1 /*
2 * Copyright (c) 2000, 2008, 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
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21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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23 * questions.
24 */
25
26 package java.util.prefs;
27
28 import java.io.InputStream;
29 import java.io.IOException;
30 import java.io.OutputStream;
31 import java.security.AccessController;
32 import java.security.Permission;
33 import java.security.PrivilegedAction;
34 import java.util.Iterator;
35 import java.util.ServiceLoader;
36 import java.util.ServiceConfigurationError;
37
38 // These imports needed only as a workaround for a JavaDoc bug
39 import java.lang.RuntimePermission;
40 import java.lang.Integer;
41 import java.lang.Long;
42 import java.lang.Float;
43 import java.lang.Double;
44
45 /**
46 * A node in a hierarchical collection of preference data. This class
47 * allows applications to store and retrieve user and system
48 * preference and configuration data. This data is stored
49 * persistently in an implementation-dependent backing store. Typical
50 * implementations include flat files, OS-specific registries,
51 * directory servers and SQL databases. The user of this class needn't
52 * be concerned with details of the backing store.
53 *
54 * <p>There are two separate trees of preference nodes, one for user
55 * preferences and one for system preferences. Each user has a separate user
56 * preference tree, and all users in a given system share the same system
57 * preference tree. The precise description of "user" and "system" will vary
58 * from implementation to implementation. Typical information stored in the
59 * user preference tree might include font choice, color choice, or preferred
60 * window location and size for a particular application. Typical information
61 * stored in the system preference tree might include installation
62 * configuration data for an application.
63 *
64 * <p>Nodes in a preference tree are named in a similar fashion to
65 * directories in a hierarchical file system. Every node in a preference
66 * tree has a <i>node name</i> (which is not necessarily unique),
67 * a unique <i>absolute path name</i>, and a path name <i>relative</i> to each
68 * ancestor including itself.
69 *
70 * <p>The root node has a node name of the empty string (""). Every other
71 * node has an arbitrary node name, specified at the time it is created. The
72 * only restrictions on this name are that it cannot be the empty string, and
73 * it cannot contain the slash character ('/').
74 *
75 * <p>The root node has an absolute path name of <tt>"/"</tt>. Children of
76 * the root node have absolute path names of <tt>"/" + </tt><i><node
77 * name></i>. All other nodes have absolute path names of <i><parent's
78 * absolute path name></i><tt> + "/" + </tt><i><node name></i>.
79 * Note that all absolute path names begin with the slash character.
80 *
81 * <p>A node <i>n</i>'s path name relative to its ancestor <i>a</i>
82 * is simply the string that must be appended to <i>a</i>'s absolute path name
83 * in order to form <i>n</i>'s absolute path name, with the initial slash
84 * character (if present) removed. Note that:
85 * <ul>
86 * <li>No relative path names begin with the slash character.
87 * <li>Every node's path name relative to itself is the empty string.
88 * <li>Every node's path name relative to its parent is its node name (except
89 * for the root node, which does not have a parent).
90 * <li>Every node's path name relative to the root is its absolute path name
91 * with the initial slash character removed.
92 * </ul>
93 *
94 * <p>Note finally that:
95 * <ul>
96 * <li>No path name contains multiple consecutive slash characters.
97 * <li>No path name with the exception of the root's absolute path name
98 * ends in the slash character.
99 * <li>Any string that conforms to these two rules is a valid path name.
100 * </ul>
101 *
102 * <p>All of the methods that modify preferences data are permitted to operate
103 * asynchronously; they may return immediately, and changes will eventually
104 * propagate to the persistent backing store with an implementation-dependent
105 * delay. The <tt>flush</tt> method may be used to synchronously force
106 * updates to the backing store. Normal termination of the Java Virtual
107 * Machine will <i>not</i> result in the loss of pending updates -- an explicit
108 * <tt>flush</tt> invocation is <i>not</i> required upon termination to ensure
109 * that pending updates are made persistent.
110 *
111 * <p>All of the methods that read preferences from a <tt>Preferences</tt>
112 * object require the invoker to provide a default value. The default value is
113 * returned if no value has been previously set <i>or if the backing store is
114 * unavailable</i>. The intent is to allow applications to operate, albeit
115 * with slightly degraded functionality, even if the backing store becomes
116 * unavailable. Several methods, like <tt>flush</tt>, have semantics that
117 * prevent them from operating if the backing store is unavailable. Ordinary
118 * applications should have no need to invoke any of these methods, which can
119 * be identified by the fact that they are declared to throw {@link
120 * BackingStoreException}.
121 *
122 * <p>The methods in this class may be invoked concurrently by multiple threads
123 * in a single JVM without the need for external synchronization, and the
124 * results will be equivalent to some serial execution. If this class is used
125 * concurrently <i>by multiple JVMs</i> that store their preference data in
126 * the same backing store, the data store will not be corrupted, but no
127 * other guarantees are made concerning the consistency of the preference
128 * data.
129 *
130 * <p>This class contains an export/import facility, allowing preferences
131 * to be "exported" to an XML document, and XML documents representing
132 * preferences to be "imported" back into the system. This facility
133 * may be used to back up all or part of a preference tree, and
134 * subsequently restore from the backup.
135 *
136 * <p>The XML document has the following DOCTYPE declaration:
137 * <pre>
138 * <!DOCTYPE preferences SYSTEM "http://java.sun.com/dtd/preferences.dtd">
139 * </pre>
140 * Note that the system URI (http://java.sun.com/dtd/preferences.dtd) is
141 * <i>not</i> accessed when exporting or importing preferences; it merely
142 * serves as a string to uniquely identify the DTD, which is:
143 * <pre>
144 * <?xml version="1.0" encoding="UTF-8"?>
145 *
146 * <!-- DTD for a Preferences tree. -->
147 *
148 * <!-- The preferences element is at the root of an XML document
149 * representing a Preferences tree. -->
150 * <!ELEMENT preferences (root)>
151 *
152 * <!-- The preferences element contains an optional version attribute,
153 * which specifies version of DTD. -->
154 * <!ATTLIST preferences EXTERNAL_XML_VERSION CDATA "0.0" >
155 *
156 * <!-- The root element has a map representing the root's preferences
157 * (if any), and one node for each child of the root (if any). -->
158 * <!ELEMENT root (map, node*) >
159 *
160 * <!-- Additionally, the root contains a type attribute, which
161 * specifies whether it's the system or user root. -->
162 * <!ATTLIST root
163 * type (system|user) #REQUIRED >
164 *
165 * <!-- Each node has a map representing its preferences (if any),
166 * and one node for each child (if any). -->
167 * <!ELEMENT node (map, node*) >
168 *
169 * <!-- Additionally, each node has a name attribute -->
170 * <!ATTLIST node
171 * name CDATA #REQUIRED >
172 *
173 * <!-- A map represents the preferences stored at a node (if any). -->
174 * <!ELEMENT map (entry*) >
175 *
176 * <!-- An entry represents a single preference, which is simply
177 * a key-value pair. -->
178 * <!ELEMENT entry EMPTY >
179 * <!ATTLIST entry
180 * key CDATA #REQUIRED
181 * value CDATA #REQUIRED >
182 * </pre>
183 *
184 * Every <tt>Preferences</tt> implementation must have an associated {@link
185 * PreferencesFactory} implementation. Every Java(TM) SE implementation must provide
186 * some means of specifying which <tt>PreferencesFactory</tt> implementation
187 * is used to generate the root preferences nodes. This allows the
188 * administrator to replace the default preferences implementation with an
189 * alternative implementation.
