Java tutorial
/* * Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.util.prefs; import java.util.*; import java.io.*; import java.security.AccessController; import java.security.PrivilegedAction; // These imports needed only as a workaround for a JavaDoc bug import java.lang.Integer; import java.lang.Long; import java.lang.Float; import java.lang.Double; /** * This class provides a skeletal implementation of the {@link Preferences} * class, greatly easing the task of implementing it. * * <p><strong>This class is for {@code Preferences} implementers only. * Normal users of the {@code Preferences} facility should have no need to * consult this documentation. The {@link Preferences} documentation * should suffice.</strong> * * <p>Implementors must override the nine abstract service-provider interface * (SPI) methods: {@link #getSpi(String)}, {@link #putSpi(String,String)}, * {@link #removeSpi(String)}, {@link #childSpi(String)}, {@link * #removeNodeSpi()}, {@link #keysSpi()}, {@link #childrenNamesSpi()}, {@link * #syncSpi()} and {@link #flushSpi()}. All of the concrete methods specify * precisely how they are implemented atop these SPI methods. The implementor * may, at his discretion, override one or more of the concrete methods if the * default implementation is unsatisfactory for any reason, such as * performance. * * <p>The SPI methods fall into three groups concerning exception * behavior. The {@code getSpi} method should never throw exceptions, but it * doesn't really matter, as any exception thrown by this method will be * intercepted by {@link #get(String,String)}, which will return the specified * default value to the caller. The {@code removeNodeSpi, keysSpi, * childrenNamesSpi, syncSpi} and {@code flushSpi} methods are specified * to throw {@link BackingStoreException}, and the implementation is required * to throw this checked exception if it is unable to perform the operation. * The exception propagates outward, causing the corresponding API method * to fail. * * <p>The remaining SPI methods {@link #putSpi(String,String)}, {@link * #removeSpi(String)} and {@link #childSpi(String)} have more complicated * exception behavior. They are not specified to throw * {@code BackingStoreException}, as they can generally obey their contracts * even if the backing store is unavailable. This is true because they return * no information and their effects are not required to become permanent until * a subsequent call to {@link Preferences#flush()} or * {@link Preferences#sync()}. Generally speaking, these SPI methods should not * throw exceptions. In some implementations, there may be circumstances * under which these calls cannot even enqueue the requested operation for * later processing. Even under these circumstances it is generally better to * simply ignore the invocation and return, rather than throwing an * exception. Under these circumstances, however, subsequently invoking * {@code flush()} or {@code sync} would not imply that all previous * operations had successfully been made permanent. * * <p>There is one circumstance under which {@code putSpi, removeSpi and * childSpi} <i>should</i> throw an exception: if the caller lacks * sufficient privileges on the underlying operating system to perform the * requested operation. This will, for instance, occur on most systems * if a non-privileged user attempts to modify system preferences. * (The required privileges will vary from implementation to * implementation. On some implementations, they are the right to modify the * contents of some directory in the file system; on others they are the right * to modify contents of some key in a registry.) Under any of these * circumstances, it would generally be undesirable to let the program * continue executing as if these operations would become permanent at a later * time. While implementations are not required to throw an exception under * these circumstances, they are encouraged to do so. A {@link * SecurityException} would be appropriate. * * <p>Most of the SPI methods require the implementation to read or write * information at a preferences node. The implementor should beware of the * fact that another VM may have concurrently deleted this node from the * backing store. It is the implementation's responsibility to recreate the * node if it has been deleted. * * <p>Implementation note: In Sun's default {@code Preferences} * implementations, the user's identity is inherited from the underlying * operating system and does not change for the lifetime of the virtual * machine. It is recognized that server-side {@code Preferences} * implementations may have the user identity change from request to request, * implicitly passed to {@code Preferences} methods via the use of a * static {@link ThreadLocal} instance. Authors of such implementations are * <i>strongly</i> encouraged to determine the user at the time preferences * are accessed (for example by the {@link #get(String,String)} or {@link * #put(String,String)} method) rather than permanently associating a user * with each {@code Preferences} instance. The latter behavior conflicts * with normal {@code Preferences} usage and would lead to great confusion. * * @author Josh Bloch * @see Preferences * @since 1.4 */ public abstract class AbstractPreferences extends Preferences { /** * The code point U+0000, assigned to the null control character, is the * only character encoded in Unicode and ISO/IEC 10646 that is always * invalid in any XML 1.0 and 1.1 document. */ static final int CODE_POINT_U0000 = '\u0000'; /** * Our name relative to parent. */ private final String name; /** * Our absolute path name. */ private final String absolutePath; /** * Our parent node. */ final AbstractPreferences parent; /** * Our root node. */ private final AbstractPreferences root; // Relative to this node /** * This field should be {@code true} if this node did not exist in the * backing store prior to the creation of this object. The field * is initialized to false, but may be set to true by a subclass * constructor (and should not be modified thereafter). This field * indicates whether a node change event should be fired when * creation is complete. */ protected boolean newNode = false; /** * All known unremoved children of this node. (This "cache" is consulted * prior to calling childSpi() or getChild(). */ private Map<String, AbstractPreferences> kidCache = new HashMap<>(); /** * This field is used to keep track of whether or not this node has * been removed. Once it's set to true, it will never be reset to false. */ private boolean removed = false; /** * Registered preference change listeners. */ private PreferenceChangeListener[] prefListeners = new PreferenceChangeListener[0]; /** * Registered node change listeners. */ private NodeChangeListener[] nodeListeners = new NodeChangeListener[0]; /** * An object whose monitor is used to lock this node. This object * is used in preference to the node itself to reduce the likelihood of * intentional or unintentional denial of service due to a locked node. * To avoid deadlock, a node is <i>never</i> locked by a thread that * holds a lock on a descendant of that node. */ protected final Object lock = new Object(); /** * Creates a preference node with the specified parent and the specified * name relative to its parent. * * @param parent the parent of this preference node, or null if this * is the root. * @param name the name of this preference node, relative to its parent, * or {@code ""} if this is the root. * @throws IllegalArgumentException if {@code name} contains a slash * ({@code '/'}), or {@code parent} is {@code null} and * name isn't {@code ""}. */ protected AbstractPreferences(AbstractPreferences parent, String name) { if (parent == null) { if (!name.isEmpty()) throw new IllegalArgumentException("Root name '" + name + "' must be \"\""); this.absolutePath = "/"; root = this; } else { if (name.indexOf('/') != -1) throw new IllegalArgumentException("Name '" + name + "' contains '/'"); if (name.isEmpty()) throw new IllegalArgumentException("Illegal name: empty string"); root = parent.root; absolutePath = (parent == root ? "/" + name : parent.absolutePath() + "/" + name); } this.name = name; this.parent = parent; } /** * Implements the {@code put} method as per the specification in * {@link Preferences#put(String,String)}. * * <p>This implementation checks that the key and value are legal, * obtains this preference node's lock, checks that the node * has not been removed, invokes {@link #putSpi(String,String)}, and if * there are any preference change listeners, enqueues a notification * event for processing by the event dispatch thread. * * @param key key with which the specified value is to be associated. * @param value value to be associated with the specified key. * @throws NullPointerException if key or value is {@code null}. * @throws IllegalArgumentException if {@code key.length()} exceeds * {@code MAX_KEY_LENGTH} or if {@code value.length} exceeds * {@code MAX_VALUE_LENGTH}. * @throws IllegalArgumentException if either key or value contain * the null control character, code point U+0000. * @throws IllegalStateException if this node (or an ancestor) has been * removed with the {@link #removeNode()} method. */ public void put(String key, String value) { if (key == null || value == null) throw new NullPointerException(); if (key.length() > MAX_KEY_LENGTH) throw new IllegalArgumentException("Key too long: " + key); if (value.length() > MAX_VALUE_LENGTH) throw new IllegalArgumentException("Value too long: " + value); if (key.indexOf(CODE_POINT_U0000) != -1) throw new IllegalArgumentException("Key contains code point U+0000"); if (value.indexOf(CODE_POINT_U0000) != -1) throw new IllegalArgumentException("Value contains code point U+0000"); synchronized (lock) { if (removed) throw new IllegalStateException("Node has been removed."); putSpi(key, value); enqueuePreferenceChangeEvent(key, value); } } /** * Implements the {@code get} method as per the specification in * {@link Preferences#get(String,String)}. * * <p>This implementation first checks to see if {@code key} is * {@code null} throwing a {@code NullPointerException} if this is * the case. Then it obtains this preference node's lock, * checks that the node has not been removed, invokes {@link * #getSpi(String)}, and returns the result, unless the {@code getSpi} * invocation returns {@code null} or throws an exception, in which case * this invocation returns {@code def}. * * @param key key whose associated value is to be returned. * @param def the value to be returned in the event that this * preference node has no value associated with {@code key}. * @return the value associated with {@code key}, or {@code def} * if no value is associated with {@code key}. * @throws IllegalStateException if this node (or an ancestor) has been * removed with the {@link #removeNode()} method. * @throws NullPointerException if key is {@code null}. (A * {@code null} default <i>is</i> permitted.) * @throws IllegalArgumentException if key contains the null control * character, code point U+0000. */ public String get(String key, String def) { if (key == null) throw new NullPointerException("Null key"); if (key.indexOf(CODE_POINT_U0000) != -1) throw new IllegalArgumentException("Key contains code point U+0000"); synchronized (lock) { if (removed) throw new IllegalStateException("Node has been removed."); String result = null; try { result = getSpi(key); } catch (Exception e) { // Ignoring exception causes default to be returned } return (result == null ? def : result); } } /** * Implements the {@code remove(String)} method as per the specification * in {@link Preferences#remove(String)}. * * <p>This implementation obtains this preference node's lock, * checks that the node has not been removed, invokes * {@link #removeSpi(String)} and if there are any preference * change listeners, enqueues a notification event for processing by the * event dispatch thread. * * @param key key whose mapping is to be removed from the preference node. * @throws IllegalStateException if this node (or an ancestor) has been * removed with the {@link #removeNode()} method. * @throws IllegalArgumentException if key contains the null control * character, code point U+0000. * @throws NullPointerException {@inheritDoc}. */ public void remove(String key) { Objects.requireNonNull(key, "Specified key cannot be null"); if (key.indexOf(CODE_POINT_U0000) != -1) throw new IllegalArgumentException("Key contains code point U+0000"); synchronized (lock) { if (removed) throw new IllegalStateException("Node has been removed."); removeSpi(key); enqueuePreferenceChangeEvent(key, null); } } /** * Implements the {@code clear} method as per the specification in * {@link Preferences#clear()}. * * <p>This implementation obtains this preference node's lock, * invokes {@link #keys()} to obtain an array of keys, and * iterates over the array invoking {@link #remove(String)} on each key. * * @throws BackingStoreException if this operation cannot be completed * due to a failure in the backing store, or inability to * communicate with it. * @throws IllegalStateException if this node (or an ancestor) has been * removed with the {@link #removeNode()} method. */ public void clear() throws BackingStoreException { synchronized (lock) { for (String key : keys()) remove(key); } } /** * Implements the {@code putInt} method as per the specification in * {@link Preferences#putInt(String,int)}. * * <p>This implementation translates {@code value} to a string with * {@link Integer#toString(int)} and invokes {@link #put(String,String)} * on the result. * * @param key key with which the string form of value is to be associated. * @param value value whose string form is to be associated with key. * @throws NullPointerException if key is {@code null}. * @throws IllegalArgumentException if {@code key.length()} exceeds * {@code MAX_KEY_LENGTH}. * @throws IllegalArgumentException if key contains * the null control character, code point U+0000. * @throws IllegalStateException if this node (or an ancestor) has been * removed with the {@link #removeNode()} method. */ public void putInt(String key, int value) { put(key, Integer.toString(value)); } /** * Implements the {@code getInt} method as per the specification in * {@link Preferences#getInt(String,int)}. * * <p>This implementation invokes {@link #get(String,String) get(key, * null)}. If the return value is non-null, the implementation * attempts to translate it to an {@code int} with * {@link Integer#parseInt(String)}. If the attempt succeeds, the return * value is returned by this method. Otherwise, {@code def} is returned. * * @param key key whose associated value is to be returned as an int. * @param def the value to be returned in the event that this * preference node has no value associated with {@code key} * or the associated value cannot be interpreted as an int. * @return the int value represented by the string associated with * {@code key} in this preference node, or {@code def} if the * associated value does not exist or cannot be interpreted as * an int. * @throws IllegalStateException if this node (or an