JDK8/Java8源码在线阅读
/*
* Copyright (c) 2000, 2013, 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 <tt>Preferences</tt> implementers only.
* Normal users of the <tt>Preferences</tt> 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 <tt>getSpi</tt> 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 <tt>removeNodeSpi, keysSpi,
* childrenNamesSpi, syncSpi</tt> and <tt>flushSpi</tt> 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
* <tt>BackingStoreException</tt>, 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, all subsequent invocations
* of <tt>flush()</tt> and <tt>sync</tt> should return <tt>false</tt>, as
* returning <tt>true</tt> would imply that all previous operations had
* successfully been made permanent.
*
* <p>There is one circumstance under which <tt>putSpi, removeSpi and
* childSpi</tt> <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 <tt>Preferences</tt>
* 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 <tt>Preferences</tt>
* implementations may have the user identity change from request to request,
* implicitly passed to <tt>Preferences</tt> 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 <tt>Preferences</tt> instance. The latter behavior conflicts
* with normal <tt>Preferences</tt> usage and would lead to great confusion.
*
* @author Josh Bloch
* @see Preferences
* @since 1.4
*/
public abstract class AbstractPreferences extends Preferences {
/**
* 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 <tt>true</tt> 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 <tt>""</tt> if this is the root.
* @throws IllegalArgumentException if <tt>name</tt> contains a slash
* (<tt>'/'</tt>), or <tt>parent</tt> is <tt>null</tt> and
* name isn't <tt>""</tt>.
*/
protected AbstractPreferences(AbstractPreferences parent, String name) {
if (parent==null) {
if (!name.equals(""))
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.equals(""))
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 <tt>put</tt> 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 <tt>null</tt>.
* @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
* <tt>MAX_KEY_LENGTH</tt> or if <tt>value.length</tt> exceeds
* <tt>MAX_VALUE_LENGTH</tt>.
* @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);
synchronized(lock) {
if (removed)
throw new IllegalStateException("Node has been removed.");
putSpi(key, value);
enqueuePreferenceChangeEvent(key, value);
}
}
/**
* Implements the <tt>get</tt> method as per the specification in
* {@link Preferences#get(String,String)}.
*
* <p>This implementation first checks to see if <tt>key</tt> is
* <tt>null</tt> throwing a <tt>NullPointerException</tt> 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 <tt>getSpi</tt>
* invocation returns <tt>null</tt> or throws an exception, in which case
* this invocation returns <tt>def</tt>.
*
* @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 <tt>key</tt>.
* @return the value associated with <tt>key</tt>, or <tt>def</tt>
* if no value is associated with <tt>key</tt>.
* @throws IllegalStateException if this node (or an ancestor) has been
* removed with the {@link #removeNode()} method.
* @throws NullPointerException if key is <tt>null</tt>. (A
* <tt>null</tt> default <i>is</i> permitted.)
*/
public String get(String key, String def) {
if (key==null)
throw new NullPointerException("Null key");
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 <tt>remove(String)</tt> 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 NullPointerException {@inheritDoc}.
*/
public void remove(String key) {
Objects.requireNonNull(key, "Specified key cannot be null");
synchronized(lock) {
if (removed)
throw new IllegalStateException("Node has been removed.");
removeSpi(key);
enqueuePreferenceChangeEvent(key, null);
}
}
/**
* Implements the <tt>clear</tt> 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) {
String[] keys = keys();
for (int i=0; i<keys.length; i++)
remove(keys[i]);
}
}
/**
* Implements the <tt>putInt</tt> method as per the specification in
* {@link Preferences#putInt(String,int)}.
*
* <p>This implementation translates <tt>value</tt> 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 <tt>null</tt>.
* @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
* <tt>MAX_KEY_LENGTH</tt>.
* @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 <tt>getInt</tt> method as per the specification in
* {@link Preferences#getInt(String,int)}.
*
* <p>This implementation invokes {@link #get(String,String) <tt>get(key,
* null)</tt>}. If the return value is non-null, the implementation
* attempts to translate it to an <tt>int</tt> with
* {@link Integer#parseInt(String)}. If the attempt succeeds, the return
* value is returned by this method. Otherwise, <tt>def</tt> 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 <tt>key</tt>
* or the associated value cannot be interpreted as an int.
