AutoDiscovery.java

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/*
 * This file is available under and governed by the GNU General Public
 * License version 2 only, as published by the Free Software Foundation.
 * However, the following notice accompanied the original version of this
 * file, and Oracle licenses the original version of this file under the BSD
 * license:
 */
/*
   Copyright 2009-2013 Attila Szegedi

   Licensed under both the Apache License, Version 2.0 (the "Apache License")
   and the BSD License (the "BSD License"), with licensee being free to
   choose either of the two at their discretion.

   You may not use this file except in compliance with either the Apache
   License or the BSD License.

   If you choose to use this file in compliance with the Apache License, the
   following notice applies to you:

       You may obtain a copy of the Apache License at

           http://www.apache.org/licenses/LICENSE-2.0

       Unless required by applicable law or agreed to in writing, software
       distributed under the License is distributed on an "AS IS" BASIS,
       WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
       implied. See the License for the specific language governing
       permissions and limitations under the License.

   If you choose to use this file in compliance with the BSD License, the
   following notice applies to you:

       Redistribution and use in source and binary forms, with or without
       modification, are permitted provided that the following conditions are
       met:
       * Redistributions of source code must retain the above copyright
         notice, this list of conditions and the following disclaimer.
       * Redistributions in binary form must reproduce the above copyright
         notice, this list of conditions and the following disclaimer in the
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       * Neither the name of the copyright holder nor the names of
         contributors may be used to endorse or promote products derived from
         this software without specific prior written permission.

       THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
       IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
       TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
       PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL COPYRIGHT HOLDER
       BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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       ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

package jdk.internal.dynalink.support;

import java.util.LinkedList;
import java.util.List;
import java.util.ServiceLoader;
import jdk.internal.dynalink.DynamicLinkerFactory;
import jdk.internal.dynalink.linker.GuardingDynamicLinker;

/**
 * Provides methods for automatic discovery of all guarding dynamic linkers listed in the
 * <tt>/META-INF/services/jdk.internal.dynalink.linker.GuardingDynamicLinker</tt> resources of all JAR files for a
 * particular class loader. Ordinarily, you will not use this class directly, but you will use a
 * {@link DynamicLinkerFactory} instead.
 */
public class AutoDiscovery {

    private AutoDiscovery() {
    }

    /**
     * Discovers all guarding dynamic linkers listed in JAR files of the context class loader of the current thread.
     *
     * @return a list of available linkers. Can be zero-length list but not null.
     */
    public static List<GuardingDynamicLinker> loadLinkers() {
        return getLinkers(ServiceLoader.load(GuardingDynamicLinker.class));
    }

    /**
     * Discovers all guarding dynamic linkers listed in JAR files of the specified class loader.
     *
     * @param cl the class loader to use
     * @return a list of guarding dynamic linkers available through the specified class loader. Can be zero-length list
     * but not null.
     */
    public static List<GuardingDynamicLinker> loadLinkers(final ClassLoader cl) {
        return getLinkers(ServiceLoader.load(GuardingDynamicLinker.class, cl));
    }

    /**
     * I can't believe there's no Collections API for making a List given an Iterator...
     */
    private static <T> List<T> getLinkers(final ServiceLoader<T> loader) {
        final List<T> list = new LinkedList<>();
        for(final T linker: loader) {
            list.add(linker);
        }
        return list;
    }
}