944 String[] kidNames = childrenNamesSpi();
945 for (int i=0; i<kidNames.length; i++)
946 if (!kidCache.containsKey(kidNames[i]))
947 kidCache.put(kidNames[i], childSpi(kidNames[i]));
948
949 // Recursively remove all cached children
950 for (Iterator i = kidCache.values().iterator(); i.hasNext();) {
951 try {
952 ((AbstractPreferences)i.next()).removeNode2();
953 i.remove();
954 } catch (BackingStoreException x) { }
955 }
956
957 // Now we have no descendants - it's time to die!
958 removeNodeSpi();
959 removed = true;
960 parent.enqueueNodeRemovedEvent(this);
961 }
962 }
963
964 /**
965 * Implements the <tt>name</tt> method as per the specification in
966 * {@link Preferences#name()}.
967 *
968 * <p>This implementation merely returns the name that was
969 * passed to this node's constructor.
970 *
971 * @return this preference node's name, relative to its parent.
972 */
973 public String name() {
974 return name;
975 }
976
977 /**
978 * Implements the <tt>absolutePath</tt> method as per the specification in
979 * {@link Preferences#absolutePath()}.
980 *
981 * <p>This implementation merely returns the absolute path name that
982 * was computed at the time that this node was constructed (based on
983 * the name that was passed to this node's constructor, and the names
984 * that were passed to this node's ancestors' constructors).
985 *
986 * @return this preference node's absolute path name.
987 */
988 public String absolutePath() {
989 return absolutePath;
990 }
991
992 /**
993 * Implements the <tt>isUserNode</tt> method as per the specification in
994 * {@link Preferences#isUserNode()}.
995 *
996 * <p>This implementation compares this node's root node (which is stored
997 * in a private field) with the value returned by
998 * {@link Preferences#userRoot()}. If the two object references are
999 * identical, this method returns true.
1000 *
1001 * @return <tt>true</tt> if this preference node is in the user
1002 * preference tree, <tt>false</tt> if it's in the system
1003 * preference tree.
1004 */
1005 public boolean isUserNode() {
1006 Boolean result = (Boolean)
1007 AccessController.doPrivileged( new PrivilegedAction() {
1008 public Object run() {
1009 return new Boolean(root == Preferences.userRoot());
1010 }
1011 });
1012 return result.booleanValue();
1013 }
1014
1015 public void addPreferenceChangeListener(PreferenceChangeListener pcl) {
1016 if (pcl==null)
1017 throw new NullPointerException("Change listener is null.");
1018 synchronized(lock) {
1019 if (removed)
1020 throw new IllegalStateException("Node has been removed.");
1021
1022 // Copy-on-write
1023 PreferenceChangeListener[] old = prefListeners;
1024 prefListeners = new PreferenceChangeListener[old.length + 1];
1025 System.arraycopy(old, 0, prefListeners, 0, old.length);
1026 prefListeners[old.length] = pcl;
1027 }
1028 startEventDispatchThreadIfNecessary();
1029 }
1030
1031 public void removePreferenceChangeListener(PreferenceChangeListener pcl) {
1032 synchronized(lock) {
1033 if (removed)
1034 throw new IllegalStateException("Node has been removed.");
1035 if ((prefListeners == null) || (prefListeners.length == 0))
1036 throw new IllegalArgumentException("Listener not registered.");
1037
1038 // Copy-on-write
1039 PreferenceChangeListener[] newPl =
1040 new PreferenceChangeListener[prefListeners.length - 1];
1041 int i = 0;
1042 while (i < newPl.length && prefListeners[i] != pcl)
1043 newPl[i] = prefListeners[i++];
1044
1045 if (i == newPl.length && prefListeners[i] != pcl)
1046 throw new IllegalArgumentException("Listener not registered.");
1047 while (i < newPl.length)
1048 newPl[i] = prefListeners[++i];
1049 prefListeners = newPl;
1050 }
1051 }
1052
1053 public void addNodeChangeListener(NodeChangeListener ncl) {
1054 if (ncl==null)
1055 throw new NullPointerException("Change listener is null.");
1056 synchronized(lock) {
1057 if (removed)
1058 throw new IllegalStateException("Node has been removed.");
1059
1060 // Copy-on-write
1061 if (nodeListeners == null) {
1062 nodeListeners = new NodeChangeListener[1];
1063 nodeListeners[0] = ncl;
1064 } else {