ancestor) has been * removed with the {@link #removeNode()} method. * @throws NullPointerException if {@code key} is {@code null}. * @throws IllegalArgumentException if key contains the null control * character, code point U+0000. */ public int getInt(String key, int def) { int result = def; try { String value = get(key, null); if (value != null) result = Integer.parseInt(value); } catch (NumberFormatException e) { // Ignoring exception causes specified default to be returned } return result; } /** * Implements the {@code putLong} method as per the specification in * {@link Preferences#putLong(String,long)}. * * <p>This implementation translates {@code value} to a string with * {@link Long#toString(long)} and invokes {@link #put(String,String)} * on the result. * * @param key key with which the string form of value is to be associated. * @param value value whose string form is to be associated with key. * @throws NullPointerException if key is {@code null}. * @throws IllegalArgumentException if {@code key.length()} exceeds * {@code MAX_KEY_LENGTH}. * @throws IllegalArgumentException if key contains * the null control character, code point U+0000. * @throws IllegalStateException if this node (or an ancestor) has been * removed with the {@link #removeNode()} method. */ public void putLong(String key, long value) { put(key, Long.toString(value)); } /** * Implements the {@code getLong} method as per the specification in * {@link Preferences#getLong(String,long)}. * * <p>This implementation invokes {@link #get(String,String) get(key, * null)}. If the return value is non-null, the implementation * attempts to translate it to a {@code long} with * {@link Long#parseLong(String)}. If the attempt succeeds, the return * value is returned by this method. Otherwise, {@code def} is returned. * * @param key key whose associated value is to be returned as a long. * @param def the value to be returned in the event that this * preference node has no value associated with {@code key} * or the associated value cannot be interpreted as a long. * @return the long value represented by the string associated with * {@code key} in this preference node, or {@code def} if the * associated value does not exist or cannot be interpreted as * a long. * @throws IllegalStateException if this node (or an ancestor) has been * removed with the {@link #removeNode()} method. * @throws NullPointerException if {@code key} is {@code null}. * @throws IllegalArgumentException if key contains the null control * character, code point U+0000. */ public long getLong(String key, long def) { long result = def; try { String value = get(key, null); if (value != null) result = Long.parseLong(value); } catch (NumberFormatException e) { // Ignoring exception causes specified default to be returned } return result; } /** * Implements the {@code putBoolean} method as per the specification in * {@link Preferences#putBoolean(String,boolean)}. * * <p>This implementation translates {@code value} to a string with * {@link String#valueOf(boolean)} and invokes {@link #put(String,String)} * on the result. * * @param key key with which the string form of value is to be associated. * @param value value whose string form is to be associated with key. * @throws NullPointerException if key is {@code null}. * @throws IllegalArgumentException if {@code key.length()} exceeds * {@code MAX_KEY_LENGTH}. * @throws IllegalArgumentException if key contains * the null control character, code point U+0000. * @throws IllegalStateException if this node (or an ancestor) has been * removed with the {@link #removeNode()} method. */ public void putBoolean(String key, boolean value) { put(key, String.valueOf(value)); } /** * Implements the {@code getBoolean} method as per the specification in * {@link Preferences#getBoolean(String,boolean)}. * * <p>This implementation invokes {@link #get(String,String) get(key, * null)}. If the return value is non-null, it is compared with * {@code "true"} using {@link String#equalsIgnoreCase(String)}. If the * comparison returns {@code true}, this invocation returns * {@code true}. Otherwise, the original return value is compared with * {@code "false"}, again using {@link String#equalsIgnoreCase(String)}. * If the comparison returns {@code true}, this invocation returns * {@code false}. Otherwise, this invocation returns {@code def}. * * @param key key whose associated value is to be returned as a boolean. * @param def the value to be returned in the event that this * preference node has no value associated with {@code key} * or the associated value cannot be interpreted as a boolean. * @return the boolean value represented by the string associated with * {@code key} in this preference node, or {@code def} if the * associated value does not exist or cannot be interpreted as * a boolean. * @throws IllegalStateException if this node (or an ancestor) has been * removed with the {@link #removeNode()} method. * @throws NullPointerException if {@code key} is {@code null}. * @throws IllegalArgumentException if key contains the null control * character, code point U+0000. */ public boolean getBoolean(String key, boolean def) { boolean result = def; String value = get(key, null); if (value != null) { if (value.equalsIgnoreCase("true")) result = true; else if (value.equalsIgnoreCase("false")) result = false; } return result; } /** * Implements the {@code putFloat} method as per the specification in * {@link Preferences#putFloat(String,float)}. * * <p>This implementation translates {@code value} to a string with * {@link Float#toString(float)} and invokes {@link #put(String,String)} * on the result. * * @param key key with which the string form of value is to be associated. * @param value value whose string form is to be associated with key. * @throws NullPointerException if key is {@code null}. * @throws IllegalArgumentException if {@code key.length()} exceeds * {@code MAX_KEY_LENGTH}. * @throws IllegalArgumentException if key contains * the null control character, code point U+0000. * @throws IllegalStateException if this node (or an ancestor) has been * removed with the {@link #removeNode()} method. */ public void putFloat(String key, float value) { put(key, Float.toString(value)); } /** * Implements the {@code getFloat} method as per the specification in * {@link Preferences#getFloat(String,float)}. * * <p>This implementation invokes {@link #get(String,String) get(key, * null)}. If the return value is non-null, the implementation * attempts to translate it to an {@code float} with * {@link Float#parseFloat(String)}. If the attempt succeeds, the return * value is returned by this method. Otherwise, {@code def} is returned. * * @param key key whose associated value is to be returned as a float. * @param def the value to be returned in the event that this * preference node has no value associated with {@code key} * or the associated value cannot be interpreted as a float. * @return the float value represented by the string associated with * {@code key} in this preference node, or {@code def} if the * associated value does not exist or cannot be interpreted as * a float. * @throws IllegalStateException if this node (or an ancestor) has been * removed with the {@link #removeNode()} method. * @throws NullPointerException if {@code key} is {@code null}. * @throws IllegalArgumentException if key contains the null control * character, code point U+0000. */ public float getFloat(String key, float def) { float result = def; try { String value = get(key, null); if (value != null) result = Float.parseFloat(value); } catch (NumberFormatException