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	/*
	* Copyright (c) 2013, 2015, 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 java.lang;

	import java.io.InputStream;
	import java.io.IOException;
	import java.io.File;
	import java.lang.reflect.Constructor;
	import java.lang.reflect.InvocationTargetException;
	import java.net.MalformedURLException;
	import java.net.URL;
	import java.security.AccessController;
	import java.security.AccessControlContext;
	import java.security.CodeSource;
	import java.security.Policy;
	import java.security.PrivilegedAction;
	import java.security.PrivilegedActionException;
	import java.security.PrivilegedExceptionAction;
	import java.security.ProtectionDomain;
	import java.security.cert.Certificate;
	import java.util.Collections;
	import java.util.Enumeration;
	import java.util.HashMap;
	import java.util.HashSet;
	import java.util.Set;
	import java.util.Stack;
	import java.util.Map;
	import java.util.Vector;
	import java.util.Hashtable;
	import java.util.WeakHashMap;
	import java.util.concurrent.ConcurrentHashMap;
	import sun.misc.CompoundEnumeration;
	import sun.misc.Resource;
	import sun.misc.URLClassPath;
	import sun.misc.VM;
	import sun.reflect.CallerSensitive;
	import sun.reflect.Reflection;
	import sun.reflect.misc.ReflectUtil;
	import sun.security.util.SecurityConstants;

	/**
	* A class loader is an object that is responsible for loading classes. The
	* class <tt>ClassLoader</tt> is an abstract class. Given the <a
	* href="#name">binary name</a> of a class, a class loader should attempt to
	* locate or generate data that constitutes a definition for the class. A
	* typical strategy is to transform the name into a file name and then read a
	* "class file" of that name from a file system.
	*
	* <p> Every {@link Class <tt>Class</tt>} object contains a {@link
	* Class#getClassLoader() reference} to the <tt>ClassLoader</tt> that defined
	* it.
	*
	* <p> <tt>Class</tt> objects for array classes are not created by class
	* loaders, but are created automatically as required by the Java runtime.
	* The class loader for an array class, as returned by {@link
	* Class#getClassLoader()} is the same as the class loader for its element
	* type; if the element type is a primitive type, then the array class has no
	* class loader.
	*
	* <p> Applications implement subclasses of <tt>ClassLoader</tt> in order to
	* extend the manner in which the Java virtual machine dynamically loads
	* classes.
	*
	* <p> Class loaders may typically be used by security managers to indicate
	* security domains.
	*
	* <p> The <tt>ClassLoader</tt> class uses a delegation model to search for
	* classes and resources. Each instance of <tt>ClassLoader</tt> has an
	* associated parent class loader. When requested to find a class or
	* resource, a <tt>ClassLoader</tt> instance will delegate the search for the
	* class or resource to its parent class loader before attempting to find the
	* class or resource itself. The virtual machine's built-in class loader,
	* called the "bootstrap class loader", does not itself have a parent but may
	* serve as the parent of a <tt>ClassLoader</tt> instance.
	*
	* <p> Class loaders that support concurrent loading of classes are known as
	* <em>parallel capable</em> class loaders and are required to register
	* themselves at their class initialization time by invoking the
	* {@link
	* #registerAsParallelCapable <tt>ClassLoader.registerAsParallelCapable</tt>}
	* method. Note that the <tt>ClassLoader</tt> class is registered as parallel
	* capable by default. However, its subclasses still need to register themselves
	* if they are parallel capable. <br>
	* In environments in which the delegation model is not strictly
	* hierarchical, class loaders need to be parallel capable, otherwise class
	* loading can lead to deadlocks because the loader lock is held for the
	* duration of the class loading process (see {@link #loadClass
	* <tt>loadClass</tt>} methods).
	*
	* <p> Normally, the Java virtual machine loads classes from the local file
	* system in a platform-dependent manner. For example, on UNIX systems, the
	* virtual machine loads classes from the directory defined by the
	* <tt>CLASSPATH</tt> environment variable.
	*
	* <p> However, some classes may not originate from a file; they may originate
	* from other sources, such as the network, or they could be constructed by an
	* application. The method {@link #defineClass(String, byte[], int, int)
	* <tt>defineClass</tt>} converts an array of bytes into an instance of class
	* <tt>Class</tt>. Instances of this newly defined class can be created using
	* {@link Class#newInstance <tt>Class.newInstance</tt>}.
	*
	* <p> The methods and constructors of objects created by a class loader may
	* reference other classes. To determine the class(es) referred to, the Java
	* virtual machine invokes the {@link #loadClass <tt>loadClass</tt>} method of
	* the class loader that originally created the class.
	*
	* <p> For example, an application could create a network class loader to
	* download class files from a server. Sample code might look like:
	*
	* <blockquote><pre>
	* ClassLoader loader = new NetworkClassLoader(host, port);
	* Object main = loader.loadClass("Main", true).newInstance();
	*  . . .
	* </pre></blockquote>
	*
	* <p> The network class loader subclass must define the methods {@link
	* #findClass <tt>findClass</tt>} and <tt>loadClassData</tt> to load a class
	* from the network. Once it has downloaded the bytes that make up the class,
	* it should use the method {@link #defineClass <tt>defineClass</tt>} to
	* create a class instance. A sample implementation is:
	*
	* <blockquote><pre>
	* class NetworkClassLoader extends ClassLoader {
	* String host;
	* int port;
	*
	* public Class findClass(String name) {
	* byte[] b = loadClassData(name);
	* return defineClass(name, b, 0, b.length);
	* }
	*
	* private byte[] loadClassData(String name) {
	* // load the class data from the connection
	*  . . .
	* }
	* }
	* </pre></blockquote>
	*
	* <h3> <a name="name">Binary names</a> </h3>
	*
	* <p> Any class name provided as a {@link String} parameter to methods in
	* <tt>ClassLoader</tt> must be a binary name as defined by
	* <cite>The Java™ Language Specification</cite>.
	*
	* <p> Examples of valid class names include:
	* <blockquote><pre>
	* "java.lang.String"
	* "javax.swing.JSpinner$DefaultEditor"
	* "java.security.KeyStore$Builder$FileBuilder$1"
	* "java.net.URLClassLoader$3$1"
	* </pre></blockquote>
	*
	* @see #resolveClass(Class)
	* @since 1.0
	*/
	public abstract class ClassLoader {

	private static native void registerNatives();
	static {
	registerNatives();
	}

	// The parent class loader for delegation
	// Note: VM hardcoded the offset of this field, thus all new fields
	// must be added after it.
	private final ClassLoader parent;

	/**
	* Encapsulates the set of parallel capable loader types.
	*/
	private static class ParallelLoaders {
	private ParallelLoaders() {}

	// the set of parallel capable loader types
	private static final Set<Class<? extends ClassLoader>> loaderTypes =
	Collections.newSetFromMap(
	new WeakHashMap<Class<? extends ClassLoader>, Boolean>());
	static {
	synchronized (loaderTypes) { loaderTypes.add(ClassLoader.class); }
	}

	/**
	* Registers the given class loader type as parallel capabale.
	* Returns {@code true} is successfully registered; {@code false} if
	* loader's super class is not registered.
	*/
	static boolean register(Class<? extends ClassLoader> c) {
	synchronized (loaderTypes) {
	if (loaderTypes.contains(c.getSuperclass())) {
	// register the class loader as parallel capable
	// if and only if all of its super classes are.
	// Note: given current classloading sequence, if
	// the immediate super class is parallel capable,
	// all the super classes higher up must be too.
	loaderTypes.add(c);
	return true;
	} else {
	return false;
	}
	}
	}

	/**
	* Returns {@code true} if the given class loader type is
	* registered as parallel capable.
	*/
	static boolean isRegistered(Class<? extends ClassLoader> c) {
	synchronized (loaderTypes) {
	return loaderTypes.contains(c);
	}
	}
	}

	// Maps class name to the corresponding lock object when the current
	// class loader is parallel capable.
	// Note: VM also uses this field to decide if the current class loader
	// is parallel capable and the appropriate lock object for class loading.
	private final ConcurrentHashMap<String, Object> parallelLockMap;

	// Hashtable that maps packages to certs
	private final Map <String, Certificate[]> package2certs;

	// Shared among all packages with unsigned classes
	private static final Certificate[] nocerts = new Certificate[0];

	// The classes loaded by this class loader. The only purpose of this table
	// is to keep the classes from being GC'ed until the loader is GC'ed.
	private final Vector<Class<?>> classes = new Vector<>();

	// The "default" domain. Set as the default ProtectionDomain on newly
	// created classes.
	private final ProtectionDomain defaultDomain =
	new ProtectionDomain(new CodeSource(null, (Certificate[]) null),
	null, this, null);

