/*

 * Copyright (c) 2013, 2017, 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

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 * 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.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.Collections;

import java.util.Enumeration;

import java.util.HashMap;

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.Stack;

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.perf.PerfCounter;

import jdk.internal.loader.BootLoader;

import jdk.internal.loader.ClassLoaders;

import jdk.internal.misc.SharedSecrets;

import jdk.internal.misc.Unsafe;

import jdk.internal.misc.VM;

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="#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="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;

    /**

     * 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;

        }

    }

    /**

     * 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="#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="#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);

    }