Class AbstractPreferences
- java.lang.Object
-
- java.util.prefs.Preferences
-
- java.util.prefs.AbstractPreferences
public abstract class AbstractPreferences extends Preferences
This class provides a skeletal implementation of the Preferences
class, greatly easing the task of implementing it.
This class is for Preferences
implementers only. Normal users of the Preferences
facility should have no need to consult this documentation. The Preferences
documentation should suffice.
Implementors must override the nine abstract service-provider interface (SPI) methods: getSpi(String)
, putSpi(String,String)
, removeSpi(String)
, childSpi(String)
, removeNodeSpi()
, keysSpi()
, childrenNamesSpi()
, syncSpi()
and 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 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 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 putSpi(String,String)
, removeSpi(String)
and 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 Preferences.flush()
or Preferences.sync()
. Generally speaking, these SPI methods should not throw exceptions. In some implementations, there may be circumstances under which these calls cannot even enqueue the requested operation for later processing. Even under these circumstances it is generally better to simply ignore the invocation and return, rather than throwing an exception. Under these circumstances, however, subsequently invoking flush()
or sync
would not 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 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 ThreadLocal
instance. Authors of such implementations are strongly encouraged to determine the user at the time preferences are accessed (for example by the get(String,String)
or 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.
- Since:
- 1.4
- See Also:
Preferences
Field Summary
Modifier and Type | Field | Description |
---|---|---|
protected Object | lock | An object whose monitor is used to lock this node. |
protected boolean | newNode | This field should be |
Fields declared in class java.util.prefs.Preferences
MAX_KEY_LENGTH, MAX_NAME_LENGTH, MAX_VALUE_LENGTH
Constructor Summary
Modifier | Constructor | Description |
---|---|---|
protected | AbstractPreferences(AbstractPreferences parent,
String name) | Creates a preference node with the specified parent and the specified name relative to its parent. |
Method Summary
Modifier and Type | Method | Description |
---|---|---|
String | absolutePath() | Implements the |
protected AbstractPreferences[] | cachedChildren() | Returns all known unremoved children of this node. |
String[] | childrenNames() | Implements the |
protected abstract String[] | childrenNamesSpi() | Returns the names of the children of this preference node. |
protected abstract AbstractPreferences | childSpi(String name) | Returns the named child of this preference node, creating it if it does not already exist. |
void | clear() | Implements the |
void | exportNode(OutputStream os) | Implements the |
void | exportSubtree(OutputStream os) | Implements the |
void | flush() | Implements the |
protected abstract void | flushSpi() | This method is invoked with this node locked. |
String | get(String key,
String def) | Implements the |
boolean | getBoolean(String key,
boolean def) | Implements the |
byte[] | getByteArray(String key,
byte[] def) | Implements the |
protected AbstractPreferences | getChild(String nodeName) | Returns the named child if it exists, or |
double | getDouble(String key,
double def) | Implements the |
float | getFloat(String key,
float def) | Implements the |
int | getInt(String key,
int def) | Implements the |
long | getLong(String key,
long def) | Implements the |
protected abstract String | getSpi(String key) | Return the value associated with the specified key at this preference node, or |
protected boolean | isRemoved() | Returns |
boolean | isUserNode() | Implements the |
String[] | keys() | Implements the |
protected abstract String[] | keysSpi() | Returns all of the keys that have an associated value in this preference node. |
String | name() | Implements the |
Preferences | node(String path) | Implements the |
boolean | nodeExists(String path) | Implements the |
Preferences | parent() | Implements the |
void | put(String key,
String value) | Implements the |
void | putBoolean(String key,
boolean value) | Implements the |
void | putByteArray(String key,
byte[] value) | Implements the |
void | putDouble(String key,
double value) | Implements the |
void | putFloat(String key,
float value) | Implements the |
void | putInt(String key,
int value) | Implements the |
void | putLong(String key,
long value) | Implements the |
protected abstract void | putSpi(String key,
String value) | Put the given key-value association into this preference node. |
void | remove(String key) | Implements the |
void | removeNode() | Implements the |
protected abstract void | removeNodeSpi() | Removes this preference node, invalidating it and any preferences that it contains. |
protected abstract void | removeSpi(String key) | Remove the association (if any) for the specified key at this preference node. |
void | sync() | Implements the |
protected abstract void | syncSpi() | This method is invoked with this node locked. |
String | toString() | Returns the absolute path name of this preferences node. |
Methods declared in class java.util.prefs.Preferences
addNodeChangeListener, addPreferenceChangeListener, importPreferences, removeNodeChangeListener, removePreferenceChangeListener, systemNodeForPackage, systemRoot, userNodeForPackage, userRoot
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
Field Detail
newNode
protected boolean newNode
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.
lock
protected final Object lock
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 never locked by a thread that holds a lock on a descendant of that node.