190 *
191 * <p>Implementation note: In Sun's JRE, the <tt>PreferencesFactory</tt>
192 * implementation is located as follows:
193 *
194 * <ol>
195 *
196 * <li><p>If the system property
197 * <tt>java.util.prefs.PreferencesFactory</tt> is defined, then it is
198 * taken to be the fully-qualified name of a class implementing the
199 * <tt>PreferencesFactory</tt> interface. The class is loaded and
200 * instantiated; if this process fails then an unspecified error is
201 * thrown.</p></li>
202 *
203 * <li><p> If a <tt>PreferencesFactory</tt> implementation class file
204 * has been installed in a jar file that is visible to the
205 * {@link java.lang.ClassLoader#getSystemClassLoader system class loader},
206 * and that jar file contains a provider-configuration file named
207 * <tt>java.util.prefs.PreferencesFactory</tt> in the resource
208 * directory <tt>META-INF/services</tt>, then the first class name
209 * specified in that file is taken. If more than one such jar file is
210 * provided, the first one found will be used. The class is loaded
211 * and instantiated; if this process fails then an unspecified error
212 * is thrown. </p></li>
213 *
214 * <li><p>Finally, if neither the above-mentioned system property nor
215 * an extension jar file is provided, then the system-wide default
216 * <tt>PreferencesFactory</tt> implementation for the underlying
217 * platform is loaded and instantiated.</p></li>
218 *
219 * </ol>
220 *
221 * @author Josh Bloch
222 * @since 1.4
223 */
224 public abstract class Preferences {
225
226 private static final PreferencesFactory factory = factory();
227
228 private static PreferencesFactory factory() {
229 // 1. Try user-specified system property
230 String factoryName = AccessController.doPrivileged(
231 new PrivilegedAction<String>() {
232 public String run() {
233 return System.getProperty(
234 "java.util.prefs.PreferencesFactory");}});
235 if (factoryName != null) {
236 // FIXME: This code should be run in a doPrivileged and
237 // not use the context classloader, to avoid being
238 // dependent on the invoking thread.
239 // Checking AllPermission also seems wrong.
240 try {
241 return (PreferencesFactory)
242 Class.forName(factoryName, false,
243 ClassLoader.getSystemClassLoader())
244 .newInstance();
245 } catch (Exception ex) {
246 try {
247 // workaround for javaws, plugin,
248 // load factory class using non-system classloader
249 SecurityManager sm = System.getSecurityManager();
250 if (sm != null) {
251 sm.checkPermission(new java.security.AllPermission());
252 }
253 return (PreferencesFactory)
254 Class.forName(factoryName, false,
255 Thread.currentThread()
256 .getContextClassLoader())
257 .newInstance();
258 } catch (Exception e) {
259 throw new InternalError(
260 "Can't instantiate Preferences factory "
261 + factoryName, e);
262 }
263 }
264 }
265
266 return AccessController.doPrivileged(
267 new PrivilegedAction<PreferencesFactory>() {
268 public PreferencesFactory run() {
269 return factory1();}});
270 }
271
272 private static PreferencesFactory factory1() {
273 // 2. Try service provider interface
274 Iterator<PreferencesFactory> itr = ServiceLoader
275 .load(PreferencesFactory.class, ClassLoader.getSystemClassLoader())
276 .iterator();
277
278 // choose first provider instance
279 while (itr.hasNext()) {
280 try {
281 return itr.next();
282 } catch (ServiceConfigurationError sce) {
283 if (sce.getCause() instanceof SecurityException) {
284 // Ignore the security exception, try the next provider
285 continue;
286 }
287 throw sce;
288 }
289 }
290
291 // 3. Use platform-specific system-wide default
292 String platformFactory =
293 System.getProperty("os.name").startsWith("Windows")
294 ? "java.util.prefs.WindowsPreferencesFactory"
295 : "java.util.prefs.FileSystemPreferencesFactory";
296 try {
297 return (PreferencesFactory)
298 Class.forName(platformFactory, false, null).newInstance();
299 } catch (Exception e) {
300 throw new InternalError(
301 "Can't instantiate platform default Preferences factory "
302 + platformFactory, e);
303 }
304 }
305
306 /**
307 * Maximum length of string allowed as a key (80 characters).
308 */
309 public static final int MAX_KEY_LENGTH = 80;
310
311 /**
312 * Maximum length of string allowed as a value (8192 characters).
313 */
314 public static final int MAX_VALUE_LENGTH = 8*1024;
315
316 /**
317 * Maximum length of a node name (80 characters).
318 */
319 public static final int MAX_NAME_LENGTH = 80;
320
321 /**
322 * Returns the preference node from the calling user's preference tree
323 * that is associated (by convention) with the specified class's package.
324 * The convention is as follows: the absolute path name of the node is the
325 * fully qualified package name, preceded by a slash (<tt>'/'</tt>), and
326 * with each period (<tt>'.'</tt>) replaced by a slash. For example the
327 * absolute path name of the node associated with the class
328 * <tt>com.acme.widget.Foo</tt> is <tt>/com/acme/widget</tt>.
329 *
330 * <p>This convention does not apply to the unnamed package, whose
331 * associated preference node is <tt><unnamed></tt>. This node
332 * is not intended for long term use, but for convenience in the early
333 * development of programs that do not yet belong to a package, and
334 * for "throwaway" programs. <i>Valuable data should not be stored
335 * at this node as it is shared by all programs that use it.</i>
336 *
337 * <p>A class <tt>Foo</tt> wishing to access preferences pertaining to its
338 * package can obtain a preference node as follows: <pre>
339 * static Preferences prefs = Preferences.userNodeForPackage(Foo.class);
340 * </pre>
341 * This idiom obviates the need for using a string to describe the
342 * preferences node and decreases the likelihood of a run-time failure.
