This class is for Preferences implementers only. * Normal users of the Preferences facility should have no need to * consult this documentation. The {@link Preferences} documentation * should suffice. * *
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. * *
The SPI methods fall into three groups concerning exception * behavior. The 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 removeNodeSpi, keysSpi, * childrenNamesSpi, syncSpi and 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. * *
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 * 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, all subsequent invocations * of flush() and sync should return false, as * returning true would imply that all previous operations had * successfully been made permanent. * *
There is one circumstance under which putSpi, removeSpi and * childSpi should 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. * *
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. * *
Implementation note: In Sun's default 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 Preferences
* implementations may have the user identity change from request to request,
* implicitly passed to Preferences methods via the use of a
* static {@link ThreadLocal} instance. Authors of such implementations are
* strongly 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 Preferences instance. The latter behavior conflicts
* with normal Preferences 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 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 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 null.
* @throws IllegalArgumentException if key.length() exceeds
* MAX_KEY_LENGTH or if value.length exceeds
* MAX_VALUE_LENGTH.
* @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 get method as per the specification in
* {@link Preferences#get(String,String)}.
*
* This implementation first checks to see if key is
* null throwing a 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 getSpi
* invocation returns null or throws an exception, in which case
* this invocation returns 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 key.
* @return the value associated with key, or def
* if no value is associated with key.
* @throws IllegalStateException if this node (or an ancestor) has been
* removed with the {@link #removeNode()} method.
* @throws NullPointerException if key is null. (A
* null default is 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 remove(String) method as per the specification
* in {@link Preferences#remove(String)}.
*
* 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.
*/
public void remove(String key) {
synchronized(lock) {
if (removed)
throw new IllegalStateException("Node has been removed.");
removeSpi(key);
enqueuePreferenceChangeEvent(key, null);
}
}
/**
* Implements the clear method as per the specification in
* {@link Preferences#clear()}.
*
* 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 This implementation translates 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 null.
* @throws IllegalArgumentException if key.length() exceeds
* MAX_KEY_LENGTH.
* @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 getInt method as per the specification in
* {@link Preferences#getInt(String,int)}.
*
* 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 int with
* {@link Integer#parseInt(String)}. If the attempt succeeds, the return
* value is returned by this method. Otherwise, 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 key
* or the associated value cannot be interpreted as an int.
* @return the int value represented by the string associated with
* key in this preference node, or 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 key is null.
*/
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 putLong method as per the specification in
* {@link Preferences#putLong(String,long)}.
*
* This implementation translates 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 null.
* @throws IllegalArgumentException if key.length() exceeds
* MAX_KEY_LENGTH.
* @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 getLong method as per the specification in
* {@link Preferences#getLong(String,long)}.
*
* 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 long with
* {@link Long#parseLong(String)}. If the attempt succeeds, the return
* value is returned by this method. Otherwise, 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 key
* or the associated value cannot be interpreted as a long.
* @return the long value represented by the string associated with
* key in this preference node, or 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 key is null.
*/
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 putBoolean method as per the specification in
* {@link Preferences#putBoolean(String,boolean)}.
*
* This implementation translates 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 null.
* @throws IllegalArgumentException if key.length() exceeds
* MAX_KEY_LENGTH.
* @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 getBoolean method as per the specification in
* {@link Preferences#getBoolean(String,boolean)}.
*
* This implementation invokes {@link #get(String,String) get(key,
* null)}. If the return value is non-null, it is compared with
* "true" using {@link String#equalsIgnoreCase(String)}. If the
* comparison returns true, this invocation returns
* true. Otherwise, the original return value is compared with
* "false", again using {@link String#equalsIgnoreCase(String)}.
* If the comparison returns true, this invocation returns
* false. Otherwise, this invocation returns 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 key
* or the associated value cannot be interpreted as a boolean.
* @return the boolean value represented by the string associated with
* key in this preference node, or 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 key is null.
*/
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 putFloat method as per the specification in
* {@link Preferences#putFloat(String,float)}.
*
* This implementation translates 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 null.
* @throws IllegalArgumentException if key.length() exceeds
* MAX_KEY_LENGTH.
* @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 getFloat method as per the specification in
* {@link Preferences#getFloat(String,float)}.
