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java.util.prefs

Class Preferences

java.lang.Object
|
+--java.util.prefs.Preferences


public abstract class Preferences

extends Object

Preference node containing key value entries and subnodes.

There are two preference node trees, a system tree which can be accessed by calling systemRoot() containing system preferences usefull for all users, and a user tree that can be accessed by calling userRoot() containing preferences that can differ between different users. How different users are identified is implementation depended. It can be determined by Thread, Access Control Context or Subject.

This implementation uses the "java.util.prefs.PreferencesFactory" system property to find a class that implement PreferencesFactory and initialized that class (if it has a public no arguments contructor) to get at the actual system or user root. If the system property is not set, or the class cannot be initialized it uses the default implementation gnu.java.util.prefs.FileBasedFactory.

Besides the two static method above to get the roots of the system and user preference node trees there are also two convenience methods to access the default preference node for a particular package an object is in. These are userNodeForPackage() and systemNodeForPackage(). Both methods take an Object as an argument so accessing preferences values can be as easy as calling Preferences.userNodeForPackage(this).

Note that if a security manager is installed all static methods check for RuntimePermission("preferences"). But if this permission is given to the code then it can access and change all (user) preference nodes and entries. So you should be carefull not to store to sensitive information or make security decissions based on preference values since there is no more fine grained control over what preference values can be changed once code has been given the correct runtime permission.

XXX

Since:Author:

Field Summary

static intMAX_KEY_LENGTH

Maximum entry key length.
static intMAX_NAME_LENGTH

Maximum node name length.
static intMAX_VALUE_LENGTH

Maximum entry value length.

Constructor Summary

Preferences()

Creates a new Preferences node.

Method Summary

java.lang.StringabsolutePath()

Returns the absolute path name of this preference node.
voidaddNodeChangeListener(java.util.prefs.NodeChangeListener listener)

voidaddPreferenceChangeListener(java.util.prefs.PreferenceChangeListener listener)

java.lang.String[]childrenNames()

Returns all the direct sub nodes of this preferences node.
voidclear()

Removes all entries from this preferences node.
voidexportNode(java.io.OutputStream os)

XXX
voidexportSubtree(java.io.OutputStream os)

XXX
voidflush()

Writes all preference changes on this and any subnode that have not yet been written to the backing store.
java.lang.Stringget(java.lang.String key, java.lang.String defaultVal)

Returns the value associated with the key in this preferences node.
booleangetBoolean(java.lang.String key, boolean defaultVal)

Convenience method for getting the given entry as a boolean.
byte[]getByteArray(java.lang.String key, byte[] defaultVal)

Convenience method for getting the given entry as a byte array.
doublegetDouble(java.lang.String key, double defaultVal)

Convenience method for getting the given entry as a double.
floatgetFloat(java.lang.String key, float defaultVal)

Convenience method for getting the given entry as a float.
intgetInt(java.lang.String key, int defaultVal)

Convenience method for getting the given entry as an integer.
longgetLong(java.lang.String key, long defaultVal)

Convenience method for getting the given entry as a long.
static voidimportPreferences(java.io.InputStream is)

XXX
booleanisUserNode()

Returns true if this node comes from the user preferences tree, false if it comes from the system preferences tree.
java.lang.String[]keys()

Returns an (possibly empty) array with all the keys of the preference entries of this node.
java.lang.Stringname()

Returns the name of this preferences node.
java.util.prefs.Preferencesnode(java.lang.String path)

Returns a sub node of this preferences node if the given path is relative (does not start with a '/') or a sub node of the root if the path is absolute (does start with a '/').
booleannodeExists(java.lang.String path)

Returns true if the node that the path points to exists in memory or in the backing store.
java.util.prefs.Preferencesparent()

Returns the parent preferences node of this node or null if this is the root of the preferences tree.
voidput(java.lang.String key, java.lang.String value)

Sets the value of the given preferences entry for this node.
voidputBoolean(java.lang.String key, boolean value)

Convenience method for setting the given entry as a boolean.
voidputByteArray(java.lang.String key, byte[] value)

Convenience method for setting the given entry as an array of bytes.
voidputDouble(java.lang.String key, double value)

Convenience method for setting the given entry as a double.
voidputFloat(java.lang.String key, float value)

Convenience method for setting the given entry as a float.
voidputInt(java.lang.String key, int value)

Convenience method for setting the given entry as an integer.
voidputLong(java.lang.String key, long value)

Convenience method for setting the given entry as a long.
voidremove(java.lang.String key)

Removes the preferences entry from this preferences node.
voidremoveNode()

Removes this and all subnodes from the backing store and clears all entries.
voidremoveNodeChangeListener(java.util.prefs.NodeChangeListener listener)

voidremovePreferenceChangeListener(java.util.prefs.PreferenceChangeListener listener)

voidsync()

Writes and reads all preference changes to and from this and any subnodes.
static java.util.prefs.PreferencessystemNodeForPackage(java.lang.Object o)

Returns the system preferences node for the package of an object.
static java.util.prefs.PreferencessystemRoot()

Returns the system preferences root node containing usefull preferences for all users.
java.lang.StringtoString()

Returns the String given by (isUserNode() ? "User":"System") + " Preference Node: " + absolutePath()
static java.util.prefs.PreferencesuserNodeForPackage(java.lang.Object o)

Returns the user preferences node for the package of an object.
static java.util.prefs.PreferencesuserRoot()

Returns the user preferences root node containing preferences for the the current user.