343 * (If the class name is misspelled, it will typically result in a
344 * compile-time error.)
345 *
346 * <p>Invoking this method will result in the creation of the returned
347 * node and its ancestors if they do not already exist. If the returned
348 * node did not exist prior to this call, this node and any ancestors that
349 * were created by this call are not guaranteed to become permanent until
350 * the <tt>flush</tt> method is called on the returned node (or one of its
351 * ancestors or descendants).
352 *
353 * @param c the class for whose package a user preference node is desired.
354 * @return the user preference node associated with the package of which
355 * <tt>c</tt> is a member.
356 * @throws NullPointerException if <tt>c</tt> is <tt>null</tt>.
357 * @throws SecurityException if a security manager is present and
358 * it denies <tt>RuntimePermission("preferences")</tt>.
359 * @see RuntimePermission
360 */
361 public static Preferences userNodeForPackage(Class<?> c) {
362 return userRoot().node(nodeName(c));
363 }
364
365 /**
366 * Returns the preference node from the system preference tree that is
367 * associated (by convention) with the specified class's package. The
368 * convention is as follows: the absolute path name of the node is the
369 * fully qualified package name, preceded by a slash (<tt>'/'</tt>), and
370 * with each period (<tt>'.'</tt>) replaced by a slash. For example the
371 * absolute path name of the node associated with the class
372 * <tt>com.acme.widget.Foo</tt> is <tt>/com/acme/widget</tt>.
373 *
374 * <p>This convention does not apply to the unnamed package, whose
375 * associated preference node is <tt><unnamed></tt>. This node
376 * is not intended for long term use, but for convenience in the early
377 * development of programs that do not yet belong to a package, and
378 * for "throwaway" programs. <i>Valuable data should not be stored
379 * at this node as it is shared by all programs that use it.</i>
380 *
381 * <p>A class <tt>Foo</tt> wishing to access preferences pertaining to its
382 * package can obtain a preference node as follows: <pre>
383 * static Preferences prefs = Preferences.systemNodeForPackage(Foo.class);
384 * </pre>
385 * This idiom obviates the need for using a string to describe the
386 * preferences node and decreases the likelihood of a run-time failure.
387 * (If the class name is misspelled, it will typically result in a
388 * compile-time error.)
389 *
390 * <p>Invoking this method will result in the creation of the returned
391 * node and its ancestors if they do not already exist. If the returned
392 * node did not exist prior to this call, this node and any ancestors that
393 * were created by this call are not guaranteed to become permanent until
394 * the <tt>flush</tt> method is called on the returned node (or one of its
395 * ancestors or descendants).
396 *
397 * @param c the class for whose package a system preference node is desired.
398 * @return the system preference node associated with the package of which
399 * <tt>c</tt> is a member.
400 * @throws NullPointerException if <tt>c</tt> is <tt>null</tt>.
401 * @throws SecurityException if a security manager is present and
402 * it denies <tt>RuntimePermission("preferences")</tt>.
403 * @see RuntimePermission
404 */
405 public static Preferences systemNodeForPackage(Class<?> c) {
406 return systemRoot().node(nodeName(c));
407 }
408
409 /**
410 * Returns the absolute path name of the node corresponding to the package
411 * of the specified object.
412 *
413 * @throws IllegalArgumentException if the package has node preferences
414 * node associated with it.
415 */
416 private static String nodeName(Class c) {
417 if (c.isArray())
418 throw new IllegalArgumentException(
419 "Arrays have no associated preferences node.");
420 String className = c.getName();
421 int pkgEndIndex = className.lastIndexOf('.');
422 if (pkgEndIndex < 0)
423 return "/<unnamed>";
424 String packageName = className.substring(0, pkgEndIndex);
425 return "/" + packageName.replace('.', '/');
426 }
427
428 /**
429 * This permission object represents the permission required to get
430 * access to the user or system root (which in turn allows for all
431 * other operations).
432 */
433 private static Permission prefsPerm = new RuntimePermission("preferences");
434
435 /**
436 * Returns the root preference node for the calling user.
437 *
438 * @return the root preference node for the calling user.
439 * @throws SecurityException If a security manager is present and
440 * it denies <tt>RuntimePermission("preferences")</tt>.
441 * @see RuntimePermission
442 */
443 public static Preferences userRoot() {
444 SecurityManager security = System.getSecurityManager();
445 if (security != null)
446 security.checkPermission(prefsPerm);
447
448 return factory.userRoot();
449 }
450
451 /**
452 * Returns the root preference node for the system.
453 *
454 * @return the root preference node for the system.
455 * @throws SecurityException If a security manager is present and
456 * it denies <tt>RuntimePermission("preferences")</tt>.
457 * @see RuntimePermission
458 */
459 public static Preferences systemRoot() {
460 SecurityManager security = System.getSecurityManager();
461 if (security != null)
462 security.checkPermission(prefsPerm);
463
464 return factory.systemRoot();
465 }
466
467 /**
468 * Sole constructor. (For invocation by subclass constructors, typically
469 * implicit.)
470 */
471 protected Preferences() {
472 }
473
474 /**
475 * Associates the specified value with the specified key in this
476 * preference node.
477 *
478 * @param key key with which the specified value is to be associated.
479 * @param value value to be associated with the specified key.
480 * @throws NullPointerException if key or value is <tt>null</tt>.
481 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
482 * <tt>MAX_KEY_LENGTH</tt> or if <tt>value.length</tt> exceeds
483 * <tt>MAX_VALUE_LENGTH</tt>.
484 * @throws IllegalStateException if this node (or an ancestor) has been
485 * removed with the {@link #removeNode()} method.
486 */
487 public abstract void put(String key, String value);
488
489 /**
490 * Returns the value associated with the specified key in this preference
491 * node. Returns the specified default if there is no value associated
492 * with the key, or the backing store is inaccessible.
493 *
494 * <p>Some implementations may store default values in their backing
495 * stores. If there is no value associated with the specified key
496 * but there is such a <i>stored default</i>, it is returned in
497 * preference to the specified default.
498 *
499 * @param key key whose associated value is to be returned.
500 * @param def the value to be returned in the event that this
501 * preference node has no value associated with <tt>key</tt>.