	// Invoked by the VM to record every loaded class with this loader.
	void addClass(Class<?> c) {
	classes.addElement(c);
	}

	// The packages defined in this class loader. Each package name is mapped
	// to its corresponding Package object.
	// @GuardedBy("itself")
	private final HashMap<String, Package> packages = new HashMap<>();

	private static Void checkCreateClassLoader() {
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	security.checkCreateClassLoader();
	}
	return null;
	}

	private ClassLoader(Void unused, ClassLoader parent) {
	this.parent = parent;
	if (ParallelLoaders.isRegistered(this.getClass())) {
	parallelLockMap = new ConcurrentHashMap<>();
	package2certs = new ConcurrentHashMap<>();
	assertionLock = new Object();
	} else {
	// no finer-grained lock; lock on the classloader instance
	parallelLockMap = null;
	package2certs = new Hashtable<>();
	assertionLock = this;
	}
	}

	/**
	* Creates a new class loader using the specified parent class loader for
	* delegation.
	*
	* <p> If there is a security manager, its {@link
	* SecurityManager#checkCreateClassLoader()
	* <tt>checkCreateClassLoader</tt>} method is invoked. This may result in
	* a security exception. </p>
	*
	* @param parent
	* The parent class loader
	*
	* @throws SecurityException
	* If a security manager exists and its
	* <tt>checkCreateClassLoader</tt> method doesn't allow creation
	* of a new class loader.
	*
	* @since 1.2
	*/
	protected ClassLoader(ClassLoader parent) {
	this(checkCreateClassLoader(), parent);
	}

	/**
	* Creates a new class loader using the <tt>ClassLoader</tt> returned by
	* the method {@link #getSystemClassLoader()
	* <tt>getSystemClassLoader()</tt>} as the parent class loader.
	*
	* <p> If there is a security manager, its {@link
	* SecurityManager#checkCreateClassLoader()
	* <tt>checkCreateClassLoader</tt>} method is invoked. This may result in
	* a security exception. </p>
	*
	* @throws SecurityException
	* If a security manager exists and its
	* <tt>checkCreateClassLoader</tt> method doesn't allow creation
	* of a new class loader.
	*/
	protected ClassLoader() {
	this(checkCreateClassLoader(), getSystemClassLoader());
	}

	// -- Class --

	/**
	* Loads the class with the specified <a href="#name">binary name</a>.
	* This method searches for classes in the same manner as the {@link
	* #loadClass(String, boolean)} method. It is invoked by the Java virtual
	* machine to resolve class references. Invoking this method is equivalent
	* to invoking {@link #loadClass(String, boolean) <tt>loadClass(name,
	* false)</tt>}.
	*
	* @param name
	* The <a href="#name">binary name</a> of the class
	*
	* @return The resulting <tt>Class</tt> object
	*
	* @throws ClassNotFoundException
	* If the class was not found
	*/
	public Class<?> loadClass(String name) throws ClassNotFoundException {
	return loadClass(name, false);
	}

	/**
	* Loads the class with the specified <a href="#name">binary name</a>. The
	* default implementation of this method searches for classes in the
	* following order:
	*
	* <ol>
	*
	* <li><p> Invoke {@link #findLoadedClass(String)} to check if the class
	* has already been loaded. </p></li>
	*
	* <li><p> Invoke the {@link #loadClass(String) <tt>loadClass</tt>} method
	* on the parent class loader. If the parent is <tt>null</tt> the class
	* loader built-in to the virtual machine is used, instead. </p></li>
	*
	* <li><p> Invoke the {@link #findClass(String)} method to find the
	* class. </p></li>
	*
	* </ol>
	*
	* <p> If the class was found using the above steps, and the
	* <tt>resolve</tt> flag is true, this method will then invoke the {@link
	* #resolveClass(Class)} method on the resulting <tt>Class</tt> object.
	*
	* <p> Subclasses of <tt>ClassLoader</tt> are encouraged to override {@link
	* #findClass(String)}, rather than this method. </p>
	*
	* <p> Unless overridden, this method synchronizes on the result of
	* {@link #getClassLoadingLock <tt>getClassLoadingLock</tt>} method
	* during the entire class loading process.
	*
	* @param name
	* The <a href="#name">binary name</a> of the class
	*
	* @param resolve
	* If <tt>true</tt> then resolve the class
	*
	* @return The resulting <tt>Class</tt> object
	*
	* @throws ClassNotFoundException
	* If the class could not be found
	*/
	protected Class<?> loadClass(String name, boolean resolve)
	throws ClassNotFoundException
	{
	synchronized (getClassLoadingLock(name)) {
	// First, check if the class has already been loaded
	Class<?> c = findLoadedClass(name);
	if (c == null) {
	long t0 = System.nanoTime();
	try {
	if (parent != null) {
	c = parent.loadClass(name, false);
	} else {
	c = findBootstrapClassOrNull(name);
	}
	} catch (ClassNotFoundException e) {
	// ClassNotFoundException thrown if class not found
	// from the non-null parent class loader
	}

	if (c == null) {
	// If still not found, then invoke findClass in order
	// to find the class.
	long t1 = System.nanoTime();
	c = findClass(name);

	// this is the defining class loader; record the stats
	sun.misc.PerfCounter.getParentDelegationTime().addTime(t1 - t0);
	sun.misc.PerfCounter.getFindClassTime().addElapsedTimeFrom(t1);
	sun.misc.PerfCounter.getFindClasses().increment();
	}
	}
	if (resolve) {
	resolveClass(c);
	}
	return c;
	}
	}

	/**
	* Returns the lock object for class loading operations.
	* For backward compatibility, the default implementation of this method
	* behaves as follows. If this ClassLoader object is registered as
	* parallel capable, the method returns a dedicated object associated
	* with the specified class name. Otherwise, the method returns this
	* ClassLoader object.
	*
	* @param className
	* The name of the to-be-loaded class
	*
	* @return the lock for class loading operations
	*
	* @throws NullPointerException
	* If registered as parallel capable and <tt>className</tt> is null
	*
	* @see #loadClass(String, boolean)
	*
	* @since 1.7
	*/
	protected Object getClassLoadingLock(String className) {
	Object lock = this;
	if (parallelLockMap != null) {
	Object newLock = new Object();
	lock = parallelLockMap.putIfAbsent(className, newLock);
	if (lock == null) {
	lock = newLock;
	}
	}
	return lock;
	}

	// This method is invoked by the virtual machine to load a class.
	private Class<?> loadClassInternal(String name)
	throws ClassNotFoundException
	{
	// For backward compatibility, explicitly lock on 'this' when
	// the current class loader is not parallel capable.
	if (parallelLockMap == null) {
	synchronized (this) {
	return loadClass(name);
	}
	} else {
	return loadClass(name);
	}
	}

	// Invoked by the VM after loading class with this loader.
	private void checkPackageAccess(Class<?> cls, ProtectionDomain pd) {
	final SecurityManager sm = System.getSecurityManager();
	if (sm != null) {
	if (ReflectUtil.isNonPublicProxyClass(cls)) {
	for (Class<?> intf: cls.getInterfaces()) {
	checkPackageAccess(intf, pd);
	}
	return;
	}

	final String name = cls.getName();
	final int i = name.lastIndexOf('.');
	if (i != -1) {
	AccessController.doPrivileged(new PrivilegedAction<Void>() {
	public Void run() {
	sm.checkPackageAccess(name.substring(0, i));
	return null;
	}
	}, new AccessControlContext(new ProtectionDomain[] {pd}));
	}
	}
	}

	/**
	* Finds the class with the specified <a href="#name">binary name</a>.
	* This method should be overridden by class loader implementations that
	* follow the delegation model for loading classes, and will be invoked by
	* the {@link #loadClass <tt>loadClass</tt>} method after checking the
	* parent class loader for the requested class. The default implementation
	* throws a <tt>ClassNotFoundException</tt>.
	*
	* @param name
	* The <a href="#name">binary name</a> of the class
	*
	* @return The resulting <tt>Class</tt> object
	*
	* @throws ClassNotFoundException
	* If the class could not be found
	*
	* @since 1.2
	*/
	protected Class<?> findClass(String name) throws ClassNotFoundException {
	throw new ClassNotFoundException(name);
	}