1065 NodeChangeListener[] old = nodeListeners;
1066 nodeListeners = new NodeChangeListener[old.length + 1];
1067 System.arraycopy(old, 0, nodeListeners, 0, old.length);
1068 nodeListeners[old.length] = ncl;
1069 }
1070 }
1071 startEventDispatchThreadIfNecessary();
1072 }
1073
1074 public void removeNodeChangeListener(NodeChangeListener ncl) {
1075 synchronized(lock) {
1076 if (removed)
1077 throw new IllegalStateException("Node has been removed.");
1078 if ((nodeListeners == null) || (nodeListeners.length == 0))
1079 throw new IllegalArgumentException("Listener not registered.");
1080
1081 // Copy-on-write
1082 int i = 0;
1083 while (i < nodeListeners.length && nodeListeners[i] != ncl)
1084 i++;
1085 if (i == nodeListeners.length)
1086 throw new IllegalArgumentException("Listener not registered.");
1087 NodeChangeListener[] newNl =
1088 new NodeChangeListener[nodeListeners.length - 1];
1089 if (i != 0)
1090 System.arraycopy(nodeListeners, 0, newNl, 0, i);
1091 if (i != newNl.length)
1092 System.arraycopy(nodeListeners, i + 1,
1093 newNl, i, newNl.length - i);
1094 nodeListeners = newNl;
1095 }
1096 }
1097
1098 // "SPI" METHODS
1099
1100 /**
1101 * Put the given key-value association into this preference node. It is
1102 * guaranteed that <tt>key</tt> and <tt>value</tt> are non-null and of
1103 * legal length. Also, it is guaranteed that this node has not been
1104 * removed. (The implementor needn't check for any of these things.)
1105 *
1106 * <p>This method is invoked with the lock on this node held.
1107 */
1108 protected abstract void putSpi(String key, String value);
1109
1110 /**
1111 * Return the value associated with the specified key at this preference
1112 * node, or <tt>null</tt> if there is no association for this key, or the
1113 * association cannot be determined at this time. It is guaranteed that
1114 * <tt>key</tt> is non-null. Also, it is guaranteed that this node has
1115 * not been removed. (The implementor needn't check for either of these
1116 * things.)
1117 *
1118 * <p> Generally speaking, this method should not throw an exception
1119 * under any circumstances. If, however, if it does throw an exception,
1120 * the exception will be intercepted and treated as a <tt>null</tt>
1121 * return value.
1122 *
1123 * <p>This method is invoked with the lock on this node held.
1124 *
1125 * @return the value associated with the specified key at this preference
1126 * node, or <tt>null</tt> if there is no association for this
1127 * key, or the association cannot be determined at this time.
1128 */
1129 protected abstract String getSpi(String key);
1130
1131 /**
1132 * Remove the association (if any) for the specified key at this
1133 * preference node. It is guaranteed that <tt>key</tt> is non-null.
1134 * Also, it is guaranteed that this node has not been removed.
1135 * (The implementor needn't check for either of these things.)
1136 *
1137 * <p>This method is invoked with the lock on this node held.
1138 */
1139 protected abstract void removeSpi(String key);
1140
1141 /**
1142 * Removes this preference node, invalidating it and any preferences that
1143 * it contains. The named child will have no descendants at the time this
1144 * invocation is made (i.e., the {@link Preferences#removeNode()} method
1145 * invokes this method repeatedly in a bottom-up fashion, removing each of
1146 * a node's descendants before removing the node itself).
1147 *
1148 * <p>This method is invoked with the lock held on this node and its
1149 * parent (and all ancestors that are being removed as a
1150 * result of a single invocation to {@link Preferences#removeNode()}).
1151 *
1152 * <p>The removal of a node needn't become persistent until the
1153 * <tt>flush</tt> method is invoked on this node (or an ancestor).
1154 *
1155 * <p>If this node throws a <tt>BackingStoreException</tt>, the exception
1156 * will propagate out beyond the enclosing {@link #removeNode()}
1157 * invocation.
1158 *
1159 * @throws BackingStoreException if this operation cannot be completed
1160 * due to a failure in the backing store, or inability to
1161 * communicate with it.
