001    /* AccessController.java --- Access control context and permission checker
002       Copyright (C) 2001, 2004  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    package java.security;
039    
040    /**
041     * Access control context and permission checker.
042     * Can check permissions in the access control context of the current thread
043     * through the <code>checkPermission()</code> method.
044     * Manipulates the access control context for code that needs to be executed
045     * the protection domain of the calling class (by explicitly ignoring the
046     * context of the calling code) in the <code>doPrivileged()</code> methods.
047     * And provides a <code>getContext()</code> method which gives the access
048     * control context of the current thread that can be used for checking
049     * permissions at a later time and/or in another thread.
050     *
051     * @author Mark Wielaard (mark@klomp.org)
052     * @since 1.2
053     */
054    public final class AccessController
055    {
056      /**
057       * This class only has static methods so there is no public contructor.
058       */
059      private AccessController()
060      {
061      }
062    
063      /**
064       * Checks wether the access control context of the current thread allows
065       * the given Permission. Throws an <code>AccessControlException</code>
066       * when the permission is not allowed in the current context. Otherwise
067       * returns silently without throwing an exception.
068       *
069       * @param perm the permission to be checked.
070       * @exception AccessControlException thrown if the current context does not
071       * allow the given permission.
072       */
073      public static void checkPermission(Permission perm)
074        throws AccessControlException
075      {
076        getContext().checkPermission(perm);
077      }
078    
079      /**
080       * Calls the <code>run()</code> method of the given action with as
081       * (initial) access control context only the protection domain of the
082       * calling class. Calls to <code>checkPermission()</code> in the
083       * <code>run()</code> method ignore all earlier protection domains of
084       * classes in the call chain. Note that the protection domains of classes
085       * called by the code in the <code>run()</code> method are not ignored.
086       *
087       * @param action the <code>PrivilegedAction</code> whose <code>run()</code>
088       * should be be called.
089       * @return the result of the <code>action.run()</code> method.
090       */
091      public static <T> T doPrivileged(PrivilegedAction<T> action)
092      {
093        VMAccessController.pushContext(null);
094        try
095          {
096            return action.run();
097          }
098        finally
099          {
100            VMAccessController.popContext();
101          }
102      }
103    
104      /**
105       * Calls the <code>run()</code> method of the given action with as
106       * (initial) access control context the given context combined with the
107       * protection domain of the calling class. Calls to
108       * <code>checkPermission()</code> in the <code>run()</code> method ignore
109       * all earlier protection domains of classes in the call chain, but add
110       * checks for the protection domains given in the supplied context.
111       *
112       * @param action the <code>PrivilegedAction</code> whose <code>run()</code>
113       * should be be called.
114       * @param context the <code>AccessControlContext</code> whose protection
115       * domains should be added to the protection domain of the calling class.
116       * @return the result of the <code>action.run()</code> method.
117       */
118      public static <T> T doPrivileged(PrivilegedAction<T> action,
119                                       AccessControlContext context)
120      {
121        VMAccessController.pushContext(context);
122        try
123          {
124            return action.run();
125          }
126        finally
127          {
128            VMAccessController.popContext();
129          }
130      }
131    
132      /**
133       * Calls the <code>run()</code> method of the given action with as
134       * (initial) access control context only the protection domain of the
135       * calling class. Calls to <code>checkPermission()</code> in the
136       * <code>run()</code> method ignore all earlier protection domains of
137       * classes in the call chain. Note that the protection domains of classes
138       * called by the code in the <code>run()</code> method are not ignored.
139       * If the <code>run()</code> method throws an exception then this method
140       * will wrap that exception in an <code>PrivilegedActionException</code>.
141       *
142       * @param action the <code>PrivilegedExceptionAction</code> whose
143       * <code>run()</code> should be be called.
144       * @return the result of the <code>action.run()</code> method.
145       * @exception PrivilegedActionException wrapped around any checked exception
146       * that is thrown in the <code>run()</code> method.
147       */
148      public static <T> T doPrivileged(PrivilegedExceptionAction<T> action)
149        throws PrivilegedActionException
150      {
151        VMAccessController.pushContext(null);
152        try
153          {
154            return action.run();
155          }
156        catch (RuntimeException e)
157          {
158            throw e;
159          }
160        catch (Exception e)
161          {
162            throw new PrivilegedActionException(e);
163          }
164        finally
165          {
166            VMAccessController.popContext();
167          }
168      }
169    
170      /**
171       * Calls the <code>run()</code> method of the given action with as
172       * (initial) access control context the given context combined with the
173       * protection domain of the calling class. Calls to
174       * <code>checkPermission()</code> in the <code>run()</code> method ignore
175       * all earlier protection domains of classes in the call chain, but add
176       * checks for the protection domains given in the supplied context.
177       * If the <code>run()</code> method throws an exception then this method
178       * will wrap that exception in an <code>PrivilegedActionException</code>.
179       *
180       * @param action the <code>PrivilegedExceptionAction</code> whose
181       * <code>run()</code> should be be called.
182       * @param context the <code>AccessControlContext</code> whose protection
183       * domains should be added to the protection domain of the calling class.
184       * @return the result of the <code>action.run()</code> method.
185       * @exception PrivilegedActionException wrapped around any checked exception
186       * that is thrown in the <code>run()</code> method.
187       */
188      public static <T> T doPrivileged(PrivilegedExceptionAction<T> action,
189                                       AccessControlContext context)
190        throws PrivilegedActionException
191      {
192        VMAccessController.pushContext(context);
193        try
194          {
195            return action.run();
196          }
197        catch (RuntimeException e)
198          {
199            throw e;
200          }
201        catch (Exception e)
202          {
203            throw new PrivilegedActionException(e);
204          }
205        finally
206          {
207            VMAccessController.popContext();
208          }
209      }
210    
211      /**
212       * Returns the complete access control context of the current thread.
213       * The returned object encompasses all {@link ProtectionDomain} objects
214       * for all classes in the current call stack, or the set of protection
215       * domains until the last call to {@link
216       * #doPrivileged(java.security.PrivilegedAction)}.
217       *
218       * <p>Additionally, if a call was made to {@link
219       * #doPrivileged(java.security.PrivilegedAction,java.security.AccessControlContext)}
220       * that supplied an {@link AccessControlContext}, then that context
221       * will be intersected with the calculated one.
222       *
223       * @return The context.
224       */
225      public static AccessControlContext getContext()
226      {
227        return VMAccessController.getContext();
228      }
229    }