001    /* Permission.java -- The superclass for all permission objects
002       Copyright (C) 1998, 2001, 2002, 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    package java.security;
039    
040    import gnu.java.lang.CPStringBuilder;
041    
042    import java.io.Serializable;
043    
044    /**
045     * This class is the abstract superclass of all classes that implement
046     * the concept of a permission.  A permission consists of a permission name
047     * and optionally a list of actions that relate to the permission.  The
048     * actual meaning of the name of the permission is defined only in the
049     * context of a subclass.  It may name a resource to which access permissions
050     * are granted (for example, the name of a file) or it might represent
051     * something else entirely.  Similarly, the action list only has meaning
052     * within the context of a subclass.  Some permission names may have no
053     * actions associated with them.  That is, you either have the permission
054     * or you don't.
055     *
056     * <p>The most important method in this class is <code>implies</code>.  This
057     * checks whether if one has this permission, then the specified
058     * permission is also implied.  As a conceptual example, consider the
059     * permissions "Read All Files" and "Read File foo".  The permission
060     * "Read All Files" implies that the caller has permission to read the
061     * file foo.
062     *
063     * <p><code>Permission</code>'s must be immutable - do not change their
064     * state after creation.
065     *
066     * @author Aaron M. Renn (arenn@urbanophile.com)
067     * @see Permissions
068     * @see PermissionCollection
069     * @since 1.1
070     * @status updated to 1.4
071     */
072    public abstract class Permission implements Guard, Serializable
073    {
074      /**
075       * Compatible with JDK 1.1+.
076       */
077      private static final long serialVersionUID = -5636570222231596674L;
078    
079      /**
080       * This is the name assigned to this permission object.
081       *
082       * @serial the name of the permission
083       */
084      private String name;
085    
086      /**
087       * Create an instance with the specified name.
088       *
089       * @param name the permission name
090       */
091      public Permission(String name)
092      {
093        this.name = name;
094      }
095    
096      /**
097       * This method implements the <code>Guard</code> interface for this class.
098       * It calls the <code>checkPermission</code> method in
099       * <code>SecurityManager</code> with this <code>Permission</code> as its
100       * argument.  This method returns silently if the security check succeeds
101       * or throws an exception if it fails.
102       *
103       * @param obj the <code>Object</code> being guarded - ignored by this class
104       * @throws SecurityException if the security check fails
105       * @see GuardedObject
106       * @see SecurityManager#checkPermission(Permission)
107       */
108      public void checkGuard(Object obj)
109      {
110        SecurityManager sm = System.getSecurityManager();
111        if (sm != null)
112          sm.checkPermission(this);
113      }
114    
115      /**
116       * This method tests whether this <code>Permission</code> implies that the
117       * specified <code>Permission</code> is also granted.
118       *
119       * @param perm the <code>Permission</code> to test against
120       * @return true if perm is implied by this
121       */
122      public abstract boolean implies(Permission perm);
123    
124      /**
125       * Check to see if this object equals obj. Use <code>implies</code>, rather
126       * than <code>equals</code>, when making access control decisions.
127       *
128       * @param obj the object to compare to
129       */
130      public abstract boolean equals(Object obj);
131    
132      /**
133       * This method returns a hash code for this <code>Permission</code>. It
134       * must satisfy the contract of <code>Object.hashCode</code>: it must be
135       * the same for all objects that equals considers to be the same.
136       *
137       * @return a hash value
138       */
139      public abstract int hashCode();
140    
141      /**
142       * Get the name of this <code>Permission</code>.
143       *
144       * @return the name
145       */
146      public final String getName()
147      {
148        return name;
149      }
150    
151      /**
152       * This method returns the list of actions for this <code>Permission</code>
153       * as a <code>String</code>. The string should be in canonical order, for
154       * example, both <code>new FilePermission(f, "write,read")</code> and
155       * <code>new FilePermission(f, "read,write")</code> have the action list
156       * "read,write".
157       *
158       * @return the action list for this <code>Permission</code>
159       */
160      public abstract String getActions();
161    
162      /**
163       * This method returns an empty <code>PermissionCollection</code> object
164       * that can store permissions of this type, or <code>null</code> if no
165       * such collection is defined. Subclasses must override this to provide
166       * an appropriate collection when one is needed to accurately calculate
167       * <code>implies</code>.
168       *
169       * @return a new <code>PermissionCollection</code>
170       */
171      public PermissionCollection newPermissionCollection()
172      {
173        return null;
174      }
175    
176      /**
177       * This method returns a <code>String</code> representation of this
178       * <code>Permission</code> object. This is in the format:
179       * <code>'(' + getClass().getName() + ' ' + getName() + ' ' + getActions
180       * + ')'</code>.
181       *
182       * @return this object as a <code>String</code>
183       */
184      public String toString()
185      {
186        CPStringBuilder string = new CPStringBuilder();
187    
188        string = string.append('(');
189        string = string.append(getClass().getName());
190        string = string.append(' ');
191        string = string.append(getName());
192    
193        if (!(getActions().equals("")))
194          {
195            string = string.append(' ');
196            string = string.append(getActions());
197          }
198    
199        string = string.append(')');
200        return string.toString();
201      }
202    } // class Permission