1162 */
1163 protected abstract void removeNodeSpi() throws BackingStoreException;
1164
1165 /**
1166 * Returns all of the keys that have an associated value in this
1167 * preference node. (The returned array will be of size zero if
1168 * this node has no preferences.) It is guaranteed that this node has not
1169 * been removed.
1170 *
1171 * <p>This method is invoked with the lock on this node held.
1172 *
1173 * <p>If this node throws a <tt>BackingStoreException</tt>, the exception
1174 * will propagate out beyond the enclosing {@link #keys()} invocation.
1175 *
1176 * @return an array of the keys that have an associated value in this
1177 * preference node.
1178 * @throws BackingStoreException if this operation cannot be completed
1179 * due to a failure in the backing store, or inability to
1180 * communicate with it.
1181 */
1182 protected abstract String[] keysSpi() throws BackingStoreException;
1183
1184 /**
1185 * Returns the names of the children of this preference node. (The
1186 * returned array will be of size zero if this node has no children.)
1187 * This method need not return the names of any nodes already cached,
1188 * but may do so without harm.
1189 *
1190 * <p>This method is invoked with the lock on this node held.
1191 *
1192 * <p>If this node throws a <tt>BackingStoreException</tt>, the exception
1193 * will propagate out beyond the enclosing {@link #childrenNames()}
1194 * invocation.
1195 *
1196 * @return an array containing the names of the children of this
1197 * preference node.
1198 * @throws BackingStoreException if this operation cannot be completed
1199 * due to a failure in the backing store, or inability to
1200 * communicate with it.
1201 */
1202 protected abstract String[] childrenNamesSpi()
1203 throws BackingStoreException;
1204
1205 /**
1206 * Returns the named child if it exists, or <tt>null</tt> if it does not.
1207 * It is guaranteed that <tt>nodeName</tt> is non-null, non-empty,
1208 * does not contain the slash character ('/'), and is no longer than
1209 * {@link #MAX_NAME_LENGTH} characters. Also, it is guaranteed
1210 * that this node has not been removed. (The implementor needn't check
1211 * for any of these things if he chooses to override this method.)
1212 *
1213 * <p>Finally, it is guaranteed that the named node has not been returned
1214 * by a previous invocation of this method or {@link #childSpi} after the
1215 * last time that it was removed. In other words, a cached value will
1216 * always be used in preference to invoking this method. (The implementor
1217 * needn't maintain his own cache of previously returned children if he
1218 * chooses to override this method.)
1219 *
1220 * <p>This implementation obtains this preference node's lock, invokes
1221 * {@link #childrenNames()} to get an array of the names of this node's
1222 * children, and iterates over the array comparing the name of each child
1223 * with the specified node name. If a child node has the correct name,
1224 * the {@link #childSpi(String)} method is invoked and the resulting
1225 * node is returned. If the iteration completes without finding the
1226 * specified name, <tt>null</tt> is returned.
1227 *
1228 * @param nodeName name of the child to be searched for.
1229 * @return the named child if it exists, or null if it does not.
1230 * @throws BackingStoreException if this operation cannot be completed
1231 * due to a failure in the backing store, or inability to
1232 * communicate with it.
1233 */
1234 protected AbstractPreferences getChild(String nodeName)
1235 throws BackingStoreException {
1236 synchronized(lock) {
1237 // assert kidCache.get(nodeName)==null;
1238 String[] kidNames = childrenNames();
1239 for (int i=0; i<kidNames.length; i++)
1240 if (kidNames[i].equals(nodeName))
1241 return childSpi(kidNames[i]);
1242 }
1243 return null;
1244 }
1245
1246 /**
1247 * Returns the named child of this preference node, creating it if it does
1248 * not already exist. It is guaranteed that <tt>name</tt> is non-null,
1249 * non-empty, does not contain the slash character ('/'), and is no longer
1250 * than {@link #MAX_NAME_LENGTH} characters. Also, it is guaranteed that
1251 * this node has not been removed. (The implementor needn't check for any
1252 * of these things.)
1253 *
1254 * <p>Finally, it is guaranteed that the named node has not been returned
1255 * by a previous invocation of this method or {@link #getChild(String)}
1256 * after the last time that it was removed. In other words, a cached
1257 * value will always be used in preference to invoking this method.
1258 * Subclasses need not maintain their own cache of previously returned
1259 * children.
