1 /*
2 * Copyright (c) 2000, 2012, 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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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 osName = System.getProperty("os.name");
293 String platformFactory;
294 if (osName.startsWith("Windows")) {
295 platformFactory = "java.util.prefs.WindowsPreferencesFactory";
296 } else if (osName.contains("OS X")) {
297 platformFactory = "java.util.prefs.MacOSXPreferencesFactory";
298 } else {
299 platformFactory = "java.util.prefs.FileSystemPreferencesFactory";
300 }
301 try {
302 return (PreferencesFactory)
303 Class.forName(platformFactory, false, null).newInstance();
304 } catch (Exception e) {
305 throw new InternalError(
306 "Can't instantiate platform default Preferences factory "
307 + platformFactory, e);
308 }
309 }
310
311 /**
312 * Maximum length of string allowed as a key (80 characters).
313 */
314 public static final int MAX_KEY_LENGTH = 80;
315
316 /**
317 * Maximum length of string allowed as a value (8192 characters).
318 */
319 public static final int MAX_VALUE_LENGTH = 8*1024;
320
321 /**
322 * Maximum length of a node name (80 characters).
323 */
324 public static final int MAX_NAME_LENGTH = 80;
325
326 /**
327 * Returns the preference node from the calling user's preference tree
328 * that is associated (by convention) with the specified class's package.
329 * The convention is as follows: the absolute path name of the node is the
330 * fully qualified package name, preceded by a slash (<tt>'/'</tt>), and
331 * with each period (<tt>'.'</tt>) replaced by a slash. For example the
332 * absolute path name of the node associated with the class
333 * <tt>com.acme.widget.Foo</tt> is <tt>/com/acme/widget</tt>.
334 *
335 * <p>This convention does not apply to the unnamed package, whose
336 * associated preference node is <tt><unnamed></tt>. This node
337 * is not intended for long term use, but for convenience in the early
338 * development of programs that do not yet belong to a package, and
339 * for "throwaway" programs. <i>Valuable data should not be stored
340 * at this node as it is shared by all programs that use it.</i>
341 *
342 * <p>A class <tt>Foo</tt> wishing to access preferences pertaining to its
343 * package can obtain a preference node as follows: <pre>
344 * static Preferences prefs = Preferences.userNodeForPackage(Foo.class);
345 * </pre>
346 * This idiom obviates the need for using a string to describe the
347 * preferences node and decreases the likelihood of a run-time failure.
348 * (If the class name is misspelled, it will typically result in a
349 * compile-time error.)
350 *
351 * <p>Invoking this method will result in the creation of the returned
352 * node and its ancestors if they do not already exist. If the returned
353 * node did not exist prior to this call, this node and any ancestors that
354 * were created by this call are not guaranteed to become permanent until
355 * the <tt>flush</tt> method is called on the returned node (or one of its
356 * ancestors or descendants).
357 *
358 * @param c the class for whose package a user preference node is desired.
359 * @return the user preference node associated with the package of which
360 * <tt>c</tt> is a member.
361 * @throws NullPointerException if <tt>c</tt> is <tt>null</tt>.
362 * @throws SecurityException if a security manager is present and
363 * it denies <tt>RuntimePermission("preferences")</tt>.
364 * @see RuntimePermission
365 */
366 public static Preferences userNodeForPackage(Class<?> c) {
367 return userRoot().node(nodeName(c));
368 }
369
370 /**
371 * Returns the preference node from the system preference tree that is
372 * associated (by convention) with the specified class's package. The
373 * convention is as follows: the absolute path name of the node is the
374 * fully qualified package name, preceded by a slash (<tt>'/'</tt>), and
375 * with each period (<tt>'.'</tt>) replaced by a slash. For example the
376 * absolute path name of the node associated with the class
377 * <tt>com.acme.widget.Foo</tt> is <tt>/com/acme/widget</tt>.
378 *
379 * <p>This convention does not apply to the unnamed package, whose
380 * associated preference node is <tt><unnamed></tt>. This node
381 * is not intended for long term use, but for convenience in the early
382 * development of programs that do not yet belong to a package, and
383 * for "throwaway" programs. <i>Valuable data should not be stored
384 * at this node as it is shared by all programs that use it.</i>
385 *
386 * <p>A class <tt>Foo</tt> wishing to access preferences pertaining to its
387 * package can obtain a preference node as follows: <pre>
388 * static Preferences prefs = Preferences.systemNodeForPackage(Foo.class);
389 * </pre>
390 * This idiom obviates the need for using a string to describe the
391 * preferences node and decreases the likelihood of a run-time failure.
392 * (If the class name is misspelled, it will typically result in a
393 * compile-time error.)
394 *
395 * <p>Invoking this method will result in the creation of the returned
396 * node and its ancestors if they do not already exist. If the returned
397 * node did not exist prior to this call, this node and any ancestors that
398 * were created by this call are not guaranteed to become permanent until
399 * the <tt>flush</tt> method is called on the returned node (or one of its
400 * ancestors or descendants).
401 *
402 * @param c the class for whose package a system preference node is desired.
403 * @return the system preference node associated with the package of which
404 * <tt>c</tt> is a member.
