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AspectJ tools most notably contains the AspectJ compiler (AJC). AJC applies aspects to Java classes during compilation, fully replacing Javac for plain Java classes and also compiling native AspectJ or annotation-based @AspectJ syntax. Furthermore, AJC can weave aspects into existing class files in a post-compile binary weaving step. This library is a superset of AspectJ weaver and hence also of AspectJ runtime.

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/*******************************************************************************
 * Copyright (c) 2005, 2021 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.osgi.internal.loader.buddy;

import java.io.IOException;
import java.net.URL;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Enumeration;

public class SystemPolicy implements IBuddyPolicy {

	public static final byte BOOT = 0;
	public static final byte EXT = 1;
	public static final byte APP = 2;

	private static SystemPolicy[] instances = new SystemPolicy[3];

	private ClassLoader classLoader;

	public static SystemPolicy getInstance(final byte type, final ClassLoader bootLoader) {
		if (instances[type] == null) {
			instances[type] = new SystemPolicy();
			instances[type].classLoader = AccessController.doPrivileged((PrivilegedAction) () -> createClassLoader(type, bootLoader));
		}
		return instances[type];
	}

	public SystemPolicy() {
		//Nothing to do
	}

	public SystemPolicy(ClassLoader parent) {
		classLoader = parent;
	}

	static ClassLoader createClassLoader(byte type, ClassLoader bootLoader) {
		switch (type) {
			case APP :
				if (ClassLoader.getSystemClassLoader() != null)
					return ClassLoader.getSystemClassLoader();
				return bootLoader;

			case BOOT :
				return bootLoader;

			case EXT :
				if (ClassLoader.getSystemClassLoader() != null)
					return ClassLoader.getSystemClassLoader().getParent();
				return bootLoader;
		}
		return null;
	}

	@Override
	public Class loadClass(String name) {
		try {
			return classLoader.loadClass(name);
		} catch (ClassNotFoundException e) {
			return null;
		}
	}

	@Override
	public URL loadResource(String name) {
		return classLoader.getResource(name);
	}

	@Override
	public Enumeration loadResources(String name) {
		try {
			return classLoader.getResources(name);
		} catch (IOException e) {
			return null;
		}
	}

}