Constructor Detail
AbstractPreferences
protected AbstractPreferences(AbstractPreferences parent, String name)
Creates a preference node with the specified parent and the specified name relative to its parent.
- Parameters:
-
parent
- the parent of this preference node, or null if this is the root. -
name
- the name of this preference node, relative to its parent, or""
if this is the root. - Throws:
-
IllegalArgumentException
- ifname
contains a slash ('/'
), orparent
isnull
and name isn't""
.
Method Detail
put
public void put(String key, String value)
Implements the put
method as per the specification in Preferences.put(String,String)
.
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 putSpi(String,String)
, and if there are any preference change listeners, enqueues a notification event for processing by the event dispatch thread.
- Specified by:
-
put
in classPreferences
- Parameters:
-
key
- key with which the specified value is to be associated. -
value
- value to be associated with the specified key. - Throws:
-
NullPointerException
- if key or value isnull
. -
IllegalArgumentException
- ifkey.length()
exceedsMAX_KEY_LENGTH
or ifvalue.length
exceedsMAX_VALUE_LENGTH
. -
IllegalArgumentException
- if either key or value contain the null control character, code point U+0000. -
IllegalStateException
- if this node (or an ancestor) has been removed with theremoveNode()
method.
get
public String get(String key, String def)
Implements the get
method as per the specification in 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 getSpi(String)
, and returns the result, unless the getSpi
invocation returns null
or throws an exception, in which case this invocation returns def
.
- Specified by:
-
get
in classPreferences
- Parameters:
-
key
- key whose associated value is to be returned. -
def
- the value to be returned in the event that this preference node has no value associated withkey
. - Returns:
- the value associated with
key
, ordef
if no value is associated withkey
. - Throws:
-
IllegalStateException
- if this node (or an ancestor) has been removed with theremoveNode()
method. -
NullPointerException
- if key isnull
. (Anull
default is permitted.) -
IllegalArgumentException
- if key contains the null control character, code point U+0000.
remove
public void remove(String key)
Implements the remove(String)
method as per the specification in Preferences.remove(String)
.
This implementation obtains this preference node's lock, checks that the node has not been removed, invokes removeSpi(String)
and if there are any preference change listeners, enqueues a notification event for processing by the event dispatch thread.
- Specified by:
-
remove
in classPreferences
- Parameters:
-
key
- key whose mapping is to be removed from the preference node. - Throws:
-
IllegalStateException
- if this node (or an ancestor) has been removed with theremoveNode()
method. -
IllegalArgumentException
- if key contains the null control character, code point U+0000. -
NullPointerException
- ifkey
isnull
..
clear
public void clear() throws BackingStoreException
Implements the clear
method as per the specification in Preferences.clear()
.
This implementation obtains this preference node's lock, invokes keys()
to obtain an array of keys, and iterates over the array invoking remove(String)
on each key.
- Specified by:
-
clear
in classPreferences
- Throws:
-
BackingStoreException
- if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it. -
IllegalStateException
- if this node (or an ancestor) has been removed with theremoveNode()
method. - See Also:
Preferences.removeNode()
putInt
public void putInt(String key, int value)
Implements the putInt
method as per the specification in Preferences.putInt(String,int)
.
This implementation translates value
to a string with Integer.toString(int)
and invokes put(String,String)
on the result.
- Specified by:
-
putInt
in classPreferences
- Parameters:
-
key
- key with which the string form of value is to be associated. -
value
- value whose string form is to be associated with key. - Throws:
-
NullPointerException
- if key isnull
. -
IllegalArgumentException
- ifkey.length()
exceedsMAX_KEY_LENGTH
. -
IllegalArgumentException
- if key contains the null control character, code point U+0000. -
IllegalStateException
- if this node (or an ancestor) has been removed with theremoveNode()
method. - See Also:
Preferences.getInt(String,int)
getInt
public int getInt(String key, int def)
Implements the getInt
method as per the specification in Preferences.getInt(String,int)
.
