1 /* 2 * Copyright (C) 2014 The Android Open Source Project 3 * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved. 4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 5 * 6 * This code is free software; you can redistribute it and/or modify it 7 * under the terms of the GNU General Public License version 2 only, as 8 * published by the Free Software Foundation. Oracle designates this 9 * particular file as subject to the "Classpath" exception as provided 10 * by Oracle in the LICENSE file that accompanied this code. 11 * 12 * This code is distributed in the hope that it will be useful, but WITHOUT 13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 14 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 15 * version 2 for more details (a copy is included in the LICENSE file that 16 * accompanied this code). 17 * 18 * You should have received a copy of the GNU General Public License version 19 * 2 along with this work; if not, write to the Free Software Foundation, 20 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 21 * 22 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 23 * or visit www.oracle.com if you need additional information or have any 24 * questions. 25 */ 26 27 package java.util.prefs; 28 29 import java.util.*; 30 import java.io.*; 31 import java.security.AccessController; 32 import java.security.PrivilegedAction; 33 // These imports needed only as a workaround for a JavaDoc bug 34 import java.lang.Integer; 35 import java.lang.Long; 36 import java.lang.Float; 37 import java.lang.Double; 38 39 /** 40 * This class provides a skeletal implementation of the {@link Preferences} 41 * class, greatly easing the task of implementing it. 42 * 43 * <p><strong>This class is for <tt>Preferences</tt> implementers only. 44 * Normal users of the <tt>Preferences</tt> facility should have no need to 45 * consult this documentation. The {@link Preferences} documentation 46 * should suffice.</strong> 47 * 48 * <p>Implementors must override the nine abstract service-provider interface 49 * (SPI) methods: {@link #getSpi(String)}, {@link #putSpi(String,String)}, 50 * {@link #removeSpi(String)}, {@link #childSpi(String)}, {@link 51 * #removeNodeSpi()}, {@link #keysSpi()}, {@link #childrenNamesSpi()}, {@link 52 * #syncSpi()} and {@link #flushSpi()}. All of the concrete methods specify 53 * precisely how they are implemented atop these SPI methods. The implementor 54 * may, at his discretion, override one or more of the concrete methods if the 55 * default implementation is unsatisfactory for any reason, such as 56 * performance. 57 * 58 * <p>The SPI methods fall into three groups concerning exception 59 * behavior. The <tt>getSpi</tt> method should never throw exceptions, but it 60 * doesn't really matter, as any exception thrown by this method will be 61 * intercepted by {@link #get(String,String)}, which will return the specified 62 * default value to the caller. The <tt>removeNodeSpi, keysSpi, 63 * childrenNamesSpi, syncSpi</tt> and <tt>flushSpi</tt> methods are specified 64 * to throw {@link BackingStoreException}, and the implementation is required 65 * to throw this checked exception if it is unable to perform the operation. 66 * The exception propagates outward, causing the corresponding API method 67 * to fail. 68 * 69 * <p>The remaining SPI methods {@link #putSpi(String,String)}, {@link 70 * #removeSpi(String)} and {@link #childSpi(String)} have more complicated 71 * exception behavior. They are not specified to throw 72 * <tt>BackingStoreException</tt>, as they can generally obey their contracts 73 * even if the backing store is unavailable. This is true because they return 74 * no information and their effects are not required to become permanent until 75 * a subsequent call to {@link Preferences#flush()} or 76 * {@link Preferences#sync()}. Generally speaking, these SPI methods should not 77 * throw exceptions. In some implementations, there may be circumstances 78 * under which these calls cannot even enqueue the requested operation for 79 * later processing. Even under these circumstances it is generally better to 80 * simply ignore the invocation and return, rather than throwing an 81 * exception. Under these circumstances, however, all subsequent invocations 82 * of <tt>flush()</tt> and <tt>sync</tt> should return <tt>false</tt>, as 83 * returning <tt>true</tt> would imply that all previous operations had 84 * successfully been made permanent. 85 * 86 * <p>There is one circumstance under which <tt>putSpi, removeSpi and 87 * childSpi</tt> <i>should</i> throw an exception: if the caller lacks 88 * sufficient privileges on the underlying operating system to perform the 89 * requested operation. This will, for instance, occur on most systems 90 * if a non-privileged user attempts to modify system preferences. 91 * (The required privileges will vary from implementation to 92 * implementation. On some implementations, they are the right to modify the 93 * contents of some directory in the file system; on others they are the right 94 * to modify contents of some key in a registry.) Under any of these 95 * circumstances, it would generally be undesirable to let the program 96 * continue executing as if these operations would become permanent at a later 97 * time. While implementations are not required to throw an exception under 98 * these circumstances, they are encouraged to do so. A {@link 99 * SecurityException} would be appropriate. 100 * 101 * <p>Most of the SPI methods require the implementation to read or write 102 * information at a preferences node. The implementor should beware of the 103 * fact that another VM may have concurrently deleted this node from the 104 * backing store. It is the implementation's responsibility to recreate the 105 * node if it has been deleted. 106 * 107 * <p>Implementation note: In Sun's default <tt>Preferences</tt> 108 * implementations, the user's identity is inherited from the underlying 109 * operating system and does not change for the lifetime of the virtual 110 * machine. It is recognized that server-side <tt>Preferences</tt> 111 * implementations may have the user identity change from request to request, 112 * implicitly passed to <tt>Preferences</tt> methods via the use of a 113 * static {@link ThreadLocal} instance. Authors of such implementations are 114 * <i>strongly</i> encouraged to determine the user at the time preferences 115 * are accessed (for example by the {@link #get(String,String)} or {@link 116 * #put(String,String)} method) rather than permanently associating a user 117 * with each <tt>Preferences</tt> instance. The latter behavior conflicts 118 * with normal <tt>Preferences</tt> usage and would lead to great confusion. 119 * 120 * @author Josh Bloch 121 * @see Preferences 122 * @since 1.4 123 */ 124 public abstract class AbstractPreferences extends Preferences { 125 /** 126 * Our name relative to parent. 127 */ 128 private final String name; 129 130 /** 131 * Our absolute path name. 132 */ 133 private final String absolutePath; 134 135 /** 136 * Our parent node. 137 */ 138 final AbstractPreferences parent; 139 140 /** 141 * Our root node. 142 */ 143 private final AbstractPreferences root; // Relative to this node 144 145 /** 146 * This field should be <tt>true</tt> if this node did not exist in the 147 * backing store prior to the creation of this object. The field 148 * is initialized to false, but may be set to true by a subclass 149 * constructor (and should not be modified thereafter). This field 150 * indicates whether a node change event should be fired when 151 * creation is complete. 152 */ 153 protected boolean newNode = false; 154 155 /** 156 * All known unremoved children of this node. (This "cache" is consulted 157 * prior to calling childSpi() or getChild(). 158 */ 159 private Map<String, AbstractPreferences> kidCache = new HashMap<>(); 160 161 /** 162 * This field is used to keep track of whether or not this node has 163 * been removed. Once it's set to true, it will never be reset to false. 164 */ 165 private boolean removed = false; 166 167 /** 168 * Registered preference change listeners. 169 */ 170 private final ArrayList<PreferenceChangeListener> prefListeners = new ArrayList<>(); 171 172 /** 173 * Registered node change listeners. 