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	/*
	* Copyright (c) 2015, 2018, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package jdk.internal.loader;

	import java.io.IOException;
	import java.net.URL;
	import java.nio.file.InvalidPathException;
	import java.nio.file.Path;
	import java.security.CodeSource;
	import java.security.PermissionCollection;
	import java.util.jar.Manifest;

	import jdk.internal.misc.JavaLangAccess;
	import jdk.internal.misc.SharedSecrets;
	import jdk.internal.misc.VM;

	/**
	* Creates and provides access to the built-in platform and application class
	* loaders. It also creates the class loader that is used to locate resources
	* in modules defined to the boot class loader.
	*/

	public class ClassLoaders {

	private ClassLoaders() { }

	private static final JavaLangAccess JLA = SharedSecrets.getJavaLangAccess();

	// the built-in class loaders
	private static final BootClassLoader BOOT_LOADER;
	private static final PlatformClassLoader PLATFORM_LOADER;
	private static final AppClassLoader APP_LOADER;

	// Creates the built-in class loaders.
	static {
	// -Xbootclasspath/a or -javaagent with Boot-Class-Path attribute
	String append = VM.getSavedProperty("jdk.boot.class.path.append");
	BOOT_LOADER =
	new BootClassLoader((append != null && append.length() > 0)
	? new URLClassPath(append, true)
	: null);
	PLATFORM_LOADER = new PlatformClassLoader(BOOT_LOADER);

	// A class path is required when no initial module is specified.
	// In this case the class path defaults to "", meaning the current
	// working directory. When an initial module is specified, on the
	// contrary, we drop this historic interpretation of the empty
	// string and instead treat it as unspecified.
	String cp = System.getProperty("java.class.path");
	if (cp == null \|\| cp.length() == 0) {
	String initialModuleName = System.getProperty("jdk.module.main");
	cp = (initialModuleName == null) ? "" : null;
	}
	URLClassPath ucp = new URLClassPath(cp, false);
	APP_LOADER = new AppClassLoader(PLATFORM_LOADER, ucp);
	}

	/**
	* Returns the class loader that is used to find resources in modules
	* defined to the boot class loader.
	*
	* @apiNote This method is not public, it should instead be used via
	* the BootLoader class that provides a restricted API to this class
	* loader.
	*/
	static BuiltinClassLoader bootLoader() {
	return BOOT_LOADER;
	}

	/**
	* Returns the platform class loader.
	*/
	public static ClassLoader platformClassLoader() {
	return PLATFORM_LOADER;
	}

	/**
	* Returns the application class loader.
	*/
	public static ClassLoader appClassLoader() {
	return APP_LOADER;
	}

	/**
	* The class loader that is used to find resources in modules defined to
	* the boot class loader. It is not used for class loading.
	*/
	private static class BootClassLoader extends BuiltinClassLoader {
	BootClassLoader(URLClassPath bcp) {
	super(null, null, bcp);
	}

	@Override
	protected Class<?> loadClassOrNull(String cn) {
	return JLA.findBootstrapClassOrNull(this, cn);
	}
	};

	/**
	* The platform class loader, a unique type to make it easier to distinguish
	* from the application class loader.
	*/
	private static class PlatformClassLoader extends BuiltinClassLoader {
	static {
	if (!ClassLoader.registerAsParallelCapable())
	throw new InternalError();
	}

	PlatformClassLoader(BootClassLoader parent) {
	super("platform", parent, null);
	}

	/**
	* Called by the VM to support define package for AppCDS.
	*
	* Shared classes are returned in ClassLoader::findLoadedClass
	* that bypass the defineClass call.
	*/
	private Package definePackage(String pn, Module module) {
	return JLA.definePackage(this, pn, module);
	}
	}

	/**
	* The application class loader that is a {@code BuiltinClassLoader} with
	* customizations to be compatible with long standing behavior.
	*/
	private static class AppClassLoader extends BuiltinClassLoader {
	static {
	if (!ClassLoader.registerAsParallelCapable())
	throw new InternalError();
	}

	final URLClassPath ucp;

	AppClassLoader(PlatformClassLoader parent, URLClassPath ucp) {
	super("app", parent, ucp);
	this.ucp = ucp;
	}

	@Override
	protected Class<?> loadClass(String cn, boolean resolve)
	throws ClassNotFoundException
	{
	// for compatibility reasons, say where restricted package list has
	// been updated to list API packages in the unnamed module.
	SecurityManager sm = System.getSecurityManager();
	if (sm != null) {
	int i = cn.lastIndexOf('.');
	if (i != -1) {
	sm.checkPackageAccess(cn.substring(0, i));
	}
	}

	return super.loadClass(cn, resolve);
	}

	@Override
	protected PermissionCollection getPermissions(CodeSource cs) {
	PermissionCollection perms = super.getPermissions(cs);
	perms.add(new RuntimePermission("exitVM"));
	return perms;
	}

	/**
	* Called by the VM to support dynamic additions to the class path
	*
	* @see java.lang.instrument.Instrumentation#appendToSystemClassLoaderSearch
	*/
	void appendToClassPathForInstrumentation(String path) {
	ucp.addFile(path);
	}

	/**
	* Called by the VM to support define package for AppCDS
	*
	* Shared classes are returned in ClassLoader::findLoadedClass
	* that bypass the defineClass call.
	*/
	private Package definePackage(String pn, Module module) {
	return JLA.definePackage(this, pn, module);
	}

	/**
	* Called by the VM to support define package for AppCDS
	*/
	protected Package defineOrCheckPackage(String pn, Manifest man, URL url) {
	return super.defineOrCheckPackage(pn, man, url);
	}
	}

	/**
	* Attempts to convert the given string to a file URL.
	*
	* @apiNote This is called by the VM
	*/
	@Deprecated
	private static URL toFileURL(String s) {
	try {
	// Use an intermediate File object to construct a URI/URL without
	// authority component as URLClassPath can't handle URLs with a UNC
	// server name in the authority component.
	return Path.of(s).toRealPath().toFile().toURI().toURL();
	} catch (InvalidPathException \| IOException ignore) {
	// malformed path string or class path element does not exist
	return null;
	}
	}
	}

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