This implementation invokes get(key,
null)
. If the return value is non-null, the implementation attempts to translate it to an int
with Integer.parseInt(String)
. If the attempt succeeds, the return value is returned by this method. Otherwise, def
is returned.
- Specified by:
-
getInt
in classPreferences
- Parameters:
-
key
- key whose associated value is to be returned as an int. -
def
- the value to be returned in the event that this preference node has no value associated withkey
or the associated value cannot be interpreted as an int. - Returns:
- the int value represented by the string associated with
key
in this preference node, ordef
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 theremoveNode()
method. -
NullPointerException
- ifkey
isnull
. -
IllegalArgumentException
- if key contains the null control character, code point U+0000. - See Also:
-
Preferences.putInt(String,int)
,Preferences.get(String,String)
putLong
public void putLong(String key, long value)
Implements the putLong
method as per the specification in Preferences.putLong(String,long)
.
This implementation translates value
to a string with Long.toString(long)
and invokes put(String,String)
on the result.
- Specified by:
-
putLong
in classPreferences
- Parameters:
-
key
- key with which the string form of value is to be associated. -
value
- value whose string form is to be associated with key. - Throws:
-
NullPointerException
- if key isnull
. -
IllegalArgumentException
- ifkey.length()
exceedsMAX_KEY_LENGTH
. -
IllegalArgumentException
- if key contains the null control character, code point U+0000. -
IllegalStateException
- if this node (or an ancestor) has been removed with theremoveNode()
method. - See Also:
Preferences.getLong(String,long)
getLong
public long getLong(String key, long def)
Implements the getLong
method as per the specification in Preferences.getLong(String,long)
.
This implementation invokes get(key,
null)
. If the return value is non-null, the implementation attempts to translate it to a long
with Long.parseLong(String)
. If the attempt succeeds, the return value is returned by this method. Otherwise, def
is returned.
- Specified by:
-
getLong
in classPreferences
- Parameters:
-
key
- key whose associated value is to be returned as a long. -
def
- the value to be returned in the event that this preference node has no value associated withkey
or the associated value cannot be interpreted as a long. - Returns:
- the long value represented by the string associated with
key
in this preference node, ordef
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 theremoveNode()
method. -
NullPointerException
- ifkey
isnull
. -
IllegalArgumentException
- if key contains the null control character, code point U+0000. - See Also:
-
Preferences.putLong(String,long)
,Preferences.get(String,String)
putBoolean
public void putBoolean(String key, boolean value)
Implements the putBoolean
method as per the specification in Preferences.putBoolean(String,boolean)
.
This implementation translates value
to a string with String.valueOf(boolean)
and invokes put(String,String)
on the result.
- Specified by:
-
putBoolean
in classPreferences
- Parameters:
-
key
- key with which the string form of value is to be associated. -
value
- value whose string form is to be associated with key. - Throws:
-
NullPointerException
- if key isnull
. -
IllegalArgumentException
- ifkey.length()
exceedsMAX_KEY_LENGTH
. -
IllegalArgumentException
- if key contains the null control character, code point U+0000. -
IllegalStateException
- if this node (or an ancestor) has been removed with theremoveNode()
method. - See Also:
-
Preferences.getBoolean(String,boolean)
,Preferences.get(String,String)
getBoolean
public boolean getBoolean(String key, boolean def)
Implements the getBoolean
method as per the specification in Preferences.getBoolean(String,boolean)
.
This implementation invokes get(key,
null)
. If the return value is non-null, it is compared with "true"
using String.equalsIgnoreCase(String)
. If the comparison returns true
, this invocation returns true
. Otherwise, the original return value is compared with "false"
, again using String.equalsIgnoreCase(String)
. If the comparison returns true
, this invocation returns false
. Otherwise, this invocation returns def
.
- Specified by:
-
getBoolean
in classPreferences
- Parameters:
-
key
- key whose associated value is to be returned as a boolean. -
def
- the value to be returned in the event that this preference node has no value associated withkey
or the associated value cannot be interpreted as a boolean. - Returns:
- the boolean value represented by the string associated with
key
in this preference node, ordef
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 theremoveNode()
method. -
NullPointerException
- ifkey
isnull
. -
IllegalArgumentException
- if key contains the null control character, code point U+0000. - See Also:
-
Preferences.get(String,String)
,Preferences.putBoolean(String,boolean)
putFloat
public void putFloat(String key, float value)
Implements the putFloat
method as per the specification in Preferences.putFloat(String,float)
.