1260 *
1261 * <p>The implementer must ensure that the returned node has not been
1262 * removed. If a like-named child of this node was previously removed, the
1263 * implementer must return a newly constructed <tt>AbstractPreferences</tt>
1264 * node; once removed, an <tt>AbstractPreferences</tt> node
1265 * cannot be "resuscitated."
1266 *
1267 * <p>If this method causes a node to be created, this node is not
1268 * guaranteed to be persistent until the <tt>flush</tt> method is
1269 * invoked on this node or one of its ancestors (or descendants).
1270 *
1271 * <p>This method is invoked with the lock on this node held.
1272 *
1273 * @param name The name of the child node to return, relative to
1274 * this preference node.
1275 * @return The named child node.
1276 */
1277 protected abstract AbstractPreferences childSpi(String name);
1278
1279 /**
1280 * Returns the absolute path name of this preferences node.
1281 */
1282 public String toString() {
1283 return (this.isUserNode() ? "User" : "System") +
1284 " Preference Node: " + this.absolutePath();
1285 }
1286
1287 /**
1288 * Implements the <tt>sync</tt> method as per the specification in
1289 * {@link Preferences#sync()}.
1290 *
1291 * <p>This implementation calls a recursive helper method that locks this
1292 * node, invokes syncSpi() on it, unlocks this node, and recursively
1293 * invokes this method on each "cached child." A cached child is a child
1294 * of this node that has been created in this VM and not subsequently
1295 * removed. In effect, this method does a depth first traversal of the
1296 * "cached subtree" rooted at this node, calling syncSpi() on each node in
1297 * the subTree while only that node is locked. Note that syncSpi() is
1298 * invoked top-down.
1299 *
1300 * @throws BackingStoreException if this operation cannot be completed
1301 * due to a failure in the backing store, or inability to
1302 * communicate with it.
1303 * @throws IllegalStateException if this node (or an ancestor) has been
1304 * removed with the {@link #removeNode()} method.
1305 * @see #flush()
1306 */
1307 public void sync() throws BackingStoreException {
1308 sync2();
1309 }
1310
1311 private void sync2() throws BackingStoreException {
1312 AbstractPreferences[] cachedKids;
1313
1314 synchronized(lock) {
1315 if (removed)
1316 throw new IllegalStateException("Node has been removed");
1317 syncSpi();
1318 cachedKids = cachedChildren();
1319 }
1320
1321 for (int i=0; i<cachedKids.length; i++)
1322 cachedKids[i].sync2();
1323 }
1324
1325 /**
1326 * This method is invoked with this node locked. The contract of this
1327 * method is to synchronize any cached preferences stored at this node
1328 * with any stored in the backing store. (It is perfectly possible that
1329 * this node does not exist on the backing store, either because it has
1330 * been deleted by another VM, or because it has not yet been created.)
1331 * Note that this method should <i>not</i> synchronize the preferences in
1332 * any subnodes of this node. If the backing store naturally syncs an
1333 * entire subtree at once, the implementer is encouraged to override
1334 * sync(), rather than merely overriding this method.
1335 *
1336 * <p>If this node throws a <tt>BackingStoreException</tt>, the exception
1337 * will propagate out beyond the enclosing {@link #sync()} invocation.
1338 *
1339 * @throws BackingStoreException if this operation cannot be completed
1340 * due to a failure in the backing store, or inability to
1341 * communicate with it.
1342 */
1343 protected abstract void syncSpi() throws BackingStoreException;
1344
1345 /**
1346 * Implements the <tt>flush</tt> method as per the specification in
1347 * {@link Preferences#flush()}.
1348 *
1349 * <p>This implementation calls a recursive helper method that locks this
1350 * node, invokes flushSpi() on it, unlocks this node, and recursively
1351 * invokes this method on each "cached child." A cached child is a child
1352 * of this node that has been created in this VM and not subsequently
1353 * removed. In effect, this method does a depth first traversal of the
1354 * "cached subtree" rooted at this node, calling flushSpi() on each node in
1355 * the subTree while only that node is locked. Note that flushSpi() is
1356 * invoked top-down.
1357 *
1358 * <p> If this method is invoked on a node that has been removed with
1359 * the {@link #removeNode()} method, flushSpi() is invoked on this node,
1360 * but not on others.
1361 *
1362 * @throws BackingStoreException if this operation cannot be completed
1363 * due to a failure in the backing store, or inability to
1364 * communicate with it.