e) { // Ignoring exception causes specified default to be returned } return result; } /** * Implements the {@code putDouble} method as per the specification in * {@link Preferences#putDouble(String,double)}. * * <p>This implementation translates {@code value} to a string with * {@link Double#toString(double)} and invokes {@link #put(String,String)} * on the result. * * @param key key with which the string form of value is to be associated. * @param value value whose string form is to be associated with key. * @throws NullPointerException if key is {@code null}. * @throws IllegalArgumentException if {@code key.length()} exceeds * {@code MAX_KEY_LENGTH}. * @throws IllegalArgumentException if key contains * the null control character, code point U+0000. * @throws IllegalStateException if this node (or an ancestor) has been * removed with the {@link #removeNode()} method. */ public void putDouble(String key, double value) { put(key, Double.toString(value)); } /** * Implements the {@code getDouble} method as per the specification in * {@link Preferences#getDouble(String,double)}. * * <p>This implementation invokes {@link #get(String,String) get(key, * null)}. If the return value is non-null, the implementation * attempts to translate it to an {@code double} with * {@link Double#parseDouble(String)}. If the attempt succeeds, the return * value is returned by this method. Otherwise, {@code def} is returned. * * @param key key whose associated value is to be returned as a double. * @param def the value to be returned in the event that this * preference node has no value associated with {@code key} * or the associated value cannot be interpreted as a double. * @return the double value represented by the string associated with * {@code key} in this preference node, or {@code def} if the * associated value does not exist or cannot be interpreted as * a double. * @throws IllegalStateException if this node (or an ancestor) has been * removed with the {@link #removeNode()} method. * @throws NullPointerException if {@code key} is {@code null}. * @throws IllegalArgumentException if key contains the null control * character, code point U+0000. */ public double getDouble(String key, double def) { double result = def; try { String value = get(key, null); if (value != null) result = Double.parseDouble(value); } catch (NumberFormatException e) { // Ignoring exception causes specified default to be returned } return result; } /** * Implements the {@code putByteArray} method as per the specification in * {@link Preferences#putByteArray(String,byte[])}. * * @param key key with which the string form of value is to be associated. * @param value value whose string form is to be associated with key. * @throws NullPointerException if key or value is {@code null}. * @throws IllegalArgumentException if key.length() exceeds MAX_KEY_LENGTH * or if value.length exceeds MAX_VALUE_LENGTH*3/4. * @throws IllegalArgumentException if key contains * the null control character, code point U+0000. * @throws IllegalStateException if this node (or an ancestor) has been * removed with the {@link #removeNode()} method. */ public void putByteArray(String key, byte[] value) { put(key, Base64.byteArrayToBase64(value)); } /** * Implements the {@code getByteArray} method as per the specification in * {@link Preferences#getByteArray(String,byte[])}. * * @param key key whose associated value is to be returned as a byte array. * @param def the value to be returned in the event that this * preference node has no value associated with {@code key} * or the associated value cannot be interpreted as a byte array. * @return the byte array value represented by the string associated with * {@code key} in this preference node, or {@code def} if the * associated value does not exist or cannot be interpreted as * a byte array. * @throws IllegalStateException if this node (or an ancestor) has been * removed with the {@link #removeNode()} method. * @throws NullPointerException if {@code key} is {@code null}. (A * {@code null} value for {@code def} <i>is</i> permitted.) * @throws IllegalArgumentException if key contains the null control * character, code point U+0000. */ public byte[] getByteArray(String key, byte[] def) { byte[] result = def; String value = get(key, null); try { if (value != null) result = Base64.base64ToByteArray(value); } catch (RuntimeException e) { // Ignoring exception causes specified default to be returned } return result; } /** * Implements the {@code keys} method as per the specification in * {@link Preferences#keys()}. * * <p>This implementation obtains this preference node's lock, checks that * the node has not been removed and invokes {@link #keysSpi()}. * * @return an array of the keys that have an associated value in this * preference node. * @throws BackingStoreException if this operation cannot be completed * due to a failure in the backing store, or inability to * communicate with it. * @throws IllegalStateException if this node (or an ancestor) has been * removed with the {@link #removeNode()} method. */ public String[] keys() throws BackingStoreException { synchronized (lock) { if (removed) throw new IllegalStateException("Node has been removed."); return keysSpi(); } } /** * Implements the {@code children} method as per the specification in * {@link Preferences#childrenNames()}. * * <p>This implementation obtains this preference node's lock, checks that * the node has not been removed, constructs a {@code TreeSet} initialized * to the names of children already cached (the children in this node's * "child-cache"), invokes {@link #childrenNamesSpi()}, and adds all of the * returned child-names into the set. The elements of the tree set are * dumped into a {@code String} array using the {@code toArray} method, * and this array is returned. * * @return the names of the children of this preference node. * @throws BackingStoreException if this operation cannot be completed * due to a failure in the backing store, or inability to * communicate with it. * @throws IllegalStateException if this node (or an ancestor) has been * removed with the {@link #removeNode()} method. * @see #cachedChildren() */ public String[] childrenNames() throws BackingStoreException { synchronized (lock) { if (removed) throw new IllegalStateException("Node has been removed."); Set<String> s = new TreeSet<>(kidCache.keySet()); for (String kid : childrenNamesSpi()) s.add(kid); return s.toArray(EMPTY_STRING_ARRAY); } } private static final String[] EMPTY_STRING_ARRAY = new String[0]; /** * Returns all known unremoved children of this node. * * @return all known unremoved children of this node. */ protected final AbstractPreferences[] cachedChildren() { return kidCache.values().toArray(EMPTY_ABSTRACT_PREFS_ARRAY); } private static final AbstractPreferences[] EMPTY_ABSTRACT_PREFS_ARRAY = new AbstractPreferences[0]; /** * Implements the {@code parent} method as per the specification in * {@link Preferences#parent()}. * * <p>This implementation obtains this preference node's lock, checks that * the node has not been removed and returns the parent value that was * passed to this node's constructor. * * @return the parent of this preference node. * @throws IllegalStateException if this node (or an ancestor) has been * removed with the {@link #removeNode()} method. */ public Preferences parent() { synchronized (lock) { if (removed) throw new IllegalStateException("Node has been removed."); return parent; } } /** * Implements the {@code node} method as per the specification in * {@link Preferences#node(String)}. * * <p>This