	/**
	* Converts an array of bytes into an instance of class <tt>Class</tt>.
	* Before the <tt>Class</tt> can be used it must be resolved. This method
	* is deprecated in favor of the version that takes a <a
	* href="#name">binary name</a> as its first argument, and is more secure.
	*
	* @param b
	* The bytes that make up the class data. The bytes in positions
	* <tt>off</tt> through <tt>off+len-1</tt> should have the format
	* of a valid class file as defined by
	* <cite>The Java™ Virtual Machine Specification</cite>.
	*
	* @param off
	* The start offset in <tt>b</tt> of the class data
	*
	* @param len
	* The length of the class data
	*
	* @return The <tt>Class</tt> object that was created from the specified
	* class data
	*
	* @throws ClassFormatError
	* If the data did not contain a valid class
	*
	* @throws IndexOutOfBoundsException
	* If either <tt>off</tt> or <tt>len</tt> is negative, or if
	* <tt>off+len</tt> is greater than <tt>b.length</tt>.
	*
	* @throws SecurityException
	* If an attempt is made to add this class to a package that
	* contains classes that were signed by a different set of
	* certificates than this class, or if an attempt is made
	* to define a class in a package with a fully-qualified name
	* that starts with "{@code java.}".
	*
	* @see #loadClass(String, boolean)
	* @see #resolveClass(Class)
	*
	* @deprecated Replaced by {@link #defineClass(String, byte[], int, int)
	* defineClass(String, byte[], int, int)}
	*/
	@Deprecated
	protected final Class<?> defineClass(byte[] b, int off, int len)
	throws ClassFormatError
	{
	return defineClass(null, b, off, len, null);
	}

	/**
	* Converts an array of bytes into an instance of class <tt>Class</tt>.
	* Before the <tt>Class</tt> can be used it must be resolved.
	*
	* <p> This method assigns a default {@link java.security.ProtectionDomain
	* <tt>ProtectionDomain</tt>} to the newly defined class. The
	* <tt>ProtectionDomain</tt> is effectively granted the same set of
	* permissions returned when {@link
	* java.security.Policy#getPermissions(java.security.CodeSource)
	* <tt>Policy.getPolicy().getPermissions(new CodeSource(null, null))</tt>}
	* is invoked. The default domain is created on the first invocation of
	* {@link #defineClass(String, byte[], int, int) <tt>defineClass</tt>},
	* and re-used on subsequent invocations.
	*
	* <p> To assign a specific <tt>ProtectionDomain</tt> to the class, use
	* the {@link #defineClass(String, byte[], int, int,
	* java.security.ProtectionDomain) <tt>defineClass</tt>} method that takes a
	* <tt>ProtectionDomain</tt> as one of its arguments. </p>
	*
	* @param name
	* The expected <a href="#name">binary name</a> of the class, or
	* <tt>null</tt> if not known
	*
	* @param b
	* The bytes that make up the class data. The bytes in positions
	* <tt>off</tt> through <tt>off+len-1</tt> should have the format
	* of a valid class file as defined by
	* <cite>The Java™ Virtual Machine Specification</cite>.
	*
	* @param off
	* The start offset in <tt>b</tt> of the class data
	*
	* @param len
	* The length of the class data
	*
	* @return The <tt>Class</tt> object that was created from the specified
	* class data.
	*
	* @throws ClassFormatError
	* If the data did not contain a valid class
	*
	* @throws IndexOutOfBoundsException
	* If either <tt>off</tt> or <tt>len</tt> is negative, or if
	* <tt>off+len</tt> is greater than <tt>b.length</tt>.
	*
	* @throws SecurityException
	* If an attempt is made to add this class to a package that
	* contains classes that were signed by a different set of
	* certificates than this class (which is unsigned), or if
	* <tt>name</tt> begins with "<tt>java.</tt>".
	*
	* @see #loadClass(String, boolean)
	* @see #resolveClass(Class)
	* @see java.security.CodeSource
	* @see java.security.SecureClassLoader
	*
	* @since 1.1
	*/
	protected final Class<?> defineClass(String name, byte[] b, int off, int len)
	throws ClassFormatError
	{
	return defineClass(name, b, off, len, null);
	}

	/* Determine protection domain, and check that:
	- not define java.* class,
	- signer of this class matches signers for the rest of the classes in
	package.
	*/
	private ProtectionDomain preDefineClass(String name,
	ProtectionDomain pd)
	{
	if (!checkName(name))
	throw new NoClassDefFoundError("IllegalName: " + name);

	// Note: Checking logic in java.lang.invoke.MemberName.checkForTypeAlias
	// relies on the fact that spoofing is impossible if a class has a name
	// of the form "java.*"
	if ((name != null) && name.startsWith("java.")) {
	throw new SecurityException
	("Prohibited package name: " +
	name.substring(0, name.lastIndexOf('.')));
	}
	if (pd == null) {
	pd = defaultDomain;
	}

	if (name != null) checkCerts(name, pd.getCodeSource());

	return pd;
	}

	private String defineClassSourceLocation(ProtectionDomain pd)
	{
	CodeSource cs = pd.getCodeSource();
	String source = null;
	if (cs != null && cs.getLocation() != null) {
	source = cs.getLocation().toString();
	}
	return source;
	}

	private void postDefineClass(Class<?> c, ProtectionDomain pd)
	{
	if (pd.getCodeSource() != null) {
	Certificate certs[] = pd.getCodeSource().getCertificates();
	if (certs != null)
	setSigners(c, certs);
	}
	}

	/**
	* Converts an array of bytes into an instance of class <tt>Class</tt>,
	* with an optional <tt>ProtectionDomain</tt>. If the domain is
	* <tt>null</tt>, then a default domain will be assigned to the class as
	* specified in the documentation for {@link #defineClass(String, byte[],
	* int, int)}. Before the class can be used it must be resolved.
	*
	* <p> The first class defined in a package determines the exact set of
	* certificates that all subsequent classes defined in that package must
	* contain. The set of certificates for a class is obtained from the
	* {@link java.security.CodeSource <tt>CodeSource</tt>} within the
	* <tt>ProtectionDomain</tt> of the class. Any classes added to that
	* package must contain the same set of certificates or a
	* <tt>SecurityException</tt> will be thrown. Note that if
	* <tt>name</tt> is <tt>null</tt>, this check is not performed.
	* You should always pass in the <a href="#name">binary name</a> of the
	* class you are defining as well as the bytes. This ensures that the
	* class you are defining is indeed the class you think it is.
	*
	* <p> The specified <tt>name</tt> cannot begin with "<tt>java.</tt>", since
	* all classes in the "<tt>java.*</tt> packages can only be defined by the
	* bootstrap class loader. If <tt>name</tt> is not <tt>null</tt>, it
	* must be equal to the <a href="#name">binary name</a> of the class
	* specified by the byte array "<tt>b</tt>", otherwise a {@link
	* NoClassDefFoundError <tt>NoClassDefFoundError</tt>} will be thrown. </p>
	*
	* @param name
	* The expected <a href="#name">binary name</a> of the class, or
	* <tt>null</tt> if not known
	*
	* @param b
	* The bytes that make up the class data. The bytes in positions
	* <tt>off</tt> through <tt>off+len-1</tt> should have the format
	* of a valid class file as defined by
	* <cite>The Java™ Virtual Machine Specification</cite>.
	*
	* @param off
	* The start offset in <tt>b</tt> of the class data
	*
	* @param len
	* The length of the class data
	*
	* @param protectionDomain
	* The ProtectionDomain of the class
	*
	* @return The <tt>Class</tt> object created from the data,
	* and optional <tt>ProtectionDomain</tt>.
	*
	* @throws ClassFormatError
	* If the data did not contain a valid class
	*
	* @throws NoClassDefFoundError
	* If <tt>name</tt> is not equal to the <a href="#name">binary
	* name</a> of the class specified by <tt>b</tt>
	*
	* @throws IndexOutOfBoundsException
	* If either <tt>off</tt> or <tt>len</tt> is negative, or if
	* <tt>off+len</tt> is greater than <tt>b.length</tt>.
	*
	* @throws SecurityException
	* If an attempt is made to add this class to a package that
	* contains classes that were signed by a different set of
	* certificates than this class, or if <tt>name</tt> begins with
	* "<tt>java.</tt>".
	*/
	protected final Class<?> defineClass(String name, byte[] b, int off, int len,
	ProtectionDomain protectionDomain)
	throws ClassFormatError
	{
	protectionDomain = preDefineClass(name, protectionDomain);
	String source = defineClassSourceLocation(protectionDomain);
	Class<?> c = defineClass1(name, b, off, len, protectionDomain, source);
	postDefineClass(c, protectionDomain);
	return c;
	}