502 * @return the value associated with <tt>key</tt>, or <tt>def</tt>
503 * if no value is associated with <tt>key</tt>, or the backing
504 * store is inaccessible.
505 * @throws IllegalStateException if this node (or an ancestor) has been
506 * removed with the {@link #removeNode()} method.
507 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>. (A
508 * <tt>null</tt> value for <tt>def</tt> <i>is</i> permitted.)
509 */
510 public abstract String get(String key, String def);
511
512 /**
513 * Removes the value associated with the specified key in this preference
514 * node, if any.
515 *
516 * <p>If this implementation supports <i>stored defaults</i>, and there is
517 * such a default for the specified preference, the stored default will be
518 * "exposed" by this call, in the sense that it will be returned
519 * by a succeeding call to <tt>get</tt>.
520 *
521 * @param key key whose mapping is to be removed from the preference node.
522 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
523 * @throws IllegalStateException if this node (or an ancestor) has been
524 * removed with the {@link #removeNode()} method.
525 */
526 public abstract void remove(String key);
527
528 /**
529 * Removes all of the preferences (key-value associations) in this
530 * preference node. This call has no effect on any descendants
531 * of this node.
532 *
533 * <p>If this implementation supports <i>stored defaults</i>, and this
534 * node in the preferences hierarchy contains any such defaults,
535 * the stored defaults will be "exposed" by this call, in the sense that
536 * they will be returned by succeeding calls to <tt>get</tt>.
537 *
538 * @throws BackingStoreException if this operation cannot be completed
539 * due to a failure in the backing store, or inability to
540 * communicate with it.
541 * @throws IllegalStateException if this node (or an ancestor) has been
542 * removed with the {@link #removeNode()} method.
543 * @see #removeNode()
544 */
545 public abstract void clear() throws BackingStoreException;
546
547 /**
548 * Associates a string representing the specified int value with the
549 * specified key in this preference node. The associated string is the
550 * one that would be returned if the int value were passed to
551 * {@link Integer#toString(int)}. This method is intended for use in
552 * conjunction with {@link #getInt}.
553 *
554 * @param key key with which the string form of value is to be associated.
555 * @param value value whose string form is to be associated with key.
556 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
557 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
558 * <tt>MAX_KEY_LENGTH</tt>.
559 * @throws IllegalStateException if this node (or an ancestor) has been
560 * removed with the {@link #removeNode()} method.
561 * @see #getInt(String,int)
562 */
563 public abstract void putInt(String key, int value);
564
565 /**
566 * Returns the int value represented by the string associated with the
567 * specified key in this preference node. The string is converted to
568 * an integer as by {@link Integer#parseInt(String)}. Returns the
569 * specified default if there is no value associated with the key,
570 * the backing store is inaccessible, or if
571 * <tt>Integer.parseInt(String)</tt> would throw a {@link
572 * NumberFormatException} if the associated value were passed. This
573 * method is intended for use in conjunction with {@link #putInt}.
574 *
575 * <p>If the implementation supports <i>stored defaults</i> and such a
576 * default exists, is accessible, and could be converted to an int
577 * with <tt>Integer.parseInt</tt>, this int is returned in preference to
578 * the specified default.
579 *
580 * @param key key whose associated value is to be returned as an int.
581 * @param def the value to be returned in the event that this
582 * preference node has no value associated with <tt>key</tt>
583 * or the associated value cannot be interpreted as an int,
584 * or the backing store is inaccessible.
585 * @return the int value represented by the string associated with
586 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
587 * associated value does not exist or cannot be interpreted as
588 * an int.
589 * @throws IllegalStateException if this node (or an ancestor) has been
590 * removed with the {@link #removeNode()} method.
591 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
592 * @see #putInt(String,int)
593 * @see #get(String,String)
594 */
595 public abstract int getInt(String key, int def);
596
597 /**
598 * Associates a string representing the specified long value with the
599 * specified key in this preference node. The associated string is the
600 * one that would be returned if the long value were passed to
601 * {@link Long#toString(long)}. This method is intended for use in
602 * conjunction with {@link #getLong}.
603 *
604 * @param key key with which the string form of value is to be associated.
605 * @param value value whose string form is to be associated with key.
606 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
607 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
608 * <tt>MAX_KEY_LENGTH</tt>.
609 * @throws IllegalStateException if this node (or an ancestor) has been
610 * removed with the {@link #removeNode()} method.
611 * @see #getLong(String,long)
612 */
613 public abstract void putLong(String key, long value);
614
615 /**
616 * Returns the long value represented by the string associated with the
617 * specified key in this preference node. The string is converted to
618 * a long as by {@link Long#parseLong(String)}. Returns the
619 * specified default if there is no value associated with the key,
620 * the backing store is inaccessible, or if
621 * <tt>Long.parseLong(String)</tt> would throw a {@link
622 * NumberFormatException} if the associated value were passed. This
623 * method is intended for use in conjunction with {@link #putLong}.
624 *
625 * <p>If the implementation supports <i>stored defaults</i> and such a
626 * default exists, is accessible, and could be converted to a long
627 * with <tt>Long.parseLong</tt>, this long is returned in preference to
628 * the specified default.
629 *
630 * @param key key whose associated value is to be returned as a long.
631 * @param def the value to be returned in the event that this
632 * preference node has no value associated with <tt>key</tt>
633 * or the associated value cannot be interpreted as a long,
634 * or the backing store is inaccessible.
635 * @return the long value represented by the string associated with
636 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
637 * associated value does not exist or cannot be interpreted as
638 * a long.
639 * @throws IllegalStateException if this node (or an ancestor) has been
640 * removed with the {@link #removeNode()} method.
641 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
642 * @see #putLong(String,long)
643 * @see #get(String,String)
644 */
645 public abstract long getLong(String key, long def);
646
647 /**
648 * Associates a string representing the specified boolean value with the
649 * specified key in this preference node. The associated string is
650 * <tt>"true"</tt> if the value is true, and <tt>"false"</tt> if it is
651 * false. This method is intended for use in conjunction with
652 * {@link #getBoolean}.
653 *
654 * @param key key with which the string form of value is to be associated.
655 * @param value value whose string form is to be associated with key.
656 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
657 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
658 * <tt>MAX_KEY_LENGTH</tt>.
659 * @throws IllegalStateException if this node (or an ancestor) has been
660 * removed with the {@link #removeNode()} method.
