/*

 * Copyright (c) 2013, 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 java.lang;

import java.io.InputStream;

import java.io.IOException;

import java.io.UncheckedIOException;

import java.io.File;

import java.lang.reflect.Constructor;

import java.lang.reflect.InvocationTargetException;

import java.net.URL;

import java.security.AccessController;

import java.security.AccessControlContext;

import java.security.CodeSource;

import java.security.PrivilegedAction;

import java.security.ProtectionDomain;

import java.security.cert.Certificate;

import java.util.ArrayDeque;

import java.util.Arrays;

import java.util.Collections;

import java.util.Deque;

import java.util.Enumeration;

import java.util.HashMap;

import java.util.HashSet;

import java.util.Hashtable;

import java.util.Map;

import java.util.NoSuchElementException;

import java.util.Objects;

import java.util.Set;

import java.util.Spliterator;

import java.util.Spliterators;

import java.util.Vector;

import java.util.WeakHashMap;

import java.util.concurrent.ConcurrentHashMap;

import java.util.function.Supplier;

import java.util.stream.Stream;

import java.util.stream.StreamSupport;

import jdk.internal.loader.BuiltinClassLoader;

import jdk.internal.perf.PerfCounter;

import jdk.internal.loader.BootLoader;

import jdk.internal.loader.ClassLoaders;

import jdk.internal.misc.Unsafe;

import jdk.internal.misc.VM;

import jdk.internal.ref.CleanerFactory;

import jdk.internal.reflect.CallerSensitive;

import jdk.internal.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 {@code ClassLoader} is an abstract class.  Given the <a

 * href="#binary-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 java.lang.Class Class} object contains a {@link

 * Class#getClassLoader() reference} to the {@code ClassLoader} that defined

 * it.

 *

 * <p> {@code Class} 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 {@code ClassLoader} 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> In addition to loading classes, a class loader is also responsible for

 * locating resources. A resource is some data (a "{@code .class}" file,

 * configuration data, or an image for example) that is identified with an

 * abstract '/'-separated path name. Resources are typically packaged with an

 * application or library so that they can be located by code in the

 * application or library. In some cases, the resources are included so that

 * they can be located by other libraries.

 *

 * <p> The {@code ClassLoader} class uses a delegation model to search for

 * classes and resources.  Each instance of {@code ClassLoader} has an

 * associated parent class loader. When requested to find a class or

 * resource, a {@code ClassLoader} instance will usually delegate the search

 * for the class or resource to its parent class loader before attempting to

 * find the class or resource itself.

 *

 * <p> Class loaders that support concurrent loading of classes are known as

 * <em>{@linkplain #isRegisteredAsParallelCapable() parallel capable}</em> class

 * loaders and are required to register themselves at their class initialization

 * time by invoking the {@link

 * #registerAsParallelCapable ClassLoader.registerAsParallelCapable}

 * method. Note that the {@code ClassLoader} class is registered as parallel

 * capable by default. However, its subclasses still need to register themselves

 * if they are parallel capable.

 * 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

 * loadClass} methods).

 *

 * <h3> <a id="builtinLoaders">Run-time Built-in Class Loaders</a></h3>

 *

 * The Java run-time has the following built-in class loaders:

 *

 * <ul>

 * <li><p>Bootstrap class loader.

 *     It is the virtual machine's built-in class loader, typically represented

 *     as {@code null}, and does not have a parent.</li>

 * <li><p>{@linkplain #getPlatformClassLoader() Platform class loader}.

 *     All <em>platform classes</em> are visible to the platform class loader

 *     that can be used as the parent of a {@code ClassLoader} instance.

 *     Platform classes include Java SE platform APIs, their implementation

 *     classes and JDK-specific run-time classes that are defined by the

 *     platform class loader or its ancestors.

 *     <p> To allow for upgrading/overriding of modules defined to the platform

 *     class loader, and where upgraded modules read modules defined to class

 *     loaders other than the platform class loader and its ancestors, then

 *     the platform class loader may have to delegate to other class loaders,

 *     the application class loader for example.

 *     In other words, classes in named modules defined to class loaders

 *     other than the platform class loader and its ancestors may be visible

 *     to the platform class loader. </li>

 * <li><p>{@linkplain #getSystemClassLoader() System class loader}.