This implementation translates value
to a string with Float.toString(float)
and invokes put(String,String)
on the result.
- Specified by:
-
putFloat
in classPreferences
- Parameters:
-
key
- key with which the string form of value is to be associated. -
value
- value whose string form is to be associated with key. - Throws:
-
NullPointerException
- if key isnull
. -
IllegalArgumentException
- ifkey.length()
exceedsMAX_KEY_LENGTH
. -
IllegalArgumentException
- if key contains the null control character, code point U+0000. -
IllegalStateException
- if this node (or an ancestor) has been removed with theremoveNode()
method. - See Also:
Preferences.getFloat(String,float)
getFloat
public float getFloat(String key, float def)
Implements the getFloat
method as per the specification in Preferences.getFloat(String,float)
.
This implementation invokes get(key,
null)
. If the return value is non-null, the implementation attempts to translate it to an float
with Float.parseFloat(String)
. If the attempt succeeds, the return value is returned by this method. Otherwise, def
is returned.
- Specified by:
-
getFloat
in classPreferences
- Parameters:
-
key
- key whose associated value is to be returned as a float. -
def
- the value to be returned in the event that this preference node has no value associated withkey
or the associated value cannot be interpreted as a float. - Returns:
- the float value represented by the string associated with
key
in this preference node, ordef
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 theremoveNode()
method. -
NullPointerException
- ifkey
isnull
. -
IllegalArgumentException
- if key contains the null control character, code point U+0000. - See Also:
-
Preferences.putFloat(String,float)
,Preferences.get(String,String)
putDouble
public void putDouble(String key, double value)
Implements the putDouble
method as per the specification in Preferences.putDouble(String,double)
.
This implementation translates value
to a string with Double.toString(double)
and invokes put(String,String)
on the result.
- Specified by:
-
putDouble
in classPreferences
- Parameters:
-
key
- key with which the string form of value is to be associated. -
value
- value whose string form is to be associated with key. - Throws:
-
NullPointerException
- if key isnull
. -
IllegalArgumentException
- ifkey.length()
exceedsMAX_KEY_LENGTH
. -
IllegalArgumentException
- if key contains the null control character, code point U+0000. -
IllegalStateException
- if this node (or an ancestor) has been removed with theremoveNode()
method. - See Also:
Preferences.getDouble(String,double)
getDouble
public double getDouble(String key, double def)
Implements the getDouble
method as per the specification in Preferences.getDouble(String,double)
.
This implementation invokes get(key,
null)
. If the return value is non-null, the implementation attempts to translate it to an double
with Double.parseDouble(String)
. If the attempt succeeds, the return value is returned by this method. Otherwise, def
is returned.
- Specified by:
-
getDouble
in classPreferences
- Parameters:
-
key
- key whose associated value is to be returned as a double. -
def
- the value to be returned in the event that this preference node has no value associated withkey
or the associated value cannot be interpreted as a double. - Returns:
- the double value represented by the string associated with
key
in this preference node, ordef
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 theremoveNode()
method. -
NullPointerException
- ifkey
isnull
. -
IllegalArgumentException
- if key contains the null control character, code point U+0000. - See Also:
-
Preferences.putDouble(String,double)
,Preferences.get(String,String)
putByteArray
public void putByteArray(String key, byte[] value)
Implements the putByteArray
method as per the specification in Preferences.putByteArray(String,byte[])
.
- Specified by:
-
putByteArray
in classPreferences
- Parameters:
-
key
- key with which the string form of value is to be associated. -
value
- value whose string form is to be associated with key. - Throws:
-
NullPointerException
- if key or value isnull
. -
IllegalArgumentException
- if key.length() exceeds MAX_KEY_LENGTH or if value.length exceeds MAX_VALUE_LENGTH*3/4. -
IllegalArgumentException
- if key contains the null control character, code point U+0000. -
IllegalStateException
- if this node (or an ancestor) has been removed with theremoveNode()
method. - See Also:
-
Preferences.getByteArray(String,byte[])
,Preferences.get(String,String)
getByteArray
public byte[] getByteArray(String key, byte[] def)
Implements the getByteArray
method as per the specification in Preferences.getByteArray(String,byte[])
.