1365 * @see #flush()
1366 */
1367 public void flush() throws BackingStoreException {
1368 flush2();
1369 }
1370
1371 private void flush2() throws BackingStoreException {
1372 AbstractPreferences[] cachedKids;
1373
1374 synchronized(lock) {
1375 flushSpi();
1376 if(removed)
1377 return;
1378 cachedKids = cachedChildren();
1379 }
1380
1381 for (int i = 0; i < cachedKids.length; i++)
1382 cachedKids[i].flush2();
1383 }
1384
1385 /**
1386 * This method is invoked with this node locked. The contract of this
1387 * method is to force any cached changes in the contents of this
1388 * preference node to the backing store, guaranteeing their persistence.
1389 * (It is perfectly possible that this node does not exist on the backing
1390 * store, either because it has been deleted by another VM, or because it
1391 * has not yet been created.) Note that this method should <i>not</i>
1392 * flush the preferences in any subnodes of this node. If the backing
1393 * store naturally flushes an entire subtree at once, the implementer is
1394 * encouraged to override flush(), rather than merely overriding this
1395 * method.
1396 *
1397 * <p>If this node throws a <tt>BackingStoreException</tt>, the exception
1398 * will propagate out beyond the enclosing {@link #flush()} invocation.
1399 *
1400 * @throws BackingStoreException if this operation cannot be completed
1401 * due to a failure in the backing store, or inability to
1402 * communicate with it.
1403 */
1404 protected abstract void flushSpi() throws BackingStoreException;
1405
1406 /**
1407 * Returns <tt>true</tt> iff this node (or an ancestor) has been
1408 * removed with the {@link #removeNode()} method. This method
1409 * locks this node prior to returning the contents of the private
1410 * field used to track this state.
1411 *
1412 * @return <tt>true</tt> iff this node (or an ancestor) has been
1413 * removed with the {@link #removeNode()} method.
1414 */
1415 protected boolean isRemoved() {
1416 synchronized(lock) {
1417 return removed;
1418 }
1419 }
1420
1421 /**
1422 * Queue of pending notification events. When a preference or node
1423 * change event for which there are one or more listeners occurs,
1424 * it is placed on this queue and the queue is notified. A background
1425 * thread waits on this queue and delivers the events. This decouples
1426 * event delivery from preference activity, greatly simplifying
1427 * locking and reducing opportunity for deadlock.
1428 */
1429 private static final List eventQueue = new LinkedList();
1430
1431 /**
1432 * These two classes are used to distinguish NodeChangeEvents on
1433 * eventQueue so the event dispatch thread knows whether to call
1434 * childAdded or childRemoved.
1435 */
1436 private class NodeAddedEvent extends NodeChangeEvent {
1437 private static final long serialVersionUID = -6743557530157328528L;
1438 NodeAddedEvent(Preferences parent, Preferences child) {
1439 super(parent, child);
1440 }
1441 }
1442 private class NodeRemovedEvent extends NodeChangeEvent {
1443 private static final long serialVersionUID = 8735497392918824837L;
1444 NodeRemovedEvent(Preferences parent, Preferences child) {
1445 super(parent, child);
1446 }
1447 }
1448
1449 /**
1450 * A single background thread ("the event notification thread") monitors
1451 * the event queue and delivers events that are placed on the queue.
1452 */
1453 private static class EventDispatchThread extends Thread {
1454 public void run() {
1455 while(true) {
1456 // Wait on eventQueue till an event is present
1457 EventObject event = null;
1458 synchronized(eventQueue) {
1459 try {
1460 while (eventQueue.isEmpty())
1461 eventQueue.wait();
1462 event = (EventObject) eventQueue.remove(0);
1463 } catch (InterruptedException e) {
1464 // XXX Log "Event dispatch thread interrupted. Exiting"
1465 return;
1466 }
1467 }
1468
1469 // Now we have event & hold no locks; deliver evt to listeners
1470 AbstractPreferences src=(AbstractPreferences)event.getSource();
1471 if (event instanceof PreferenceChangeEvent) {
1472 PreferenceChangeEvent pce = (PreferenceChangeEvent)event;
1473 PreferenceChangeListener[] listeners = src.prefListeners();
1474 for (int i=0; i<listeners.length; i++)
1475 listeners[i].preferenceChange(pce);
1476 } else {
1477 NodeChangeEvent nce = (NodeChangeEvent)event;
1478 NodeChangeListener[] listeners = src.nodeListeners();
1479 if (nce instanceof NodeAddedEvent) {
1480 for (int i=0; i<listeners.length; i++)
1481 listeners[i].childAdded(nce);
1482 } else {
1483 // assert nce instanceof NodeRemovedEvent;
1484 for (int i=0; i<listeners.length; i++)
1485 listeners[i].childRemoved(nce);
1486 }
1487 }
1488 }
1489 }
1490 }
1491
1492 private static Thread eventDispatchThread = null;
1493
1494 /**
1495 * This method starts the event dispatch thread the first time it
1496 * is called. The event dispatch thread will be started only
1497 * if someone registers a listener.