Field Details

MAX_KEY_LENGTH

public static final int MAX_KEY_LENGTH

Maximum entry key length. 80 characters.


MAX_NAME_LENGTH

public static final int MAX_NAME_LENGTH

Maximum node name length. 80 characters.


MAX_VALUE_LENGTH

public static final int MAX_VALUE_LENGTH

Maximum entry value length. 8192 characters.


Constructor Details

Preferences

protected Preferences()

Creates a new Preferences node. Can only be used by subclasses. Empty implementation.


Method Details

absolutePath

public String absolutePath()

Returns the absolute path name of this preference node. The absolute path name of a node is the path name of its parent node plus a '/' plus its own name. If the node is the root node and has no parent then its name is "" and its absolute path name is "/".


addNodeChangeListener

public void addNodeChangeListener(java.util.prefs.NodeChangeListener listener)

Parameters:


addPreferenceChangeListener

public void addPreferenceChangeListener(java.util.prefs.PreferenceChangeListener listener)

Parameters:


childrenNames

public String[] childrenNames()

Returns all the direct sub nodes of this preferences node. Needs access to the backing store to give a meaningfull answer.

Throws:


clear

public void clear()

Removes all entries from this preferences node. May need access to the backing store to get and clear all entries.

The result will be immediatly visible in this VM, but may not be immediatly written to the backing store.

Throws:


exportNode

public void exportNode(java.io.OutputStream os)

XXX

Parameters:


exportSubtree

public void exportSubtree(java.io.OutputStream os)

XXX

Parameters:


flush

public void flush()

Writes all preference changes on this and any subnode that have not yet been written to the backing store. This has no effect on the preference entries in this VM, but it makes sure that all changes are visible to other programs (other VMs might need to call the sync() method to actually see the changes to the backing store.

Throws:


get

public String get(java.lang.String key, java.lang.String defaultVal)

Returns the value associated with the key in this preferences node. If the default value of the key cannot be found in the preferences node entries or something goes wrong with the backing store the supplied default value is returned.

Parameters:

Throws:


getBoolean

public boolean getBoolean(java.lang.String key, boolean defaultVal)

Convenience method for getting the given entry as a boolean. When the string representation of the requested entry is either "true" or "false" (ignoring case) then that value is returned, otherwise the given default boolean value is returned.

Parameters:

Throws:


getByteArray

public byte[] getByteArray(java.lang.String key, byte[] defaultVal)

Convenience method for getting the given entry as a byte array. When the string representation of the requested entry is a valid Base64 encoded string (without any other characters, such as newlines) then the decoded Base64 string is returned as byte array, otherwise the given default byte array value is returned.

Parameters:

Throws:


getDouble

public double getDouble(java.lang.String key, double defaultVal)

Convenience method for getting the given entry as a double. When the string representation of the requested entry can be decoded with Double.parseDouble() then that double is returned, otherwise the given default double value is returned.

Parameters:

Throws:


getFloat

public float getFloat(java.lang.String key, float defaultVal)

Convenience method for getting the given entry as a float. When the string representation of the requested entry can be decoded with Float.parseFloat() then that float is returned, otherwise the given default float value is returned.

Parameters:

Throws:


getInt

public int getInt(java.lang.String key, int defaultVal)

Convenience method for getting the given entry as an integer. When the string representation of the requested entry can be decoded with Integer.parseInt() then that integer is returned, otherwise the given default integer value is returned.

Parameters:

Throws:


getLong

public long getLong(java.lang.String key, long defaultVal)

Convenience method for getting the given entry as a long. When the string representation of the requested entry can be decoded with Long.parseLong() then that long is returned, otherwise the given default long value is returned.

Parameters:

Throws:


importPreferences

public static void importPreferences(java.io.InputStream is)

XXX

Parameters:


isUserNode

public boolean isUserNode()

Returns true if this node comes from the user preferences tree, false if it comes from the system preferences tree.


keys

public String[] keys()

Returns an (possibly empty) array with all the keys of the preference entries of this node.