174 */ 175 private final ArrayList<NodeChangeListener> nodeListeners = new ArrayList<>(); 176 177 /** 178 * An object whose monitor is used to lock this node. This object 179 * is used in preference to the node itself to reduce the likelihood of 180 * intentional or unintentional denial of service due to a locked node. 181 * To avoid deadlock, a node is <i>never</i> locked by a thread that 182 * holds a lock on a descendant of that node. 183 */ 184 protected final Object lock = new Object(); 185 186 /** 187 * Creates a preference node with the specified parent and the specified 188 * name relative to its parent. 189 * 190 * @param parent the parent of this preference node, or null if this 191 * is the root. 192 * @param name the name of this preference node, relative to its parent, 193 * or <tt>""</tt> if this is the root. 194 * @throws IllegalArgumentException if <tt>name</tt> contains a slash 195 * (<tt>'/'</tt>), or <tt>parent</tt> is <tt>null</tt> and 196 * name isn't <tt>""</tt>. 197 */ AbstractPreferences(AbstractPreferences parent, String name)198 protected AbstractPreferences(AbstractPreferences parent, String name) { 199 if (parent==null) { 200 if (!name.equals("")) 201 throw new IllegalArgumentException("Root name '"+name+ 202 "' must be \"\""); 203 this.absolutePath = "/"; 204 root = this; 205 } else { 206 if (name.indexOf('/') != -1) 207 throw new IllegalArgumentException("Name '" + name + 208 "' contains '/'"); 209 if (name.equals("")) 210 throw new IllegalArgumentException("Illegal name: empty string"); 211 212 root = parent.root; 213 absolutePath = (parent==root ? "/" + name 214 : parent.absolutePath() + "/" + name); 215 } 216 this.name = name; 217 this.parent = parent; 218 } 219 220 /** 221 * Implements the <tt>put</tt> method as per the specification in 222 * {@link Preferences#put(String,String)}. 223 * 224 * <p>This implementation checks that the key and value are legal, 225 * obtains this preference node's lock, checks that the node 226 * has not been removed, invokes {@link #putSpi(String,String)}, and if 227 * there are any preference change listeners, enqueues a notification 228 * event for processing by the event dispatch thread. 229 * 230 * @param key key with which the specified value is to be associated. 231 * @param value value to be associated with the specified key. 232 * @throws NullPointerException if key or value is <tt>null</tt>. 233 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds 234 * <tt>MAX_KEY_LENGTH</tt> or if <tt>value.length</tt> exceeds 235 * <tt>MAX_VALUE_LENGTH</tt>. 236 * @throws IllegalStateException if this node (or an ancestor) has been 237 * removed with the {@link #removeNode()} method. 238 */ put(String key, String value)239 public void put(String key, String value) { 240 if (key==null || value==null) 241 throw new NullPointerException(); 242 if (key.length() > MAX_KEY_LENGTH) 243 throw new IllegalArgumentException("Key too long: "+key); 244 if (value.length() > MAX_VALUE_LENGTH) 245 throw new IllegalArgumentException("Value too long: "+value); 246 247 synchronized(lock) { 248 if (removed) 249 throw new IllegalStateException("Node has been removed."); 250 251 putSpi(key, value); 252 enqueuePreferenceChangeEvent(key, value); 253 } 254 } 255 256 /** 257 * Implements the <tt>get</tt> method as per the specification in 258 * {@link Preferences#get(String,String)}. 259 * 260 * <p>This implementation first checks to see if <tt>key</tt> is 261 * <tt>null</tt> throwing a <tt>NullPointerException</tt> if this is 262 * the case. Then it obtains this preference node's lock, 263 * checks that the node has not been removed, invokes {@link 264 * #getSpi(String)}, and returns the result, unless the <tt>getSpi</tt> 265 * invocation returns <tt>null</tt> or throws an exception, in which case 266 * this invocation returns <tt>def</tt>. 267 * 268 * @param key key whose associated value is to be returned. 269 * @param def the value to be returned in the event that this 270 * preference node has no value associated with <tt>key</tt>. 271 * @return the value associated with <tt>key</tt>, or <tt>def</tt> 272 * if no value is associated with <tt>key</tt>. 273 * @throws IllegalStateException if this node (or an ancestor) has been 274 * removed with the {@link #removeNode()} method. 275 * @throws NullPointerException if key is <tt>null</tt>. (A 276 * <tt>null</tt> default <i>is</i> permitted.) 277 */ get(String key, String def)278 public String get(String key, String def) { 279 if (key==null) 280 throw new NullPointerException("Null key"); 281 synchronized(lock) { 282 if (removed) 283 throw new IllegalStateException("Node has been removed."); 284 285 String result = null; 286 try { 287 result = getSpi(key); 288 } catch (Exception e) { 289 // Ignoring exception causes default to be returned 290 } 291 return (result==null ? def : result); 292 } 293 } 294 295 /** 296 * Implements the <tt>remove(String)</tt> method as per the specification 297 * in {@link Preferences#remove(String)}. 298 * 299 * <p>This implementation obtains this preference node's lock, 300 * checks that the node has not been removed, invokes 301 * {@link #removeSpi(String)} and if there are any preference 302 * change listeners, enqueues a notification event for processing by the 303 * event dispatch thread. 304 * 305 * @param key key whose mapping is to be removed from the preference node. 306 * @throws IllegalStateException if this node (or an ancestor) has been 307 * removed with the {@link #removeNode()} method. 308 * @throws NullPointerException {@inheritDoc}. 309 */ remove(String key)310 public void remove(String key) { 311 Objects.requireNonNull(key, "Specified key cannot be null"); 312 synchronized(lock) { 313 if (removed) 314 throw new IllegalStateException("Node has been removed."); 315 316 removeSpi(key); 317 enqueuePreferenceChangeEvent(key, null); 318 } 319 } 320 321 /** 322 * Implements the <tt>clear</tt> method as per the specification in 323 * {@link Preferences#clear()}. 324 * 325 * <p>This implementation obtains this preference node's lock, 326 * invokes {@link #keys()} to obtain an array of keys, and 327 * iterates over the array invoking {@link #remove(String)} on each key. 328 * 329 * @throws BackingStoreException if this operation cannot be completed 330 * due to a failure in the backing store, or inability to 331 * communicate with it. 332 * @throws IllegalStateException if this node (or an ancestor) has been 333 * removed with the {@link #removeNode()} method. 334 */ clear()335 public void clear() throws BackingStoreException { 336 synchronized(lock) { 337 String[] keys = keys(); 338 for (int i=0; i<keys.length; i++) 339 remove(keys[i]); 340 } 341 } 342 343 /** 344 * Implements the <tt>putInt</tt> method as per the specification in 345 * {@link Preferences#putInt(String,int)}. 346 * 347 * <p>This implementation translates <tt>value</tt> to a string with 348 * {@link Integer#toString(int)} and invokes {@link #put(String,String)} 349 * on the result. 350 * 351 * @param key key with which the string form of value is to be associated. 352 * @param value value whose string form is to be associated with key. 353 * @throws NullPointerException if key is <tt>null</tt>. 354 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds 355 * <tt>MAX_KEY_LENGTH</tt>. 356 * @throws IllegalStateException if this node (or an ancestor) has been 357 * removed with the {@link #removeNode()} method. 358 */ putInt(String key, int value)359 public void putInt(String key, int value) { 360 put(key, Integer.toString(value)); 361 } 362 363 /** 364 * Implements the <tt>getInt</tt> method as per the specification in 365 * {@link Preferences#getInt(String,int)}. 366 * 367 * <p>This implementation invokes {@link #get(String,String) <tt>get(key, 368 * null)</tt>}. If the return value is non-null, the implementation 369 * attempts to translate it to an <tt>int</tt> with 370 * {@link Integer#parseInt(String)}. If the attempt succeeds, the return 371 * value is returned by this method. Otherwise, <tt>def</tt> is returned. 