1 /*
   2  * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 package javax.accessibility;
  26 
  27 /**
  28  * Service Provider Interface (SPI) for Assistive Technology.
  29  * <p>
  30  * This service provider class provides mappings from the platform
  31  * specific accessibility APIs to the Java Accessibility API.
  32  * <p>
  33  * Each service provider implementation is named and can be activated via the
  34  * {@link #activate} method. Service providers can be loaded when the default
  35  * {@link java.awt.Toolkit toolkit} is initialized.
  36  * 
  37  * @apiNote There will typically be one provider per platform, such as Windows
  38  * or Linux, to support accessibility for screen readers and magnifiers.  However,
  39  * more than one service provider can be activated.  For example, a test tool
  40  * which provides visual results obtained by interrogating the Java Accessibility
  41  * API can be activated along with the activation of the support for screen readers
  42  * and screen magnifiers.
  43  * 
  44  * @see java.awt.Toolkit#getDefaultToolkit
  45  * @see java.util.ServiceLoader
  46  * @since 1.9
  47  */
  48 public abstract class AccessibilityProvider {
  49     
  50 
  51     /**
  52      * Initializes a new accessibility provider.
  53      *
  54      * @throws  SecurityException
  55      *          If a security manager has been installed and it denies
  56      *          {@link RuntimePermission}{@code("accessibilityProvider")}
  57      */
  58     protected AccessibilityProvider() {
  59         // Use a permission check when calling a private constructor to check that
  60         // the proper security permission has been granted before the Object superclass
  61         // is called.  If an exception is thrown before the Object superclass is
  62         // constructed a finalizer in a subclass of this class will not be run.
  63         // This protects against a finalizer vulnerability.
  64         this(checkPermission());
  65     }
  66 
  67     private AccessibilityProvider(Void ignore) { }
  68 
  69     /**
  70      * If this code is running with a security manager and if the permission
  71      * "accessibilityProvider" has not been granted SecurityException will be thrown.
  72      *
  73      */
  74     private static Void checkPermission() {
  75         SecurityManager sm = System.getSecurityManager();
  76         if (sm != null)
  77             sm.checkPermission(new RuntimePermission("accessibilityProvider"));
  78         return null;
  79     }
  80 
  81     /**
  82      * Returns the name of this service provider.  This name is used to locate a
  83      * requested service provider.
  84      * 
  85      * @return the name of this service provider
  86      */
  87     public abstract String name();
  88 
  89     /**
  90      * Activates the support provided by this service provider.
  91      */
  92     public abstract void activate();
  93 }