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 */ GuardingDynamicLinkerExporter()68 protected GuardingDynamicLinkerExporter() { 69 final SecurityManager sm = System.getSecurityManager(); 70 if (sm != null) { 71 sm.checkPermission(AUTOLOAD_PERMISSION); 72 } 73 } 74 } 75