Throws:


name

public String name()

Returns the name of this preferences node. The name of the node cannot be null, can be mostly 80 characters and cannot contain any '/' characters. The root node has as name "".


node

public Preferences node(java.lang.String path)

Returns a sub node of this preferences node if the given path is relative (does not start with a '/') or a sub node of the root if the path is absolute (does start with a '/').

Parameters:

Throws:


nodeExists

public boolean nodeExists(java.lang.String path)

Returns true if the node that the path points to exists in memory or in the backing store. Otherwise it returns false or an exception is thrown. When this node is removed the only valid parameter is the empty string (indicating this node), the return value in that case will be false.

Parameters:

Throws:


parent

public Preferences parent()

Returns the parent preferences node of this node or null if this is the root of the preferences tree.

Throws:


put

public void put(java.lang.String key, java.lang.String value)

Sets the value of the given preferences entry for this node. Key and value cannot be null, the key cannot exceed 80 characters and the value cannot exceed 8192 characters.

The result will be immediatly visible in this VM, but may not be immediatly written to the backing store.

Parameters:

Throws:


putBoolean

public void putBoolean(java.lang.String key, boolean value)

Convenience method for setting the given entry as a boolean. The boolean is converted with Boolean.toString(value) and then stored in the preference entry as that string.

Parameters:

Throws:


putByteArray

public void putByteArray(java.lang.String key, byte[] value)

Convenience method for setting the given entry as an array of bytes. The byte array is converted to a Base64 encoded string and then stored in the preference entry as that string.

Note that a byte array encoded as a Base64 string will be about 1.3 times larger then the original length of the byte array, which means that the byte array may not be larger about 6 KB.

Parameters:

Throws:


putDouble

public void putDouble(java.lang.String key, double value)

Convenience method for setting the given entry as a double. The double is converted with Double.toString(double) and then stored in the preference entry as that string.

Parameters:

Throws:


putFloat

public void putFloat(java.lang.String key, float value)

Convenience method for setting the given entry as a float. The float is converted with Float.toString(float) and then stored in the preference entry as that string.

Parameters:

Throws:


putInt

public void putInt(java.lang.String key, int value)

Convenience method for setting the given entry as an integer. The integer is converted with Integer.toString(int) and then stored in the preference entry as that string.

Parameters:

Throws:


putLong

public void putLong(java.lang.String key, long value)

Convenience method for setting the given entry as a long. The long is converted with Long.toString(long) and then stored in the preference entry as that string.

Parameters:

Throws:


remove

public void remove(java.lang.String key)

Removes the preferences entry from this preferences node.

The result will be immediatly visible in this VM, but may not be immediatly written to the backing store.

Parameters:

Throws:


removeNode

public void removeNode()

Removes this and all subnodes from the backing store and clears all entries. After removal this instance will not be useable (except for a few methods that don't throw a InvalidStateException), even when a new node with the same path name is created this instance will not be usable again. The root (system or user) may never be removed.

Note that according to the specification an implementation may delay removal of the node from the backing store till the flush() method is called. But the flush() method may throw a IllegalStateException when the node has been removed. So most implementations will actually remove the node and any subnodes from the backing store immediatly.

Throws:


removeNodeChangeListener

public void removeNodeChangeListener(java.util.prefs.NodeChangeListener listener)

Parameters:


removePreferenceChangeListener

public void removePreferenceChangeListener(java.util.prefs.PreferenceChangeListener listener)

Parameters:


sync

public void sync()

Writes and reads all preference changes to and from this and any subnodes. This makes sure that all local changes are written to the backing store and that all changes to the backing store are visible in this preference node (and all subnodes).

Throws:


systemNodeForPackage

public static Preferences systemNodeForPackage(java.lang.Object o)

Returns the system preferences node for the package of an object. The package node name of the object is determined by dropping the class name of the object of the fully quallified class name and replacing all '.' to '/' in the package name. If the class of the object has no package then the package node name is "". The returened node is systemRoot().node(packageNodeName).

Parameters:

Throws:


systemRoot

public static Preferences systemRoot()

Returns the system preferences root node containing usefull preferences for all users. It is save to cache this value since it should always return the same preference node.

Returns:

Throws:


toString

public String toString()

Returns the String given by (isUserNode() ? "User":"System") + " Preference Node: " + absolutePath()


userNodeForPackage

public static Preferences userNodeForPackage(java.lang.Object o)

Returns the user preferences node for the package of an object. The package node name of the object is determined by dropping the class name of the object of the fully quallified class name and replacing all '.' to '/' in the package name. If the class of the object has no package then the package node name is "". The returened node is userRoot().node(packageNodeName).

Parameters:

Throws:


userRoot

public static Preferences userRoot()

Returns the user preferences root node containing preferences for the the current user. How different users are identified is implementation depended. It can be determined by Thread, Access Control Context or Subject.

Returns:

Throws: