Java tutorial
/* * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.security; /** * Abstract class for representing access to a system resource. * All permissions have a name (whose interpretation depends on the subclass), * as well as abstract functions for defining the semantics of the * particular Permission subclass. * * <p>Most Permission objects also include an "actions" list that tells the actions * that are permitted for the object. For example, * for a {@code java.io.FilePermission} object, the permission name is * the pathname of a file (or directory), and the actions list * (such as "read, write") specifies which actions are granted for the * specified file (or for files in the specified directory). * The actions list is optional for Permission objects, such as * {@code java.lang.RuntimePermission}, * that don't need such a list; you either have the named permission (such * as "system.exit") or you don't. * * <p>An important method that must be implemented by each subclass is * the {@code implies} method to compare Permissions. Basically, * "permission p1 implies permission p2" means that * if one is granted permission p1, one is naturally granted permission p2. * Thus, this is not an equality test, but rather more of a * subset test. * * <P> Permission objects are similar to String objects in that they * are immutable once they have been created. Subclasses should not * provide methods that can change the state of a permission * once it has been created. * * @see Permissions * @see PermissionCollection * * * @author Marianne Mueller * @author Roland Schemers * @since 1.2 */ public abstract class Permission implements Guard, java.io.Serializable { private static final long serialVersionUID = -5636570222231596674L; private String name; /** * Constructs a permission with the specified name. * * @param name name of the Permission object being created. * */ public Permission(String name) { this.name = name; } /** * Implements the guard interface for a permission. The * {@code SecurityManager.checkPermission} method is called, * passing this permission object as the permission to check. * Returns silently if access is granted. Otherwise, throws * a SecurityException. * * @param object the object being guarded (currently ignored). * * @throws SecurityException * if a security manager exists and its * {@code checkPermission} method doesn't allow access. * * @see Guard * @see GuardedObject * @see SecurityManager#checkPermission * */ public void checkGuard(Object object) throws SecurityException { SecurityManager sm = System.getSecurityManager(); if (sm != null) sm.checkPermission(this); } /** * Checks if the specified permission's actions are "implied by" * this object's actions. * <P> * This must be implemented by subclasses of Permission, as they are the * only ones that can impose semantics on a Permission object. * * <p>The {@code implies} method is used by the AccessController to determine * whether or not a requested permission is implied by another permission that * is known to be valid in the current execution context. * * @param permission the permission to check against. * * @return true if the specified permission is implied by this object, * false if not. */ public abstract boolean implies(Permission permission); /** * Checks two Permission objects for equality. * <P> * Do not use the {@code equals} method for making access control * decisions; use the {@code implies} method. * * @param obj the object we are testing for equality with this object. * * @return true if both Permission objects are equivalent. */ public abstract boolean equals(Object obj); /** * Returns the hash code value for this Permission object. * <P> * The required {@code hashCode} behavior for Permission Objects is * the following: * <ul> * <li>Whenever it is invoked on the same Permission object more than * once during an execution of a Java application, the * {@code hashCode} method * must consistently return the same integer. This integer need not * remain consistent from one execution of an application to another * execution of the same application. * <li>If two Permission objects are equal according to the * {@code equals} * method, then calling the {@code hashCode} method on each of the * two Permission objects must produce the same integer result. * </ul> * * @return a hash code value for this object. */ public abstract int hashCode(); /** * Returns the name of this Permission. * For example, in the case of a {@code java.io.FilePermission}, * the name will be a pathname. * * @return the name of this Permission. * */ public final String getName() { return name; } /** * Returns the actions as a String. This is abstract * so subclasses can defer creating a String representation until * one is needed. Subclasses should always return actions in what they * consider to be their * canonical form. For example, two FilePermission objects created via * the following: * * <pre> * perm1 = new FilePermission(p1,"read,write"); * perm2 = new FilePermission(p2,"write,read"); * </pre> * * both return * "read,write" when the {@code getActions} method is invoked. * * @return the actions of this Permission. * */ public abstract String getActions(); /** * Returns an empty PermissionCollection for a given Permission object, or null if * one is not defined. Subclasses of class Permission should * override this if they need to store their permissions in a particular * PermissionCollection object in order to provide the correct semantics * when the {@code PermissionCollection.implies} method is called. * If null is returned, * then the caller of this method is free to store permissions of this * type in any PermissionCollection they choose (one that uses a Hashtable, * one that uses a Vector, etc). * * @return a new PermissionCollection object for this type of Permission, or * null if one is not defined. */ public PermissionCollection newPermissionCollection() { return null; } /** * Returns a string describing this Permission. The convention is to * specify the class name, the permission name, and the actions in * the following format: '("ClassName" "name" "actions")', or * '("ClassName" "name")' if actions list is null or empty. * * @return information about this Permission. */ public String toString() { String actions = getActions(); if (actions == null || actions.isEmpty()) { // OPTIONAL return "(\"" + getClass().getName() + "\" \"" + name + "\")"; } else { return "(\"" + getClass().getName() + "\" \"" + name + "\" \"" + actions + "\")"; } } }