	/**
	* Converts a {@link java.nio.ByteBuffer <tt>ByteBuffer</tt>}
	* into an instance of class <tt>Class</tt>,
	* with an optional <tt>ProtectionDomain</tt>. If the domain is
	* <tt>null</tt>, then a default domain will be assigned to the class as
	* specified in the documentation for {@link #defineClass(String, byte[],
	* int, int)}. Before the class can be used it must be resolved.
	*
	* <p>The rules about the first class defined in a package determining the
	* set of certificates for the package, and the restrictions on class names
	* are identical to those specified in the documentation for {@link
	* #defineClass(String, byte[], int, int, ProtectionDomain)}.
	*
	* <p> An invocation of this method of the form
	* <i>cl</i><tt>.defineClass(</tt><i>name</i><tt>,</tt>
	* <i>bBuffer</i><tt>,</tt> <i>pd</i><tt>)</tt> yields exactly the same
	* result as the statements
	*
	*<p> <tt>
	* ...<br>
	* byte[] temp = new byte[bBuffer.{@link
	* java.nio.ByteBuffer#remaining remaining}()];<br>
	* bBuffer.{@link java.nio.ByteBuffer#get(byte[])
	* get}(temp);<br>
	* return {@link #defineClass(String, byte[], int, int, ProtectionDomain)
	* cl.defineClass}(name, temp, 0,
	* temp.length, pd);<br>
	* </tt></p>
	*
	* @param name
	* The expected <a href="#name">binary name</a>. of the class, or
	* <tt>null</tt> if not known
	*
	* @param b
	* The bytes that make up the class data. The bytes from positions
	* <tt>b.position()</tt> through <tt>b.position() + b.limit() -1
	* </tt> should have the format of a valid class file as defined by
	* <cite>The Java™ Virtual Machine Specification</cite>.
	*
	* @param protectionDomain
	* The ProtectionDomain of the class, or <tt>null</tt>.
	*
	* @return The <tt>Class</tt> object created from the data,
	* and optional <tt>ProtectionDomain</tt>.
	*
	* @throws ClassFormatError
	* If the data did not contain a valid class.
	*
	* @throws NoClassDefFoundError
	* If <tt>name</tt> is not equal to the <a href="#name">binary
	* name</a> of the class specified by <tt>b</tt>
	*
	* @throws SecurityException
	* If an attempt is made to add this class to a package that
	* contains classes that were signed by a different set of
	* certificates than this class, or if <tt>name</tt> begins with
	* "<tt>java.</tt>".
	*
	* @see #defineClass(String, byte[], int, int, ProtectionDomain)
	*
	* @since 1.5
	*/
	protected final Class<?> defineClass(String name, java.nio.ByteBuffer b,
	ProtectionDomain protectionDomain)
	throws ClassFormatError
	{
	int len = b.remaining();

	// Use byte[] if not a direct ByteBufer:
	if (!b.isDirect()) {
	if (b.hasArray()) {
	return defineClass(name, b.array(),
	b.position() + b.arrayOffset(), len,
	protectionDomain);
	} else {
	// no array, or read-only array
	byte[] tb = new byte[len];
	b.get(tb); // get bytes out of byte buffer.
	return defineClass(name, tb, 0, len, protectionDomain);
	}
	}

	protectionDomain = preDefineClass(name, protectionDomain);
	String source = defineClassSourceLocation(protectionDomain);
	Class<?> c = defineClass2(name, b, b.position(), len, protectionDomain, source);
	postDefineClass(c, protectionDomain);
	return c;
	}

	private native Class<?> defineClass0(String name, byte[] b, int off, int len,
	ProtectionDomain pd);

	private native Class<?> defineClass1(String name, byte[] b, int off, int len,
	ProtectionDomain pd, String source);

	private native Class<?> defineClass2(String name, java.nio.ByteBuffer b,
	int off, int len, ProtectionDomain pd,
	String source);

	// true if the name is null or has the potential to be a valid binary name
	private boolean checkName(String name) {
	if ((name == null) \|\| (name.length() == 0))
	return true;
	if ((name.indexOf('/') != -1)
	\|\| (!VM.allowArraySyntax() && (name.charAt(0) == '[')))
	return false;
	return true;
	}

	private void checkCerts(String name, CodeSource cs) {
	int i = name.lastIndexOf('.');
	String pname = (i == -1) ? "" : name.substring(0, i);

	Certificate[] certs = null;
	if (cs != null) {
	certs = cs.getCertificates();
	}
	Certificate[] pcerts = null;
	if (parallelLockMap == null) {
	synchronized (this) {
	pcerts = package2certs.get(pname);
	if (pcerts == null) {
	package2certs.put(pname, (certs == null? nocerts:certs));
	}
	}
	} else {
	pcerts = ((ConcurrentHashMap<String, Certificate[]>)package2certs).
	putIfAbsent(pname, (certs == null? nocerts:certs));
	}
	if (pcerts != null && !compareCerts(pcerts, certs)) {
	throw new SecurityException("class \""+ name +
	"\"'s signer information does not match signer information of other classes in the same package");
	}
	}

	/**
	* check to make sure the certs for the new class (certs) are the same as
	* the certs for the first class inserted in the package (pcerts)
	*/
	private boolean compareCerts(Certificate[] pcerts,
	Certificate[] certs)
	{
	// certs can be null, indicating no certs.
	if ((certs == null) \|\| (certs.length == 0)) {
	return pcerts.length == 0;
	}

	// the length must be the same at this point
	if (certs.length != pcerts.length)
	return false;

	// go through and make sure all the certs in one array
	// are in the other and vice-versa.
	boolean match;
	for (int i = 0; i < certs.length; i++) {
	match = false;
	for (int j = 0; j < pcerts.length; j++) {
	if (certs[i].equals(pcerts[j])) {
	match = true;
	break;
	}
	}
	if (!match) return false;
	}

	// now do the same for pcerts
	for (int i = 0; i < pcerts.length; i++) {
	match = false;
	for (int j = 0; j < certs.length; j++) {
	if (pcerts[i].equals(certs[j])) {
	match = true;
	break;
	}
	}
	if (!match) return false;
	}

	return true;
	}

	/**
	* Links the specified class. This (misleadingly named) method may be
	* used by a class loader to link a class. If the class <tt>c</tt> has
	* already been linked, then this method simply returns. Otherwise, the
	* class is linked as described in the "Execution" chapter of
	* <cite>The Java™ Language Specification</cite>.
	*
	* @param c
	* The class to link
	*
	* @throws NullPointerException
	* If <tt>c</tt> is <tt>null</tt>.
	*
	* @see #defineClass(String, byte[], int, int)
	*/
	protected final void resolveClass(Class<?> c) {
	resolveClass0(c);
	}

	private native void resolveClass0(Class<?> c);

	/**
	* Finds a class with the specified <a href="#name">binary name</a>,
	* loading it if necessary.
	*
	* <p> This method loads the class through the system class loader (see
	* {@link #getSystemClassLoader()}). The <tt>Class</tt> object returned
	* might have more than one <tt>ClassLoader</tt> associated with it.
	* Subclasses of <tt>ClassLoader</tt> need not usually invoke this method,
	* because most class loaders need to override just {@link
	* #findClass(String)}. </p>
	*
	* @param name
	* The <a href="#name">binary name</a> of the class
	*
	* @return The <tt>Class</tt> object for the specified <tt>name</tt>
	*
	* @throws ClassNotFoundException
	* If the class could not be found
	*
	* @see #ClassLoader(ClassLoader)
	* @see #getParent()
	*/
	protected final Class<?> findSystemClass(String name)
	throws ClassNotFoundException
	{
	ClassLoader system = getSystemClassLoader();
	if (system == null) {
	if (!checkName(name))
	throw new ClassNotFoundException(name);
	Class<?> cls = findBootstrapClass(name);
	if (cls == null) {
	throw new ClassNotFoundException(name);
	}
	return cls;
	}
	return system.loadClass(name);
	}

	/**
	* Returns a class loaded by the bootstrap class loader;
	* or return null if not found.
	*/
	private Class<?> findBootstrapClassOrNull(String name)
	{
	if (!checkName(name)) return null;

	return findBootstrapClass(name);
	}

	// return null if not found
	private native Class<?> findBootstrapClass(String name);

	/**
	* Returns the class with the given <a href="#name">binary name</a> if this
	* loader has been recorded by the Java virtual machine as an initiating
	* loader of a class with that <a href="#name">binary name</a>. Otherwise
	* <tt>null</tt> is returned.
	*
	* @param name
	* The <a href="#name">binary name</a> of the class
	*
	* @return The <tt>Class</tt> object, or <tt>null</tt> if the class has
	* not been loaded
	*
	* @since 1.1
	*/
	protected final Class<?> findLoadedClass(String name) {
	if (!checkName(name))
	return null;
	return findLoadedClass0(name);
	}

	private native final Class<?> findLoadedClass0(String name);

	/**
	* Sets the signers of a class. This should be invoked after defining a
	* class.
	*
	* @param c
	* The <tt>Class</tt> object
	*
	* @param signers
	* The signers for the class
	*
	* @since 1.1
	*/
	protected final void setSigners(Class<?> c, Object[] signers) {
	c.setSigners(signers);
	}


