gcc/libjava/java/util/prefs/Preferences.java

/* Preferences -- Preference node containing key value entries and subnodes
   Copyright (C) 2001, 2004, 2005  Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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any later version.
 
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WITHOUT ANY WARRANTY; without even the implied warranty of
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02111-1307 USA.

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making a combined work based on this library.  Thus, the terms and
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permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
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terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
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exception statement from your version. */

package java.util.prefs;

import gnu.java.util.prefs.NodeReader;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.security.AccessController;
import java.security.Permission;
import java.security.PrivilegedAction;

/**
 * Preference node containing key value entries and subnodes.
 * <p>
 * There are two preference node trees, a system tree which can be accessed
 * by calling <code>systemRoot()</code> containing system preferences usefull
 * for all users, and a user tree that can be accessed by calling
 * <code>userRoot()</code> 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.
 * <p>
 * This implementation uses the "java.util.prefs.PreferencesFactory" system
 * property to find a class that implement <code>PreferencesFactory</code>
 * 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
 * <code>gnu.java.util.prefs.FileBasedFactory</code>.
 * <p>
 * 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
 * <code>userNodeForPackage()</code> and <code>systemNodeForPackage()</code>.
 * Both methods take an Object as an argument so accessing preferences values
 * can be as easy as calling <code>Preferences.userNodeForPackage(this)</code>.
 * <p>
 * Note that if a security manager is installed all static methods check for
 * <code>RuntimePermission("preferences")</code>. 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.
 * <p>
 * XXX
 *
 * @since 1.4
 * @author Mark Wielaard (mark@klomp.org)
 */
public abstract class Preferences {

    // Static Fields

    /**
     * Default PreferencesFactory class used when the system property
     * "java.util.prefs.PreferencesFactory" is not set.
	 * <p>
	 * XXX - Currently set to MemoryBasedFactory, should be changed
	 * when FileBasedPreferences backend works.
     */
    private static final String defaultFactoryClass
        = "gnu.java.util.prefs.MemoryBasedFactory";

    /** Permission needed to access system or user root. */
    private static final Permission prefsPermission
        = new RuntimePermission("preferences");

    /**
     * The preferences factory object that supplies the system and user root.
     * Set and returned by the getFactory() method.
     */
    private static PreferencesFactory factory;

    /** Maximum node name length. 80 characters. */
    public static final int MAX_NAME_LENGTH = 80;

    /** Maximum entry key length. 80 characters. */
    public static final int MAX_KEY_LENGTH = 80;

    /** Maximum entry value length. 8192 characters. */
    public static final int MAX_VALUE_LENGTH = 8192;

    // Constructors

    /**
     * Creates a new Preferences node. Can only be used by subclasses.
     * Empty implementation.
     */
    protected Preferences() {}

    // Static methods

    /**
     * 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.
     *
     * @return the root system preference node
     * @exception SecurityException when a security manager is installed and
     * the caller does not have <code>RuntimePermission("preferences")</code>.
     */
    public static Preferences systemRoot() throws SecurityException {
        // Get the preferences factory and check for permission
        PreferencesFactory factory = getFactory();

        return factory.systemRoot();
    }

    /**
     * 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.
     *
     * @return the root user preference node
     * @exception SecurityException when a security manager is installed and
     * the caller does not have <code>RuntimePermission("preferences")</code>.
     */
    public static Preferences userRoot() throws SecurityException {
        // Get the preferences factory and check for permission
        PreferencesFactory factory = getFactory();
        return factory.userRoot();
    }

    /**
     * Private helper method for <code>systemRoot()</code> and
     * <code>userRoot()</code>. Checks security permission and instantiates the
     * correct factory if it has not yet been set.
     * <p>
     * When the preferences factory has not yet been set this method first
     * tries to get the system propery "java.util.prefs.PreferencesFactory"
     * and tries to initializes that class. If the system property is not set
     * or initialization fails it returns an instance of the default factory
     * <code>gnu.java.util.prefs.FileBasedPreferencesFactory</code>.
     *
     * @return the preferences factory to use
     * @exception SecurityException when a security manager is installed and
     * the caller does not have <code>RuntimePermission("preferences")</code>.
     */
    private static PreferencesFactory getFactory() throws SecurityException {

        // First check for permission
        SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            sm.checkPermission(prefsPermission);
        }