 *     It is also known as <em>application class loader</em> and is distinct

 *     from the platform class loader.

 *     The system class loader is typically used to define classes on the

 *     application class path, module path, and JDK-specific tools.

 *     The platform class loader is a parent or an ancestor of the system class

 *     loader that all platform classes are visible to it.</li>

 * </ul>

 *

 * <p> Normally, the Java virtual machine loads classes from the local file

 * system in a platform-dependent manner.

 * 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)

 * defineClass} converts an array of bytes into an instance of class

 * {@code Class}. Instances of this newly defined class can be created using

 * {@link Class#newInstance Class.newInstance}.

 *

 * <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 loadClass} 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 findClass} and {@code loadClassData} 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 defineClass} 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 id="binary-name">Binary names</a> </h3>

 *

 * <p> Any class name provided as a {@code String} parameter to methods in

 * {@code ClassLoader} must be a binary name as defined by

 * <cite>The Java&trade; 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>

 *

 * <p> Any package name provided as a {@code String} parameter to methods in

 * {@code ClassLoader} must be either the empty string (denoting an unnamed package)

 * or a fully qualified name as defined by

 * <cite>The Java&trade; Language Specification</cite>.

 *

 * @jls 6.7  Fully Qualified Names

 * @jls 13.1 The Form of a Binary

 * @see      #resolveClass(Class)

 * @since 1.0

 * @revised 9

 * @spec JPMS

 */

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;

    // class loader name

    private final String name;

    // the unnamed module for this ClassLoader

    private final Module unnamedModule;

    // a string for exception message printing

    private final String nameAndId;

    /**

     * 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<>());

        static {

            synchronized (loaderTypes) { loaderTypes.add(ClassLoader.class); }

        }

        /**

         * Registers the given class loader type as parallel capable.

         * 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;

    // 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 NamedPackage object.

    //

    // The value is a Package object if ClassLoader::definePackage,

    // Class::getPackage, ClassLoader::getDefinePackage(s) or

    // Package::getPackage(s) method is called to define it.

    // Otherwise, the value is a NamedPackage object.

    private final ConcurrentHashMap<String, NamedPackage> packages

            = new ConcurrentHashMap<>();

    /*

     * Returns a named package for the given module.

     */

    private NamedPackage getNamedPackage(String pn, Module m) {

        NamedPackage p = packages.get(pn);

        if (p == null) {

            p = new NamedPackage(pn, m);

            NamedPackage value = packages.putIfAbsent(pn, p);

            if (value != null) {

                // Package object already be defined for the named package

                p = value;

                // if definePackage is called by this class loader to define

                // a package in a named module, this will return Package

                // object of the same name.  Package object may contain

                // unexpected information but it does not impact the runtime.

                // this assertion may be helpful for troubleshooting

                assert value.module() == m;

            }

        }

        return p;

    }

    private static Void checkCreateClassLoader() {

        return checkCreateClassLoader(null);

    }

    private static Void checkCreateClassLoader(String name) {

        if (name != null && name.isEmpty()) {

            throw new IllegalArgumentException("name must be non-empty or null");

        }

        SecurityManager security = System.getSecurityManager();

        if (security != null) {

            security.checkCreateClassLoader();

        }

        return null;

    }

    private ClassLoader(Void unused, String name, ClassLoader parent) {

        this.name = name;

        this.parent = parent;

        this.unnamedModule = new Module(this);

        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;

        }

        this.nameAndId = nameAndId(this);

    }

    /**

     * If the defining loader has a name explicitly set then

     *       '<loader-name>' @<id>

     * If the defining loader has no name then

     *       <qualified-class-name> @<id>

     * If it's built-in loader then omit `@<id>` as there is only one instance.

     */

    private static String nameAndId(ClassLoader ld) {

        String nid = ld.getName() != null ? "\'" + ld.getName() + "\'"

                                          : ld.getClass().getName();

        if (!(ld instanceof BuiltinClassLoader)) {

            String id = Integer.toHexString(System.identityHashCode(ld));

            nid = nid + " @" + id;

        }

        return nid;

    }

    /**

     * Creates a new class loader of the specified name and using the

     * specified parent class loader for delegation.

     *

     * @apiNote If the parent is specified as {@code null} (for the

     * bootstrap class loader) then there is no guarantee that all platform

     * classes are visible.

     *

     * @param  name   class loader name; or {@code null} if not named

     * @param  parent the parent class loader

     *

     * @throws IllegalArgumentException if the given name is empty.

     *

     * @throws SecurityException

     *         If a security manager exists and its

     *         {@link SecurityManager#checkCreateClassLoader()}

     *         method doesn't allow creation of a new class loader.

     *

     * @since  9

     * @spec JPMS

     */

    protected ClassLoader(String name, ClassLoader parent) {

        this(checkCreateClassLoader(name), name, parent);

    }

    /**

     * Creates a new class loader using the specified parent class loader for

     * delegation.

     *

     * <p> If there is a security manager, its {@link

     * SecurityManager#checkCreateClassLoader() checkCreateClassLoader} method

     * is invoked.  This may result in a security exception.  </p>

     *

     * @apiNote If the parent is specified as {@code null} (for the

     * bootstrap class loader) then there is no guarantee that all platform

     * classes are visible.

     *

     * @param  parent

     *         The parent class loader

     *

     * @throws  SecurityException

     *          If a security manager exists and its

     *          {@code checkCreateClassLoader} method doesn't allow creation

     *          of a new class loader.

     *

     * @since  1.2

     */

    protected ClassLoader(ClassLoader parent) {

        this(checkCreateClassLoader(), null, parent);

    }

    /**

     * Creates a new class loader using the {@code ClassLoader} returned by

     * the method {@link #getSystemClassLoader()

     * getSystemClassLoader()} as the parent class loader.

     *

     * <p> If there is a security manager, its {@link

     * SecurityManager#checkCreateClassLoader()

     * checkCreateClassLoader} method is invoked.  This may result in

     * a security exception.  </p>

     *

     * @throws  SecurityException

     *          If a security manager exists and its

     *          {@code checkCreateClassLoader} method doesn't allow creation

     *          of a new class loader.

     */

    protected ClassLoader() {

        this(checkCreateClassLoader(), null, getSystemClassLoader());

    }

    /**

     * Returns the name of this class loader or {@code null} if

     * this class loader is not named.

     *

     * @apiNote This method is non-final for compatibility.  If this

     * method is overridden, this method must return the same name

     * as specified when this class loader was instantiated.

     *

     * @return name of this class loader; or {@code null} if

     * this class loader is not named.

     *

     * @since 9

     * @spec JPMS

     */

    public String getName() {

        return name;

    }

    // package-private used by StackTraceElement to avoid

    // calling the overrideable getName method

    final String name() {

        return name;

    }

    // -- Class --

    /**

     * Loads the class with the specified <a href="#binary-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) loadClass(name,

     * false)}.

     *

     * @param  name

     *         The <a href="#binary-name">binary name</a> of the class

     *

     * @return  The resulting {@code Class} 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="#binary-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) loadClass} method

     *   on the parent class loader.  If the parent is {@code null} the class

     *   loader built into 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

     * {@code resolve} flag is true, this method will then invoke the {@link

     * #resolveClass(Class)} method on the resulting {@code Class} object.

     *

     * <p> Subclasses of {@code ClassLoader} are encouraged to override {@link

     * #findClass(String)}, rather than this method.  </p>

     *

     * <p> Unless overridden, this method synchronizes on the result of

     * {@link #getClassLoadingLock getClassLoadingLock} method

     * during the entire class loading process.

     *

     * @param  name

     *         The <a href="#binary-name">binary name</a> of the class

     *

     * @param  resolve

     *         If {@code true} then resolve the class

     *

     * @return  The resulting {@code Class} 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

                    PerfCounter.getParentDelegationTime().addTime(t1 - t0);

                    PerfCounter.getFindClassTime().addElapsedTimeFrom(t1);

                    PerfCounter.getFindClasses().increment();

                }

            }

            if (resolve) {

                resolveClass(c);

            }

            return c;

        }

    }

    /**

     * Loads the class with the specified <a href="#binary-name">binary name</a>

     * in a module defined to this class loader.  This method returns {@code null}

     * if the class could not be found.

     *

     * @apiNote This method does not delegate to the parent class loader.

     *

     * @implSpec The default implementation of this method searches for classes

     * in the following order:

     *

     * <ol>

     *   <li>Invoke {@link #findLoadedClass(String)} to check if the class

     *   has already been loaded.</li>

     *   <li>Invoke the {@link #findClass(String, String)} method to find the

     *   class in the given module.</li>

     * </ol>

     *

     * @param  module

     *         The module

     * @param  name

     *         The <a href="#binary-name">binary name</a> of the class

     *

     * @return The resulting {@code Class} object in a module defined by

     *         this class loader, or {@code null} if the class could not be found.

     */

    final Class<?> loadClass(Module module, String name) {

        synchronized (getClassLoadingLock(name)) {

            // First, check if the class has already been loaded

            Class<?> c = findLoadedClass(name);

            if (c == null) {

                c = findClass(module.getName(), name);

            }

            if (c != null && c.getModule() == module) {

                return c;

            } else {

                return null;

            }

        }

    }

    /**

     * 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 {@code className} 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;

    }

    // 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 packageName = cls.getPackageName();

            if (!packageName.isEmpty()) {

                AccessController.doPrivileged(new PrivilegedAction<>() {

                    public Void run() {

                        sm.checkPackageAccess(packageName);

                        return null;

                    }

                }, new AccessControlContext(new ProtectionDomain[] {pd}));

            }

        }

    }

    /**

     * Finds the class with the specified <a href="#binary-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 loadClass} method after checking the

     * parent class loader for the requested class.

     *

     * @implSpec The default implementation throws {@code ClassNotFoundException}.

     *

     * @param  name

     *         The <a href="#binary-name">binary name</a> of the class

     *

     * @return  The resulting {@code Class} object

     *

     * @throws  ClassNotFoundException

     *          If the class could not be found

     *

     * @since  1.2

     */

    protected Class<?> findClass(String name) throws ClassNotFoundException {

        throw new ClassNotFoundException(name);

    }

    /**

     * Finds the class with the given <a href="#binary-name">binary name</a>

     * in a module defined to this class loader.

     * Class loader implementations that support loading from modules

     * should override this method.

     *

     * @apiNote This method returns {@code null} rather than throwing

     *          {@code ClassNotFoundException} if the class could not be found.

     *

     * @implSpec The default implementation attempts to find the class by

     * invoking {@link #findClass(String)} when the {@code moduleName} is

     * {@code null}. It otherwise returns {@code null}.

     *

     * @param  moduleName

     *         The module name; or {@code null} to find the class in the

     *         {@linkplain #getUnnamedModule() unnamed module} for this

     *         class loader

     * @param  name

     *         The <a href="#binary-name">binary name</a> of the class

     *

     * @return The resulting {@code Class} object, or {@code null}

     *         if the class could not be found.

     *

     * @since 9

     * @spec JPMS

     */

    protected Class<?> findClass(String moduleName, String name) {

        if (moduleName == null) {

            try {

                return findClass(name);

            } catch (ClassNotFoundException ignore) { }

        }

        return null;

    }

    /**

     * Converts an array of bytes into an instance of class {@code Class}.

     * Before the {@code Class} can be used it must be resolved.  This method

     * is deprecated in favor of the version that takes a <a

     * href="#binary-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

     *         {@code off} through {@code off+len-1} should have the format

     *         of a valid class file as defined by

     *         <cite>The Java&trade; Virtual Machine Specification</cite>.

     *

     * @param  off

     *         The start offset in {@code b} of the class data

     *

     * @param  len

     *         The length of the class data

     *

     * @return  The {@code Class} object that was created from the specified

     *          class data

     *

     * @throws  ClassFormatError

     *          If the data did not contain a valid class

     *

     * @throws  IndexOutOfBoundsException

     *          If either {@code off} or {@code len} is negative, or if

     *          {@code off+len} is greater than {@code b.length}.

     *

     * @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(since="1.1")

    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 {@code Class}.

     * Before the {@code Class} can be used it must be resolved.

     *

     * <p> This method assigns a default {@link java.security.ProtectionDomain

     * ProtectionDomain} to the newly defined class.  The

     * {@code ProtectionDomain} is effectively granted the same set of

     * permissions returned when {@link

     * java.security.Policy#getPermissions(java.security.CodeSource)

     * Policy.getPolicy().getPermissions(new CodeSource(null, null))}

     * is invoked.  The default protection domain is created on the first invocation

     * of {@link #defineClass(String, byte[], int, int) defineClass},

     * and re-used on subsequent invocations.

     *

     * <p> To assign a specific {@code ProtectionDomain} to the class, use

     * the {@link #defineClass(String, byte[], int, int,

     * java.security.ProtectionDomain) defineClass} method that takes a

     * {@code ProtectionDomain} as one of its arguments.  </p>

     *

     * <p>

     * This method defines a package in this class loader corresponding to the

     * package of the {@code Class} (if such a package has not already been defined

     * in this class loader). The name of the defined package is derived from

     * the <a href="#binary-name">binary name</a> of the class specified by

     * the byte array {@code b}.

     * Other properties of the defined package are as specified by {@link Package}.

     *

     * @param  name

     *         The expected <a href="#binary-name">binary name</a> of the class, or

     *         {@code null} if not known

     *

     * @param  b

     *         The bytes that make up the class data.  The bytes in positions

     *         {@code off} through {@code off+len-1} should have the format

     *         of a valid class file as defined by

     *         <cite>The Java&trade; Virtual Machine Specification</cite>.

     *

     * @param  off

     *         The start offset in {@code b} of the class data

     *

     * @param  len

     *         The length of the class data

     *

     * @return  The {@code Class} object that was created from the specified

     *          class data.

     *

     * @throws  ClassFormatError

     *          If the data did not contain a valid class

     *

     * @throws  IndexOutOfBoundsException

     *          If either {@code off} or {@code len} is negative, or if

     *          {@code off+len} is greater than {@code b.length}.

     *

     * @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

     *          {@code name} begins with "{@code java.}".

     *

     * @see  #loadClass(String, boolean)

     * @see  #resolveClass(Class)

     * @see  java.security.CodeSource

     * @see  java.security.SecureClassLoader

     *

     * @since  1.1

     * @revised 9

     * @spec JPMS

     */

    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.")

                && this != getBuiltinPlatformClassLoader()) {

            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) {

        // define a named package, if not present

        getNamedPackage(c.getPackageName(), c.getModule());

        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 {@code Class},

     * with a given {@code ProtectionDomain}.

     *

     * <p> If the given {@code ProtectionDomain} is {@code null},

     * then a default protection 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 CodeSource} within the

     * {@code ProtectionDomain} of the class.  Any classes added to that

     * package must contain the same set of certificates or a

     * {@code SecurityException} will be thrown.  Note that if

     * {@code name} is {@code null}, this check is not performed.

     * You should always pass in the <a href="#binary-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> If the specified {@code name} begins with "{@code java.}", it can

     * only be defined by the {@linkplain #getPlatformClassLoader()

     * platform class loader} or its ancestors; otherwise {@code SecurityException}

     * will be thrown.  If {@code name} is not {@code null}, it must be equal to

     * the <a href="#binary-name">binary name</a> of the class

     * specified by the byte array {@code b}, otherwise a {@link

     * NoClassDefFoundError NoClassDefFoundError} will be thrown.

     *

     * <p> This method defines a package in this class loader corresponding to the

     * package of the {@code Class} (if such a package has not already been defined

     * in this class loader). The name of the defined package is derived from

     * the <a href="#binary-name">binary name</a> of the class specified by

     * the byte array {@code b}.

     * Other properties of the defined package are as specified by {@link Package}.

     *

     * @param  name

     *         The expected <a href="#binary-name">binary name</a> of the class, or

     *         {@code null} if not known

     *

     * @param  b

     *         The bytes that make up the class data. The bytes in positions

     *         {@code off} through {@code off+len-1} should have the format

     *         of a valid class file as defined by

     *         <cite>The Java&trade; Virtual Machine Specification</cite>.

     *

     * @param  off

     *         The start offset in {@code b} of the class data

     *

     * @param  len

     *         The length of the class data

     *

     * @param  protectionDomain

     *         The {@code ProtectionDomain} of the class

     *

     * @return  The {@code Class} object created from the data,

     *          and {@code ProtectionDomain}.

     *

     * @throws  ClassFormatError

     *          If the data did not contain a valid class

     *

     * @throws  NoClassDefFoundError

     *          If {@code name} is not {@code null} and not equal to the

     *          <a href="#binary-name">binary name</a> of the class specified by {@code b}

     *

     * @throws  IndexOutOfBoundsException

     *          If either {@code off} or {@code len} is negative, or if

     *          {@code off+len} is greater than {@code b.length}.

     *

     * @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 {@code name} begins with

     *          "{@code java.}" and this class loader is not the platform

     *          class loader or its ancestor.

     *

     * @revised 9

     * @spec JPMS

     */

    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(this, name, b, off, len, protectionDomain, source);

        postDefineClass(c, protectionDomain);

        return c;

    }

    /**

     * Converts a {@link java.nio.ByteBuffer ByteBuffer} into an instance

     * of class {@code Class}, with the given {@code ProtectionDomain}.

     * If the given {@code ProtectionDomain} is {@code null}, then a default

     * protection 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, the restrictions on class names,

     * and the defined package of the class

     * 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>{@code .defineClass(}<i>name</i>{@code ,}

     * <i>bBuffer</i>{@code ,} <i>pd</i>{@code )} yields exactly the same

     * result as the statements

     *

     *<p> <code>

     * ...<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>

     * </code></p>

     *

     * @param  name

     *         The expected <a href="#binary-name">binary name</a>. of the class, or

     *         {@code null} if not known

     *

     * @param  b

     *         The bytes that make up the class data. The bytes from positions

     *         {@code b.position()} through {@code b.position() + b.limit() -1

     *         } should have the format of a valid class file as defined by

     *         <cite>The Java&trade; Virtual Machine Specification</cite>.

     *

     * @param  protectionDomain

     *         The {@code ProtectionDomain} of the class, or {@code null}.

     *

     * @return  The {@code Class} object created from the data,

     *          and {@code ProtectionDomain}.

     *

     * @throws  ClassFormatError

     *          If the data did not contain a valid class.

     *

     * @throws  NoClassDefFoundError

     *          If {@code name} is not {@code null} and not equal to the

     *          <a href="#binary-name">binary name</a> of the class specified by {@code b}

     *

     * @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 {@code name} begins with

     *          "{@code java.}".

     *

     * @see      #defineClass(String, byte[], int, int, ProtectionDomain)

     *

     * @since  1.5

     * @revised 9

     * @spec JPMS

     */

    protected final Class<?> defineClass(String name, java.nio.ByteBuffer b,

                                         ProtectionDomain protectionDomain)

        throws ClassFormatError

    {

        int len = b.remaining();

        // Use byte[] if not a direct ByteBuffer:

        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(this, name, b, b.position(), len, protectionDomain, source);

        postDefineClass(c, protectionDomain);

        return c;

    }

    static native Class<?> defineClass1(ClassLoader loader, String name, byte[] b, int off, int len,

                                        ProtectionDomain pd, String source);

    static native Class<?> defineClass2(ClassLoader loader, 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) || (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 (Certificate cert : certs) {

            match = false;

            for (Certificate pcert : pcerts) {

                if (cert.equals(pcert)) {

                    match = true;

                    break;

                }

            }

            if (!match) return false;

        }

        // now do the same for pcerts

        for (Certificate pcert : pcerts) {

            match = false;

            for (Certificate cert : certs) {

                if (pcert.equals(cert)) {

                    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 {@code c} has

     * already been linked, then this method simply returns. Otherwise, the

     * class is linked as described in the "Execution" chapter of

     * <cite>The Java&trade; Language Specification</cite>.

     *

     * @param  c

     *         The class to link

     *

     * @throws  NullPointerException

     *          If {@code c} is {@code null}.

     *

     * @see  #defineClass(String, byte[], int, int)

     */

    protected final void resolveClass(Class<?> c) {

        if (c == null) {

            throw new NullPointerException();

        }

    }

    /**

     * Finds a class with the specified <a href="#binary-name">binary name</a>,

     * loading it if necessary.

     *

     * <p> This method loads the class through the system class loader (see

     * {@link #getSystemClassLoader()}).  The {@code Class} object returned

     * might have more than one {@code ClassLoader} associated with it.

     * Subclasses of {@code ClassLoader} need not usually invoke this method,

     * because most class loaders need to override just {@link