	// -- Resource --

	/**
	* Finds the resource with the given name. A resource is some data
	* (images, audio, text, etc) that can be accessed by class code in a way
	* that is independent of the location of the code.
	*
	* <p> The name of a resource is a '<tt>/</tt>'-separated path name that
	* identifies the resource.
	*
	* <p> This method will first search the parent class loader for the
	* resource; if the parent is <tt>null</tt> the path of the class loader
	* built-in to the virtual machine is searched. That failing, this method
	* will invoke {@link #findResource(String)} to find the resource. </p>
	*
	* @apiNote When overriding this method it is recommended that an
	* implementation ensures that any delegation is consistent with the {@link
	* #getResources(java.lang.String) getResources(String)} method.
	*
	* @param name
	* The resource name
	*
	* @return A <tt>URL</tt> object for reading the resource, or
	* <tt>null</tt> if the resource could not be found or the invoker
	* doesn't have adequate privileges to get the resource.
	*
	* @since 1.1
	*/
	public URL getResource(String name) {
	URL url;
	if (parent != null) {
	url = parent.getResource(name);
	} else {
	url = getBootstrapResource(name);
	}
	if (url == null) {
	url = findResource(name);
	}
	return url;
	}

	/**
	* Finds all the resources with the given name. A resource is some data
	* (images, audio, text, etc) that can be accessed by class code in a way
	* that is independent of the location of the code.
	*
	* <p>The name of a resource is a <tt>/</tt>-separated path name that
	* identifies the resource.
	*
	* <p> The search order is described in the documentation for {@link
	* #getResource(String)}. </p>
	*
	* @apiNote When overriding this method it is recommended that an
	* implementation ensures that any delegation is consistent with the {@link
	* #getResource(java.lang.String) getResource(String)} method. This should
	* ensure that the first element returned by the Enumeration's
	* {@code nextElement} method is the same resource that the
	* {@code getResource(String)} method would return.
	*
	* @param name
	* The resource name
	*
	* @return An enumeration of {@link java.net.URL <tt>URL</tt>} objects for
	* the resource. If no resources could be found, the enumeration
	* will be empty. Resources that the class loader doesn't have
	* access to will not be in the enumeration.
	*
	* @throws IOException
	* If I/O errors occur
	*
	* @see #findResources(String)
	*
	* @since 1.2
	*/
	public Enumeration<URL> getResources(String name) throws IOException {
	@SuppressWarnings("unchecked")
	Enumeration<URL>[] tmp = (Enumeration<URL>[]) new Enumeration<?>[2];
	if (parent != null) {
	tmp[0] = parent.getResources(name);
	} else {
	tmp[0] = getBootstrapResources(name);
	}
	tmp[1] = findResources(name);

	return new CompoundEnumeration<>(tmp);
	}

	/**
	* Finds the resource with the given name. Class loader implementations
	* should override this method to specify where to find resources.
	*
	* @param name
	* The resource name
	*
	* @return A <tt>URL</tt> object for reading the resource, or
	* <tt>null</tt> if the resource could not be found
	*
	* @since 1.2
	*/
	protected URL findResource(String name) {
	return null;
	}

	/**
	* Returns an enumeration of {@link java.net.URL <tt>URL</tt>} objects
	* representing all the resources with the given name. Class loader
	* implementations should override this method to specify where to load
	* resources from.
	*
	* @param name
	* The resource name
	*
	* @return An enumeration of {@link java.net.URL <tt>URL</tt>} objects for
	* the resources
	*
	* @throws IOException
	* If I/O errors occur
	*
	* @since 1.2
	*/
	protected Enumeration<URL> findResources(String name) throws IOException {
	return java.util.Collections.emptyEnumeration();
	}

	/**
	* Registers the caller as parallel capable.
	* The registration succeeds if and only if all of the following
	* conditions are met:
	* <ol>
	* <li> no instance of the caller has been created</li>
	* <li> all of the super classes (except class Object) of the caller are
	* registered as parallel capable</li>
	* </ol>
	* <p>Note that once a class loader is registered as parallel capable, there
	* is no way to change it back.</p>
	*
	* @return true if the caller is successfully registered as
	* parallel capable and false if otherwise.
	*
	* @since 1.7
	*/
	@CallerSensitive
	protected static boolean registerAsParallelCapable() {
	Class<? extends ClassLoader> callerClass =
	Reflection.getCallerClass().asSubclass(ClassLoader.class);
	return ParallelLoaders.register(callerClass);
	}

	/**
	* Find a resource of the specified name from the search path used to load
	* classes. This method locates the resource through the system class
	* loader (see {@link #getSystemClassLoader()}).
	*
	* @param name
	* The resource name
	*
	* @return A {@link java.net.URL <tt>URL</tt>} object for reading the
	* resource, or <tt>null</tt> if the resource could not be found
	*
	* @since 1.1
	*/
	public static URL getSystemResource(String name) {
	ClassLoader system = getSystemClassLoader();
	if (system == null) {
	return getBootstrapResource(name);
	}
	return system.getResource(name);
	}

	/**
	* Finds all resources of the specified name from the search path used to
	* load classes. The resources thus found are returned as an
	* {@link java.util.Enumeration <tt>Enumeration</tt>} of {@link
	* java.net.URL <tt>URL</tt>} objects.
	*
	* <p> The search order is described in the documentation for {@link
	* #getSystemResource(String)}. </p>
	*
	* @param name
	* The resource name
	*
	* @return An enumeration of resource {@link java.net.URL <tt>URL</tt>}
	* objects
	*
	* @throws IOException
	* If I/O errors occur

	* @since 1.2
	*/
	public static Enumeration<URL> getSystemResources(String name)
	throws IOException
	{
	ClassLoader system = getSystemClassLoader();
	if (system == null) {
	return getBootstrapResources(name);
	}
	return system.getResources(name);
	}

	/**
	* Find resources from the VM's built-in classloader.
	*/
	private static URL getBootstrapResource(String name) {
	URLClassPath ucp = getBootstrapClassPath();
	Resource res = ucp.getResource(name);
	return res != null ? res.getURL() : null;
	}

	/**
	* Find resources from the VM's built-in classloader.
	*/
	private static Enumeration<URL> getBootstrapResources(String name)
	throws IOException
	{
	final Enumeration<Resource> e =
	getBootstrapClassPath().getResources(name);
	return new Enumeration<URL> () {
	public URL nextElement() {
	return e.nextElement().getURL();
	}
	public boolean hasMoreElements() {
	return e.hasMoreElements();
	}
	};
	}

	// Returns the URLClassPath that is used for finding system resources.
	static URLClassPath getBootstrapClassPath() {
	return sun.misc.Launcher.getBootstrapClassPath();
	}


	/**
	* Returns an input stream for reading the specified resource.
	*
	* <p> The search order is described in the documentation for {@link
	* #getResource(String)}. </p>
	*
	* @param name
	* The resource name
	*
	* @return An input stream for reading the resource, or <tt>null</tt>
	* if the resource could not be found
	*
	* @since 1.1
	*/
	public InputStream getResourceAsStream(String name) {
	URL url = getResource(name);
	try {
	return url != null ? url.openStream() : null;
	} catch (IOException e) {
	return null;
	}
	}

	/**
	* Open for reading, a resource of the specified name from the search path
	* used to load classes. This method locates the resource through the
	* system class loader (see {@link #getSystemClassLoader()}).
	*
	* @param name
	* The resource name
	*
	* @return An input stream for reading the resource, or <tt>null</tt>
	* if the resource could not be found
	*
	* @since 1.1
	*/
	public static InputStream getSystemResourceAsStream(String name) {
	URL url = getSystemResource(name);
	try {
	return url != null ? url.openStream() : null;
	} catch (IOException e) {
	return null;
	}
	}


	// -- Hierarchy --

	/**
	* Returns the parent class loader for delegation. Some implementations may
	* use <tt>null</tt> to represent the bootstrap class loader. This method
	* will return <tt>null</tt> in such implementations if this class loader's
	* parent is the bootstrap class loader.
	*
	* <p> If a security manager is present, and the invoker's class loader is
	* not <tt>null</tt> and is not an ancestor of this class loader, then this
	* method invokes the security manager's {@link
	* SecurityManager#checkPermission(java.security.Permission)
	* <tt>checkPermission</tt>} method with a {@link
	* RuntimePermission#RuntimePermission(String)
	* <tt>RuntimePermission("getClassLoader")</tt>} permission to verify
	* access to the parent class loader is permitted. If not, a
	* <tt>SecurityException</tt> will be thrown. </p>
	*
	* @return The parent <tt>ClassLoader</tt>
	*
	* @throws SecurityException
	* If a security manager exists and its <tt>checkPermission</tt>
	* method doesn't allow access to this class loader's parent class
	* loader.
	*
	* @since 1.2
	*/
	@CallerSensitive
	public final ClassLoader getParent() {
	if (parent == null)
	return null;
	SecurityManager sm = System.getSecurityManager();
	if (sm != null) {
	// Check access to the parent class loader
	// If the caller's class loader is same as this class loader,
	// permission check is performed.
	checkClassLoaderPermission(parent, Reflection.getCallerClass());
	}
	return parent;
	}