405 * @throws NullPointerException if <tt>c</tt> is <tt>null</tt>.
406 * @throws SecurityException if a security manager is present and
407 * it denies <tt>RuntimePermission("preferences")</tt>.
408 * @see RuntimePermission
409 */
410 public static Preferences systemNodeForPackage(Class<?> c) {
411 return systemRoot().node(nodeName(c));
412 }
413
414 /**
415 * Returns the absolute path name of the node corresponding to the package
416 * of the specified object.
417 *
418 * @throws IllegalArgumentException if the package has node preferences
419 * node associated with it.
420 */
421 private static String nodeName(Class<?> c) {
422 if (c.isArray())
423 throw new IllegalArgumentException(
424 "Arrays have no associated preferences node.");
425 String className = c.getName();
426 int pkgEndIndex = className.lastIndexOf('.');
427 if (pkgEndIndex < 0)
428 return "/<unnamed>";
429 String packageName = className.substring(0, pkgEndIndex);
430 return "/" + packageName.replace('.', '/');
431 }
432
433 /**
434 * This permission object represents the permission required to get
435 * access to the user or system root (which in turn allows for all
436 * other operations).
437 */
438 private static Permission prefsPerm = new RuntimePermission("preferences");
439
440 /**
441 * Returns the root preference node for the calling user.
442 *
443 * @return the root preference node for the calling user.
444 * @throws SecurityException If a security manager is present and
445 * it denies <tt>RuntimePermission("preferences")</tt>.
446 * @see RuntimePermission
447 */
448 public static Preferences userRoot() {
449 SecurityManager security = System.getSecurityManager();
450 if (security != null)
451 security.checkPermission(prefsPerm);
452
453 return factory.userRoot();
454 }
455
456 /**
457 * Returns the root preference node for the system.
458 *
459 * @return the root preference node for the system.
460 * @throws SecurityException If a security manager is present and
461 * it denies <tt>RuntimePermission("preferences")</tt>.
462 * @see RuntimePermission
463 */
464 public static Preferences systemRoot() {
465 SecurityManager security = System.getSecurityManager();
466 if (security != null)
467 security.checkPermission(prefsPerm);
468
469 return factory.systemRoot();
470 }
471
472 /**
473 * Sole constructor. (For invocation by subclass constructors, typically
474 * implicit.)
475 */
476 protected Preferences() {
477 }
478
479 /**
480 * Associates the specified value with the specified key in this
481 * preference node.
482 *
483 * @param key key with which the specified value is to be associated.
484 * @param value value to be associated with the specified key.
485 * @throws NullPointerException if key or value is <tt>null</tt>.
486 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
487 * <tt>MAX_KEY_LENGTH</tt> or if <tt>value.length</tt> exceeds
488 * <tt>MAX_VALUE_LENGTH</tt>.
489 * @throws IllegalStateException if this node (or an ancestor) has been
490 * removed with the {@link #removeNode()} method.
491 */
492 public abstract void put(String key, String value);
493
494 /**
495 * Returns the value associated with the specified key in this preference
496 * node. Returns the specified default if there is no value associated
497 * with the key, or the backing store is inaccessible.
498 *
499 * <p>Some implementations may store default values in their backing
500 * stores. If there is no value associated with the specified key
501 * but there is such a <i>stored default</i>, it is returned in
502 * preference to the specified default.
503 *
504 * @param key key whose associated value is to be returned.
505 * @param def the value to be returned in the event that this
506 * preference node has no value associated with <tt>key</tt>.
507 * @return the value associated with <tt>key</tt>, or <tt>def</tt>
508 * if no value is associated with <tt>key</tt>, or the backing
509 * store is inaccessible.
510 * @throws IllegalStateException if this node (or an ancestor) has been
511 * removed with the {@link #removeNode()} method.
512 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>. (A
513 * <tt>null</tt> value for <tt>def</tt> <i>is</i> permitted.)
514 */
515 public abstract String get(String key, String def);
516
517 /**
518 * Removes the value associated with the specified key in this preference
519 * node, if any.
520 *
521 * <p>If this implementation supports <i>stored defaults</i>, and there is
522 * such a default for the specified preference, the stored default will be
523 * "exposed" by this call, in the sense that it will be returned
524 * by a succeeding call to <tt>get</tt>.
525 *
526 * @param key key whose mapping is to be removed from the preference node.
527 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
528 * @throws IllegalStateException if this node (or an ancestor) has been
529 * removed with the {@link #removeNode()} method.
530 */
531 public abstract void remove(String key);
532
533 /**
534 * Removes all of the preferences (key-value associations) in this
535 * preference node. This call has no effect on any descendants
536 * of this node.
537 *
538 * <p>If this implementation supports <i>stored defaults</i>, and this
539 * node in the preferences hierarchy contains any such defaults,
540 * the stored defaults will be "exposed" by this call, in the sense that
541 * they will be returned by succeeding calls to <tt>get</tt>.
542 *
543 * @throws BackingStoreException if this operation cannot be completed
544 * due to a failure in the backing store, or inability to
545 * communicate with it.
546 * @throws IllegalStateException if this node (or an ancestor) has been
547 * removed with the {@link #removeNode()} method.
