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 

    26 package jdk.dynalink.linker;

    27 

    28 import java.security.Permission;

    29 import java.util.List;

    30 import java.util.ServiceLoader;

    31 import java.util.function.Supplier;

    32 import jdk.dynalink.DynamicLinkerFactory;

    33 

    34 /**

    35  * A class acting as a supplier of guarding dynamic linkers that can be

    36  * automatically loaded by other language runtimes. Language runtimes wishing

    37  * to export their own linkers should subclass this class and implement the

    38  * {@link #get()} method to return a list of exported linkers and declare the

    39  * subclass in

    40  * {@code /META-INF/services/jdk.dynalink.linker.GuardingDynamicLinkerExporter}

    41  * resource of their distribution (typically, JAR file) so that dynamic linker

    42  * factories can discover them using the {@link ServiceLoader} mechanism. Note

    43  * that instantiating this class is tied to a security check for the

    44  * {@code RuntimePermission("dynalink.exportLinkersAutomatically")} when a

    45  * security manager is present, to ensure that only trusted runtimes can

    46  * automatically export their linkers into other runtimes.

    47  * @see DynamicLinkerFactory#setClassLoader(ClassLoader)

    48  */

    49 public abstract class GuardingDynamicLinkerExporter implements Supplier<List<GuardingDynamicLinker>> {

    50     /**

    51      * The name of the runtime permission for creating instances of this class.

    52      * Granting this permission to a language runtime allows it to export its

    53      * linkers for automatic loading into other language runtimes.

    54      */

    55     public static final String AUTOLOAD_PERMISSION_NAME = "dynalink.exportLinkersAutomatically";

    56 

    57     private static final Permission AUTOLOAD_PERMISSION = new RuntimePermission(AUTOLOAD_PERMISSION_NAME);

    58 

    59     /**

    60      * Creates a new linker exporter. If there is a security manager installed

    61      * checks for the

    62      * {@code RuntimePermission("dynalink.exportLinkersAutomatically")} runtime

    63      * permission. This ensures only language runtimes granted this permission

    64      * will be allowed to export their linkers for automatic loading.

    65      * @throws SecurityException if the necessary runtime permission is not

    66      * granted.

    67      */

    68     protected GuardingDynamicLinkerExporter() {

    69         final SecurityManager sm = System.getSecurityManager();

    70         if (sm != null) {

    71             sm.checkPermission(AUTOLOAD_PERMISSION);

    72         }

    73     }

    74 }