1498 */
1499 private static synchronized void startEventDispatchThreadIfNecessary() {
1500 if (eventDispatchThread == null) {
1501 // XXX Log "Starting event dispatch thread"
1502 eventDispatchThread = new EventDispatchThread();
1503 eventDispatchThread.setDaemon(true);
1504 eventDispatchThread.start();
1505 }
1506 }
1507
1508 /**
1509 * Return this node's preference/node change listeners. Even though
1510 * we're using a copy-on-write lists, we use synchronized accessors to
1511 * ensure information transmission from the writing thread to the
1512 * reading thread.
1513 */
1514 PreferenceChangeListener[] prefListeners() {
1515 synchronized(lock) {
1516 return prefListeners;
1517 }
1518 }
1519 NodeChangeListener[] nodeListeners() {
1520 synchronized(lock) {
1521 return nodeListeners;
1522 }
1523 }
1524
1525 /**
1526 * Enqueue a preference change event for delivery to registered
1527 * preference change listeners unless there are no registered
1528 * listeners. Invoked with this.lock held.
1529 */
1530 private void enqueuePreferenceChangeEvent(String key, String newValue) {
1531 if (prefListeners.length != 0) {
1532 synchronized(eventQueue) {
1533 eventQueue.add(new PreferenceChangeEvent(this, key, newValue));
1534 eventQueue.notify();
1535 }
1536 }
1537 }
1538
1539 /**
1540 * Enqueue a "node added" event for delivery to registered node change
1541 * listeners unless there are no registered listeners. Invoked with
1542 * this.lock held.
1543 */
1544 private void enqueueNodeAddedEvent(Preferences child) {
1545 if (nodeListeners.length != 0) {
1546 synchronized(eventQueue) {
1547 eventQueue.add(new NodeAddedEvent(this, child));
1548 eventQueue.notify();
1549 }
1550 }
1551 }
1552
1553 /**
1554 * Enqueue a "node removed" event for delivery to registered node change
1555 * listeners unless there are no registered listeners. Invoked with
1556 * this.lock held.
1557 */
1558 private void enqueueNodeRemovedEvent(Preferences child) {
1559 if (nodeListeners.length != 0) {
1560 synchronized(eventQueue) {
1561 eventQueue.add(new NodeRemovedEvent(this, child));
1562 eventQueue.notify();
1563 }
1564 }
1565 }
1566
1567 /**
1568 * Implements the <tt>exportNode</tt> method as per the specification in
1569 * {@link Preferences#exportNode(OutputStream)}.
1570 *
1571 * @param os the output stream on which to emit the XML document.
1572 * @throws IOException if writing to the specified output stream
1573 * results in an <tt>IOException</tt>.
1574 * @throws BackingStoreException if preference data cannot be read from
1575 * backing store.
1576 */
1577 public void exportNode(OutputStream os)
1578 throws IOException, BackingStoreException
1579 {
1580 XmlSupport.export(os, this, false);
1581 }
1582
1583 /**
1584 * Implements the <tt>exportSubtree</tt> method as per the specification in
1585 * {@link Preferences#exportSubtree(OutputStream)}.
1586 *
1587 * @param os the output stream on which to emit the XML document.
1588 * @throws IOException if writing to the specified output stream
1589 * results in an <tt>IOException</tt>.
1590 * @throws BackingStoreException if preference data cannot be read from
1591 * backing store.
1592 */
1593 public void exportSubtree(OutputStream os)
1594 throws IOException, BackingStoreException
1595 {
1596 XmlSupport.export(os, this, true);
1597 }
1598}
1599