implementation obtains this preference node's lock and checks * that the node has not been removed. If {@code path} is {@code ""}, * this node is returned; if {@code path} is {@code "/"}, this node's * root is returned. If the first character in {@code path} is * not {@code '/'}, the implementation breaks {@code path} into * tokens and recursively traverses the path from this node to the * named node, "consuming" a name and a slash from {@code path} at * each step of the traversal. At each step, the current node is locked * and the node's child-cache is checked for the named node. If it is * not found, the name is checked to make sure its length does not * exceed {@code MAX_NAME_LENGTH}. Then the {@link #childSpi(String)} * method is invoked, and the result stored in this node's child-cache. * If the newly created {@code Preferences} object's {@link #newNode} * field is {@code true} and there are any node change listeners, * a notification event is enqueued for processing by the event dispatch * thread. * * <p>When there are no more tokens, the last value found in the * child-cache or returned by {@code childSpi} is returned by this * method. If during the traversal, two {@code "/"} tokens occur * consecutively, or the final token is {@code "/"} (rather than a name), * an appropriate {@code IllegalArgumentException} is thrown. * * <p> If the first character of {@code path} is {@code '/'} * (indicating an absolute path name) this preference node's * lock is dropped prior to breaking {@code path} into tokens, and * this method recursively traverses the path starting from the root * (rather than starting from this node). The traversal is otherwise * identical to the one described for relative path names. Dropping * the lock on this node prior to commencing the traversal at the root * node is essential to avoid the possibility of deadlock, as per the * {@link #lock locking invariant}. * * @param path the path name of the preference node to return. * @return the specified preference node. * @throws IllegalArgumentException if the path name is invalid (i.e., * it contains multiple consecutive slash characters, or ends * with a slash character and is more than one character long). * @throws IllegalStateException if this node (or an ancestor) has been * removed with the {@link #removeNode()} method. */ public Preferences node(String path) { synchronized (lock) { if (removed) throw new IllegalStateException("Node has been removed."); if (path.isEmpty()) return this; if (path.equals("/")) return root; if (path.charAt(0) != '/') return node(new StringTokenizer(path, "/", true)); } // Absolute path. Note that we've dropped our lock to avoid deadlock return root.node(new StringTokenizer(path.substring(1), "/", true)); } /** * tokenizer contains <name> {'/' <name>}* */ private Preferences node(StringTokenizer path) { String token = path.nextToken(); if (token.equals("/")) // Check for consecutive slashes throw new IllegalArgumentException("Consecutive slashes in path"); synchronized (lock) { AbstractPreferences child = kidCache.get(token); if (child == null) { if (token.length() > MAX_NAME_LENGTH) throw new IllegalArgumentException("Node name " + token + " too long"); child = childSpi(token); if (child.newNode) enqueueNodeAddedEvent(child); kidCache.put(token, child); } if (!path.hasMoreTokens()) return child; path.nextToken(); // Consume slash if (!path.hasMoreTokens()) throw new IllegalArgumentException("Path ends with slash"); return child.node(path); } } /** * Implements the {@code nodeExists} method as per the specification in * {@link Preferences#nodeExists(String)}. * * <p>This implementation is very similar to {@link #node(String)}, * except that {@link #getChild(String)} is used instead of {@link * #childSpi(String)}. * * @param path the path name of the node whose existence is to be checked. * @return true if the specified node exists. * @throws BackingStoreException if this operation cannot be completed * due to a failure in the backing store, or inability to * communicate with it. * @throws IllegalArgumentException if the path name is invalid (i.e., * it contains multiple consecutive slash characters, or ends * with a slash character and is more than one character long). * @throws IllegalStateException if this node (or an ancestor) has been * removed with the {@link #removeNode()} method and * {@code pathname} is not the empty string ({@code ""}). */ public boolean nodeExists(String path) throws BackingStoreException { synchronized (lock) { if (path.isEmpty()) return !removed; if (removed) throw new IllegalStateException("Node has been removed."); if (path.equals("/")) return true; if (path.charAt(0) != '/') return nodeExists(new StringTokenizer(path, "/", true)); } // Absolute path. Note that we've dropped our lock to avoid deadlock return root.nodeExists(new StringTokenizer(path.substring(1), "/", true)); } /** * tokenizer contains <name> {'/' <name>}* */ private boolean nodeExists(StringTokenizer path) throws BackingStoreException { String token = path.nextToken(); if (token.equals("/")) // Check for consecutive slashes throw new IllegalArgumentException("Consecutive slashes in path"); synchronized (lock) { AbstractPreferences child = kidCache.get(token); if (child == null) child = getChild(token); if (child == null) return false; if (!path.hasMoreTokens()) return true; path.nextToken(); // Consume slash if (!path.hasMoreTokens()) throw new IllegalArgumentException("Path ends with slash"); return child.nodeExists(path); } } /** * Implements the {@code removeNode()} method as per the specification in * {@link Preferences#removeNode()}. * * <p>This implementation checks to see that this node is the root; if so, * it throws an appropriate exception. Then, it locks this node's parent, * and calls a recursive helper method that traverses the subtree rooted at * this node. The recursive method locks the node on which it was called, * checks that it has not already been removed, and then ensures that all * of its children are cached: The {@link #childrenNamesSpi()} method is * invoked and each returned child name is checked for containment in the * child-cache. If a child is not already cached, the {@link * #childSpi(String)} method is invoked to create a {@code Preferences} * instance for it, and this instance is put into the child-cache. Then * the helper method calls itself recursively on each node contained in its * child-cache. Next, it invokes {@link #removeNodeSpi()}, marks itself * as removed, and removes itself from its parent's child-cache. Finally, * if there are any node change listeners, it enqueues a notification * event for processing by the event dispatch thread. * * <p>Note that the helper method is always invoked with all ancestors up * to the "closest non-removed ancestor" locked. * * @throws IllegalStateException if this node (or an ancestor) has already * been removed with the {@link #removeNode()} method. * @throws UnsupportedOperationException if this method is invoked on * the root node. * @throws BackingStoreException if this operation cannot be completed * due to a failure in the backing store, or inability to * communicate with it. */ public void removeNode() throws BackingStoreException { if (this == root) throw new UnsupportedOperationException("Can't remove the root!"); synchronized (parent.lock) { removeNode2(); parent.kidCache.remove(name); } } /* * Called with locks on all nodes on path from parent of "removal root" * to this (including the former but excluding the latter). */ private void removeNode2() throws BackingStoreException { synchronized (lock) { if (removed) throw new IllegalStateException("Node already removed."); // Ensure that all children are cached String[] kidNames = childrenNamesSpi(); for (String kidName : kidNames) if (!kidCache.containsKey(kidName)) kidCache.put(kidName, childSpi(kidName)); // Recursively remove all cached children for (Iterator<AbstractPreferences> i = kidCache.values().iterator(); i.hasNext();) { try { i.next().removeNode2(); i.remove(); } catch (BackingStoreException x) { } } // Now we have no descendants - it's time to die! removeNodeSpi(); removed = true; parent.enqueueNodeRemovedEvent(this); } } /** * Implements the {@code name} method as per the specification in * {@link Preferences#name()}. * * <p>This implementation merely returns the name that was * passed to this node's constructor. * * @return this preference node's name, relative to its parent. */ public String name() { return name; } /** * Implements the {@code absolutePath} method as per the specification in * {@link Preferences#absolutePath()}. * * <p>This implementation merely returns the absolute path name that * was computed at the time that this node was constructed (based on * the name that was passed to this node's constructor, and the names * that were passed to this node's ancestors' constructors). * * @return this preference node's absolute path name. */ public String absolutePath() { return absolutePath; } /** * Implements the {@code isUserNode} method as per the specification in * {@link Preferences#isUserNode()}. * * <p>This implementation compares this node's root node (which is stored * in a private field) with the value returned by * {@link Preferences#userRoot()}. If the two object references are * identical, this method returns true. * * @return {@code true} if this preference node is in the user * preference tree, {@code false} if it's in the system * preference tree. */ public boolean isUserNode() { return AccessController.doPrivileged(new PrivilegedAction<Boolean>() { public Boolean run() { return root == Preferences.userRoot(); } }).booleanValue(); } public void addPreferenceChangeListener(PreferenceChangeListener pcl) { if (pcl == null) throw new NullPointerException("Change listener is null."); synchronized (lock) { if (removed) throw new IllegalStateException("Node has been removed."); // Copy-on-write PreferenceChangeListener[] old = prefListeners; prefListeners = new PreferenceChangeListener[old.length + 1]; System.arraycopy(old, 0, prefListeners, 0, old.length); prefListeners[old.length] = pcl; } startEventDispatchThreadIfNecessary(); } public void removePreferenceChangeListener(PreferenceChangeListener pcl) { synchronized (lock) { if (removed) throw new IllegalStateException("Node has been removed."); if ((prefListeners == null) || (prefListeners.length == 0)) throw new IllegalArgumentException("Listener not registered."); // Copy-on-write PreferenceChangeListener[] newPl = new PreferenceChangeListener[prefListeners.length - 1]; int i = 0; while (i < newPl.length && prefListeners[i] != pcl) newPl[i] = prefListeners[i++]; if (i == newPl.length && prefListeners[i] != pcl) throw new IllegalArgumentException("Listener not registered."); while (i < newPl.length) newPl[i] = prefListeners[++i]; prefListeners = newPl; } } public void addNodeChangeListener(NodeChangeListener ncl) { if (ncl == null) throw new NullPointerException("Change listener is null."); synchronized (lock) { if (removed) throw new IllegalStateException("Node has been removed."); // Copy-on-write if (nodeListeners == null) { nodeListeners = new NodeChangeListener[1]; nodeListeners[0] = ncl; } else { NodeChangeListener[] old = nodeListeners; nodeListeners = new NodeChangeListener[old.length + 1]; System.arraycopy(old, 0, nodeListeners, 0, old.length); nodeListeners[old.length] = ncl; } } startEventDispatchThreadIfNecessary(); } public void removeNodeChangeListener(NodeChangeListener ncl) { synchronized (lock) { if (removed) throw new IllegalStateException("Node has been removed."); if ((nodeListeners == null) || (nodeListeners.length == 0)) throw new IllegalArgumentException("Listener not registered."); // Copy-on-write int i = 0; while (i < nodeListeners.length && nodeListeners[i] != ncl) i++; if (i == nodeListeners.length) throw new IllegalArgumentException("Listener not registered."); NodeChangeListener[] newNl = new NodeChangeListener[nodeListeners.length - 1]; if (i != 0) System.arraycopy(nodeListeners, 0, newNl, 0, i); if (i != newNl.length) System.arraycopy(nodeListeners, i + 1, newNl, i, newNl.length - i); nodeListeners = newNl; } } // "SPI" METHODS /** * Put the given key-value association into this preference node. It is * guaranteed that {@code key} and {@code value} are non-null and of * legal length. Also, it is guaranteed that this node has not been * removed. (The implementor needn't check for any of these things.) * * <p>This method is invoked with the lock on this node held. * @param key the key * @param value the value */ protected abstract void putSpi(String key, String value); /** * Return the value associated with the specified key at this preference * node, or {@code null} if there is no association for this key, or the * association cannot be determined at this time. It is guaranteed that * {@code key} is non-null. Also, it is guaranteed that this node has * not been removed. (The implementor needn't check for either of these * things.) * * <p> Generally speaking, this method should not throw an exception * under any circumstances. If, however, if it does throw an exception, * the exception will be intercepted and treated as a {@code null} * return value. * * <p>This method is invoked with the lock on this node held. * * @param key the key * @return the value associated with the specified key at this preference * node, or {@code null} if there is no association for this * key, or the association cannot be determined at this time. */ protected abstract String getSpi(String key); /** * Remove the association (if any) for the specified key at this * preference node. It is guaranteed that {@code key} is non-null. * Also, it is guaranteed that this node has not been removed. * (The implementor needn't check for either of these things.) * * <p>This method is invoked with the lock on this node held. * @param key the key */ protected abstract void removeSpi(String key); /** * Removes this preference node, invalidating it and any preferences that * it contains. The named child will have no descendants at the time this * invocation is made (i.e., the {@link Preferences#removeNode()} method * invokes this method repeatedly in a bottom-up fashion, removing each of * a node's descendants before removing the node itself). * * <p>This method is invoked with the lock held on this node and its * parent (and all ancestors that are being removed as a * result of a single invocation to {@link Preferences#removeNode()}). * * <p>The removal of a node needn't become persistent until the * {@code flush} method is invoked on this node (or an ancestor). * * <p>If this node throws a {@code BackingStoreException}, the exception * will propagate out beyond the enclosing {@link #removeNode()} * invocation. * * @throws BackingStoreException if this operation cannot be completed * due to a failure in the backing store, or inability to * communicate with it. */ protected abstract void removeNodeSpi() throws BackingStoreException; /** * Returns all of the keys that have an associated value in this * preference node. (The returned array will be of size zero if * this node has no preferences.) It is guaranteed that this node has not * been removed. * * <p>This method is invoked with the lock on this node held. * * <p>If this node throws a {@code BackingStoreException}, the exception * will propagate out beyond the enclosing {@link #keys()} invocation. * * @return an array of the keys that have an associated value in this * preference node. * @throws BackingStoreException if this operation cannot be completed * due to a failure in the backing store, or inability to * communicate with it. */ protected abstract String[] keysSpi() throws BackingStoreException; /** * Returns the names of the children of this preference node. (The * returned array will be of size zero if this node has no children.) * This method need not return the names of any nodes already cached, * but may do so without harm. * * <p>This method is invoked with the lock on this node held. * * <p>If this node throws a {@code BackingStoreException}, the exception * will propagate out beyond the enclosing {@link #childrenNames()} * invocation. * * @return an array containing the names of the children of this * preference node. * @throws BackingStoreException if this operation cannot be completed * due to a failure in the backing store, or inability to * communicate with it. */ protected abstract String[] childrenNamesSpi() throws BackingStoreException; /** * Returns the named child if it exists, or {@code null} if it does not. * It is guaranteed that {@code nodeName} is non-null, non-empty, * does not contain the slash character ('/'), and is no longer than * {@link #MAX_NAME_LENGTH} characters. Also, it is guaranteed * that this node has not been removed. (The implementor needn't check * for any of these things if he chooses to override this method.) * * <p>Finally, it is guaranteed that the named node has not been returned * by a previous invocation of this method or {@link #childSpi} after the * last time that it was removed. In other words, a cached value will * always be used in preference to invoking this method. (The implementor * needn't maintain his own cache of previously returned children if he * chooses to override this method.) * * <p>This implementation obtains this preference node's lock, invokes * {@link #childrenNames()} to get an array of the names of this node's * children, and iterates over the array comparing the name of each child * with the specified node name. If a child node has the correct name, * the {@link #childSpi(String)} method is invoked and the resulting * node is returned. If the iteration completes without finding the * specified name, {@code null} is returned. * * @param nodeName name of the child to be searched for. * @return the named child if it exists, or null if it does not. * @throws BackingStoreException if this operation cannot be completed * due to a failure in the backing store, or inability to * communicate with it. */ protected AbstractPreferences getChild(String nodeName) throws BackingStoreException { synchronized (lock) { // assert kidCache.get(nodeName)==null; String[] kidNames = childrenNames(); for (String kidName : kidNames) if (kidName.equals(nodeName)) return childSpi(kidName); } return null; } /** * Returns the named child of this preference node, creating it if it does * not already exist. It is guaranteed that {@code name} is non-null, * non-empty, does not contain the slash character ('/'), and is no longer * than {@link #MAX_NAME_LENGTH} characters. Also, it is guaranteed that * this node has not been removed. (The implementor needn't check for any * of these things.) * * <p>Finally, it is guaranteed that the named node has not been returned * by a previous invocation of this method or {@link #getChild(String)} * after the last time that it was removed. In other words, a cached * value will always be used in preference to invoking this method. * Subclasses need not maintain their own cache of previously returned * children. * * <p>The implementer must ensure that the returned node has not been * removed. If a like-named child of this node was previously removed, the * implementer must return a newly constructed {@code AbstractPreferences} * node; once removed, an {@code AbstractPreferences} node * cannot be "resuscitated." * * <p>If this method causes a node to be created, this node is not * guaranteed to be persistent until the {@code flush} method is * invoked on this node or one of its ancestors (or descendants). * * <p>This method is invoked with the lock on this node held. * * @param name The name of the child node to return, relative to * this preference node. * @return The named child node. */ protected abstract AbstractPreferences childSpi(String name); /** * Returns the absolute path name of this preferences node. */ public String toString() { return (this.isUserNode() ? "User" : "System") + " Preference Node: " + this.absolutePath(); } /** * Implements the {@code sync} method as per the specification in * {@link Preferences#sync()}. * * <p>This implementation calls a recursive helper method that locks this * node, invokes syncSpi() on it, unlocks this node, and recursively * invokes this method on each "cached child." A cached child is a child * of this node that has been created in this VM and not subsequently * removed. In effect, this method does a depth first traversal of the * "cached subtree" rooted at this node, calling syncSpi() on each node in * the subTree while only that node is locked. Note that syncSpi() is * invoked top-down. * * @throws BackingStoreException if this operation cannot be completed * due to a failure in the backing store, or inability to * communicate with it. * @throws IllegalStateException if this node (or an ancestor) has been * removed with the {@link #removeNode()} method. * @see #flush() */ public void sync() throws BackingStoreException { sync2(); } private void sync2() throws BackingStoreException { AbstractPreferences[] cachedKids; synchronized (lock) { if (removed) throw new IllegalStateException("Node has been removed"); syncSpi(); cachedKids = cachedChildren(); } for (AbstractPreferences cachedKid : cachedKids) cachedKid.sync2(); } /** * This method is invoked with this node locked. The contract of this * method is to synchronize any cached preferences stored at this node * with any stored in the backing store. (It is perfectly possible that * this node does not exist on the backing store, either because it has * been deleted by another VM, or because it has not yet been created.) * Note that this method should <i>not</i> synchronize the preferences in * any subnodes of this node. If the backing store naturally syncs an * entire subtree at once, the implementer is encouraged to override * sync(), rather than merely overriding this method. * * <p>If this node throws a {@code BackingStoreException}, the exception * will propagate out beyond the enclosing {@link #sync()} invocation. * * @throws BackingStoreException if this operation cannot be completed * due to a failure in the backing store, or inability to * communicate with it. */ protected abstract void syncSpi() throws BackingStoreException; /** * Implements the {@code flush} method as per the specification in * {@link Preferences#flush()}. * * <p>This implementation calls a recursive helper method that locks this * node, invokes flushSpi() on it, unlocks this node, and recursively * invokes this method on each "cached child." A cached child is a child * of this node that has been created in this VM and not subsequently * removed. In effect, this method does a depth first traversal of the * "cached subtree" rooted at this node, calling