661 * @see #getBoolean(String,boolean)
662 * @see #get(String,String)
663 */
664 public abstract void putBoolean(String key, boolean value);
665
666 /**
667 * Returns the boolean value represented by the string associated with the
668 * specified key in this preference node. Valid strings
669 * are <tt>"true"</tt>, which represents true, and <tt>"false"</tt>, which
670 * represents false. Case is ignored, so, for example, <tt>"TRUE"</tt>
671 * and <tt>"False"</tt> are also valid. This method is intended for use in
672 * conjunction with {@link #putBoolean}.
673 *
674 * <p>Returns the specified default if there is no value
675 * associated with the key, the backing store is inaccessible, or if the
676 * associated value is something other than <tt>"true"</tt> or
677 * <tt>"false"</tt>, ignoring case.
678 *
679 * <p>If the implementation supports <i>stored defaults</i> and such a
680 * default exists and is accessible, it is used in preference to the
681 * specified default, unless the stored default is something other than
682 * <tt>"true"</tt> or <tt>"false"</tt>, ignoring case, in which case the
683 * specified default is used.
684 *
685 * @param key key whose associated value is to be returned as a boolean.
686 * @param def the value to be returned in the event that this
687 * preference node has no value associated with <tt>key</tt>
688 * or the associated value cannot be interpreted as a boolean,
689 * or the backing store is inaccessible.
690 * @return the boolean value represented by the string associated with
691 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
692 * associated value does not exist or cannot be interpreted as
693 * a boolean.
694 * @throws IllegalStateException if this node (or an ancestor) has been
695 * removed with the {@link #removeNode()} method.
696 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
697 * @see #get(String,String)
698 * @see #putBoolean(String,boolean)
699 */
700 public abstract boolean getBoolean(String key, boolean def);
701
702 /**
703 * Associates a string representing the specified float value with the
704 * specified key in this preference node. The associated string is the
705 * one that would be returned if the float value were passed to
706 * {@link Float#toString(float)}. This method is intended for use in
707 * conjunction with {@link #getFloat}.
708 *
709 * @param key key with which the string form of value is to be associated.
710 * @param value value whose string form is to be associated with key.
711 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
712 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
713 * <tt>MAX_KEY_LENGTH</tt>.
714 * @throws IllegalStateException if this node (or an ancestor) has been
715 * removed with the {@link #removeNode()} method.
716 * @see #getFloat(String,float)
717 */
718 public abstract void putFloat(String key, float value);
719
720 /**
721 * Returns the float value represented by the string associated with the
722 * specified key in this preference node. The string is converted to an
723 * integer as by {@link Float#parseFloat(String)}. Returns the specified
724 * default if there is no value associated with the key, the backing store
725 * is inaccessible, or if <tt>Float.parseFloat(String)</tt> would throw a
726 * {@link NumberFormatException} if the associated value were passed.
727 * This method is intended for use in conjunction with {@link #putFloat}.
728 *
729 * <p>If the implementation supports <i>stored defaults</i> and such a
730 * default exists, is accessible, and could be converted to a float
731 * with <tt>Float.parseFloat</tt>, this float is returned in preference to
732 * the specified default.
733 *
734 * @param key key whose associated value is to be returned as a float.
735 * @param def the value to be returned in the event that this
736 * preference node has no value associated with <tt>key</tt>
737 * or the associated value cannot be interpreted as a float,
738 * or the backing store is inaccessible.
739 * @return the float value represented by the string associated with
740 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
741 * associated value does not exist or cannot be interpreted as
742 * a float.
743 * @throws IllegalStateException if this node (or an ancestor) has been
744 * removed with the {@link #removeNode()} method.
745 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
746 * @see #putFloat(String,float)
747 * @see #get(String,String)
748 */
749 public abstract float getFloat(String key, float def);
750
751 /**
752 * Associates a string representing the specified double value with the
753 * specified key in this preference node. The associated string is the
754 * one that would be returned if the double value were passed to
755 * {@link Double#toString(double)}. This method is intended for use in
756 * conjunction with {@link #getDouble}.
757 *
758 * @param key key with which the string form of value is to be associated.
759 * @param value value whose string form is to be associated with key.
760 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
761 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
762 * <tt>MAX_KEY_LENGTH</tt>.
763 * @throws IllegalStateException if this node (or an ancestor) has been
764 * removed with the {@link #removeNode()} method.
765 * @see #getDouble(String,double)
766 */
767 public abstract void putDouble(String key, double value);
768
769 /**
770 * Returns the double value represented by the string associated with the
771 * specified key in this preference node. The string is converted to an
772 * integer as by {@link Double#parseDouble(String)}. Returns the specified
773 * default if there is no value associated with the key, the backing store
774 * is inaccessible, or if <tt>Double.parseDouble(String)</tt> would throw a
775 * {@link NumberFormatException} if the associated value were passed.
776 * This method is intended for use in conjunction with {@link #putDouble}.
777 *
778 * <p>If the implementation supports <i>stored defaults</i> and such a
779 * default exists, is accessible, and could be converted to a double
780 * with <tt>Double.parseDouble</tt>, this double is returned in preference
781 * to the specified default.
782 *
783 * @param key key whose associated value is to be returned as a double.
784 * @param def the value to be returned in the event that this
785 * preference node has no value associated with <tt>key</tt>
786 * or the associated value cannot be interpreted as a double,
787 * or the backing store is inaccessible.
788 * @return the double value represented by the string associated with
789 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
790 * associated value does not exist or cannot be interpreted as
791 * a double.
792 * @throws IllegalStateException if this node (or an ancestor) has been
793 * removed with the {@link #removeNode()} method.
794 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
795 * @see #putDouble(String,double)
796 * @see #get(String,String)
797 */
798 public abstract double getDouble(String key, double def);
799
800 /**
801 * Associates a string representing the specified byte array with the
802 * specified key in this preference node. The associated string is
803 * the <i>Base64</i> encoding of the byte array, as defined in <a
804 * href=http://www.ietf.org/rfc/rfc2045.txt>RFC 2045</a>, Section 6.8,
805 * with one minor change: the string will consist solely of characters
806 * from the <i>Base64 Alphabet</i>; it will not contain any newline
807 * characters. Note that the maximum length of the byte array is limited
808 * to three quarters of <tt>MAX_VALUE_LENGTH</tt> so that the length
809 * of the Base64 encoded String does not exceed <tt>MAX_VALUE_LENGTH</tt>.
810 * This method is intended for use in conjunction with
811 * {@link #getByteArray}.
812 *
813 * @param key key with which the string form of value is to be associated.
814 * @param value value whose string form is to be associated with key.
815 * @throws NullPointerException if key or value is <tt>null</tt>.