	/**
	* Returns the system class loader for delegation. This is the default
	* delegation parent for new <tt>ClassLoader</tt> instances, and is
	* typically the class loader used to start the application.
	*
	* <p> This method is first invoked early in the runtime's startup
	* sequence, at which point it creates the system class loader and sets it
	* as the context class loader of the invoking <tt>Thread</tt>.
	*
	* <p> The default system class loader is an implementation-dependent
	* instance of this class.
	*
	* <p> If the system property "<tt>java.system.class.loader</tt>" is defined
	* when this method is first invoked then the value of that property is
	* taken to be the name of a class that will be returned as the system
	* class loader. The class is loaded using the default system class loader
	* and must define a public constructor that takes a single parameter of
	* type <tt>ClassLoader</tt> which is used as the delegation parent. An
	* instance is then created using this constructor with the default system
	* class loader as the parameter. The resulting class loader is defined
	* to be the system class loader.
	*
	* <p> If a security manager is present, and the invoker's class loader is
	* not <tt>null</tt> and the invoker's class loader is not the same as or
	* an ancestor of the system class loader, then this method invokes the
	* security manager's {@link
	* SecurityManager#checkPermission(java.security.Permission)
	* <tt>checkPermission</tt>} method with a {@link
	* RuntimePermission#RuntimePermission(String)
	* <tt>RuntimePermission("getClassLoader")</tt>} permission to verify
	* access to the system class loader. If not, a
	* <tt>SecurityException</tt> will be thrown. </p>
	*
	* @return The system <tt>ClassLoader</tt> for delegation, or
	* <tt>null</tt> if none
	*
	* @throws SecurityException
	* If a security manager exists and its <tt>checkPermission</tt>
	* method doesn't allow access to the system class loader.
	*
	* @throws IllegalStateException
	* If invoked recursively during the construction of the class
	* loader specified by the "<tt>java.system.class.loader</tt>"
	* property.
	*
	* @throws Error
	* If the system property "<tt>java.system.class.loader</tt>"
	* is defined but the named class could not be loaded, the
	* provider class does not define the required constructor, or an
	* exception is thrown by that constructor when it is invoked. The
	* underlying cause of the error can be retrieved via the
	* {@link Throwable#getCause()} method.
	*
	* @revised 1.4
	*/
	@CallerSensitive
	public static ClassLoader getSystemClassLoader() {
	initSystemClassLoader();
	if (scl == null) {
	return null;
	}
	SecurityManager sm = System.getSecurityManager();
	if (sm != null) {
	checkClassLoaderPermission(scl, Reflection.getCallerClass());
	}
	return scl;
	}

	private static synchronized void initSystemClassLoader() {
	if (!sclSet) {
	if (scl != null)
	throw new IllegalStateException("recursive invocation");
	sun.misc.Launcher l = sun.misc.Launcher.getLauncher();
	if (l != null) {
	Throwable oops = null;
	scl = l.getClassLoader();
	try {
	scl = AccessController.doPrivileged(
	new SystemClassLoaderAction(scl));
	} catch (PrivilegedActionException pae) {
	oops = pae.getCause();
	if (oops instanceof InvocationTargetException) {
	oops = oops.getCause();
	}
	}
	if (oops != null) {
	if (oops instanceof Error) {
	throw (Error) oops;
	} else {
	// wrap the exception
	throw new Error(oops);
	}
	}
	}
	sclSet = true;
	}
	}

	// Returns true if the specified class loader can be found in this class
	// loader's delegation chain.
	boolean isAncestor(ClassLoader cl) {
	ClassLoader acl = this;
	do {
	acl = acl.parent;
	if (cl == acl) {
	return true;
	}
	} while (acl != null);
	return false;
	}

	// Tests if class loader access requires "getClassLoader" permission
	// check. A class loader 'from' can access class loader 'to' if
	// class loader 'from' is same as class loader 'to' or an ancestor
	// of 'to'. The class loader in a system domain can access
	// any class loader.
	private static boolean needsClassLoaderPermissionCheck(ClassLoader from,
	ClassLoader to)
	{
	if (from == to)
	return false;

	if (from == null)
	return false;

	return !to.isAncestor(from);
	}

	// Returns the class's class loader, or null if none.
	static ClassLoader getClassLoader(Class<?> caller) {
	// This can be null if the VM is requesting it
	if (caller == null) {
	return null;
	}
	// Circumvent security check since this is package-private
	return caller.getClassLoader0();
	}

	/*
	* Checks RuntimePermission("getClassLoader") permission
	* if caller's class loader is not null and caller's class loader
	* is not the same as or an ancestor of the given cl argument.
	*/
	static void checkClassLoaderPermission(ClassLoader cl, Class<?> caller) {
	SecurityManager sm = System.getSecurityManager();
	if (sm != null) {
	// caller can be null if the VM is requesting it
	ClassLoader ccl = getClassLoader(caller);
	if (needsClassLoaderPermissionCheck(ccl, cl)) {
	sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
	}
	}
	}

	// The class loader for the system
	// @GuardedBy("ClassLoader.class")
	private static ClassLoader scl;

	// Set to true once the system class loader has been set
	// @GuardedBy("ClassLoader.class")
	private static boolean sclSet;


	// -- Package --

	/**
	* Defines a package by name in this <tt>ClassLoader</tt>. This allows
	* class loaders to define the packages for their classes. Packages must
	* be created before the class is defined, and package names must be
	* unique within a class loader and cannot be redefined or changed once
	* created.
	*
	* @param name
	* The package name
	*
	* @param specTitle
	* The specification title
	*
	* @param specVersion
	* The specification version
	*
	* @param specVendor
	* The specification vendor
	*
	* @param implTitle
	* The implementation title
	*
	* @param implVersion
	* The implementation version
	*
	* @param implVendor
	* The implementation vendor
	*
	* @param sealBase
	* If not <tt>null</tt>, then this package is sealed with
	* respect to the given code source {@link java.net.URL
	* <tt>URL</tt>} object. Otherwise, the package is not sealed.
	*
	* @return The newly defined <tt>Package</tt> object
	*
	* @throws IllegalArgumentException
	* If package name duplicates an existing package either in this
	* class loader or one of its ancestors
	*
	* @since 1.2
	*/
	protected Package definePackage(String name, String specTitle,
	String specVersion, String specVendor,
	String implTitle, String implVersion,
	String implVendor, URL sealBase)
	throws IllegalArgumentException
	{
	synchronized (packages) {
	Package pkg = getPackage(name);
	if (pkg != null) {
	throw new IllegalArgumentException(name);
	}
	pkg = new Package(name, specTitle, specVersion, specVendor,
	implTitle, implVersion, implVendor,
	sealBase, this);
	packages.put(name, pkg);
	return pkg;
	}
	}

	/**
	* Returns a <tt>Package</tt> that has been defined by this class loader
	* or any of its ancestors.
	*
	* @param name
	* The package name
	*
	* @return The <tt>Package</tt> corresponding to the given name, or
	* <tt>null</tt> if not found
	*
	* @since 1.2
	*/
	protected Package getPackage(String name) {
	Package pkg;
	synchronized (packages) {
	pkg = packages.get(name);
	}
	if (pkg == null) {
	if (parent != null) {
	pkg = parent.getPackage(name);
	} else {
	pkg = Package.getSystemPackage(name);
	}
	if (pkg != null) {
	synchronized (packages) {
	Package pkg2 = packages.get(name);
	if (pkg2 == null) {
	packages.put(name, pkg);
	} else {
	pkg = pkg2;
	}
	}
	}
	}
	return pkg;
	}

	/**
	* Returns all of the <tt>Packages</tt> defined by this class loader and
	* its ancestors.
	*
	* @return The array of <tt>Package</tt> objects defined by this
	* <tt>ClassLoader</tt>
	*
	* @since 1.2
	*/
	protected Package[] getPackages() {
	Map<String, Package> map;
	synchronized (packages) {
	map = new HashMap<>(packages);
	}
	Package[] pkgs;
	if (parent != null) {
	pkgs = parent.getPackages();
	} else {
	pkgs = Package.getSystemPackages();
	}
	if (pkgs != null) {
	for (int i = 0; i < pkgs.length; i++) {
	String pkgName = pkgs[i].getName();
	if (map.get(pkgName) == null) {
	map.put(pkgName, pkgs[i]);
	}
	}
	}
	return map.values().toArray(new Package[map.size()]);
	}