- Specified by:
-
getByteArray
in classPreferences
- Parameters:
-
key
- key whose associated value is to be returned as a byte array. -
def
- the value to be returned in the event that this preference node has no value associated withkey
or the associated value cannot be interpreted as a byte array. - Returns:
- the byte array value represented by the string associated with
key
in this preference node, ordef
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 theremoveNode()
method. -
NullPointerException
- ifkey
isnull
. (Anull
value fordef
is permitted.) -
IllegalArgumentException
- if key contains the null control character, code point U+0000. - See Also:
-
Preferences.get(String,String)
,Preferences.putByteArray(String,byte[])
keys
public String[] keys() throws BackingStoreException
Implements the keys
method as per the specification in Preferences.keys()
.
This implementation obtains this preference node's lock, checks that the node has not been removed and invokes keysSpi()
.
- Specified by:
-
keys
in classPreferences
- Returns:
- 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. -
IllegalStateException
- if this node (or an ancestor) has been removed with theremoveNode()
method.
childrenNames
public String[] childrenNames() throws BackingStoreException
Implements the children
method as per the specification in 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 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.
- Specified by:
-
childrenNames
in classPreferences
- Returns:
- 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. -
IllegalStateException
- if this node (or an ancestor) has been removed with theremoveNode()
method. - See Also:
cachedChildren()
cachedChildren
protected final AbstractPreferences[] cachedChildren()
Returns all known unremoved children of this node.
- Returns:
- all known unremoved children of this node.
parent
public Preferences parent()
Implements the parent
method as per the specification in Preferences.parent()
.
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.
- Specified by:
-
parent
in classPreferences
- Returns:
- the parent of this preference node.
- Throws:
-
IllegalStateException
- if this node (or an ancestor) has been removed with theremoveNode()
method.
node
public Preferences node(String path)
Implements the node
method as per the specification in 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 childSpi(String)
method is invoked, and the result stored in this node's child-cache. If the newly created Preferences
object's 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 locking invariant
.
- Specified by:
-
node
in classPreferences
- Parameters:
-
path
- the path name of the preference node to return. - Returns:
- 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). -
IllegalStateException
- if this node (or an ancestor) has been removed with theremoveNode()
method. - See Also:
Preferences.flush()
nodeExists
public boolean nodeExists(String path) throws BackingStoreException
Implements the nodeExists
method as per the specification in Preferences.nodeExists(String)
.
This implementation is very similar to node(String)
, except that getChild(String)
is used instead of childSpi(String)
.
- Specified by:
-
nodeExists
in classPreferences
- Parameters:
-
path
- the path name of the node whose existence is to be checked. - Returns:
- 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. -
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). -
IllegalStateException
- if this node (or an ancestor) has been removed with theremoveNode()
method andpathname
is not the empty string (""
).
removeNode
public void removeNode() throws BackingStoreException
Implements the removeNode()
method as per the specification in Preferences.removeNode()
.
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 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 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 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.
- Specified by:
-
removeNode
in classPreferences
- Throws:
-
IllegalStateException
- if this node (or an ancestor) has already been removed with theremoveNode()
method. -
UnsupportedOperationException
- if this method is invoked on the root node. -
BackingStoreException
- if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it. - See Also:
Preferences.flush()
name
public String name()
Implements the name
method as per the specification in Preferences.name()
.
This implementation merely returns the name that was passed to this node's constructor.
- Specified by:
-
name
in classPreferences
- Returns:
- this preference node's name, relative to its parent.
absolutePath
public String absolutePath()
Implements the absolutePath
method as per the specification in 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).
- Specified by:
-
absolutePath
in classPreferences
- Returns:
- this preference node's absolute path name.
isUserNode
public boolean isUserNode()
Implements the isUserNode
method as per the specification in Preferences.isUserNode()
.
This implementation compares this node's root node (which is stored in a private field) with the value returned by Preferences.userRoot()
. If the two object references are identical, this method returns true.