548 * @see #removeNode()
549 */
550 public abstract void clear() throws BackingStoreException;
551
552 /**
553 * Associates a string representing the specified int value with the
554 * specified key in this preference node. The associated string is the
555 * one that would be returned if the int value were passed to
556 * {@link Integer#toString(int)}. This method is intended for use in
557 * conjunction with {@link #getInt}.
558 *
559 * @param key key with which the string form of value is to be associated.
560 * @param value value whose string form is to be associated with key.
561 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
562 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
563 * <tt>MAX_KEY_LENGTH</tt>.
564 * @throws IllegalStateException if this node (or an ancestor) has been
565 * removed with the {@link #removeNode()} method.
566 * @see #getInt(String,int)
567 */
568 public abstract void putInt(String key, int value);
569
570 /**
571 * Returns the int value represented by the string associated with the
572 * specified key in this preference node. The string is converted to
573 * an integer as by {@link Integer#parseInt(String)}. Returns the
574 * specified default if there is no value associated with the key,
575 * the backing store is inaccessible, or if
576 * <tt>Integer.parseInt(String)</tt> would throw a {@link
577 * NumberFormatException} if the associated value were passed. This
578 * method is intended for use in conjunction with {@link #putInt}.
579 *
580 * <p>If the implementation supports <i>stored defaults</i> and such a
581 * default exists, is accessible, and could be converted to an int
582 * with <tt>Integer.parseInt</tt>, this int is returned in preference to
583 * the specified default.
584 *
585 * @param key key whose associated value is to be returned as an int.
586 * @param def the value to be returned in the event that this
587 * preference node has no value associated with <tt>key</tt>
588 * or the associated value cannot be interpreted as an int,
589 * or the backing store is inaccessible.
590 * @return the int value represented by the string associated with
591 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
592 * associated value does not exist or cannot be interpreted as
593 * an int.
594 * @throws IllegalStateException if this node (or an ancestor) has been
595 * removed with the {@link #removeNode()} method.
596 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
597 * @see #putInt(String,int)
598 * @see #get(String,String)
599 */
600 public abstract int getInt(String key, int def);
601
602 /**
603 * Associates a string representing the specified long value with the
604 * specified key in this preference node. The associated string is the
605 * one that would be returned if the long value were passed to
606 * {@link Long#toString(long)}. This method is intended for use in
607 * conjunction with {@link #getLong}.
608 *
609 * @param key key with which the string form of value is to be associated.
610 * @param value value whose string form is to be associated with key.
611 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
612 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
613 * <tt>MAX_KEY_LENGTH</tt>.
614 * @throws IllegalStateException if this node (or an ancestor) has been
615 * removed with the {@link #removeNode()} method.
616 * @see #getLong(String,long)
617 */
618 public abstract void putLong(String key, long value);
619
620 /**
621 * Returns the long value represented by the string associated with the
622 * specified key in this preference node. The string is converted to
623 * a long as by {@link Long#parseLong(String)}. Returns the
624 * specified default if there is no value associated with the key,
625 * the backing store is inaccessible, or if
626 * <tt>Long.parseLong(String)</tt> would throw a {@link
627 * NumberFormatException} if the associated value were passed. This
628 * method is intended for use in conjunction with {@link #putLong}.
629 *
630 * <p>If the implementation supports <i>stored defaults</i> and such a
631 * default exists, is accessible, and could be converted to a long
632 * with <tt>Long.parseLong</tt>, this long is returned in preference to
633 * the specified default.
634 *
635 * @param key key whose associated value is to be returned as a long.
636 * @param def the value to be returned in the event that this
637 * preference node has no value associated with <tt>key</tt>
638 * or the associated value cannot be interpreted as a long,
639 * or the backing store is inaccessible.
640 * @return the long value represented by the string associated with
641 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
642 * associated value does not exist or cannot be interpreted as
643 * a long.
644 * @throws IllegalStateException if this node (or an ancestor) has been
645 * removed with the {@link #removeNode()} method.
646 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
647 * @see #putLong(String,long)
648 * @see #get(String,String)
649 */
650 public abstract long getLong(String key, long def);
651
652 /**
653 * Associates a string representing the specified boolean value with the
654 * specified key in this preference node. The associated string is
655 * <tt>"true"</tt> if the value is true, and <tt>"false"</tt> if it is
656 * false. This method is intended for use in conjunction with
657 * {@link #getBoolean}.
658 *
659 * @param key key with which the string form of value is to be associated.
660 * @param value value whose string form is to be associated with key.
661 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
662 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
663 * <tt>MAX_KEY_LENGTH</tt>.
664 * @throws IllegalStateException if this node (or an ancestor) has been
665 * removed with the {@link #removeNode()} method.
666 * @see #getBoolean(String,boolean)
667 * @see #get(String,String)
668 */
669 public abstract void putBoolean(String key, boolean value);
670
671 /**
672 * Returns the boolean value represented by the string associated with the
673 * specified key in this preference node. Valid strings
674 * are <tt>"true"</tt>, which represents true, and <tt>"false"</tt>, which
675 * represents false. Case is ignored, so, for example, <tt>"TRUE"</tt>
676 * and <tt>"False"</tt> are also valid. This method is intended for use in
677 * conjunction with {@link #putBoolean}.