	// -- Native library access --

	/**
	* Returns the absolute path name of a native library. The VM invokes this
	* method to locate the native libraries that belong to classes loaded with
	* this class loader. If this method returns <tt>null</tt>, the VM
	* searches the library along the path specified as the
	* "<tt>java.library.path</tt>" property.
	*
	* @param libname
	* The library name
	*
	* @return The absolute path of the native library
	*
	* @see System#loadLibrary(String)
	* @see System#mapLibraryName(String)
	*
	* @since 1.2
	*/
	protected String findLibrary(String libname) {
	return null;
	}

	/**
	* The inner class NativeLibrary denotes a loaded native library instance.
	* Every classloader contains a vector of loaded native libraries in the
	* private field <tt>nativeLibraries</tt>. The native libraries loaded
	* into the system are entered into the <tt>systemNativeLibraries</tt>
	* vector.
	*
	* <p> Every native library requires a particular version of JNI. This is
	* denoted by the private <tt>jniVersion</tt> field. This field is set by
	* the VM when it loads the library, and used by the VM to pass the correct
	* version of JNI to the native methods. </p>
	*
	* @see ClassLoader
	* @since 1.2
	*/
	static class NativeLibrary {
	// opaque handle to native library, used in native code.
	long handle;
	// the version of JNI environment the native library requires.
	private int jniVersion;
	// the class from which the library is loaded, also indicates
	// the loader this native library belongs.
	private final Class<?> fromClass;
	// the canonicalized name of the native library.
	// or static library name
	String name;
	// Indicates if the native library is linked into the VM
	boolean isBuiltin;
	// Indicates if the native library is loaded
	boolean loaded;
	native void load(String name, boolean isBuiltin);

	native long find(String name);
	native void unload(String name, boolean isBuiltin);

	public NativeLibrary(Class<?> fromClass, String name, boolean isBuiltin) {
	this.name = name;
	this.fromClass = fromClass;
	this.isBuiltin = isBuiltin;
	}

	protected void finalize() {
	synchronized (loadedLibraryNames) {
	if (fromClass.getClassLoader() != null && loaded) {
	/* remove the native library name */
	int size = loadedLibraryNames.size();
	for (int i = 0; i < size; i++) {
	if (name.equals(loadedLibraryNames.elementAt(i))) {
	loadedLibraryNames.removeElementAt(i);
	break;
	}
	}
	/* unload the library. */
	ClassLoader.nativeLibraryContext.push(this);
	try {
	unload(name, isBuiltin);
	} finally {
	ClassLoader.nativeLibraryContext.pop();
	}
	}
	}
	}
	// Invoked in the VM to determine the context class in
	// JNI_Load/JNI_Unload
	static Class<?> getFromClass() {
	return ClassLoader.nativeLibraryContext.peek().fromClass;
	}
	}

	// All native library names we've loaded.
	private static Vector<String> loadedLibraryNames = new Vector<>();

	// Native libraries belonging to system classes.
	private static Vector<NativeLibrary> systemNativeLibraries
	= new Vector<>();

	// Native libraries associated with the class loader.
	private Vector<NativeLibrary> nativeLibraries = new Vector<>();

	// native libraries being loaded/unloaded.
	private static Stack<NativeLibrary> nativeLibraryContext = new Stack<>();

	// The paths searched for libraries
	private static String usr_paths[];
	private static String sys_paths[];

	private static String[] initializePath(String propname) {
	String ldpath = System.getProperty(propname, "");
	String ps = File.pathSeparator;
	int ldlen = ldpath.length();
	int i, j, n;
	// Count the separators in the path
	i = ldpath.indexOf(ps);
	n = 0;
	while (i >= 0) {
	n++;
	i = ldpath.indexOf(ps, i + 1);
	}

	// allocate the array of paths - n :'s = n + 1 path elements
	String[] paths = new String[n + 1];

	// Fill the array with paths from the ldpath
	n = i = 0;
	j = ldpath.indexOf(ps);
	while (j >= 0) {
	if (j - i > 0) {
	paths[n++] = ldpath.substring(i, j);
	} else if (j - i == 0) {
	paths[n++] = ".";
	}
	i = j + 1;
	j = ldpath.indexOf(ps, i);
	}
	paths[n] = ldpath.substring(i, ldlen);
	return paths;
	}

	// Invoked in the java.lang.Runtime class to implement load and loadLibrary.
	static void loadLibrary(Class<?> fromClass, String name,
	boolean isAbsolute) {
	ClassLoader loader =
	(fromClass == null) ? null : fromClass.getClassLoader();
	if (sys_paths == null) {
	usr_paths = initializePath("java.library.path");
	sys_paths = initializePath("sun.boot.library.path");
	}
	if (isAbsolute) {
	if (loadLibrary0(fromClass, new File(name))) {
	return;
	}
	throw new UnsatisfiedLinkError("Can't load library: " + name);
	}
	if (loader != null) {
	String libfilename = loader.findLibrary(name);
	if (libfilename != null) {
	File libfile = new File(libfilename);
	if (!libfile.isAbsolute()) {
	throw new UnsatisfiedLinkError(
	"ClassLoader.findLibrary failed to return an absolute path: " + libfilename);
	}
	if (loadLibrary0(fromClass, libfile)) {
	return;
	}
	throw new UnsatisfiedLinkError("Can't load " + libfilename);
	}
	}
	for (int i = 0 ; i < sys_paths.length ; i++) {
	File libfile = new File(sys_paths[i], System.mapLibraryName(name));
	if (loadLibrary0(fromClass, libfile)) {
	return;
	}
	libfile = ClassLoaderHelper.mapAlternativeName(libfile);
	if (libfile != null && loadLibrary0(fromClass, libfile)) {
	return;
	}
	}
	if (loader != null) {
	for (int i = 0 ; i < usr_paths.length ; i++) {
	File libfile = new File(usr_paths[i],
	System.mapLibraryName(name));
	if (loadLibrary0(fromClass, libfile)) {
	return;
	}
	libfile = ClassLoaderHelper.mapAlternativeName(libfile);
	if (libfile != null && loadLibrary0(fromClass, libfile)) {
	return;
	}
	}
	}
	// Oops, it failed
	throw new UnsatisfiedLinkError("no " + name + " in java.library.path");
	}

	private static native String findBuiltinLib(String name);

	private static boolean loadLibrary0(Class<?> fromClass, final File file) {
	// Check to see if we're attempting to access a static library
	String name = findBuiltinLib(file.getName());
	boolean isBuiltin = (name != null);
	if (!isBuiltin) {
	boolean exists = AccessController.doPrivileged(
	new PrivilegedAction<Object>() {
	public Object run() {
	return file.exists() ? Boolean.TRUE : null;
	}})
	!= null;
	if (!exists) {
	return false;
	}
	try {
	name = file.getCanonicalPath();
	} catch (IOException e) {
	return false;
	}
	}
	ClassLoader loader =
	(fromClass == null) ? null : fromClass.getClassLoader();
	Vector<NativeLibrary> libs =
	loader != null ? loader.nativeLibraries : systemNativeLibraries;
	synchronized (libs) {
	int size = libs.size();
	for (int i = 0; i < size; i++) {
	NativeLibrary lib = libs.elementAt(i);
	if (name.equals(lib.name)) {
	return true;
	}
	}

	synchronized (loadedLibraryNames) {
	if (loadedLibraryNames.contains(name)) {
	throw new UnsatisfiedLinkError
	("Native Library " +
	name +
	" already loaded in another classloader");
	}
	/* If the library is being loaded (must be by the same thread,
	* because Runtime.load and Runtime.loadLibrary are
	* synchronous). The reason is can occur is that the JNI_OnLoad
	* function can cause another loadLibrary invocation.
	*
	* Thus we can use a static stack to hold the list of libraries
	* we are loading.
	*
	* If there is a pending load operation for the library, we
	* immediately return success; otherwise, we raise
	* UnsatisfiedLinkError.
	*/
	int n = nativeLibraryContext.size();
	for (int i = 0; i < n; i++) {
	NativeLibrary lib = nativeLibraryContext.elementAt(i);
	if (name.equals(lib.name)) {
	if (loader == lib.fromClass.getClassLoader()) {
	return true;
	} else {
	throw new UnsatisfiedLinkError
	("Native Library " +
	name +
	" is being loaded in another classloader");
	}
	}
	}
	NativeLibrary lib = new NativeLibrary(fromClass, name, isBuiltin);
	nativeLibraryContext.push(lib);
	try {
	lib.load(name, isBuiltin);
	} finally {
	nativeLibraryContext.pop();
	}
	if (lib.loaded) {
	loadedLibraryNames.addElement(name);
	libs.addElement(lib);
	return true;
	}
	return false;
	}
	}
	}