372 * 373 * @param key key whose associated value is to be returned as an int. 374 * @param def the value to be returned in the event that this 375 * preference node has no value associated with <tt>key</tt> 376 * or the associated value cannot be interpreted as an int. 377 * @return the int value represented by the string associated with 378 * <tt>key</tt> in this preference node, or <tt>def</tt> if the 379 * associated value does not exist or cannot be interpreted as 380 * an int. 381 * @throws IllegalStateException if this node (or an ancestor) has been 382 * removed with the {@link #removeNode()} method. 383 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>. 384 */ getInt(String key, int def)385 public int getInt(String key, int def) { 386 int result = def; 387 try { 388 String value = get(key, null); 389 if (value != null) 390 result = Integer.parseInt(value); 391 } catch (NumberFormatException e) { 392 // Ignoring exception causes specified default to be returned 393 } 394 395 return result; 396 } 397 398 /** 399 * Implements the <tt>putLong</tt> method as per the specification in 400 * {@link Preferences#putLong(String,long)}. 401 * 402 * <p>This implementation translates <tt>value</tt> to a string with 403 * {@link Long#toString(long)} and invokes {@link #put(String,String)} 404 * on the result. 405 * 406 * @param key key with which the string form of value is to be associated. 407 * @param value value whose string form is to be associated with key. 408 * @throws NullPointerException if key is <tt>null</tt>. 409 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds 410 * <tt>MAX_KEY_LENGTH</tt>. 411 * @throws IllegalStateException if this node (or an ancestor) has been 412 * removed with the {@link #removeNode()} method. 413 */ putLong(String key, long value)414 public void putLong(String key, long value) { 415 put(key, Long.toString(value)); 416 } 417 418 /** 419 * Implements the <tt>getLong</tt> method as per the specification in 420 * {@link Preferences#getLong(String,long)}. 421 * 422 * <p>This implementation invokes {@link #get(String,String) <tt>get(key, 423 * null)</tt>}. If the return value is non-null, the implementation 424 * attempts to translate it to a <tt>long</tt> with 425 * {@link Long#parseLong(String)}. If the attempt succeeds, the return 426 * value is returned by this method. Otherwise, <tt>def</tt> is returned. 427 * 428 * @param key key whose associated value is to be returned as a long. 429 * @param def the value to be returned in the event that this 430 * preference node has no value associated with <tt>key</tt> 431 * or the associated value cannot be interpreted as a long. 432 * @return the long value represented by the string associated with 433 * <tt>key</tt> in this preference node, or <tt>def</tt> if the 434 * associated value does not exist or cannot be interpreted as 435 * a long. 436 * @throws IllegalStateException if this node (or an ancestor) has been 437 * removed with the {@link #removeNode()} method. 438 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>. 439 */ getLong(String key, long def)440 public long getLong(String key, long def) { 441 long result = def; 442 try { 443 String value = get(key, null); 444 if (value != null) 445 result = Long.parseLong(value); 446 } catch (NumberFormatException e) { 447 // Ignoring exception causes specified default to be returned 448 } 449 450 return result; 451 } 452 453 /** 454 * Implements the <tt>putBoolean</tt> method as per the specification in 455 * {@link Preferences#putBoolean(String,boolean)}. 456 * 457 * <p>This implementation translates <tt>value</tt> to a string with 458 * {@link String#valueOf(boolean)} and invokes {@link #put(String,String)} 459 * on the result. 460 * 461 * @param key key with which the string form of value is to be associated. 462 * @param value value whose string form is to be associated with key. 463 * @throws NullPointerException if key is <tt>null</tt>. 464 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds 465 * <tt>MAX_KEY_LENGTH</tt>. 466 * @throws IllegalStateException if this node (or an ancestor) has been 467 * removed with the {@link #removeNode()} method. 468 */ putBoolean(String key, boolean value)469 public void putBoolean(String key, boolean value) { 470 put(key, String.valueOf(value)); 471 } 472 473 /** 474 * Implements the <tt>getBoolean</tt> method as per the specification in 475 * {@link Preferences#getBoolean(String,boolean)}. 476 * 477 * <p>This implementation invokes {@link #get(String,String) <tt>get(key, 478 * null)</tt>}. If the return value is non-null, it is compared with 479 * <tt>"true"</tt> using {@link String#equalsIgnoreCase(String)}. If the 480 * comparison returns <tt>true</tt>, this invocation returns 481 * <tt>true</tt>. Otherwise, the original return value is compared with 482 * <tt>"false"</tt>, again using {@link String#equalsIgnoreCase(String)}. 483 * If the comparison returns <tt>true</tt>, this invocation returns 484 * <tt>false</tt>. Otherwise, this invocation returns <tt>def</tt>. 485 * 486 * @param key key whose associated value is to be returned as a boolean. 487 * @param def the value to be returned in the event that this 488 * preference node has no value associated with <tt>key</tt> 489 * or the associated value cannot be interpreted as a boolean. 490 * @return the boolean value represented by the string associated with 491 * <tt>key</tt> in this preference node, or <tt>def</tt> if the 492 * associated value does not exist or cannot be interpreted as 493 * a boolean. 494 * @throws IllegalStateException if this node (or an ancestor) has been 495 * removed with the {@link #removeNode()} method. 496 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>. 497 */ getBoolean(String key, boolean def)498 public boolean getBoolean(String key, boolean def) { 499 boolean result = def; 500 String value = get(key, null); 501 if (value != null) { 502 if (value.equalsIgnoreCase("true")) 503 result = true; 504 else if (value.equalsIgnoreCase("false")) 505 result = false; 506 } 507 508 return result; 509 } 510 511 /** 512 * Implements the <tt>putFloat</tt> method as per the specification in 513 * {@link Preferences#putFloat(String,float)}. 514 * 515 * <p>This implementation translates <tt>value</tt> to a string with 516 * {@link Float#toString(float)} and invokes {@link #put(String,String)} 517 * on the result. 518 * 519 * @param key key with which the string form of value is to be associated. 520 * @param value value whose string form is to be associated with key. 521 * @throws NullPointerException if key is <tt>null</tt>. 522 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds 523 * <tt>MAX_KEY_LENGTH</tt>. 524 * @throws IllegalStateException if this node (or an ancestor) has been 525 * removed with the {@link #removeNode()} method. 526 */ putFloat(String key, float value)527 public void putFloat(String key, float value) { 528 put(key, Float.toString(value)); 529 } 530 531 /** 532 * Implements the <tt>getFloat</tt> method as per the specification in 533 * {@link Preferences#getFloat(String,float)}. 534 * 535 * <p>This implementation invokes {@link #get(String,String) <tt>get(key, 536 * null)</tt>}. If the return value is non-null, the implementation 537 * attempts to translate it to an <tt>float</tt> with 538 * {@link Float#parseFloat(String)}. If the attempt succeeds, the return 539 * value is returned by this method. Otherwise, <tt>def</tt> is returned. 540 * 541 * @param key key whose associated value is to be returned as a float. 542 * @param def the value to be returned in the event that this 543 * preference node has no value associated with <tt>key</tt> 544 * or the associated value cannot be interpreted as a float. 545 * @return the float value represented by the string associated with 546 * <tt>key</tt> in this preference node, or <tt>def</tt> if the 547 * associated value does not exist or cannot be interpreted as 548 * a float. 549 * @throws IllegalStateException if this node (or an ancestor) has been 550 * removed with the {@link #removeNode()} method. 551 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>. 552 */ getFloat(String key, float def)553 public float getFloat(String key, float def) { 554 float result = def; 555 try { 556 String value = get(key, null); 557 if (value != null) 558 result = Float.parseFloat(value); 559 } catch (NumberFormatException e) { 560 // Ignoring exception causes specified default to be returned 561 } 562 563 return result; 564 } 565 566 /** 567 * Implements the <tt>putDouble</tt> method as per the specification in 568 * {@link Preferences#putDouble(String,double)}. 