*
* 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 float with
* {@link Float#parseFloat(String)}. If the attempt succeeds, the return
* value is returned by this method. Otherwise, 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 key
* or the associated value cannot be interpreted as a float.
* @return the float value represented by the string associated with
* key in this preference node, or 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 key is null.
*/
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 putDouble method as per the specification in
* {@link Preferences#putDouble(String,double)}.
*
* This implementation translates 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 null.
* @throws IllegalArgumentException if key.length() exceeds
* MAX_KEY_LENGTH.
* @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 getDouble method as per the specification in
* {@link Preferences#getDouble(String,double)}.
*
* 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 double with
* {@link Double#parseDouble(String)}. If the attempt succeeds, the return
* value is returned by this method. Otherwise, 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 key
* or the associated value cannot be interpreted as a double.
* @return the double value represented by the string associated with
* key in this preference node, or 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 key is null.
*/
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 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 null.
* @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 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 key
* or the associated value cannot be interpreted as a byte array.
* @return the byte array value represented by the string associated with
* key in this preference node, or 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 key is null. (A
* null value for def is 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 keys method as per the specification in
* {@link Preferences#keys()}.
*
* 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 children method as per the specification in
* {@link Preferences#childrenNames()}.
*
* This implementation obtains this preference node's lock, checks that
* the node has not been removed, constructs a 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 String array using the 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 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 node method as per the specification in
* {@link Preferences#node(String)}.
*
* This implementation obtains this preference node's lock and checks
* that the node has not been removed. If path is "",
* this node is returned; if path is "/", this node's
* root is returned. If the first character in path is
* not '/', the implementation breaks path into
* tokens and recursively traverses the path from this node to the
* named node, "consuming" a name and a slash from 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 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 Preferences object's {@link #newNode}
* field is true and there are any node change listeners,
* a notification event is enqueued for processing by the event dispatch
* thread.
*
* When there are no more tokens, the last value found in the
* child-cache or returned by childSpi is returned by this
* method. If during the traversal, two "/" tokens occur
* consecutively, or the final token is "/" (rather than a name),
* an appropriate IllegalArgumentException is thrown.
*
* If the first character of path is '/'
* (indicating an absolute path name) this preference node's
* lock is dropped prior to breaking 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.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 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
* pathname is not the empty string ("").
*/
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 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 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.
*
* 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 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 absolutePath method as per the specification in
* {@link Preferences#absolutePath()}.
*
* 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 isUserNode method as per the specification in
* {@link Preferences#isUserNode()}.
*
* 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 true if this preference node is in the user
* preference tree, false if it's in the system
* preference tree.
*/
public boolean isUserNode() {
return AccessController.doPrivileged(
new PrivilegedAction This method is invoked with the lock on this node held.
*/
protected abstract void putSpi(String key, String value);
/**
* Return the value associated with the specified key at this preference
* node, or null if there is no association for this key, or the
* association cannot be determined at this time. It is guaranteed that
* 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.)
*
* 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 null
* return value.
*
* This method is invoked with the lock on this node held.
*
* @return the value associated with the specified key at this preference
* node, or 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 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.)
*
* This method is invoked with the lock on this node held.
*/
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).
*
* 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()}).
*
* The removal of a node needn't become persistent until the
* flush method is invoked on this node (or an ancestor).
*
* If this node throws a 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.
*
* This method is invoked with the lock on this node held.
*
* If this node throws a 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.
*
* This method is invoked with the lock on this node held.
*
* If this node throws a 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 null if it does not.
* It is guaranteed that 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.)
*
* 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.)
*
* 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, 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 (int i=0; i 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.
*
* 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 AbstractPreferences
* node; once removed, an AbstractPreferences node
* cannot be "resuscitated."
*
* If this method causes a node to be created, this node is not
* guaranteed to be persistent until the flush method is
* invoked on this node or one of its ancestors (or descendants).
*
* 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 sync method as per the specification in
* {@link Preferences#sync()}.
*
* 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 If this node throws a 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 flush method as per the specification in
* {@link Preferences#flush()}.
*
* 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.
*
* 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 not
* 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.
*
* If this node throws a 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 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 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