	// Invoked in the VM class linking code.
	static long findNative(ClassLoader loader, String name) {
	Vector<NativeLibrary> libs =
	loader != null ? loader.nativeLibraries : systemNativeLibraries;
	synchronized (libs) {
	int size = libs.size();
	for (int i = 0; i < size; i++) {
	NativeLibrary lib = libs.elementAt(i);
	long entry = lib.find(name);
	if (entry != 0)
	return entry;
	}
	}
	return 0;
	}


	// -- Assertion management --

	final Object assertionLock;

	// The default toggle for assertion checking.
	// @GuardedBy("assertionLock")
	private boolean defaultAssertionStatus = false;

	// Maps String packageName to Boolean package default assertion status Note
	// that the default package is placed under a null map key. If this field
	// is null then we are delegating assertion status queries to the VM, i.e.,
	// none of this ClassLoader's assertion status modification methods have
	// been invoked.
	// @GuardedBy("assertionLock")
	private Map<String, Boolean> packageAssertionStatus = null;

	// Maps String fullyQualifiedClassName to Boolean assertionStatus If this
	// field is null then we are delegating assertion status queries to the VM,
	// i.e., none of this ClassLoader's assertion status modification methods
	// have been invoked.
	// @GuardedBy("assertionLock")
	Map<String, Boolean> classAssertionStatus = null;

	/**
	* Sets the default assertion status for this class loader. This setting
	* determines whether classes loaded by this class loader and initialized
	* in the future will have assertions enabled or disabled by default.
	* This setting may be overridden on a per-package or per-class basis by
	* invoking {@link #setPackageAssertionStatus(String, boolean)} or {@link
	* #setClassAssertionStatus(String, boolean)}.
	*
	* @param enabled
	* <tt>true</tt> if classes loaded by this class loader will
	* henceforth have assertions enabled by default, <tt>false</tt>
	* if they will have assertions disabled by default.
	*
	* @since 1.4
	*/
	public void setDefaultAssertionStatus(boolean enabled) {
	synchronized (assertionLock) {
	if (classAssertionStatus == null)
	initializeJavaAssertionMaps();

	defaultAssertionStatus = enabled;
	}
	}

	/**
	* Sets the package default assertion status for the named package. The
	* package default assertion status determines the assertion status for
	* classes initialized in the future that belong to the named package or
	* any of its "subpackages".
	*
	* <p> A subpackage of a package named p is any package whose name begins
	* with "<tt>p.</tt>". For example, <tt>javax.swing.text</tt> is a
	* subpackage of <tt>javax.swing</tt>, and both <tt>java.util</tt> and
	* <tt>java.lang.reflect</tt> are subpackages of <tt>java</tt>.
	*
	* <p> In the event that multiple package defaults apply to a given class,
	* the package default pertaining to the most specific package takes
	* precedence over the others. For example, if <tt>javax.lang</tt> and
	* <tt>javax.lang.reflect</tt> both have package defaults associated with
	* them, the latter package default applies to classes in
	* <tt>javax.lang.reflect</tt>.
	*
	* <p> Package defaults take precedence over the class loader's default
	* assertion status, and may be overridden on a per-class basis by invoking
	* {@link #setClassAssertionStatus(String, boolean)}. </p>
	*
	* @param packageName
	* The name of the package whose package default assertion status
	* is to be set. A <tt>null</tt> value indicates the unnamed
	* package that is "current"
	* (see section 7.4.2 of
	* <cite>The Java™ Language Specification</cite>.)
	*
	* @param enabled
	* <tt>true</tt> if classes loaded by this classloader and
	* belonging to the named package or any of its subpackages will
	* have assertions enabled by default, <tt>false</tt> if they will
	* have assertions disabled by default.
	*
	* @since 1.4
	*/
	public void setPackageAssertionStatus(String packageName,
	boolean enabled) {
	synchronized (assertionLock) {
	if (packageAssertionStatus == null)
	initializeJavaAssertionMaps();

	packageAssertionStatus.put(packageName, enabled);
	}
	}

	/**
	* Sets the desired assertion status for the named top-level class in this
	* class loader and any nested classes contained therein. This setting
	* takes precedence over the class loader's default assertion status, and
	* over any applicable per-package default. This method has no effect if
	* the named class has already been initialized. (Once a class is
	* initialized, its assertion status cannot change.)
	*
	* <p> If the named class is not a top-level class, this invocation will
	* have no effect on the actual assertion status of any class. </p>
	*
	* @param className
	* The fully qualified class name of the top-level class whose
	* assertion status is to be set.
	*
	* @param enabled
	* <tt>true</tt> if the named class is to have assertions
	* enabled when (and if) it is initialized, <tt>false</tt> if the
	* class is to have assertions disabled.
	*
	* @since 1.4
	*/
	public void setClassAssertionStatus(String className, boolean enabled) {
	synchronized (assertionLock) {
	if (classAssertionStatus == null)
	initializeJavaAssertionMaps();

	classAssertionStatus.put(className, enabled);
	}
	}

	/**
	* Sets the default assertion status for this class loader to
	* <tt>false</tt> and discards any package defaults or class assertion
	* status settings associated with the class loader. This method is
	* provided so that class loaders can be made to ignore any command line or
	* persistent assertion status settings and "start with a clean slate."
	*
	* @since 1.4
	*/
	public void clearAssertionStatus() {
	/*
	* Whether or not "Java assertion maps" are initialized, set
	* them to empty maps, effectively ignoring any present settings.
	*/
	synchronized (assertionLock) {
	classAssertionStatus = new HashMap<>();
	packageAssertionStatus = new HashMap<>();
	defaultAssertionStatus = false;
	}
	}

	/**
	* Returns the assertion status that would be assigned to the specified
	* class if it were to be initialized at the time this method is invoked.
	* If the named class has had its assertion status set, the most recent
	* setting will be returned; otherwise, if any package default assertion
	* status pertains to this class, the most recent setting for the most
	* specific pertinent package default assertion status is returned;
	* otherwise, this class loader's default assertion status is returned.
	* </p>
	*
	* @param className
	* The fully qualified class name of the class whose desired
	* assertion status is being queried.
	*
	* @return The desired assertion status of the specified class.
	*
	* @see #setClassAssertionStatus(String, boolean)
	* @see #setPackageAssertionStatus(String, boolean)
	* @see #setDefaultAssertionStatus(boolean)
	*
	* @since 1.4
	*/
	boolean desiredAssertionStatus(String className) {
	synchronized (assertionLock) {
	// assert classAssertionStatus != null;
	// assert packageAssertionStatus != null;

	// Check for a class entry
	Boolean result = classAssertionStatus.get(className);
	if (result != null)
	return result.booleanValue();

	// Check for most specific package entry
	int dotIndex = className.lastIndexOf(".");
	if (dotIndex < 0) { // default package
	result = packageAssertionStatus.get(null);
	if (result != null)
	return result.booleanValue();
	}
	while(dotIndex > 0) {
	className = className.substring(0, dotIndex);
	result = packageAssertionStatus.get(className);
	if (result != null)
	return result.booleanValue();
	dotIndex = className.lastIndexOf(".", dotIndex-1);
	}

	// Return the classloader default
	return defaultAssertionStatus;
	}
	}

	// Set up the assertions with information provided by the VM.
	// Note: Should only be called inside a synchronized block
	private void initializeJavaAssertionMaps() {
	// assert Thread.holdsLock(assertionLock);

	classAssertionStatus = new HashMap<>();
	packageAssertionStatus = new HashMap<>();
	AssertionStatusDirectives directives = retrieveDirectives();

	for(int i = 0; i < directives.classes.length; i++)
	classAssertionStatus.put(directives.classes[i],
	directives.classEnabled[i]);

	for(int i = 0; i < directives.packages.length; i++)
	packageAssertionStatus.put(directives.packages[i],
	directives.packageEnabled[i]);

	defaultAssertionStatus = directives.deflt;
	}

	// Retrieves the assertion directives from the VM.
	private static native AssertionStatusDirectives retrieveDirectives();
	}


	class SystemClassLoaderAction
	implements PrivilegedExceptionAction<ClassLoader> {
	private ClassLoader parent;

	SystemClassLoaderAction(ClassLoader parent) {
	this.parent = parent;
	}

	public ClassLoader run() throws Exception {
	String cls = System.getProperty("java.system.class.loader");
	if (cls == null) {
	return parent;
	}

	Constructor<?> ctor = Class.forName(cls, true, parent)
	.getDeclaredConstructor(new Class<?>[] { ClassLoader.class });
	ClassLoader sys = (ClassLoader) ctor.newInstance(
	new Object[] { parent });
	Thread.currentThread().setContextClassLoader(sys);
	return sys;
	}
	}

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