569 * 570 * <p>This implementation translates <tt>value</tt> to a string with 571 * {@link Double#toString(double)} and invokes {@link #put(String,String)} 572 * on the result. 573 * 574 * @param key key with which the string form of value is to be associated. 575 * @param value value whose string form is to be associated with key. 576 * @throws NullPointerException if key is <tt>null</tt>. 577 * @throws IllegalArgumentException if <tt>key.length()</tt> exceeds 578 * <tt>MAX_KEY_LENGTH</tt>. 579 * @throws IllegalStateException if this node (or an ancestor) has been 580 * removed with the {@link #removeNode()} method. 581 */ putDouble(String key, double value)582 public void putDouble(String key, double value) { 583 put(key, Double.toString(value)); 584 } 585 586 /** 587 * Implements the <tt>getDouble</tt> method as per the specification in 588 * {@link Preferences#getDouble(String,double)}. 589 * 590 * <p>This implementation invokes {@link #get(String,String) <tt>get(key, 591 * null)</tt>}. If the return value is non-null, the implementation 592 * attempts to translate it to an <tt>double</tt> with 593 * {@link Double#parseDouble(String)}. If the attempt succeeds, the return 594 * value is returned by this method. Otherwise, <tt>def</tt> is returned. 595 * 596 * @param key key whose associated value is to be returned as a double. 597 * @param def the value to be returned in the event that this 598 * preference node has no value associated with <tt>key</tt> 599 * or the associated value cannot be interpreted as a double. 600 * @return the double value represented by the string associated with 601 * <tt>key</tt> in this preference node, or <tt>def</tt> if the 602 * associated value does not exist or cannot be interpreted as 603 * a double. 604 * @throws IllegalStateException if this node (or an ancestor) has been 605 * removed with the {@link #removeNode()} method. 606 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>. 607 */ getDouble(String key, double def)608 public double getDouble(String key, double def) { 609 double result = def; 610 try { 611 String value = get(key, null); 612 if (value != null) 613 result = Double.parseDouble(value); 614 } catch (NumberFormatException e) { 615 // Ignoring exception causes specified default to be returned 616 } 617 618 return result; 619 } 620 621 /** 622 * Implements the <tt>putByteArray</tt> method as per the specification in 623 * {@link Preferences#putByteArray(String,byte[])}. 624 * 625 * @param key key with which the string form of value is to be associated. 626 * @param value value whose string form is to be associated with key. 627 * @throws NullPointerException if key or value is <tt>null</tt>. 628 * @throws IllegalArgumentException if key.length() exceeds MAX_KEY_LENGTH 629 * or if value.length exceeds MAX_VALUE_LENGTH*3/4. 630 * @throws IllegalStateException if this node (or an ancestor) has been 631 * removed with the {@link #removeNode()} method. 632 */ putByteArray(String key, byte[] value)633 public void putByteArray(String key, byte[] value) { 634 put(key, Base64.byteArrayToBase64(value)); 635 } 636 637 /** 638 * Implements the <tt>getByteArray</tt> method as per the specification in 639 * {@link Preferences#getByteArray(String,byte[])}. 640 * 641 * @param key key whose associated value is to be returned as a byte array. 642 * @param def the value to be returned in the event that this 643 * preference node has no value associated with <tt>key</tt> 644 * or the associated value cannot be interpreted as a byte array. 645 * @return the byte array value represented by the string associated with 646 * <tt>key</tt> in this preference node, or <tt>def</tt> if the 647 * associated value does not exist or cannot be interpreted as 648 * a byte array. 649 * @throws IllegalStateException if this node (or an ancestor) has been 650 * removed with the {@link #removeNode()} method. 651 * @throws NullPointerException if <tt>key</tt> is <tt>null</tt>. (A 652 * <tt>null</tt> value for <tt>def</tt> <i>is</i> permitted.) 653 */ getByteArray(String key, byte[] def)654 public byte[] getByteArray(String key, byte[] def) { 655 byte[] result = def; 656 String value = get(key, null); 657 try { 658 if (value != null) 659 result = Base64.base64ToByteArray(value); 660 } 661 catch (RuntimeException e) { 662 // Ignoring exception causes specified default to be returned 663 } 664 665 return result; 666 } 667 668 /** 669 * Implements the <tt>keys</tt> method as per the specification in 670 * {@link Preferences#keys()}. 671 * 672 * <p>This implementation obtains this preference node's lock, checks that 673 * the node has not been removed and invokes {@link #keysSpi()}. 674 * 675 * @return an array of the keys that have an associated value in this 676 * preference node. 677 * @throws BackingStoreException if this operation cannot be completed 678 * due to a failure in the backing store, or inability to 679 * communicate with it. 680 * @throws IllegalStateException if this node (or an ancestor) has been 681 * removed with the {@link #removeNode()} method. 682 */ keys()683 public String[] keys() throws BackingStoreException { 684 synchronized(lock) { 685 if (removed) 686 throw new IllegalStateException("Node has been removed."); 687 688 return keysSpi(); 689 } 690 } 691 692 /** 693 * Implements the <tt>children</tt> method as per the specification in 694 * {@link Preferences#childrenNames()}. 695 * 696 * <p>This implementation obtains this preference node's lock, checks that 697 * the node has not been removed, constructs a <tt>TreeSet</tt> initialized 698 * to the names of children already cached (the children in this node's 699 * "child-cache"), invokes {@link #childrenNamesSpi()}, and adds all of the 700 * returned child-names into the set. The elements of the tree set are 701 * dumped into a <tt>String</tt> array using the <tt>toArray</tt> method, 702 * and this array is returned. 703 * 704 * @return the names of the children of this preference node. 705 * @throws BackingStoreException if this operation cannot be completed 706 * due to a failure in the backing store, or inability to 707 * communicate with it. 708 * @throws IllegalStateException if this node (or an ancestor) has been 709 * removed with the {@link #removeNode()} method. 710 * @see #cachedChildren() 711 */ childrenNames()712 public String[] childrenNames() throws BackingStoreException { 713 synchronized(lock) { 714 if (removed) 715 throw new IllegalStateException("Node has been removed."); 716 717 Set<String> s = new TreeSet<>(kidCache.keySet()); 718 for (String kid : childrenNamesSpi()) 719 s.add(kid); 720 return s.toArray(EMPTY_STRING_ARRAY); 721 } 722 } 723 724 private static final String[] EMPTY_STRING_ARRAY = new String[0]; 725 726 /** 727 * Returns all known unremoved children of this node. 728 * 729 * @return all known unremoved children of this node. 730 */ cachedChildren()731 protected final AbstractPreferences[] cachedChildren() { 732 return kidCache.values().toArray(EMPTY_ABSTRACT_PREFS_ARRAY); 733 } 734 735 private static final AbstractPreferences[] EMPTY_ABSTRACT_PREFS_ARRAY 736 = new AbstractPreferences[0]; 737 738 /** 739 * Implements the <tt>parent</tt> method as per the specification in 740 * {@link Preferences#parent()}. 741 * 742 * <p>This implementation obtains this preference node's lock, checks that 743 * the node has not been removed and returns the parent value that was 744 * passed to this node's constructor. 745 * 746 * @return the parent of this preference node. 747 * @throws IllegalStateException if this node (or an ancestor) has been 748 * removed with the {@link #removeNode()} method. 749 */ parent()750 public Preferences parent() { 751 synchronized(lock) { 752 if (removed) 753 throw new IllegalStateException("Node has been removed."); 754 755 return parent; 756 } 757 } 758 759 /** 760 * Implements the <tt>node</tt> method as per the specification in 761 * {@link Preferences#node(String)}. 