* @return the int value represented by the string associated with
* <tt>key</tt> in this preference node, or <tt>def</tt> 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 <tt>key</tt> is <tt>null</tt>.
*/
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 <tt>putLong</tt> method as per the specification in
* {@link Preferences#putLong(String,long)}.
*
* <p>This implementation translates <tt>value</tt> 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 <tt>null</tt>.
* @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
* <tt>MAX_KEY_LENGTH</tt>.
* @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 <tt>getLong</tt> method as per the specification in
* {@link Preferences#getLong(String,long)}.
*
* <p>This implementation invokes {@link #get(String,String) <tt>get(key,
* null)</tt>}. If the return value is non-null, the implementation
* attempts to translate it to a <tt>long</tt> with
* {@link Long#parseLong(String)}. If the attempt succeeds, the return
* value is returned by this method. Otherwise, <tt>def</tt> 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 <tt>key</tt>
* or the associated value cannot be interpreted as a long.
* @return the long value represented by the string associated with
* <tt>key</tt> in this preference node, or <tt>def</tt> 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 <tt>key</tt> is <tt>null</tt>.
*/
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 <tt>putBoolean</tt> method as per the specification in
* {@link Preferences#putBoolean(String,boolean)}.
*
* <p>This implementation translates <tt>value</tt> 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 <tt>null</tt>.
* @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
* <tt>MAX_KEY_LENGTH</tt>.
* @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 <tt>getBoolean</tt> method as per the specification in
* {@link Preferences#getBoolean(String,boolean)}.
*
* <p>This implementation invokes {@link #get(String,String) <tt>get(key,
* null)</tt>}. If the return value is non-null, it is compared with
* <tt>"true"</tt> using {@link String#equalsIgnoreCase(String)}. If the
* comparison returns <tt>true</tt>, this invocation returns
* <tt>true</tt>. Otherwise, the original return value is compared with
* <tt>"false"</tt>, again using {@link String#equalsIgnoreCase(String)}.
* If the comparison returns <tt>true</tt>, this invocation returns
* <tt>false</tt>. Otherwise, this invocation returns <tt>def</tt>.
*
* @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 <tt>key</tt>
* or the associated value cannot be interpreted as a boolean.
* @return the boolean value represented by the string associated with
* <tt>key</tt> in this preference node, or <tt>def</tt> 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 <tt>key</tt> is <tt>null</tt>.
*/
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 <tt>putFloat</tt> method as per the specification in
* {@link Preferences#putFloat(String,float)}.
*
* <p>This implementation translates <tt>value</tt> 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 <tt>null</tt>.
* @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
* <tt>MAX_KEY_LENGTH</tt>.
* @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 <tt>getFloat</tt> method as per the specification in
* {@link Preferences#getFloat(String,float)}.
*
* <p>This implementation invokes {@link #get(String,String) <tt>get(key,
* null)</tt>}. If the return value is non-null, the implementation
* attempts to translate it to an <tt>float</tt> with
* {@link Float#parseFloat(String)}. If the attempt succeeds, the return
* value is returned by this method. Otherwise, <tt>def</tt> 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 <tt>key</tt>
* or the associated value cannot be interpreted as a float.
* @return the float value represented by the string associated with
* <tt>key</tt> in this preference node, or <tt>def</tt> 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 <tt>key</tt> is <tt>null</tt>.
*/
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 <tt>putDouble</tt> method as per the specification in
* {@link Preferences#putDouble(String,double)}.
*
* <p>This implementation translates <tt>value</tt> 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 <tt>null</tt>.
* @throws IllegalArgumentException if <tt>key.length()</tt> exceeds
* <tt>MAX_KEY_LENGTH</tt>.
* @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 <tt>getDouble</tt> method as per the specification in
* {@link Preferences#getDouble(String,double)}.
*
* <p>This implementation invokes {@link #get(String,String) <tt>get(key,
* null)</tt>}. If the return value is non-null, the implementation
* attempts to translate it to an <tt>double</tt> with
* {@link Double#parseDouble(String)}. If the attempt succeeds, the return
* value is returned by this method. Otherwise, <tt>def</tt> 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 <tt>key</tt>
* or the associated value cannot be interpreted as a double.
* @return the double value represented by the string associated with
* <tt>key</tt> in this preference node, or <tt>def</tt> 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 <tt>key</tt> is <tt>null</tt>.
*/
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 <tt>putByteArray</tt> 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 <tt>null</tt>.