678 *
679 * <p>Returns the specified default if there is no value
680 * associated with the key, the backing store is inaccessible, or if the
681 * associated value is something other than <tt>"true"</tt> or
682 * <tt>"false"</tt>, ignoring case.
683 *
684 * <p>If the implementation supports <i>stored defaults</i> and such a
685 * default exists and is accessible, it is used in preference to the
686 * specified default, unless the stored default is something other than
687 * <tt>"true"</tt> or <tt>"false"</tt>, ignoring case, in which case the
688 * specified default is used.
689 *
690 * @param key key whose associated value is to be returned as a boolean.
691 * @param def the value to be returned in the event that this
692 * preference node has no value associated with <tt>key</tt>
693 * or the associated value cannot be interpreted as a boolean,
694 * or the backing store is inaccessible.
695 * @return the boolean value represented by the string associated with
696 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
697 * associated value does not exist or cannot be interpreted as
698 * a boolean.
699 * @throws IllegalStateException if this node (or an ancestor) has been
700 * removed with the {@link #removeNode()} method.
701 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
702 * @see #get(String,String)
703 * @see #putBoolean(String,boolean)
704 */
705 public abstract boolean getBoolean(String key, boolean def);
706
707 /**
708 * Associates a string representing the specified float value with the
709 * specified key in this preference node. The associated string is the
710 * one that would be returned if the float value were passed to
711 * {@link Float#toString(float)}. This method is intended for use in
712 * conjunction with {@link #getFloat}.
713 *
714 * @param key key with which the string form of value is to be associated.
715 * @param value value whose string form is to be associated with key.
716 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
717 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
718 * <tt>MAX_KEY_LENGTH</tt>.
719 * @throws IllegalStateException if this node (or an ancestor) has been
720 * removed with the {@link #removeNode()} method.
721 * @see #getFloat(String,float)
722 */
723 public abstract void putFloat(String key, float value);
724
725 /**
726 * Returns the float value represented by the string associated with the
727 * specified key in this preference node. The string is converted to an
728 * integer as by {@link Float#parseFloat(String)}. Returns the specified
729 * default if there is no value associated with the key, the backing store
730 * is inaccessible, or if <tt>Float.parseFloat(String)</tt> would throw a
731 * {@link NumberFormatException} if the associated value were passed.
732 * This method is intended for use in conjunction with {@link #putFloat}.
733 *
734 * <p>If the implementation supports <i>stored defaults</i> and such a
735 * default exists, is accessible, and could be converted to a float
736 * with <tt>Float.parseFloat</tt>, this float is returned in preference to
737 * the specified default.
738 *
739 * @param key key whose associated value is to be returned as a float.
740 * @param def the value to be returned in the event that this
741 * preference node has no value associated with <tt>key</tt>
742 * or the associated value cannot be interpreted as a float,
743 * or the backing store is inaccessible.
744 * @return the float value represented by the string associated with
745 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
746 * associated value does not exist or cannot be interpreted as
747 * a float.
748 * @throws IllegalStateException if this node (or an ancestor) has been
749 * removed with the {@link #removeNode()} method.
750 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
751 * @see #putFloat(String,float)
752 * @see #get(String,String)
753 */
754 public abstract float getFloat(String key, float def);
755
756 /**
757 * Associates a string representing the specified double value with the
758 * specified key in this preference node. The associated string is the
759 * one that would be returned if the double value were passed to
760 * {@link Double#toString(double)}. This method is intended for use in
761 * conjunction with {@link #getDouble}.
762 *
763 * @param key key with which the string form of value is to be associated.
764 * @param value value whose string form is to be associated with key.
765 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
766 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
767 * <tt>MAX_KEY_LENGTH</tt>.
768 * @throws IllegalStateException if this node (or an ancestor) has been
769 * removed with the {@link #removeNode()} method.
770 * @see #getDouble(String,double)
771 */
772 public abstract void putDouble(String key, double value);
773
774 /**
775 * Returns the double value represented by the string associated with the
776 * specified key in this preference node. The string is converted to an
777 * integer as by {@link Double#parseDouble(String)}. Returns the specified
778 * default if there is no value associated with the key, the backing store
779 * is inaccessible, or if <tt>Double.parseDouble(String)</tt> would throw a
780 * {@link NumberFormatException} if the associated value were passed.
781 * This method is intended for use in conjunction with {@link #putDouble}.
782 *
783 * <p>If the implementation supports <i>stored defaults</i> and such a
784 * default exists, is accessible, and could be converted to a double
785 * with <tt>Double.parseDouble</tt>, this double is returned in preference
786 * to the specified default.
787 *
788 * @param key key whose associated value is to be returned as a double.
789 * @param def the value to be returned in the event that this
790 * preference node has no value associated with <tt>key</tt>
791 * or the associated value cannot be interpreted as a double,
792 * or the backing store is inaccessible.
793 * @return the double value represented by the string associated with
794 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
795 * associated value does not exist or cannot be interpreted as
796 * a double.
797 * @throws IllegalStateException if this node (or an ancestor) has been
798 * removed with the {@link #removeNode()} method.
799 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>.