762 * 763 * <p>This implementation obtains this preference node's lock and checks 764 * that the node has not been removed. If <tt>path</tt> is <tt>""</tt>, 765 * this node is returned; if <tt>path</tt> is <tt>"/"</tt>, this node's 766 * root is returned. If the first character in <tt>path</tt> is 767 * not <tt>'/'</tt>, the implementation breaks <tt>path</tt> into 768 * tokens and recursively traverses the path from this node to the 769 * named node, "consuming" a name and a slash from <tt>path</tt> at 770 * each step of the traversal. At each step, the current node is locked 771 * and the node's child-cache is checked for the named node. If it is 772 * not found, the name is checked to make sure its length does not 773 * exceed <tt>MAX_NAME_LENGTH</tt>. Then the {@link #childSpi(String)} 774 * method is invoked, and the result stored in this node's child-cache. 775 * If the newly created <tt>Preferences</tt> object's {@link #newNode} 776 * field is <tt>true</tt> and there are any node change listeners, 777 * a notification event is enqueued for processing by the event dispatch 778 * thread. 779 * 780 * <p>When there are no more tokens, the last value found in the 781 * child-cache or returned by <tt>childSpi</tt> is returned by this 782 * method. If during the traversal, two <tt>"/"</tt> tokens occur 783 * consecutively, or the final token is <tt>"/"</tt> (rather than a name), 784 * an appropriate <tt>IllegalArgumentException</tt> is thrown. 785 * 786 * <p> If the first character of <tt>path</tt> is <tt>'/'</tt> 787 * (indicating an absolute path name) this preference node's 788 * lock is dropped prior to breaking <tt>path</tt> into tokens, and 789 * this method recursively traverses the path starting from the root 790 * (rather than starting from this node). The traversal is otherwise 791 * identical to the one described for relative path names. Dropping 792 * the lock on this node prior to commencing the traversal at the root 793 * node is essential to avoid the possibility of deadlock, as per the 794 * {@link #lock locking invariant}. 795 * 796 * @param path the path name of the preference node to return. 797 * @return the specified preference node. 798 * @throws IllegalArgumentException if the path name is invalid (i.e., 799 * it contains multiple consecutive slash characters, or ends 800 * with a slash character and is more than one character long). 801 * @throws IllegalStateException if this node (or an ancestor) has been 802 * removed with the {@link #removeNode()} method. 803 */ node(String path)804 public Preferences node(String path) { 805 synchronized(lock) { 806 if (removed) 807 throw new IllegalStateException("Node has been removed."); 808 if (path.equals("")) 809 return this; 810 if (path.equals("/")) 811 return root; 812 if (path.charAt(0) != '/') 813 return node(new StringTokenizer(path, "/", true)); 814 } 815 816 // Absolute path. Note that we've dropped our lock to avoid deadlock 817 return root.node(new StringTokenizer(path.substring(1), "/", true)); 818 } 819 820 /** 821 * tokenizer contains <name> {'/' <name>}* 822 */ node(StringTokenizer path)823 private Preferences node(StringTokenizer path) { 824 String token = path.nextToken(); 825 if (token.equals("/")) // Check for consecutive slashes 826 throw new IllegalArgumentException("Consecutive slashes in path"); 827 synchronized(lock) { 828 AbstractPreferences child = kidCache.get(token); 829 if (child == null) { 830 if (token.length() > MAX_NAME_LENGTH) 831 throw new IllegalArgumentException( 832 "Node name " + token + " too long"); 833 child = childSpi(token); 834 if (child.newNode) 835 enqueueNodeAddedEvent(child); 836 kidCache.put(token, child); 837 } 838 if (!path.hasMoreTokens()) 839 return child; 840 path.nextToken(); // Consume slash 841 if (!path.hasMoreTokens()) 842 throw new IllegalArgumentException("Path ends with slash"); 843 return child.node(path); 844 } 845 } 846 847 /** 848 * Implements the <tt>nodeExists</tt> method as per the specification in 849 * {@link Preferences#nodeExists(String)}. 850 * 851 * <p>This implementation is very similar to {@link #node(String)}, 852 * except that {@link #getChild(String)} is used instead of {@link 853 * #childSpi(String)}. 854 * 855 * @param path the path name of the node whose existence is to be checked. 856 * @return true if the specified node exists. 857 * @throws BackingStoreException if this operation cannot be completed 858 * due to a failure in the backing store, or inability to 859 * communicate with it. 860 * @throws IllegalArgumentException if the path name is invalid (i.e., 861 * it contains multiple consecutive slash characters, or ends 862 * with a slash character and is more than one character long). 863 * @throws IllegalStateException if this node (or an ancestor) has been 864 * removed with the {@link #removeNode()} method and 865 * <tt>pathname</tt> is not the empty string (<tt>""</tt>). 866 */ nodeExists(String path)867 public boolean nodeExists(String path) 868 throws BackingStoreException 869 { 870 synchronized(lock) { 871 if (path.equals("")) 872 return !removed; 873 if (removed) 874 throw new IllegalStateException("Node has been removed."); 875 if (path.equals("/")) 876 return true; 877 if (path.charAt(0) != '/') 878 return nodeExists(new StringTokenizer(path, "/", true)); 879 } 880 881 // Absolute path. Note that we've dropped our lock to avoid deadlock 882 return root.nodeExists(new StringTokenizer(path.substring(1), "/", 883 true)); 884 } 885 886 /** 887 * tokenizer contains <name> {'/' <name>}* 888 */ nodeExists(StringTokenizer path)889 private boolean nodeExists(StringTokenizer path) 890 throws BackingStoreException 891 { 892 String token = path.nextToken(); 893 if (token.equals("/")) // Check for consecutive slashes 894 throw new IllegalArgumentException("Consecutive slashes in path"); 895 synchronized(lock) { 896 AbstractPreferences child = kidCache.get(token); 897 if (child == null) 898 child = getChild(token); 899 if (child==null) 900 return false; 901 if (!path.hasMoreTokens()) 902 return true; 903 path.nextToken(); // Consume slash 904 if (!path.hasMoreTokens()) 905 throw new IllegalArgumentException("Path ends with slash"); 906 return child.nodeExists(path); 907 } 908 } 909 910 /** 911 912 * Implements the <tt>removeNode()</tt> method as per the specification in 913 * {@link Preferences#removeNode()}. 914 * 915 * <p>This implementation checks to see that this node is the root; if so, 916 * it throws an appropriate exception. Then, it locks this node's parent, 917 * and calls a recursive helper method that traverses the subtree rooted at 918 * this node. The recursive method locks the node on which it was called, 919 * checks that it has not already been removed, and then ensures that all 920 * of its children are cached: The {@link #childrenNamesSpi()} method is 921 * invoked and each returned child name is checked for containment in the 922 * child-cache. If a child is not already cached, the {@link 923 * #childSpi(String)} method is invoked to create a <tt>Preferences</tt> 924 * instance for it, and this instance is put into the child-cache. Then 925 * the helper method calls itself recursively on each node contained in its 926 * child-cache. Next, it invokes {@link #removeNodeSpi()}, marks itself 927 * as removed, and removes itself from its parent's child-cache. Finally, 928 * if there are any node change listeners, it enqueues a notification 929 * event for processing by the event dispatch thread. 930 * 931 * <p>Note that the helper method is always invoked with all ancestors up 932 * to the "closest non-removed ancestor" locked. 933 * 934 * @throws IllegalStateException if this node (or an ancestor) has already 935 * been removed with the {@link #removeNode()} method. 936 * @throws UnsupportedOperationException if this method is invoked on 937 * the root node. 938 * @throws BackingStoreException if this operation cannot be completed 939 * due to a failure in the backing store, or inability to 940 * communicate with it. 941 */ removeNode()942 public void removeNode() throws BackingStoreException { 943 if (this==root) 944 throw new UnsupportedOperationException("Can't remove the root!"); 945 synchronized(parent.lock) { 946 removeNode2(); 947 parent.kidCache.remove(name); 948 } 949 } 950 951 /* 952 * Called with locks on all nodes on path from parent of "removal root" 953 * to this (including the former but excluding the latter). 954 */ removeNode2()955 private void removeNode2() throws BackingStoreException { 956 synchronized(lock) { 957 if (removed) 958 throw new IllegalStateException("Node already removed."); 959 960 // Ensure that all children are cached 961 String[] kidNames = childrenNamesSpi(); 962 for (int i=0; i<kidNames.length; i++) 963 if (!kidCache.containsKey(kidNames[i])) 964 kidCache.put(kidNames[i], childSpi(kidNames[i])); 965 966 // Recursively remove all cached children 967 for (Iterator<AbstractPreferences> i = kidCache.values().iterator(); 968 i.hasNext();) { 969 try { 970 i.next().removeNode2(); 971 i.remove(); 972 } catch (BackingStoreException x) { } 973 } 974 975 // Now we have no descendants - it's time to die! 976 removeNodeSpi(); 977 removed = true; 978 parent.enqueueNodeRemovedEvent(this); 979 } 980 } 981 982 /** 983 * Implements the <tt>name</tt> method as per the specification in 984 * {@link Preferences#name()}. 985 * 986 * <p>This implementation merely returns the name that was 987 * passed to this node's constructor. 988 * 989 * @return this preference node's name, relative to its parent. 990 */ name()991 public String name() { 992 return name; 993 } 994 995 /** 996 * Implements the <tt>absolutePath</tt> method as per the specification in 997 * {@link Preferences#absolutePath()}. 998 * 999 * <p>This implementation merely returns the absolute path name that 1000 * was computed at the time that this node was constructed (based on 1001 * the name that was passed to this node's constructor, and the names 1002 * that were passed to this node's ancestors' constructors). 1003 * 1004 * @return this preference node's absolute path name. 1005 */ absolutePath()1006 public String absolutePath() { 1007 return absolutePath; 1008 } 1009 1010 /** 1011 * Implements the <tt>isUserNode</tt> method as per the specification in 1012 * {@link Preferences#isUserNode()}. 1013 * 1014 * <p>This implementation compares this node's root node (which is stored 1015 * in a private field) with the value returned by 1016 * {@link Preferences#userRoot()}. If the two object references are 1017 * identical, this method returns true. 1018 * 1019 * @return <tt>true</tt> if this preference node is in the user 1020 * preference tree, <tt>false</tt> if it's in the system 1021 * preference tree. 1022 */ isUserNode()1023 public boolean isUserNode() { 1024 return AccessController.doPrivileged( 1025 new PrivilegedAction<Boolean>() { 1026 public Boolean run() { 1027 return root == Preferences.userRoot(); 1028 } 1029 }).booleanValue(); 1030 } 1031 1032 public void addPreferenceChangeListener(PreferenceChangeListener pcl) { 1033 if (pcl==null) 1034 throw new NullPointerException("Change listener is null."); 1035 synchronized(lock) { 1036 if (removed) 1037 throw new IllegalStateException("Node has been removed."); 1038 1039 prefListeners.add(pcl); 1040 } 1041 startEventDispatchThreadIfNecessary(); 1042 } 1043 1044 public void removePreferenceChangeListener(PreferenceChangeListener pcl) { 1045 synchronized(lock) { 1046 if (removed) 1047 throw new IllegalStateException("Node has been removed."); 1048 1049 if (!prefListeners.contains(pcl)) { 1050 throw new IllegalArgumentException("Listener not registered."); 1051 } 1052 1053 prefListeners.remove(pcl); 1054 } 1055 } 1056 1057 public void addNodeChangeListener(NodeChangeListener ncl) { 1058 if (ncl==null) 1059 throw new NullPointerException("Change listener is null."); 1060 synchronized(lock) { 1061 if (removed) 1062 throw new IllegalStateException("Node has been removed."); 1063 1064 nodeListeners.add(ncl); 1065 } 1066 startEventDispatchThreadIfNecessary(); 1067 } 1068 1069 public void removeNodeChangeListener(NodeChangeListener ncl) { 1070 synchronized(lock) { 1071 if (removed) 1072 throw new IllegalStateException("Node has been removed."); 1073 1074 if (!nodeListeners.contains(ncl)) { 1075 throw new IllegalArgumentException("Listener not registered."); 1076 } 1077 1078 nodeListeners.remove(ncl); 1079 } 1080 } 1081 1082 // "SPI" METHODS 1083 1084 /** 1085 * Put the given key-value association into this preference node. It is 1086 * guaranteed that <tt>key</tt> and <tt>value</tt> are non-null and of 1087 * legal length. Also, it is guaranteed that this node has not been 1088 * removed. (The implementor needn't check for any of these things.) 1089 * 1090 * <p>This method is invoked with the lock on this node held. 1091 * @param key the key 1092 * @param value the value 1093 */ 1094 protected abstract void putSpi(String key, String value); 1095 1096 /** 1097 * Return the value associated with the specified key at this preference 1098 * node, or <tt>null</tt> if there is no association for this key, or the 1099 * association cannot be determined at this time. It is guaranteed that 1100 * <tt>key</tt> is non-null. Also, it is guaranteed that this node has 1101 * not been removed. (The implementor needn't check for either of these 1102 * things.) 1103 * 1104 * <p> Generally speaking, this method should not throw an exception 1105 * under any circumstances. If, however, if it does throw an exception, 1106 * the exception will be intercepted and treated as a <tt>null</tt> 1107 * return value. 1108 * 1109 * <p>This method is invoked with the lock on this node held. 1110 * 1111 * @param key the key 1112 * @return the value associated with the specified key at this preference 1113 * node, or <tt>null</tt> if there is no association for this 1114 * key, or the association cannot be determined at this time. 1115 */ 1116 protected abstract String getSpi(String key); 1117 1118 /** 1119 * Remove the association (if any) for the specified key at this 1120 * preference node. It is guaranteed that <tt>key</tt> is non-null. 1121 * Also, it is guaranteed that this node has not been removed. 1122 * (The implementor needn't check for either of these things.) 1123 * 1124 * <p>This method is invoked with the lock on this node held. 1125 * @param key the key 1126 */ 1127 protected abstract void removeSpi(String key); 1128 1129 /** 1130 * Removes this preference node, invalidating it and any preferences that 1131 * it contains. The named child will have no descendants at the time this 1132 * invocation is made (i.e., the {@link Preferences#removeNode()} method 1133 * invokes this method repeatedly in a bottom-up fashion, removing each of 1134 * a node's descendants before removing the node itself). 1135 * 1136 * <p>This method is invoked with the lock held on this node and its 1137 * parent (and all ancestors that are being removed as a 1138 * result of a single invocation to {@link Preferences#removeNode()}). 1139 * 1140 * <p>The removal of a node needn't become persistent until the 1141 * <tt>flush</tt> method is invoked on this node (or an ancestor). 1142 * 1143 * <p>If this node throws a <tt>BackingStoreException</tt>, the exception 1144 * will propagate out beyond the enclosing {@link #removeNode()} 1145 * invocation. 1146 * 1147 * @throws BackingStoreException if this operation cannot be completed 1148 * due to a failure in the backing store, or inability to 1149 * communicate with it. 1150 */ 1151 protected abstract void removeNodeSpi() throws BackingStoreException; 1152 1153 /** 1154 * Returns all of the keys that have an associated value in this 1155 * preference node. (The returned array will be of size zero if 1156 * this node has no preferences.) It is guaranteed that this node has not 1157 * been removed. 1158 * 1159 * <p>This method is invoked with the lock on this node held. 1160 * 1161 * <p>If this node throws a <tt>BackingStoreException</tt>, the exception 1162 * will propagate out beyond the enclosing {@link #keys()} invocation. 1163 * 1164 * @return an array of the keys that have an associated value in this 1165 * preference node. 1166 * @throws BackingStoreException if this operation cannot be completed 1167 * due to a failure in the backing store, or inability to 1168 * communicate with it. 1169 */ 1170 protected abstract String[] keysSpi() throws BackingStoreException; 1171 1172 /** 1173 * Returns the names of the children of this preference node. (The 1174 * returned array will be of size zero if this node has no children.) 