flushSpi() on each node in * the subTree while only that node is locked. Note that flushSpi() is * invoked top-down. * * <p> If this method is invoked on a node that has been removed with * the {@link #removeNode()} method, flushSpi() is invoked on this node, * but not on others. * * @throws BackingStoreException if this operation cannot be completed * due to a failure in the backing store, or inability to * communicate with it. * @see #flush() */ public void flush() throws BackingStoreException { flush2(); } private void flush2() throws BackingStoreException { AbstractPreferences[] cachedKids; synchronized (lock) { flushSpi(); if (removed) return; cachedKids = cachedChildren(); } for (AbstractPreferences cachedKid : cachedKids) cachedKid.flush2(); } /** * This method is invoked with this node locked. The contract of this * method is to force any cached changes in the contents of this * preference node to the backing store, guaranteeing their persistence. * (It is perfectly possible that this node does not exist on the backing * store, either because it has been deleted by another VM, or because it * has not yet been created.) Note that this method should <i>not</i> * flush the preferences in any subnodes of this node. If the backing * store naturally flushes an entire subtree at once, the implementer is * encouraged to override flush(), rather than merely overriding this * method. * * <p>If this node throws a {@code BackingStoreException}, the exception * will propagate out beyond the enclosing {@link #flush()} invocation. * * @throws BackingStoreException if this operation cannot be completed * due to a failure in the backing store, or inability to * communicate with it. */ protected abstract void flushSpi() throws BackingStoreException; /** * Returns {@code true} iff this node (or an ancestor) has been * removed with the {@link #removeNode()} method. This method * locks this node prior to returning the contents of the private * field used to track this state. * * @return {@code true} iff this node (or an ancestor) has been * removed with the {@link #removeNode()} method. */ protected boolean isRemoved() { synchronized (lock) { return removed; } } /** * Queue of pending notification events. When a preference or node * change event for which there are one or more listeners occurs, * it is placed on this queue and the queue is notified. A background * thread waits on this queue and delivers the events. This decouples * event delivery from preference activity, greatly simplifying * locking and reducing opportunity for deadlock. */ private static final List<EventObject> eventQueue = new LinkedList<>(); /** * These two classes are used to distinguish NodeChangeEvents on * eventQueue so the event dispatch thread knows whether to call * childAdded or childRemoved. */ private class NodeAddedEvent extends NodeChangeEvent { private static final long serialVersionUID = -6743557530157328528L; NodeAddedEvent(Preferences parent, Preferences child) { super(parent, child); } } private class NodeRemovedEvent extends NodeChangeEvent { private static final long serialVersionUID = 8735497392918824837L; NodeRemovedEvent(Preferences parent, Preferences child) { super(parent, child); } } /** * A single background thread ("the event notification thread") monitors * the event queue and delivers events that are placed on the queue. */ private static class EventDispatchThread extends Thread { private EventDispatchThread() { super(null, null, "Event Dispatch Thread", 0, false); } public void run() { while (true) { // Wait on eventQueue till an event is present EventObject event = null; synchronized (eventQueue) { try { while (eventQueue.isEmpty()) eventQueue.wait(); event = eventQueue.remove(0); } catch (InterruptedException e) { // XXX Log "Event dispatch thread interrupted. Exiting" return; } } // Now we have event & hold no locks; deliver evt to listeners AbstractPreferences src = (AbstractPreferences) event.getSource(); if (event instanceof PreferenceChangeEvent) { PreferenceChangeEvent pce = (PreferenceChangeEvent) event; PreferenceChangeListener[] listeners = src.prefListeners(); for (PreferenceChangeListener listener : listeners) listener.preferenceChange(pce); } else { NodeChangeEvent nce = (NodeChangeEvent) event; NodeChangeListener[] listeners = src.nodeListeners(); if (nce instanceof NodeAddedEvent) { for (NodeChangeListener listener : listeners) listener.childAdded(nce); } else { // assert nce instanceof NodeRemovedEvent; for (NodeChangeListener listener : listeners) listener.childRemoved(nce); } } } } } private static Thread eventDispatchThread = null; /** * This method starts the event dispatch thread the first time it * is called. The event dispatch thread will be started only * if someone registers a listener. */ private static synchronized void startEventDispatchThreadIfNecessary() { if (eventDispatchThread == null) { // XXX Log "Starting event dispatch thread" eventDispatchThread = new EventDispatchThread(); eventDispatchThread.setDaemon(true); eventDispatchThread.start(); } } /** * Return this node's preference/node change listeners. Even though * we're using a copy-on-write lists, we use synchronized accessors to * ensure information transmission from the writing thread to the * reading thread. */ PreferenceChangeListener[] prefListeners() { synchronized (lock) { return prefListeners; } } NodeChangeListener[] nodeListeners() { synchronized (lock) { return nodeListeners; } } /** * Enqueue a preference change event for delivery to registered * preference change listeners unless there are no registered * listeners. Invoked with this.lock held. */ private void enqueuePreferenceChangeEvent(String key, String newValue) { if (prefListeners.length != 0) { synchronized (eventQueue) { eventQueue.add(new PreferenceChangeEvent(this, key, newValue)); eventQueue.notify(); } } } /** * Enqueue a "node added" event for delivery to registered node change * listeners unless there are no registered listeners. Invoked with * this.lock held. */ private void enqueueNodeAddedEvent(Preferences child) { if (nodeListeners.length != 0) { synchronized (eventQueue) { eventQueue.add(new NodeAddedEvent(this, child)); eventQueue.notify(); } } } /** * Enqueue a "node removed" event for delivery to registered node change * listeners unless there are no registered listeners. Invoked with * this.lock held. */ private void enqueueNodeRemovedEvent(Preferences child) { if (nodeListeners.length != 0) { synchronized (eventQueue) { eventQueue.add(new NodeRemovedEvent(this, child)); eventQueue.notify(); } } } /** * Implements the {@code exportNode} method as per the specification in * {@link Preferences#exportNode(OutputStream)}. * * @param os the output stream on which to emit the XML document. * @throws IOException if writing to the specified output stream * results in an {@code IOException}. * @throws BackingStoreException if preference data cannot be read from * backing store. */ public void exportNode(OutputStream os) throws IOException, BackingStoreException { XmlSupport.export(os, this, false); } /** * Implements the {@code exportSubtree} method as per the specification in * {@link Preferences#exportSubtree(OutputStream)}. * * @param os the output stream on which to emit the XML document. * @throws IOException if writing to the specified output stream * results in an {@code IOException}. * @throws BackingStoreException if preference data cannot be read from * backing store. */ public void exportSubtree(OutputStream os) throws IOException, BackingStoreException { XmlSupport.export(os, this, true); } }