800 * @see #putDouble(String,double)
801 * @see #get(String,String)
802 */
803 public abstract double getDouble(String key, double def);
804
805 /**
806 * Associates a string representing the specified byte array with the
807 * specified key in this preference node. The associated string is
808 * the <i>Base64</i> encoding of the byte array, as defined in <a
809 * href=http://www.ietf.org/rfc/rfc2045.txt>RFC 2045</a>, Section 6.8,
810 * with one minor change: the string will consist solely of characters
811 * from the <i>Base64 Alphabet</i>; it will not contain any newline
812 * characters. Note that the maximum length of the byte array is limited
813 * to three quarters of <tt>MAX_VALUE_LENGTH</tt> so that the length
814 * of the Base64 encoded String does not exceed <tt>MAX_VALUE_LENGTH</tt>.
815 * This method is intended for use in conjunction with
816 * {@link #getByteArray}.
817 *
818 * @param key key with which the string form of value is to be associated.
819 * @param value value whose string form is to be associated with key.
820 * @throws NullPointerException if key or value is <tt>null</tt>.
821 * @throws IllegalArgumentException if key.length() exceeds MAX_KEY_LENGTH
822 * or if value.length exceeds MAX_VALUE_LENGTH*3/4.
823 * @throws IllegalStateException if this node (or an ancestor) has been
824 * removed with the {@link #removeNode()} method.
825 * @see #getByteArray(String,byte[])
826 * @see #get(String,String)
827 */
828 public abstract void putByteArray(String key, byte[] value);
829
830 /**
831 * Returns the byte array value represented by the string associated with
832 * the specified key in this preference node. Valid strings are
833 * <i>Base64</i> encoded binary data, as defined in <a
834 * href=http://www.ietf.org/rfc/rfc2045.txt>RFC 2045</a>, Section 6.8,
835 * with one minor change: the string must consist solely of characters
836 * from the <i>Base64 Alphabet</i>; no newline characters or
837 * extraneous characters are permitted. This method is intended for use
838 * in conjunction with {@link #putByteArray}.
839 *
840 * <p>Returns the specified default if there is no value
841 * associated with the key, the backing store is inaccessible, or if the
842 * associated value is not a valid Base64 encoded byte array
843 * (as defined above).
844 *
845 * <p>If the implementation supports <i>stored defaults</i> and such a
846 * default exists and is accessible, it is used in preference to the
847 * specified default, unless the stored default is not a valid Base64
848 * encoded byte array (as defined above), in which case the
849 * specified default is used.
850 *
851 * @param key key whose associated value is to be returned as a byte array.
852 * @param def the value to be returned in the event that this
853 * preference node has no value associated with <tt>key</tt>
854 * or the associated value cannot be interpreted as a byte array,
855 * or the backing store is inaccessible.
856 * @return the byte array value represented by the string associated with
857 * <tt>key</tt> in this preference node, or <tt>def</tt> if the
858 * associated value does not exist or cannot be interpreted as
859 * a byte array.
860 * @throws IllegalStateException if this node (or an ancestor) has been
861 * removed with the {@link #removeNode()} method.
862 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>. (A
863 * <tt>null</tt> value for <tt>def</tt> <i>is</i> permitted.)
864 * @see #get(String,String)
865 * @see #putByteArray(String,byte[])
866 */
867 public abstract byte[] getByteArray(String key, byte[] def);
868
869 /**
870 * Returns all of the keys that have an associated value in this
871 * preference node. (The returned array will be of size zero if
872 * this node has no preferences.)
873 *
874 * <p>If the implementation supports <i>stored defaults</i> and there
875 * are any such defaults at this node that have not been overridden,
876 * by explicit preferences, the defaults are returned in the array in
877 * addition to any explicit preferences.
878 *
879 * @return an array of the keys that have an associated value in this
880 * preference node.
881 * @throws BackingStoreException if this operation cannot be completed
882 * due to a failure in the backing store, or inability to
883 * communicate with it.
884 * @throws IllegalStateException if this node (or an ancestor) has been
885 * removed with the {@link #removeNode()} method.
886 */
887 public abstract String[] keys() throws BackingStoreException;
888
889 /**
890 * Returns the names of the children of this preference node, relative to
891 * this node. (The returned array will be of size zero if this node has
892 * no children.)
893 *
894 * @return the names of the children of this preference node.
895 * @throws BackingStoreException if this operation cannot be completed
896 * due to a failure in the backing store, or inability to
897 * communicate with it.
898 * @throws IllegalStateException if this node (or an ancestor) has been
899 * removed with the {@link #removeNode()} method.
900 */
901 public abstract String[] childrenNames() throws BackingStoreException;
902
903 /**
904 * Returns the parent of this preference node, or <tt>null</tt> if this is
905 * the root.
906 *
907 * @return the parent of this preference node.
908 * @throws IllegalStateException if this node (or an ancestor) has been
909 * removed with the {@link #removeNode()} method.
910 */
911 public abstract Preferences parent();
912
913 /**
914 * Returns the named preference node in the same tree as this node,
915 * creating it and any of its ancestors if they do not already exist.
916 * Accepts a relative or absolute path name. Relative path names
917 * (which do not begin with the slash character <tt>('/')</tt>) are
918 * interpreted relative to this preference node.
919 *
920 * <p>If the returned node did not exist prior to this call, this node and
921 * any ancestors that were created by this call are not guaranteed
922 * to become permanent until the <tt>flush</tt> method is called on
923 * the returned node (or one of its ancestors or descendants).
924 *
925 * @param pathName the path name of the preference node to return.
926 * @return the specified preference node.
927 * @throws IllegalArgumentException if the path name is invalid (i.e.,
928 * it contains multiple consecutive slash characters, or ends
929 * with a slash character and is more than one character long).
930 * @throws NullPointerException if path name is <tt>null</tt>.
931 * @throws IllegalStateException if this node (or an ancestor) has been
932 * removed with the {@link #removeNode()} method.
933 * @see #flush()
934 */
935 public abstract Preferences node(String pathName);
936
937 /**
938 * Returns true if the named preference node exists in the same tree
939 * as this node. Relative path names (which do not begin with the slash
940 * character <tt>('/')</tt>) are interpreted relative to this preference
941 * node.
942 *
943 * <p>If this node (or an ancestor) has already been removed with the
944 * {@link #removeNode()} method, it <i>is</i> legal to invoke this method,
945 * but only with the path name <tt>""</tt>; the invocation will return
946 * <tt>false</tt>. Thus, the idiom <tt>p.nodeExists("")</tt> may be
947 * used to test whether <tt>p</tt> has been removed.
948 *
949 * @param pathName the path name of the node whose existence
950 * is to be checked.
951 * @return true if the specified node exists.
952 * @throws BackingStoreException if this operation cannot be completed
953 * due to a failure in the backing store, or inability to
954 * communicate with it.
955 * @throws IllegalArgumentException if the path name is invalid (i.e.,
956 * it contains multiple consecutive slash characters, or ends
957 * with a slash character and is more than one character long).
958 * @throws NullPointerException if path name is <tt>null</tt>.
959 * @throws IllegalStateException if this node (or an ancestor) has been
960 * removed with the {@link #removeNode()} method and
961 * <tt>pathName</tt> is not the empty string (<tt>""</tt>).
962 */
963 public abstract boolean nodeExists(String pathName)
964 throws BackingStoreException;
965
966 /**
967 * Removes this preference node and all of its descendants, invalidating
968 * any preferences contained in the removed nodes. Once a node has been
969 * removed, attempting any method other than {@link #name()},
970 * {@link #absolutePath()}, {@link #isUserNode()}, {@link #flush()} or
971 * {@link #node(String) nodeExists("")} on the corresponding
972 * <tt>Preferences</tt> instance will fail with an
973 * <tt>IllegalStateException</tt>. (The methods defined on {@link Object}
974 * can still be invoked on a node after it has been removed; they will not
975 * throw <tt>IllegalStateException</tt>.)
976 *
977 * <p>The removal is not guaranteed to be persistent until the
978 * <tt>flush</tt> method is called on this node (or an ancestor).
979 *
980 * <p>If this implementation supports <i>stored defaults</i>, removing a
981 * node exposes any stored defaults at or below this node. Thus, a
982 * subsequent call to <tt>nodeExists</tt> on this node's path name may
983 * return <tt>true</tt>, and a subsequent call to <tt>node</tt> on this
984 * path name may return a (different) <tt>Preferences</tt> instance
985 * representing a non-empty collection of preferences and/or children.
986 *
987 * @throws BackingStoreException if this operation cannot be completed
988 * due to a failure in the backing store, or inability to
989 * communicate with it.
990 * @throws IllegalStateException if this node (or an ancestor) has already
991 * been removed with the {@link #removeNode()} method.
992 * @throws UnsupportedOperationException if this method is invoked on
993 * the root node.
994 * @see #flush()
995 */
996 public abstract void removeNode() throws BackingStoreException;
997
998 /**
999 * Returns this preference node's name, relative to its parent.
1000 *
1001 * @return this preference node's name, relative to its parent.
1002 */
1003 public abstract String name();
1004
1005 /**
1006 * Returns this preference node's absolute path name.
1007 *
1008 * @return this preference node's absolute path name.
1009 */
1010 public abstract String absolutePath();
1011
1012 /**
1013 * Returns <tt>true</tt> if this preference node is in the user
1014 * preference tree, <tt>false</tt> if it's in the system preference tree.
1015 *
1016 * @return <tt>true</tt> if this preference node is in the user
1017 * preference tree, <tt>false</tt> if it's in the system
1018 * preference tree.
1019 */
1020 public abstract boolean isUserNode();
1021
1022 /**
1023 * Returns a string representation of this preferences node,
1024 * as if computed by the expression:<tt>(this.isUserNode() ? "User" :
1025 * "System") + " Preference Node: " + this.absolutePath()</tt>.
1026 */
1027 public abstract String toString();
1028
1029 /**
1030 * Forces any changes in the contents of this preference node and its
1031 * descendants to the persistent store. Once this method returns
1032 * successfully, it is safe to assume that all changes made in the
1033 * subtree rooted at this node prior to the method invocation have become
1034 * permanent.
1035 *
1036 * <p>Implementations are free to flush changes into the persistent store
1037 * at any time. They do not need to wait for this method to be called.