1175 * This method need not return the names of any nodes already cached, 1176 * but may do so without harm. 1177 * 1178 * <p>This method is invoked with the lock on this node held. 1179 * 1180 * <p>If this node throws a <tt>BackingStoreException</tt>, the exception 1181 * will propagate out beyond the enclosing {@link #childrenNames()} 1182 * invocation. 1183 * 1184 * @return an array containing the names of the children of this 1185 * preference node. 1186 * @throws BackingStoreException if this operation cannot be completed 1187 * due to a failure in the backing store, or inability to 1188 * communicate with it. 1189 */ 1190 protected abstract String[] childrenNamesSpi() 1191 throws BackingStoreException; 1192 1193 /** 1194 * Returns the named child if it exists, or <tt>null</tt> if it does not. 1195 * It is guaranteed that <tt>nodeName</tt> is non-null, non-empty, 1196 * does not contain the slash character ('/'), and is no longer than 1197 * {@link #MAX_NAME_LENGTH} characters. Also, it is guaranteed 1198 * that this node has not been removed. (The implementor needn't check 1199 * for any of these things if he chooses to override this method.) 1200 * 1201 * <p>Finally, it is guaranteed that the named node has not been returned 1202 * by a previous invocation of this method or {@link #childSpi} after the 1203 * last time that it was removed. In other words, a cached value will 1204 * always be used in preference to invoking this method. (The implementor 1205 * needn't maintain his own cache of previously returned children if he 1206 * chooses to override this method.) 1207 * 1208 * <p>This implementation obtains this preference node's lock, invokes 1209 * {@link #childrenNames()} to get an array of the names of this node's 1210 * children, and iterates over the array comparing the name of each child 1211 * with the specified node name. If a child node has the correct name, 1212 * the {@link #childSpi(String)} method is invoked and the resulting 1213 * node is returned. If the iteration completes without finding the 1214 * specified name, <tt>null</tt> is returned. 1215 * 1216 * @param nodeName name of the child to be searched for. 1217 * @return the named child if it exists, or null if it does not. 1218 * @throws BackingStoreException if this operation cannot be completed 1219 * due to a failure in the backing store, or inability to 1220 * communicate with it. 1221 */ 1222 protected AbstractPreferences getChild(String nodeName) 1223 throws BackingStoreException { 1224 synchronized(lock) { 1225 // assert kidCache.get(nodeName)==null; 1226 String[] kidNames = childrenNames(); 1227 for (int i=0; i<kidNames.length; i++) 1228 if (kidNames[i].equals(nodeName)) 1229 return childSpi(kidNames[i]); 1230 } 1231 return null; 1232 } 1233 1234 /** 1235 * Returns the named child of this preference node, creating it if it does 1236 * not already exist. It is guaranteed that <tt>name</tt> is non-null, 1237 * non-empty, does not contain the slash character ('/'), and is no longer 1238 * than {@link #MAX_NAME_LENGTH} characters. Also, it is guaranteed that 1239 * this node has not been removed. (The implementor needn't check for any 1240 * of these things.) 1241 * 1242 * <p>Finally, it is guaranteed that the named node has not been returned 1243 * by a previous invocation of this method or {@link #getChild(String)} 1244 * after the last time that it was removed. In other words, a cached 1245 * value will always be used in preference to invoking this method. 1246 * Subclasses need not maintain their own cache of previously returned 1247 * children. 1248 * 1249 * <p>The implementer must ensure that the returned node has not been 1250 * removed. If a like-named child of this node was previously removed, the 1251 * implementer must return a newly constructed <tt>AbstractPreferences</tt> 1252 * node; once removed, an <tt>AbstractPreferences</tt> node 1253 * cannot be "resuscitated." 1254 * 1255 * <p>If this method causes a node to be created, this node is not 1256 * guaranteed to be persistent until the <tt>flush</tt> method is 1257 * invoked on this node or one of its ancestors (or descendants). 1258 * 1259 * <p>This method is invoked with the lock on this node held. 1260 * 1261 * @param name The name of the child node to return, relative to 1262 * this preference node. 1263 * @return The named child node. 1264 */ 1265 protected abstract AbstractPreferences childSpi(String name); 1266 1267 /** 1268 * Returns the absolute path name of this preferences node. 1269 */ 1270 public String toString() { 1271 return (this.isUserNode() ? "User" : "System") + 1272 " Preference Node: " + this.absolutePath(); 1273 } 1274 1275 /** 1276 * Implements the <tt>sync</tt> method as per the specification in 1277 * {@link Preferences#sync()}. 1278 * 1279 * <p>This implementation calls a recursive helper method that locks this 1280 * node, invokes syncSpi() on it, unlocks this node, and recursively 1281 * invokes this method on each "cached child." A cached child is a child 1282 * of this node that has been created in this VM and not subsequently 1283 * removed. In effect, this method does a depth first traversal of the 1284 * "cached subtree" rooted at this node, calling syncSpi() on each node in 1285 * the subTree while only that node is locked. Note that syncSpi() is 1286 * invoked top-down. 1287 * 1288 * @throws BackingStoreException if this operation cannot be completed 1289 * due to a failure in the backing store, or inability to 1290 * communicate with it. 1291 * @throws IllegalStateException if this node (or an ancestor) has been 1292 * removed with the {@link #removeNode()} method. 1293 * @see #flush() 1294 */ 1295 public void sync() throws BackingStoreException { 1296 sync2(); 1297 } 1298 1299 private void sync2() throws BackingStoreException { 1300 AbstractPreferences[] cachedKids; 1301 1302 synchronized(lock) { 1303 if (removed) 1304 throw new IllegalStateException("Node has been removed"); 1305 syncSpi(); 1306 cachedKids = cachedChildren(); 1307 } 1308 1309 for (int i=0; i<cachedKids.length; i++) 1310 cachedKids[i].sync2(); 1311 } 1312 1313 /** 1314 * This method is invoked with this node locked. The contract of this 1315 * method is to synchronize any cached preferences stored at this node 1316 * with any stored in the backing store. (It is perfectly possible that 1317 * this node does not exist on the backing store, either because it has 1318 * been deleted by another VM, or because it has not yet been created.) 1319 * Note that this method should <i>not</i> synchronize the preferences in 1320 * any subnodes of this node. If the backing store naturally syncs an 1321 * entire subtree at once, the implementer is encouraged to override 1322 * sync(), rather than merely overriding this method. 1323 * 1324 * <p>If this node throws a <tt>BackingStoreException</tt>, the exception 1325 * will propagate out beyond the enclosing {@link #sync()} invocation. 1326 * 1327 * @throws BackingStoreException if this operation cannot be completed 1328 * due to a failure in the backing store, or inability to 1329 * communicate with it. 1330 */ 1331 protected abstract void syncSpi() throws BackingStoreException; 1332 1333 /** 1334 * Implements the <tt>flush</tt> method as per the specification in 1335 * {@link Preferences#flush()}. 1336 * 1337 * <p>This implementation calls a recursive helper method that locks this 1338 * node, invokes flushSpi() on it, unlocks this node, and recursively 1339 * invokes this method on each "cached child." A cached child is a child 1340 * of this node that has been created in this VM and not subsequently 1341 * removed. In effect, this method does a depth first traversal of the 1342 * "cached subtree" rooted at this node, calling flushSpi() on each node in 1343 * the subTree while only that node is locked. Note that flushSpi() is 1344 * invoked top-down. 1345 * 1346 * <p> If this method is invoked on a node that has been removed with 1347 * the {@link #removeNode()} method, flushSpi() is invoked on this node, 1348 * but not on others. 