- Specified by:
-
isUserNode
in classPreferences
- Returns:
-
true
if this preference node is in the user preference tree,false
if it's in the system preference tree.
putSpi
protected abstract void putSpi(String key, String value)
Put the given key-value association into this preference node. It is guaranteed that key
and value
are non-null and of legal length. Also, it is guaranteed that this node has not been removed. (The implementor needn't check for any of these things.)
This method is invoked with the lock on this node held.
- Parameters:
-
key
- the key -
value
- the value
getSpi
protected abstract String getSpi(String key)
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.
- Parameters:
-
key
- the key - Returns:
- 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.
removeSpi
protected abstract void removeSpi(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.
- Parameters:
-
key
- the key
removeNodeSpi
protected abstract void removeNodeSpi() throws BackingStoreException
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 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 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 removeNode()
invocation.
- Throws:
-
BackingStoreException
- if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it.
keysSpi
protected abstract String[] keysSpi() 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 keys()
invocation.
- Returns:
- 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.
childrenNamesSpi
protected abstract String[] childrenNamesSpi() 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 childrenNames()
invocation.
- Returns:
- 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.
getChild
protected AbstractPreferences getChild(String nodeName) 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 Preferences.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 childSpi(java.lang.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. (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 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 childSpi(String)
method is invoked and the resulting node is returned. If the iteration completes without finding the specified name, null
is returned.
- Parameters:
-
nodeName
- name of the child to be searched for. - Returns:
- 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.
childSpi
protected abstract AbstractPreferences childSpi(String name)
Returns the named child of this preference node, creating it if it does not already exist. It is guaranteed that name
is non-null, non-empty, does not contain the slash character ('/'), and is no longer than Preferences.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.)
Finally, it is guaranteed that the named node has not been returned by a previous invocation of this method or 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.
- Parameters:
-
name
- The name of the child node to return, relative to this preference node. - Returns:
- The named child node.
toString
public String toString()
Returns the absolute path name of this preferences node.
- Specified by:
-
toString
in classPreferences
- Returns:
- a string representation of the object.
sync
public void sync() throws BackingStoreException
Implements the sync
method as per the specification in 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.
- Specified by:
-
sync
in classPreferences
- Throws:
-
BackingStoreException
- if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it. -
IllegalStateException
- if this node (or an ancestor) has been removed with theremoveNode()
method. - See Also:
flush()
syncSpi
protected abstract void syncSpi() throws BackingStoreException
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 not 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.
If this node throws a BackingStoreException
, the exception will propagate out beyond the enclosing sync()
invocation.
- Throws:
-
BackingStoreException
- if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it.
flush
public void flush() throws BackingStoreException
Implements the flush
method as per the specification in 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 removeNode()
method, flushSpi() is invoked on this node, but not on others.
- Specified by:
-
flush
in classPreferences
- Throws:
-
BackingStoreException
- if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it. - See Also:
flush()
flushSpi
protected abstract void flushSpi() throws BackingStoreException
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 flush()
invocation.
- Throws:
-
BackingStoreException
- if this operation cannot be completed due to a failure in the backing store, or inability to communicate with it.
isRemoved
protected boolean isRemoved()
Returns true
iff this node (or an ancestor) has been removed with the removeNode()
method. This method locks this node prior to returning the contents of the private field used to track this state.
- Returns:
-
true
iff this node (or an ancestor) has been removed with theremoveNode()
method.
exportNode
public void exportNode(OutputStream os) throws IOException, BackingStoreException
Implements the exportNode
method as per the specification in Preferences.exportNode(OutputStream)
.
- Specified by:
-
exportNode
in classPreferences
- Parameters:
-
os
- the output stream on which to emit the XML document. - Throws:
-
IOException
- if writing to the specified output stream results in anIOException
. -
BackingStoreException
- if preference data cannot be read from backing store. - See Also:
Preferences.importPreferences(InputStream)
exportSubtree
public void exportSubtree(OutputStream os) throws IOException, BackingStoreException
Implements the exportSubtree
method as per the specification in Preferences.exportSubtree(OutputStream)
.
- Specified by:
-
exportSubtree
in classPreferences
- Parameters:
-
os
- the output stream on which to emit the XML document. - Throws:
-
IOException
- if writing to the specified output stream results in anIOException
. -
BackingStoreException
- if preference data cannot be read from backing store. - See Also:
-
Preferences.importPreferences(InputStream)
,Preferences.exportNode(OutputStream)