816 * @throws IllegalArgumentException if key.length() exceeds MAX_KEY_LENGTH
817 * or if value.length exceeds MAX_VALUE_LENGTH*3/4.
818 * @throws IllegalStateException if this node (or an ancestor) has been
819 * removed with the {@link #removeNode()} method.
820 * @see #getByteArray(String,byte[])
821 * @see #get(String,String)
822 */
823 public abstract void putByteArray(String key, byte[] value);
824
825 /**
826 * Returns the byte array value represented by the string associated with
827 * the specified key in this preference node. Valid strings are
828 * <i>Base64</i> encoded binary data, as defined in <a
829 * href=http://www.ietf.org/rfc/rfc2045.txt>RFC 2045</a>, Section 6.8,
830 * with one minor change: the string must consist solely of characters
831 * from the <i>Base64 Alphabet</i>; no newline characters or
832 * extraneous characters are permitted. This method is intended for use
833 * in conjunction with {@link #putByteArray}.
834 *
835 * <p>Returns the specified default if there is no value
836 * associated with the key, the backing store is inaccessible, or if the
837 * associated value is not a valid Base64 encoded byte array
838 * (as defined above).
839 *
840 * <p>If the implementation supports <i>stored defaults</i> and such a
841 * default exists and is accessible, it is used in preference to the
842 * specified default, unless the stored default is not a valid Base64
843 * encoded byte array (as defined above), in which case the
844 * specified default is used.
845 *
846 * @param key key whose associated value is to be returned as a byte array.
847 * @param def the value to be returned in the event that this
848 * preference node has no value associated with <tt>key</tt>
849 * or the associated value cannot be interpreted as a byte array,
850 * or the backing store is inaccessible.
851 * @return the byte array value represented by the string associated with
852 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
853 * associated value does not exist or cannot be interpreted as
854 * a byte array.
855 * @throws IllegalStateException if this node (or an ancestor) has been
856 * removed with the {@link #removeNode()} method.
857 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>. (A
858 * <tt>null</tt> value for <tt>def</tt> <i>is</i> permitted.)
859 * @see #get(String,String)
860 * @see #putByteArray(String,byte[])
861 */
862 public abstract byte[] getByteArray(String key, byte[] def);
863
864 /**
865 * Returns all of the keys that have an associated value in this
866 * preference node. (The returned array will be of size zero if
867 * this node has no preferences.)
868 *
869 * <p>If the implementation supports <i>stored defaults</i> and there
870 * are any such defaults at this node that have not been overridden,
871 * by explicit preferences, the defaults are returned in the array in
872 * addition to any explicit preferences.
873 *
874 * @return an array of the keys that have an associated value in this
875 * preference node.
876 * @throws BackingStoreException if this operation cannot be completed
877 * due to a failure in the backing store, or inability to
878 * communicate with it.
879 * @throws IllegalStateException if this node (or an ancestor) has been
880 * removed with the {@link #removeNode()} method.
881 */
882 public abstract String[] keys() throws BackingStoreException;
883
884 /**
885 * Returns the names of the children of this preference node, relative to
886 * this node. (The returned array will be of size zero if this node has
887 * no children.)
888 *
889 * @return the names of the children of this preference node.
890 * @throws BackingStoreException if this operation cannot be completed
891 * due to a failure in the backing store, or inability to
892 * communicate with it.
893 * @throws IllegalStateException if this node (or an ancestor) has been
894 * removed with the {@link #removeNode()} method.
895 */
896 public abstract String[] childrenNames() throws BackingStoreException;
897
898 /**
899 * Returns the parent of this preference node, or <tt>null</tt> if this is
900 * the root.
901 *
902 * @return the parent of this preference node.
903 * @throws IllegalStateException if this node (or an ancestor) has been
904 * removed with the {@link #removeNode()} method.
905 */
906 public abstract Preferences parent();
907
908 /**
909 * Returns the named preference node in the same tree as this node,
910 * creating it and any of its ancestors if they do not already exist.
911 * Accepts a relative or absolute path name. Relative path names
912 * (which do not begin with the slash character <tt>('/')</tt>) are
913 * interpreted relative to this preference node.
914 *
915 * <p>If the returned node did not exist prior to this call, this node and
916 * any ancestors that were created by this call are not guaranteed
917 * to become permanent until the <tt>flush</tt> method is called on
918 * the returned node (or one of its ancestors or descendants).
919 *
920 * @param pathName the path name of the preference node to return.
921 * @return the specified preference node.
922 * @throws IllegalArgumentException if the path name is invalid (i.e.,
923 * it contains multiple consecutive slash characters, or ends
924 * with a slash character and is more than one character long).
925 * @throws NullPointerException if path name is <tt>null</tt>.
926 * @throws IllegalStateException if this node (or an ancestor) has been
927 * removed with the {@link #removeNode()} method.
928 * @see #flush()
929 */
930 public abstract Preferences node(String pathName);
931
932 /**
933 * Returns true if the named preference node exists in the same tree
934 * as this node. Relative path names (which do not begin with the slash
935 * character <tt>('/')</tt>) are interpreted relative to this preference
936 * node.
937 *
938 * <p>If this node (or an ancestor) has already been removed with the
939 * {@link #removeNode()} method, it <i>is</i> legal to invoke this method,
940 * but only with the path name <tt>""</tt>; the invocation will return
941 * <tt>false</tt>. Thus, the idiom <tt>p.nodeExists("")</tt> may be
942 * used to test whether <tt>p</tt> has been removed.
943 *
944 * @param pathName the path name of the node whose existence
945 * is to be checked.
946 * @return true if the specified node exists.
947 * @throws BackingStoreException if this operation cannot be completed
948 * due to a failure in the backing store, or inability to
949 * communicate with it.
950 * @throws IllegalArgumentException if the path name is invalid (i.e.,
951 * it contains multiple consecutive slash characters, or ends
952 * with a slash character and is more than one character long).
953 * @throws NullPointerException if path name is <tt>null</tt>.
954 * @throws IllegalStateException if this node (or an ancestor) has been
955 * removed with the {@link #removeNode()} method and
956 * <tt>pathName</tt> is not the empty string (<tt>""</tt>).
957 */
958 public abstract boolean nodeExists(String pathName)
959 throws BackingStoreException;
960
961 /**
962 * Removes this preference node and all of its descendants, invalidating
963 * any preferences contained in the removed nodes. Once a node has been
964 * removed, attempting any method other than {@link #name()},
965 * {@link #absolutePath()}, {@link #isUserNode()}, {@link #flush()} or
966 * {@link #node(String) nodeExists("")} on the corresponding
967 * <tt>Preferences</tt> instance will fail with an
968 * <tt>IllegalStateException</tt>. (The methods defined on {@link Object}
969 * can still be invoked on a node after it has been removed; they will not
970 * throw <tt>IllegalStateException</tt>.)
971 *
972 * <p>The removal is not guaranteed to be persistent until the
973 * <tt>flush</tt> method is called on this node (or an ancestor).
974 *
975 * <p>If this implementation supports <i>stored defaults</i>, removing a
976 * node exposes any stored defaults at or below this node. Thus, a
977 * subsequent call to <tt>nodeExists</tt> on this node's path name may
978 * return <tt>true</tt>, and a subsequent call to <tt>node</tt> on this
979 * path name may return a (different) <tt>Preferences</tt> instance
980 * representing a non-empty collection of preferences and/or children.
981 *
982 * @throws BackingStoreException if this operation cannot be completed
983 * due to a failure in the backing store, or inability to
984 * communicate with it.
985 * @throws IllegalStateException if this node (or an ancestor) has already
986 * been removed with the {@link #removeNode()} method.
987 * @throws UnsupportedOperationException if this method is invoked on
988 * the root node.
989 * @see #flush()
990 */
991 public abstract void removeNode() throws BackingStoreException;
992
993 /**
994 * Returns this preference node's name, relative to its parent.
995 *
996 * @return this preference node's name, relative to its parent.
997 */
998 public abstract String name();
999
1000 /**
1001 * Returns this preference node's absolute path name.
1002 *
1003 * @return this preference node's absolute path name.
1004 */
1005 public abstract String absolutePath();
1006
1007 /**
1008 * Returns <tt>true</tt> if this preference node is in the user
1009 * preference tree, <tt>false</tt> if it's in the system preference tree.
1010 *
1011 * @return <tt>true</tt> if this preference node is in the user
1012 * preference tree, <tt>false</tt> if it's in the system
1013 * preference tree.
1014 */
1015 public abstract boolean isUserNode();
1016
1017 /**
1018 * Returns a string representation of this preferences node,
1019 * as if computed by the expression:<tt>(this.isUserNode() ? "User" :
1020 * "System") + " Preference Node: " + this.absolutePath()</tt>.
1021 */
1022 public abstract String toString();
1023
1024 /**
1025 * Forces any changes in the contents of this preference node and its
1026 * descendants to the persistent store. Once this method returns
1027 * successfully, it is safe to assume that all changes made in the
1028 * subtree rooted at this node prior to the method invocation have become
1029 * permanent.
1030 *
1031 * <p>Implementations are free to flush changes into the persistent store
1032 * at any time. They do not need to wait for this method to be called.
1033 *
1034 * <p>When a flush occurs on a newly created node, it is made persistent,
1035 * as are any ancestors (and descendants) that have yet to be made
1036 * persistent. Note however that any preference value changes in
1037 * ancestors are <i>not</i> guaranteed to be made persistent.
1038 *
1039 * <p> If this method is invoked on a node that has been removed with
1040 * the {@link #removeNode()} method, flushSpi() is invoked on this node,
1041 * but not on others.
1042 *
1043 * @throws BackingStoreException if this operation cannot be completed
1044 * due to a failure in the backing store, or inability to
1045 * communicate with it.
1046 * @see #sync()
1047 */
1048 public abstract void flush() throws BackingStoreException;
1049
1050 /**
1051 * Ensures that future reads from this preference node and its
1052 * descendants reflect any changes that were committed to the persistent
1053 * store (from any VM) prior to the <tt>sync</tt> invocation. As a
1054 * side-effect, forces any changes in the contents of this preference node
1055 * and its descendants to the persistent store, as if the <tt>flush</tt>
1056 * method had been invoked on this node.
1057 *
1058 * @throws BackingStoreException if this operation cannot be completed
1059 * due to a failure in the backing store, or inability to
1060 * communicate with it.
1061 * @throws IllegalStateException if this node (or an ancestor) has been
1062 * removed with the {@link #removeNode()} method.
1063 * @see #flush()
1064 */
1065 public abstract void sync() throws BackingStoreException;
1066
1067 /**
1068 * Registers the specified listener to receive <i>preference change
1069 * events</i> for this preference node. A preference change event is
1070 * generated when a preference is added to this node, removed from this
1071 * node, or when the value associated with a preference is changed.
1072 * (Preference change events are <i>not</i> generated by the {@link
1073 * #removeNode()} method, which generates a <i>node change event</i>.
1074 * Preference change events <i>are</i> generated by the <tt>clear</tt>
1075 * method.)
1076 *
1077 * <p>Events are only guaranteed for changes made within the same JVM
1078 * as the registered listener, though some implementations may generate
1079 * events for changes made outside this JVM. Events may be generated
1080 * before the changes have been made persistent. Events are not generated
1081 * when preferences are modified in descendants of this node; a caller
1082 * desiring such events must register with each descendant.
1083 *
1084 * @param pcl The preference change listener to add.
1085 * @throws NullPointerException if <tt>pcl</tt> is null.
1086 * @throws IllegalStateException if this node (or an ancestor) has been
1087 * removed with the {@link #removeNode()} method.
1088 * @see #removePreferenceChangeListener(PreferenceChangeListener)
1089 * @see #addNodeChangeListener(NodeChangeListener)
1090 */
1091 public abstract void addPreferenceChangeListener(
1092 PreferenceChangeListener pcl);
1093
1094 /**
1095 * Removes the specified preference change listener, so it no longer
1096 * receives preference change events.
1097 *
1098 * @param pcl The preference change listener to remove.
1099 * @throws IllegalArgumentException if <tt>pcl</tt> was not a registered
1100 * preference change listener on this node.
1101 * @throws IllegalStateException if this node (or an ancestor) has been
1102 * removed with the {@link #removeNode()} method.
1103 * @see #addPreferenceChangeListener(PreferenceChangeListener)
1104 */
1105 public abstract void removePreferenceChangeListener(
1106 PreferenceChangeListener pcl);
1107
1108 /**
1109 * Registers the specified listener to receive <i>node change events</i>
1110 * for this node. A node change event is generated when a child node is
1111 * added to or removed from this node. (A single {@link #removeNode()}
1112 * invocation results in multiple <i>node change events</i>, one for every
1113 * node in the subtree rooted at the removed node.)
1114 *
1115 * <p>Events are only guaranteed for changes made within the same JVM
1116 * as the registered listener, though some implementations may generate
1117 * events for changes made outside this JVM. Events may be generated
1118 * before the changes have become permanent. Events are not generated
1119 * when indirect descendants of this node are added or removed; a
1120 * caller desiring such events must register with each descendant.
1121 *
1122 * <p>Few guarantees can be made regarding node creation. Because nodes
1123 * are created implicitly upon access, it may not be feasible for an
1124 * implementation to determine whether a child node existed in the backing
1125 * store prior to access (for example, because the backing store is
1126 * unreachable or cached information is out of date). Under these
1127 * circumstances, implementations are neither required to generate node
1128 * change events nor prohibited from doing so.
1129 *
1130 * @param ncl The <tt>NodeChangeListener</tt> to add.
1131 * @throws NullPointerException if <tt>ncl</tt> is null.
1132 * @throws IllegalStateException if this node (or an ancestor) has been
1133 * removed with the {@link #removeNode()} method.
1134 * @see #removeNodeChangeListener(NodeChangeListener)
1135 * @see #addPreferenceChangeListener(PreferenceChangeListener)
1136 */
1137 public abstract void addNodeChangeListener(NodeChangeListener ncl);
1138
1139 /**
1140 * Removes the specified <tt>NodeChangeListener</tt>, so it no longer
1141 * receives change events.
1142 *
1143 * @param ncl The <tt>NodeChangeListener</tt> to remove.
1144 * @throws IllegalArgumentException if <tt>ncl</tt> was not a registered
1145 * <tt>NodeChangeListener</tt> on this node.
1146 * @throws IllegalStateException if this node (or an ancestor) has been
1147 * removed with the {@link #removeNode()} method.
1148 * @see #addNodeChangeListener(NodeChangeListener)
1149 */
1150 public abstract void removeNodeChangeListener(NodeChangeListener ncl);
1151
1152 /**
1153 * Emits on the specified output stream an XML document representing all
1154 * of the preferences contained in this node (but not its descendants).
1155 * This XML document is, in effect, an offline backup of the node.
1156 *
1157 * <p>The XML document will have the following DOCTYPE declaration:
1158 * <pre>
1159 * <!DOCTYPE preferences SYSTEM "http://java.sun.com/dtd/preferences.dtd">
1160 * </pre>
1161 * The UTF-8 character encoding will be used.
1162 *
1163 * <p>This method is an exception to the general rule that the results of
1164 * concurrently executing multiple methods in this class yields
1165 * results equivalent to some serial execution. If the preferences
1166 * at this node are modified concurrently with an invocation of this
1167 * method, the exported preferences comprise a "fuzzy snapshot" of the
1168 * preferences contained in the node; some of the concurrent modifications
1169 * may be reflected in the exported data while others may not.
1170 *
1171 * @param os the output stream on which to emit the XML document.
1172 * @throws IOException if writing to the specified output stream
1173 * results in an <tt>IOException</tt>.
1174 * @throws BackingStoreException if preference data cannot be read from
1175 * backing store.
1176 * @see #importPreferences(InputStream)
1177 * @throws IllegalStateException if this node (or an ancestor) has been
1178 * removed with the {@link #removeNode()} method.
1179 */
1180 public abstract void exportNode(OutputStream os)
1181 throws IOException, BackingStoreException;
1182
1183 /**
1184 * Emits an XML document representing all of the preferences contained
1185 * in this node and all of its descendants. This XML document is, in
1186 * effect, an offline backup of the subtree rooted at the node.
1187 *
1188 * <p>The XML document will have the following DOCTYPE declaration:
1189 * <pre>
1190 * <!DOCTYPE preferences SYSTEM "http://java.sun.com/dtd/preferences.dtd">
1191 * </pre>
1192 * The UTF-8 character encoding will be used.
1193 *
1194 * <p>This method is an exception to the general rule that the results of
1195 * concurrently executing multiple methods in this class yields
1196 * results equivalent to some serial execution. If the preferences
1197 * or nodes in the subtree rooted at this node are modified concurrently
1198 * with an invocation of this method, the exported preferences comprise a
1199 * "fuzzy snapshot" of the subtree; some of the concurrent modifications
1200 * may be reflected in the exported data while others may not.
1201 *
1202 * @param os the output stream on which to emit the XML document.
1203 * @throws IOException if writing to the specified output stream
1204 * results in an <tt>IOException</tt>.
1205 * @throws BackingStoreException if preference data cannot be read from
1206 * backing store.
1207 * @throws IllegalStateException if this node (or an ancestor) has been
1208 * removed with the {@link #removeNode()} method.
1209 * @see #importPreferences(InputStream)
1210 * @see #exportNode(OutputStream)
1211 */
1212 public abstract void exportSubtree(OutputStream os)
1213 throws IOException, BackingStoreException;
1214
1215 /**
1216 * Imports all of the preferences represented by the XML document on the
1217 * specified input stream. The document may represent user preferences or
1218 * system preferences. If it represents user preferences, the preferences
1219 * will be imported into the calling user's preference tree (even if they
1220 * originally came from a different user's preference tree). If any of
1221 * the preferences described by the document inhabit preference nodes that
1222 * do not exist, the nodes will be created.
1223 *
1224 * <p>The XML document must have the following DOCTYPE declaration:
1225 * <pre>
1226 * <!DOCTYPE preferences SYSTEM "http://java.sun.com/dtd/preferences.dtd">
1227 * </pre>
1228 * (This method is designed for use in conjunction with
1229 * {@link #exportNode(OutputStream)} and
1230 * {@link #exportSubtree(OutputStream)}.
1231 *
1232 * <p>This method is an exception to the general rule that the results of
1233 * concurrently executing multiple methods in this class yields
1234 * results equivalent to some serial execution. The method behaves
1235 * as if implemented on top of the other public methods in this class,
1236 * notably {@link #node(String)} and {@link #put(String, String)}.
1237 *
1238 * @param is the input stream from which to read the XML document.
1239 * @throws IOException if reading from the specified input stream
1240 * results in an <tt>IOException</tt>.
1241 * @throws InvalidPreferencesFormatException Data on input stream does not
1242 * constitute a valid XML document with the mandated document type.
1243 * @throws SecurityException If a security manager is present and
1244 * it denies <tt>RuntimePermission("preferences")</tt>.
1245 * @see RuntimePermission
1246 */
1247 public static void importPreferences(InputStream is)
1248 throws IOException, InvalidPreferencesFormatException
1249 {
1250 XmlSupport.importPreferences(is);
1251 }
1252 }