        // Get the factory
        if (factory == null) {
            // Caller might not have enough permissions
            factory = (PreferencesFactory) AccessController.doPrivileged(
                        new PrivilegedAction() {
                            public Object run() {
                                PreferencesFactory pf = null;
                                String className = System.getProperty
                                    ("java.util.prefs.PreferencesFactory");
                                if (className != null) {
                                    try {
                                        Class fc = Class.forName(className);
                                        Object o = fc.newInstance();
                                        pf = (PreferencesFactory) o;
                                    } catch (ClassNotFoundException cnfe)
                                        {/*ignore*/}
                                    catch (InstantiationException ie)
                                        {/*ignore*/}
                                    catch (IllegalAccessException iae)
                                        {/*ignore*/}
                                    catch (ClassCastException cce)
                                        {/*ignore*/}
                                }
                                return pf;
                            }
                        });

            // Still no factory? Use our default.
            if (factory == null)
	      {
                try
		  {
                    Class cls = Class.forName (defaultFactoryClass);
                    factory = (PreferencesFactory) cls.newInstance();
                  }
		catch (Exception e)
		  {
                    throw new RuntimeException ("Couldn't load default factory"
                        + " '"+ defaultFactoryClass +"'");
                    // XXX - when using 1.4 compatible throwables add cause
                  }
              }

        }
	
        return factory;
    }

    /**
     * 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 "&lt;unnamed&gt;".
     * The returened node is <code>systemRoot().node(packageNodeName)</code>.
     *
     * @param o Object whose default system preference node is requested
     * @returns system preferences node that should be used by object o
     * @exception SecurityException when a security manager is installed and
     * the caller does not have <code>RuntimePermission("preferences")</code>.
     */
    public static Preferences systemNodeForPackage(Class c)
            throws SecurityException
    {
        return nodeForPackage(c, systemRoot());
    }

    /**
     * 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 "&lt;unnamed&gt;".
     * The returened node is <code>userRoot().node(packageNodeName)</code>.
     *
     * @param o Object whose default user preference node is requested
     * @returns user preferences node that should be used by object o
     * @exception SecurityException when a security manager is installed and
     * the caller does not have <code>RuntimePermission("preferences")</code>.
     */
    public static Preferences userNodeForPackage(Class c)
            throws SecurityException
    {
        return nodeForPackage(c, userRoot());
    }

    /**
     * Private helper method for <code>systemNodeForPackage()</code> and
     * <code>userNodeForPackage()</code>. Given the correct system or user
     * root it returns the correct Preference node for the package node name
     * of the given object.
     */
    private static Preferences nodeForPackage(Class c, Preferences root) {
        // Get the package path
        String className = c.getName();
        String packagePath;
        int index = className.lastIndexOf('.');
        if(index == -1) {
            packagePath = "<unnamed>";
        } else {
            packagePath = className.substring(0,index).replace('.','/');
        }

        return root.node(packagePath);
    }

    /**
     * XXX
     */
    public static void importPreferences(InputStream is) 
                                    throws InvalidPreferencesFormatException,
                                           IOException
    {
        PreferencesFactory factory = getFactory();
        NodeReader reader = new NodeReader(is, factory);
        reader.importPreferences();
    }

    // abstract methods (identification)

    /**
     * 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 "/".
     */
    public abstract String absolutePath();

    /**
     * Returns true if this node comes from the user preferences tree, false
     * if it comes from the system preferences tree.
     */
    public abstract boolean isUserNode();

    /**
     * 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 "".
     */
    public abstract String name();

    /**
     * Returns the String given by
     * <code>
     * (isUserNode() ? "User":"System") + " Preference Node: " + absolutePath()
     * </code>
     */
    public abstract String toString();

    // abstract methods (navigation)

    /**
     * Returns all the direct sub nodes of this preferences node.
     * Needs access to the backing store to give a meaningfull answer.
     *
     * @exception BackingStoreException when the backing store cannot be
     *            reached
     * @exception IllegalStateException when this node has been removed
     */
    public abstract String[] childrenNames() throws BackingStoreException;

    /**
     * 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 '/').
     *
     * @exception IllegalStateException if this node has been removed
     * @exception IllegalArgumentException if the path contains two or more
     * consecutive '/' characters, ends with a '/' charactor and is not the
     * string "/" (indicating the root node) or any name on the path is more
     * then 80 characters long
     */
    public abstract Preferences node(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.
     *
     * @exception BackingStoreException when the backing store cannot be
     *            reached
     * @exception IllegalStateException if this node has been removed
     *            and the path is not the empty string (indicating this node)
     * @exception IllegalArgumentException if the path contains two or more
     * consecutive '/' characters, ends with a '/' charactor and is not the
     * string "/" (indicating the root node) or any name on the path is more
     * then 80 characters long
     */
    public abstract boolean nodeExists(String path)
                                throws BackingStoreException;

    /**
     * Returns the parent preferences node of this node or null if this is
     * the root of the preferences tree.
     *
     * @exception IllegalStateException if this node has been removed
     */
    public abstract Preferences parent();

    // abstract methods (export)

    /**
     * XXX
     */
    public abstract void exportNode(OutputStream os)
                                throws BackingStoreException,
                                       IOException;

    /**
     * XXX
     */
    public abstract void exportSubtree(OutputStream os)
                                throws BackingStoreException,
                                       IOException;

    // abstract methods (preference entry manipulation)

    /**
     * Returns an (possibly empty) array with all the keys of the preference
     * entries of this node.
     *
     * @exception BackingStoreException when the backing store cannot be
     *            reached
     * @exception IllegalStateException if this node has been removed
     */
    public abstract String[] keys() throws BackingStoreException;

    /**
     * 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.
     *
     * @exception IllegalArgumentException if key is larger then 80 characters
     * @exception IllegalStateException if this node has been removed
     * @exception NullPointerException if key is null
     */
    public abstract String get(String key, String 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.
     *
     * @exception IllegalArgumentException if key is larger then 80 characters
     * @exception IllegalStateException if this node has been removed
     * @exception NullPointerException if key is null
     */
    public abstract boolean getBoolean(String key, boolean 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.
     *
     * @exception IllegalArgumentException if key is larger then 80 characters
     * @exception IllegalStateException if this node has been removed
     * @exception NullPointerException if key is null
     */
    public abstract byte[] getByteArray(String key, byte[] defaultVal);

    /**
     * Convenience method for getting the given entry as a double.
     * When the string representation of the requested entry can be decoded
     * with <code>Double.parseDouble()</code> then that double is returned,
     * otherwise the given default double value is returned.
     *
     * @exception IllegalArgumentException if key is larger then 80 characters
     * @exception IllegalStateException if this node has been removed
     * @exception NullPointerException if key is null
     */
    public abstract double getDouble(String key, double defaultVal);

    /**
     * Convenience method for getting the given entry as a float.
     * When the string representation of the requested entry can be decoded
     * with <code>Float.parseFloat()</code> then that float is returned,
     * otherwise the given default float value is returned.
     *
     * @exception IllegalArgumentException if key is larger then 80 characters
     * @exception IllegalStateException if this node has been removed
     * @exception NullPointerException if key is null
     */
    public abstract float getFloat(String key, float defaultVal);

    /**
     * Convenience method for getting the given entry as an integer.
     * When the string representation of the requested entry can be decoded
     * with <code>Integer.parseInt()</code> then that integer is returned,
     * otherwise the given default integer value is returned.
     *
     * @exception IllegalArgumentException if key is larger then 80 characters
     * @exception IllegalStateException if this node has been removed
     * @exception NullPointerException if key is null
     */
    public abstract int getInt(String key, int defaultVal);

    /**
     * Convenience method for getting the given entry as a long.
     * When the string representation of the requested entry can be decoded
     * with <code>Long.parseLong()</code> then that long is returned,
     * otherwise the given default long value is returned.
     *
     * @exception IllegalArgumentException if key is larger then 80 characters
     * @exception IllegalStateException if this node has been removed
     * @exception NullPointerException if key is null
     */
    public abstract long getLong(String key, long defaultVal);

    /**
     * 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.
     * <p>
     * The result will be immediatly visible in this VM, but may not be
     * immediatly written to the backing store.
     *
     * @exception NullPointerException if either key or value are null
     * @exception IllegalArgumentException if either key or value are to large
     * @exception IllegalStateException when this node has been removed
     */
    public abstract void put(String key, String value);

    /**
     * Convenience method for setting the given entry as a boolean.
     * The boolean is converted with <code>Boolean.toString(value)</code>
     * and then stored in the preference entry as that string.
     *
     * @exception NullPointerException if key is null
     * @exception IllegalArgumentException if the key length is to large
     * @exception IllegalStateException when this node has been removed
     */
    public abstract void putBoolean(String key, boolean 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.
     * <p>
     * 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.
     *
     * @exception NullPointerException if either key or value are null
     * @exception IllegalArgumentException if either key or value are to large
     * @exception IllegalStateException when this node has been removed
     */
    public abstract void putByteArray(String key, byte[] value);

    /**
     * Convenience method for setting the given entry as a double.
     * The double is converted with <code>Double.toString(double)</code>
     * and then stored in the preference entry as that string.
     *
     * @exception NullPointerException if the key is null
     * @exception IllegalArgumentException if the key length is to large
     * @exception IllegalStateException when this node has been removed
     */
    public abstract void putDouble(String key, double value);

    /**
     * Convenience method for setting the given entry as a float.
     * The float is converted with <code>Float.toString(float)</code>
     * and then stored in the preference entry as that string.
     *
     * @exception NullPointerException if the key is null
     * @exception IllegalArgumentException if the key length is to large
     * @exception IllegalStateException when this node has been removed
     */
    public abstract void putFloat(String key, float value);

    /**
     * Convenience method for setting the given entry as an integer.
     * The integer is converted with <code>Integer.toString(int)</code>
     * and then stored in the preference entry as that string.
     *
     * @exception NullPointerException if the key is null
     * @exception IllegalArgumentException if the key length is to large
     * @exception IllegalStateException when this node has been removed
     */
    public abstract void putInt(String key, int value);

    /**
     * Convenience method for setting the given entry as a long.
     * The long is converted with <code>Long.toString(long)</code>
     * and then stored in the preference entry as that string.
     *
     * @exception NullPointerException if the key is null
     * @exception IllegalArgumentException if the key length is to large
     * @exception IllegalStateException when this node has been removed
     */
    public abstract void putLong(String key, long value);

    /**
     * Removes the preferences entry from this preferences node.
     * <p>
     * The result will be immediatly visible in this VM, but may not be
     * immediatly written to the backing store.
     *
     * @exception NullPointerException if the key is null
     * @exception IllegalArgumentException if the key length is to large
     * @exception IllegalStateException when this node has been removed
     */
    public abstract void remove(String key);

    // abstract methods (preference node manipulation)

    /**
     * Removes all entries from this preferences node. May need access to the
     * backing store to get and clear all entries.
     * <p>
     * The result will be immediatly visible in this VM, but may not be
     * immediatly written to the backing store.
     *
     * @exception BackingStoreException when the backing store cannot be
     *            reached
     * @exception IllegalStateException if this node has been removed
     */
    public abstract void clear() throws BackingStoreException;

    /**
     * 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
     * <code>sync()</code> method to actually see the changes to the backing
     * store.
     *
     * @exception BackingStoreException when the backing store cannot be
     *            reached
     * @exception IllegalStateException if this node has been removed
     */
    public abstract void flush() throws BackingStoreException;

    /**
     * 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).
     *
     * @exception BackingStoreException when the backing store cannot be
     *            reached
     * @exception IllegalStateException if this node has been removed
     */
    public abstract void sync() throws BackingStoreException;

    /**
     * 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 <code>InvalidStateException</code>),
     * 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.
     * <p>
     * Note that according to the specification an implementation may delay
     * removal of the node from the backing store till the <code>flush()</code>
     * method is called. But the <code>flush()</code> method may throw a 
     * <code>IllegalStateException</code> when the node has been removed.
     * So most implementations will actually remove the node and any subnodes
     * from the backing store immediatly.
     *
     * @exception BackingStoreException when the backing store cannot be
     *            reached
     * @exception IllegalStateException if this node has already been removed
     * @exception UnsupportedOperationException if this is a root node
     */
    public abstract void removeNode() throws BackingStoreException;

    // abstract methods (listeners)

    public abstract void addNodeChangeListener(NodeChangeListener listener);

    public abstract void addPreferenceChangeListener
                            (PreferenceChangeListener listener);

    public abstract void removeNodeChangeListener(NodeChangeListener listener);

    public abstract void removePreferenceChangeListener
                            (PreferenceChangeListener listener);
}