1349 * 1350 * @throws BackingStoreException if this operation cannot be completed 1351 * due to a failure in the backing store, or inability to 1352 * communicate with it. 1353 * @see #flush() 1354 */ 1355 public void flush() throws BackingStoreException { 1356 flush2(); 1357 } 1358 1359 private void flush2() throws BackingStoreException { 1360 AbstractPreferences[] cachedKids; 1361 1362 synchronized(lock) { 1363 flushSpi(); 1364 if(removed) 1365 return; 1366 cachedKids = cachedChildren(); 1367 } 1368 1369 for (int i = 0; i < cachedKids.length; i++) 1370 cachedKids[i].flush2(); 1371 } 1372 1373 /** 1374 * This method is invoked with this node locked. The contract of this 1375 * method is to force any cached changes in the contents of this 1376 * preference node to the backing store, guaranteeing their persistence. 1377 * (It is perfectly possible that this node does not exist on the backing 1378 * store, either because it has been deleted by another VM, or because it 1379 * has not yet been created.) Note that this method should <i>not</i> 1380 * flush the preferences in any subnodes of this node. If the backing 1381 * store naturally flushes an entire subtree at once, the implementer is 1382 * encouraged to override flush(), rather than merely overriding this 1383 * method. 1384 * 1385 * <p>If this node throws a <tt>BackingStoreException</tt>, the exception 1386 * will propagate out beyond the enclosing {@link #flush()} invocation. 1387 * 1388 * @throws BackingStoreException if this operation cannot be completed 1389 * due to a failure in the backing store, or inability to 1390 * communicate with it. 1391 */ 1392 protected abstract void flushSpi() throws BackingStoreException; 1393 1394 /** 1395 * Returns <tt>true</tt> iff this node (or an ancestor) has been 1396 * removed with the {@link #removeNode()} method. This method 1397 * locks this node prior to returning the contents of the private 1398 * field used to track this state. 1399 * 1400 * @return <tt>true</tt> iff this node (or an ancestor) has been 1401 * removed with the {@link #removeNode()} method. 1402 */ 1403 protected boolean isRemoved() { 1404 synchronized(lock) { 1405 return removed; 1406 } 1407 } 1408 1409 /** 1410 * Queue of pending notification events. When a preference or node 1411 * change event for which there are one or more listeners occurs, 1412 * it is placed on this queue and the queue is notified. A background 1413 * thread waits on this queue and delivers the events. This decouples 1414 * event delivery from preference activity, greatly simplifying 1415 * locking and reducing opportunity for deadlock. 1416 */ 1417 private static final List<EventObject> eventQueue = new LinkedList<>(); 1418 1419 /** 1420 * These two classes are used to distinguish NodeChangeEvents on 1421 * eventQueue so the event dispatch thread knows whether to call 1422 * childAdded or childRemoved. 1423 */ 1424 private class NodeAddedEvent extends NodeChangeEvent { 1425 private static final long serialVersionUID = -6743557530157328528L; 1426 NodeAddedEvent(Preferences parent, Preferences child) { 1427 super(parent, child); 1428 } 1429 } 1430 private class NodeRemovedEvent extends NodeChangeEvent { 1431 private static final long serialVersionUID = 8735497392918824837L; 1432 NodeRemovedEvent(Preferences parent, Preferences child) { 1433 super(parent, child); 1434 } 1435 } 1436 1437 /** 1438 * A single background thread ("the event notification thread") monitors 1439 * the event queue and delivers events that are placed on the queue. 1440 */ 1441 private static class EventDispatchThread extends Thread { 1442 public void run() { 1443 while(true) { 1444 // Wait on eventQueue till an event is present 1445 EventObject event = null; 1446 synchronized(eventQueue) { 1447 try { 1448 while (eventQueue.isEmpty()) 1449 eventQueue.wait(); 1450 event = eventQueue.remove(0); 1451 } catch (InterruptedException e) { 1452 // XXX Log "Event dispatch thread interrupted. Exiting" 1453 return; 1454 } 1455 } 1456 1457 // Now we have event & hold no locks; deliver evt to listeners 1458 AbstractPreferences src=(AbstractPreferences)event.getSource(); 1459 if (event instanceof PreferenceChangeEvent) { 1460 PreferenceChangeEvent pce = (PreferenceChangeEvent)event; 1461 PreferenceChangeListener[] listeners = src.prefListeners(); 1462 for (int i=0; i<listeners.length; i++) 1463 listeners[i].preferenceChange(pce); 1464 } else { 1465 NodeChangeEvent nce = (NodeChangeEvent)event; 1466 NodeChangeListener[] listeners = src.nodeListeners(); 1467 if (nce instanceof NodeAddedEvent) { 1468 for (int i=0; i<listeners.length; i++) 1469 listeners[i].childAdded(nce); 1470 } else { 1471 // assert nce instanceof NodeRemovedEvent; 1472 for (int i=0; i<listeners.length; i++) 1473 listeners[i].childRemoved(nce); 1474 } 1475 } 1476 } 1477 } 1478 } 1479 1480 private static Thread eventDispatchThread = null; 1481 1482 /** 1483 * This method starts the event dispatch thread the first time it 1484 * is called. The event dispatch thread will be started only 1485 * if someone registers a listener. 1486 */ 1487 private static synchronized void startEventDispatchThreadIfNecessary() { 1488 if (eventDispatchThread == null) { 1489 // XXX Log "Starting event dispatch thread" 1490 eventDispatchThread = new EventDispatchThread(); 1491 eventDispatchThread.setDaemon(true); 1492 eventDispatchThread.start(); 1493 } 1494 } 1495 1496 /** 1497 * Return this node's preference/node change listeners. All accesses to prefListeners 1498 * and nodeListeners are guarded by |lock|. We return a copy of the list so that the 1499 * EventQueue thread will iterate over a fixed snapshot of the listeners at the time of 1500 * this call. 1501 */ 1502 PreferenceChangeListener[] prefListeners() { 1503 synchronized(lock) { 1504 return prefListeners.toArray(new PreferenceChangeListener[prefListeners.size()]); 1505 } 1506 } 1507 NodeChangeListener[] nodeListeners() { 1508 synchronized(lock) { 1509 return nodeListeners.toArray(new NodeChangeListener[nodeListeners.size()]); 1510 } 1511 } 1512 1513 /** 1514 * Enqueue a preference change event for delivery to registered 1515 * preference change listeners unless there are no registered 1516 * listeners. Invoked with this.lock held. 1517 */ 1518 private void enqueuePreferenceChangeEvent(String key, String newValue) { 1519 if (!prefListeners.isEmpty()) { 1520 synchronized(eventQueue) { 1521 eventQueue.add(new PreferenceChangeEvent(this, key, newValue)); 1522 eventQueue.notify(); 1523 } 1524 } 1525 } 1526 1527 /** 1528 * Enqueue a "node added" event for delivery to registered node change 1529 * listeners unless there are no registered listeners. Invoked with 1530 * this.lock held. 1531 */ 1532 private void enqueueNodeAddedEvent(Preferences child) { 1533 if (!nodeListeners.isEmpty()) { 1534 synchronized(eventQueue) { 1535 eventQueue.add(new NodeAddedEvent(this, child)); 1536 eventQueue.notify(); 1537 } 1538 } 1539 } 1540 1541 /** 1542 * Enqueue a "node removed" event for delivery to registered node change 1543 * listeners unless there are no registered listeners. Invoked with 1544 * this.lock held. 1545 */ 1546 private void enqueueNodeRemovedEvent(Preferences child) { 1547 if (!nodeListeners.isEmpty()) { 1548 synchronized(eventQueue) { 1549 eventQueue.add(new NodeRemovedEvent(this, child)); 1550 eventQueue.notify(); 1551 } 1552 } 1553 } 1554 1555 /** 1556 * Implements the <tt>exportNode</tt> method as per the specification in 1557 * {@link Preferences#exportNode(OutputStream)}. 1558 * 1559 * @param os the output stream on which to emit the XML document. 1560 * @throws IOException if writing to the specified output stream 1561 * results in an <tt>IOException</tt>. 1562 * @throws BackingStoreException if preference data cannot be read from 1563 * backing store. 1564 */ 1565 public void exportNode(OutputStream os) 1566 throws IOException, BackingStoreException 1567 { 1568 XmlSupport.export(os, this, false); 1569 } 1570 1571 /** 1572 * Implements the <tt>exportSubtree</tt> method as per the specification in 1573 * {@link Preferences#exportSubtree(OutputStream)}. 1574 * 1575 * @param os the output stream on which to emit the XML document. 1576 * @throws IOException if writing to the specified output stream 1577 * results in an <tt>IOException</tt>. 1578 * @throws BackingStoreException if preference data cannot be read from 1579 * backing store. 1580 */ 1581 public void exportSubtree(OutputStream os) 1582 throws IOException, BackingStoreException 1583 { 1584 XmlSupport.export(os, this, true); 1585 } 1586 } 1587