001    /* Permissions.java -- a collection of permission collections
002       Copyright (C) 1998, 2001, 2002, 2004, 2005  Free Software Foundation, Inc.
003    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010    
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
036    exception statement from your version. */
037    
038    
039    package java.security;
040    
041    import java.io.Serializable;
042    import java.util.Enumeration;
043    import java.util.Hashtable;
044    import java.util.NoSuchElementException;
045    
046    /**
047     * This class is a heterogeneous collection of permissions.  It is
048     * organized as a collection of <code>PermissionCollection</code>'s stored
049     * in a hashtable.  Each individual <code>PermissionCollection</code>
050     * contains permissions of a single type.  If a specific type of
051     * <code>Permission</code> does not provide a collection type to use
052     * via its <code>newPermissionCollection</code> method, then a default
053     * collection type which stores its permissions in a hash table will be
054     * used.
055     *
056     * @author Aaron M. Renn (arenn@urbanophile.com)
057     * @author Eric Blake (ebb9@email.byu.edu)
058     * @since 1.1
059     */
060    public final class Permissions extends PermissionCollection
061      implements Serializable
062    {
063      /**
064       * Compatible with JDK 1.1+.
065       */
066      private static final long serialVersionUID = 4858622370623524688L;
067    
068      /**
069       * Holds instances of <code>AllPermission</code>.
070       *
071       * @serial the permission collection for AllPermission
072       */
073      private PermissionCollection allPermission;
074    
075      // Package-private to avoid a trampoline.
076      /**
077       * This is the <code>Hashtable</code> that contains our collections.
078       *
079       * @serial maps Class to PermissionCollection
080       */
081      final Hashtable perms = new Hashtable();
082    
083      /**
084       * This method initializes a new instance of <code>Permissions</code>.
085       */
086      public Permissions()
087      {
088      }
089    
090      /**
091       * This method adds a new <code>Permission</code> to this collection.  It
092       * will be stored in a <code>PermissionCollection</code> of the appropriate
093       * type, as determined by calling <code>newPermissionCollection</code> on
094       * the specified permission (if an appropriate collection does not already
095       * exist). If this object does not specify a particular type of collection,
096       * a default collection, which stores in permissions in a hash table, will
097       * be used.
098       *
099       * @param perm the <code>Permission</code> to add
100       * @throws SecurityException if this collection is marked as read only
101       */
102      public void add(Permission perm)
103      {
104        if (isReadOnly())
105          throw new SecurityException("PermissionCollection is read only");
106        if (perm instanceof AllPermission)
107          {
108            if (allPermission == null)
109              {
110                allPermission = perm.newPermissionCollection();
111                allPermission.add(perm);
112                perms.put(perm.getClass(), allPermission);
113              }
114          }
115        else
116          {
117            PermissionCollection pc
118              = (PermissionCollection) perms.get(perm.getClass());
119            if (pc == null)
120              {
121                pc = perm.newPermissionCollection();
122                if (pc == null)
123                  pc = new PermissionsHash();
124                perms.put(perm.getClass(), pc);
125              }
126            pc.add(perm);
127          }
128      }
129    
130      /**
131       * This method tests whether or not the specified <code>Permission</code>
132       * is implied by this <code>PermissionCollection</code>.
133       *
134       * @param perm the <code>Permission</code> to test
135       * @return true if the specified permission is implied by this
136       */
137      public boolean implies(Permission perm)
138      {
139        if (allPermission != null)
140          return true;
141        PermissionCollection pc
142          = (PermissionCollection) perms.get(perm.getClass());
143        return pc == null ? false : pc.implies(perm);
144      }
145    
146      /**
147       * This method returns an <code>Enumeration</code> which contains a
148       * list of all <code>Permission</code> objects contained in this
149       * collection.
150       *
151       * @return an <code>Enumeration</code> of this collection's elements
152       */
153      public Enumeration<Permission> elements()
154      {
155        return new Enumeration()
156        {
157          Enumeration main_enum = perms.elements();
158          Enumeration sub_enum;
159    
160          public boolean hasMoreElements()
161          {
162            if (sub_enum == null)
163              {
164                if (main_enum == null)
165                  return false;
166                if (! main_enum.hasMoreElements())
167                  {
168                    main_enum = null;
169                    return false;
170                  }
171                PermissionCollection pc =
172                  (PermissionCollection) main_enum.nextElement();
173                sub_enum = pc.elements();
174              }
175            if (! sub_enum.hasMoreElements())
176              {
177                sub_enum = null;
178                return hasMoreElements();
179              }
180            return true;
181          }
182    
183          public Object nextElement()
184          {
185            if (! hasMoreElements())
186              throw new NoSuchElementException();
187            return sub_enum.nextElement();
188          }
189        };
190      }
191    
192      /**
193       * Implements the permission collection for all permissions without one of
194       * their own, and obeys serialization of JDK.
195       *
196       * @author Eric Blake (ebb9@email.byu.edu)
197       */
198      private static final class PermissionsHash extends PermissionCollection
199      {
200        /**
201         * Compatible with JDK 1.1+.
202         */
203        private static final long serialVersionUID = -8491988220802933440L;
204    
205        /**
206         * Hashtable where we store permissions.
207         *
208         * @serial the stored permissions, both as key and value
209         */
210        private final Hashtable perms = new Hashtable();
211    
212        /**
213         * Add a permission. We don't need to check for read-only, as this
214         * collection is never exposed outside of Permissions, which has already
215         * done that check.
216         *
217         * @param perm the permission to add
218         */
219        public void add(Permission perm)
220        {
221          perms.put(perm, perm);
222        }
223    
224        /**
225         * Returns true if perm is in the collection.
226         *
227         * @param perm the permission to check
228         * @return true if it is implied
229         */
230        // FIXME: Should this method be synchronized?
231        public boolean implies(Permission perm)
232        {
233          Enumeration elements = elements();
234    
235          while (elements.hasMoreElements())
236            {
237              Permission p = (Permission)elements.nextElement();
238              if (p.implies(perm))
239                return true;
240            }
241          return false;
242        }
243    
244        /**
245         * Return the elements.
246         *
247         * @return the elements
248         */
249        public Enumeration elements()
250        {
251          return perms.elements();
252        }
253      } // class PermissionsHash
254    } // class Permissions