1038 *
1039 * <p>When a flush occurs on a newly created node, it is made persistent,
1040 * as are any ancestors (and descendants) that have yet to be made
1041 * persistent. Note however that any preference value changes in
1042 * ancestors are <i>not</i> guaranteed to be made persistent.
1043 *
1044 * <p> If this method is invoked on a node that has been removed with
1045 * the {@link #removeNode()} method, flushSpi() is invoked on this node,
1046 * but not on others.
1047 *
1048 * @throws BackingStoreException if this operation cannot be completed
1049 * due to a failure in the backing store, or inability to
1050 * communicate with it.
1051 * @see #sync()
1052 */
1053 public abstract void flush() throws BackingStoreException;
1054
1055 /**
1056 * Ensures that future reads from this preference node and its
1057 * descendants reflect any changes that were committed to the persistent
1058 * store (from any VM) prior to the <tt>sync</tt> invocation. As a
1059 * side-effect, forces any changes in the contents of this preference node
1060 * and its descendants to the persistent store, as if the <tt>flush</tt>
1061 * method had been invoked on this node.
1062 *
1063 * @throws BackingStoreException if this operation cannot be completed
1064 * due to a failure in the backing store, or inability to
1065 * communicate with it.
1066 * @throws IllegalStateException if this node (or an ancestor) has been
1067 * removed with the {@link #removeNode()} method.
1068 * @see #flush()
1069 */
1070 public abstract void sync() throws BackingStoreException;
1071
1072 /**
1073 * Registers the specified listener to receive <i>preference change
1074 * events</i> for this preference node. A preference change event is
1075 * generated when a preference is added to this node, removed from this
1076 * node, or when the value associated with a preference is changed.
1077 * (Preference change events are <i>not</i> generated by the {@link
1078 * #removeNode()} method, which generates a <i>node change event</i>.
1079 * Preference change events <i>are</i> generated by the <tt>clear</tt>
1080 * method.)
1081 *
1082 * <p>Events are only guaranteed for changes made within the same JVM
1083 * as the registered listener, though some implementations may generate
1084 * events for changes made outside this JVM. Events may be generated
1085 * before the changes have been made persistent. Events are not generated
1086 * when preferences are modified in descendants of this node; a caller
1087 * desiring such events must register with each descendant.
1088 *
1089 * @param pcl The preference change listener to add.
1090 * @throws NullPointerException if <tt>pcl</tt> is null.
1091 * @throws IllegalStateException if this node (or an ancestor) has been
1092 * removed with the {@link #removeNode()} method.
1093 * @see #removePreferenceChangeListener(PreferenceChangeListener)
1094 * @see #addNodeChangeListener(NodeChangeListener)
1095 */
1096 public abstract void addPreferenceChangeListener(
1097 PreferenceChangeListener pcl);
1098
1099 /**
1100 * Removes the specified preference change listener, so it no longer
1101 * receives preference change events.
1102 *
1103 * @param pcl The preference change listener to remove.
1104 * @throws IllegalArgumentException if <tt>pcl</tt> was not a registered
1105 * preference change listener on this node.
1106 * @throws IllegalStateException if this node (or an ancestor) has been
1107 * removed with the {@link #removeNode()} method.
1108 * @see #addPreferenceChangeListener(PreferenceChangeListener)
1109 */
1110 public abstract void removePreferenceChangeListener(
1111 PreferenceChangeListener pcl);
1112
1113 /**
1114 * Registers the specified listener to receive <i>node change events</i>
1115 * for this node. A node change event is generated when a child node is
1116 * added to or removed from this node. (A single {@link #removeNode()}
1117 * invocation results in multiple <i>node change events</i>, one for every
1118 * node in the subtree rooted at the removed node.)
1119 *
1120 * <p>Events are only guaranteed for changes made within the same JVM
1121 * as the registered listener, though some implementations may generate
1122 * events for changes made outside this JVM. Events may be generated
1123 * before the changes have become permanent. Events are not generated
1124 * when indirect descendants of this node are added or removed; a
1125 * caller desiring such events must register with each descendant.
1126 *
1127 * <p>Few guarantees can be made regarding node creation. Because nodes
1128 * are created implicitly upon access, it may not be feasible for an
1129 * implementation to determine whether a child node existed in the backing
1130 * store prior to access (for example, because the backing store is
1131 * unreachable or cached information is out of date). Under these
1132 * circumstances, implementations are neither required to generate node
1133 * change events nor prohibited from doing so.
1134 *
1135 * @param ncl The <tt>NodeChangeListener</tt> to add.
1136 * @throws NullPointerException if <tt>ncl</tt> is null.
1137 * @throws IllegalStateException if this node (or an ancestor) has been
1138 * removed with the {@link #removeNode()} method.
1139 * @see #removeNodeChangeListener(NodeChangeListener)
1140 * @see #addPreferenceChangeListener(PreferenceChangeListener)
1141 */
1142 public abstract void addNodeChangeListener(NodeChangeListener ncl);
1143
1144 /**
1145 * Removes the specified <tt>NodeChangeListener</tt>, so it no longer
1146 * receives change events.
1147 *
1148 * @param ncl The <tt>NodeChangeListener</tt> to remove.
1149 * @throws IllegalArgumentException if <tt>ncl</tt> was not a registered
1150 * <tt>NodeChangeListener</tt> on this node.
1151 * @throws IllegalStateException if this node (or an ancestor) has been
1152 * removed with the {@link #removeNode()} method.
1153 * @see #addNodeChangeListener(NodeChangeListener)
1154 */
1155 public abstract void removeNodeChangeListener(NodeChangeListener ncl);
1156
1157 /**
1158 * Emits on the specified output stream an XML document representing all
1159 * of the preferences contained in this node (but not its descendants).
1160 * This XML document is, in effect, an offline backup of the node.
1161 *
1162 * <p>The XML document will have the following DOCTYPE declaration:
1163 * <pre>
1164 * <!DOCTYPE preferences SYSTEM "http://java.sun.com/dtd/preferences.dtd">
1165 * </pre>
1166 * The UTF-8 character encoding will be used.
1167 *
1168 * <p>This method is an exception to the general rule that the results of
1169 * concurrently executing multiple methods in this class yields
1170 * results equivalent to some serial execution. If the preferences
1171 * at this node are modified concurrently with an invocation of this
1172 * method, the exported preferences comprise a "fuzzy snapshot" of the
1173 * preferences contained in the node; some of the concurrent modifications
1174 * may be reflected in the exported data while others may not.
1175 *
1176 * @param os the output stream on which to emit the XML document.
1177 * @throws IOException if writing to the specified output stream
1178 * results in an <tt>IOException</tt>.
1179 * @throws BackingStoreException if preference data cannot be read from
1180 * backing store.
1181 * @see #importPreferences(InputStream)
1182 * @throws IllegalStateException if this node (or an ancestor) has been
1183 * removed with the {@link #removeNode()} method.
1184 */
1185 public abstract void exportNode(OutputStream os)
1186 throws IOException, BackingStoreException;
1187
1188 /**
1189 * Emits an XML document representing all of the preferences contained
1190 * in this node and all of its descendants. This XML document is, in
1191 * effect, an offline backup of the subtree rooted at the node.
1192 *
1193 * <p>The XML document will have the following DOCTYPE declaration:
1194 * <pre>
1195 * <!DOCTYPE preferences SYSTEM "http://java.sun.com/dtd/preferences.dtd">
1196 * </pre>
1197 * The UTF-8 character encoding will be used.
1198 *
1199 * <p>This method is an exception to the general rule that the results of
1200 * concurrently executing multiple methods in this class yields
1201 * results equivalent to some serial execution. If the preferences
1202 * or nodes in the subtree rooted at this node are modified concurrently
1203 * with an invocation of this method, the exported preferences comprise a
1204 * "fuzzy snapshot" of the subtree; some of the concurrent modifications
1205 * may be reflected in the exported data while others may not.
1206 *
1207 * @param os the output stream on which to emit the XML document.
1208 * @throws IOException if writing to the specified output stream
1209 * results in an <tt>IOException</tt>.
1210 * @throws BackingStoreException if preference data cannot be read from
1211 * backing store.
1212 * @throws IllegalStateException if this node (or an ancestor) has been
1213 * removed with the {@link #removeNode()} method.
1214 * @see #importPreferences(InputStream)
1215 * @see #exportNode(OutputStream)
1216 */
1217 public abstract void exportSubtree(OutputStream os)
1218 throws IOException, BackingStoreException;
1219
1220 /**
1221 * Imports all of the preferences represented by the XML document on the
1222 * specified input stream. The document may represent user preferences or
1223 * system preferences. If it represents user preferences, the preferences
1224 * will be imported into the calling user's preference tree (even if they
1225 * originally came from a different user's preference tree). If any of
1226 * the preferences described by the document inhabit preference nodes that
1227 * do not exist, the nodes will be created.
1228 *
1229 * <p>The XML document must have the following DOCTYPE declaration:
1230 * <pre>
1231 * <!DOCTYPE preferences SYSTEM "http://java.sun.com/dtd/preferences.dtd">
1232 * </pre>
1233 * (This method is designed for use in conjunction with
1234 * {@link #exportNode(OutputStream)} and
1235 * {@link #exportSubtree(OutputStream)}.
1236 *
1237 * <p>This method is an exception to the general rule that the results of
1238 * concurrently executing multiple methods in this class yields
1239 * results equivalent to some serial execution. The method behaves
1240 * as if implemented on top of the other public methods in this class,
1241 * notably {@link #node(String)} and {@link #put(String, String)}.
1242 *
1243 * @param is the input stream from which to read the XML document.
1244 * @throws IOException if reading from the specified input stream
1245 * results in an <tt>IOException</tt>.
1246 * @throws InvalidPreferencesFormatException Data on input stream does not
1247 * constitute a valid XML document with the mandated document type.
1248 * @throws SecurityException If a security manager is present and
1249 * it denies <tt>RuntimePermission("preferences")</tt>.
1250 * @see RuntimePermission
1251 */
1252 public static void importPreferences(InputStream is)
1253 throws IOException, InvalidPreferencesFormatException
1254 {
1255 XmlSupport.importPreferences(is);
1256 }
1257 }