* @throws IllegalArgumentException if key.length() exceeds MAX_KEY_LENGTH
* or if value.length exceeds MAX_VALUE_LENGTH*3/4.
* @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 <tt>getByteArray</tt> 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 <tt>key</tt>
* or the associated value cannot be interpreted as a byte array.
* @return the byte array value represented by the string associated with
* <tt>key</tt> in this preference node, or <tt>def</tt> 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 <tt>key</tt> is <tt>null</tt>. (A
* <tt>null</tt> value for <tt>def</tt> <i>is</i> permitted.)
*/
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 <tt>keys</tt> 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 <tt>children</tt> 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 <tt>TreeSet</tt> 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 <tt>String</tt> array using the <tt>toArray</tt> 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 <tt>parent</tt> 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 <tt>node</tt> 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 <tt>path</tt> is <tt>""</tt>,
* this node is returned; if <tt>path</tt> is <tt>"/"</tt>, this node's
* root is returned. If the first character in <tt>path</tt> is
* not <tt>'/'</tt>, the implementation breaks <tt>path</tt> into
* tokens and recursively traverses the path from this node to the
* named node, "consuming" a name and a slash from <tt>path</tt> 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 <tt>MAX_NAME_LENGTH</tt>. Then the {@link #childSpi(String)}
* method is invoked, and the result stored in this node's child-cache.
* If the newly created <tt>Preferences</tt> object's {@link #newNode}
* field is <tt>true</tt> 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 <tt>childSpi</tt> is returned by this
* method. If during the traversal, two <tt>"/"</tt> tokens occur
* consecutively, or the final token is <tt>"/"</tt> (rather than a name),
* an appropriate <tt>IllegalArgumentException</tt> is thrown.
*
* <p> If the first character of <tt>path</tt> is <tt>'/'</tt>
* (indicating an absolute path name) this preference node's
* lock is dropped prior to breaking <tt>path</tt> 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.equals(""))
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 <tt>nodeExists</tt> 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
* <tt>pathname</tt> is not the empty string (<tt>""</tt>).
*/
public boolean nodeExists(String path)
throws BackingStoreException
{
synchronized(lock) {
if (path.equals(""))
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 <tt>removeNode()</tt> 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 <tt>Preferences</tt>
* 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 (int i=0; i<kidNames.length; i++)
if (!kidCache.containsKey(kidNames[i]))
kidCache.put(kidNames[i], childSpi(kidNames[i]));
// 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 <tt>name</tt> 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 <tt>absolutePath</tt> 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 <tt>isUserNode</tt> 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 <tt>true</tt> if this preference node is in the user
* preference tree, <tt>false</tt> 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 <tt>key</tt> and <tt>value</tt> 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 <tt>null</tt> if there is no association for this key, or the
* association cannot be determined at this time. It is guaranteed that
* <tt>key</tt> 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 <tt>null</tt>
* 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 <tt>null</tt> 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 <tt>key</tt> 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
* <tt>flush</tt> method is invoked on this node (or an ancestor).
*
* <p>If this node throws a <tt>BackingStoreException</tt>, 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 <tt>BackingStoreException</tt>, 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 <tt>BackingStoreException</tt>, 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 <tt>null</tt> if it does not.
* It is guaranteed that <tt>nodeName</tt> 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, <tt>null</tt> 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 (int i=0; i<kidNames.length; i++)
if (kidNames[i].equals(nodeName))
return childSpi(kidNames[i]);
}
return null;
}
/**
* Returns the named child of this preference node, creating it if it does
* not already exist. It is guaranteed that <tt>name</tt> 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 <tt>AbstractPreferences</tt>
* node; once removed, an <tt>AbstractPreferences</tt> node
* cannot be "resuscitated."
*
* <p>If this method causes a node to be created, this node is not
* guaranteed to be persistent until the <tt>flush</tt> 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 <tt>sync</tt> 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 (int i=0; i<cachedKids.length; i++)
cachedKids[i].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 <tt>BackingStoreException</tt>, 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 <tt>flush</tt> 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 (int i = 0; i < cachedKids.length; i++)
cachedKids[i].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 <tt>BackingStoreException</tt>, 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 <tt>true</tt> 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.
*
/**代码未完, 请加载全部代码(NowJava.com).**/
关注时代Java
关注时代Java