/*
 * Copyright (c) 1999, 2013, 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.reflect;

import java.lang.ref.WeakReference;
import java.lang.reflect.WeakCache.BiFunction;
import java.security.AccessController;
import java.security.Permission;
import java.security.PrivilegedAction;
import java.util.Arrays;
import java.util.IdentityHashMap;
import java.util.Map;
import java.util.concurrent.atomic.AtomicLong;
import sun.misc.ProxyGenerator;
import sun.reflect.CallerSensitive;
import sun.reflect.Reflection;
import sun.reflect.misc.ReflectUtil;
import sun.security.util.SecurityConstants;

/**
 * {@code Proxy} provides static methods for creating dynamic proxy
 * classes and instances, and it is also the superclass of all
 * dynamic proxy classes created by those methods.
 *
 * <p>To create a proxy for some interface {@code Foo}:
 * <pre>
 *     InvocationHandler handler = new MyInvocationHandler(...);
 *     Class proxyClass = Proxy.getProxyClass(
 *         Foo.class.getClassLoader(), new Class[] { Foo.class });
 *     Foo f = (Foo) proxyClass.
 *         getConstructor(new Class[] { InvocationHandler.class }).
 *         newInstance(new Object[] { handler });
 * </pre>
 * or more simply:
 * <pre>
 *     Foo f = (Foo) Proxy.newProxyInstance(Foo.class.getClassLoader(),
 *                                          new Class[] { Foo.class },
 *                                          handler);
 * </pre>
 *
 * <p>A <i>dynamic proxy class</i> (simply referred to as a <i>proxy
 * class</i> below) is a class that implements a list of interfaces
 * specified at runtime when the class is created, with behavior as
 * described below.
 *
 * A <i>proxy interface</i> is such an interface that is implemented
 * by a proxy class.
 *
 * A <i>proxy instance</i> is an instance of a proxy class.
 *
 * Each proxy instance has an associated <i>invocation handler</i>
 * object, which implements the interface {@link InvocationHandler}.
 * A method invocation on a proxy instance through one of its proxy
 * interfaces will be dispatched to the {@link InvocationHandler#invoke
 * invoke} method of the instance's invocation handler, passing the proxy
 * instance, a {@code java.lang.reflect.Method} object identifying
 * the method that was invoked, and an array of type {@code Object}
 * containing the arguments.  The invocation handler processes the
 * encoded method invocation as appropriate and the result that it
 * returns will be returned as the result of the method invocation on
 * the proxy instance.
 *
 * <p>A proxy class has the following properties:
 *
 * <ul>
 * <li>Proxy classes are public, final, and not abstract.
 *
 * <li>The unqualified name of a proxy class is unspecified.  The space
 * of class names that begin with the string {@code "$Proxy"}
 * should be, however, reserved for proxy classes.
 *
 * <li>A proxy class extends {@code java.lang.reflect.Proxy}.
 *
 * <li>A proxy class implements exactly the interfaces specified at its
 * creation, in the same order.
 *
 * <li>If a proxy class implements a non-public interface, then it will
 * be defined in the same package as that interface.  Otherwise, the
 * package of a proxy class is also unspecified.  Note that package
 * sealing will not prevent a proxy class from being successfully defined
 * in a particular package at runtime, and neither will classes already
 * defined by the same class loader and the same package with particular
 * signers.
 *
 * <li>Since a proxy class implements all of the interfaces specified at
 * its creation, invoking {@code getInterfaces} on its
 * {@code Class} object will return an array containing the same
 * list of interfaces (in the order specified at its creation), invoking
 * {@code getMethods} on its {@code Class} object will return
 * an array of {@code Method} objects that include all of the
 * methods in those interfaces, and invoking {@code getMethod} will
 * find methods in the proxy interfaces as would be expected.
 *
 * <li>The {@link Proxy#isProxyClass Proxy.isProxyClass} method will
 * return true if it is passed a proxy class-- a class returned by
 * {@code Proxy.getProxyClass} or the class of an object returned by
 * {@code Proxy.newProxyInstance}-- and false otherwise.
 *
 * <li>The {@code java.security.ProtectionDomain} of a proxy class
 * is the same as that of system classes loaded by the bootstrap class
 * loader, such as {@code java.lang.Object}, because the code for a
 * proxy class is generated by trusted system code.  This protection
 * domain will typically be granted
 * {@code java.security.AllPermission}.
 *
 * <li>Each proxy class has one public constructor that takes one argument,
 * an implementation of the interface {@link InvocationHandler}, to set
 * the invocation handler for a proxy instance.  Rather than having to use
 * the reflection API to access the public constructor, a proxy instance
 * can be also be created by calling the {@link Proxy#newProxyInstance
 * Proxy.newProxyInstance} method, which combines the actions of calling
 * {@link Proxy#getProxyClass Proxy.getProxyClass} with invoking the
 * constructor with an invocation handler.
 * </ul>
 *
 * <p>A proxy instance has the following properties:
 *
 * <ul>
 * <li>Given a proxy instance {@code proxy} and one of the
 * interfaces implemented by its proxy class {@code Foo}, the
 * following expression will return true:
 * <pre>
 *     {@code proxy instanceof Foo}
 * </pre>
 * and the following cast operation will succeed (rather than throwing
 * a {@code ClassCastException}):
 * <pre>
 *     {@code (Foo) proxy}
 * </pre>
 *
 * <li>Each proxy instance has an associated invocation handler, the one
 * that was passed to its constructor.  The static
 * {@link Proxy#getInvocationHandler Proxy.getInvocationHandler} method
 * will return the invocation handler associated with the proxy instance
 * passed as its argument.
 *
 * <li>An interface method invocation on a proxy instance will be
 * encoded and dispatched to the invocation handler's {@link
 * InvocationHandler#invoke invoke} method as described in the
 * documentation for that method.
 *
 * <li>An invocation of the {@code hashCode},
 * {@code equals}, or {@code toString} methods declared in
 * {@code java.lang.Object} on a proxy instance will be encoded and
 * dispatched to the invocation handler's {@code invoke} method in
 * the same manner as interface method invocations are encoded and
 * dispatched, as described above.  The declaring class of the
 * {@code Method} object passed to {@code invoke} will be
 * {@code java.lang.Object}.  Other public methods of a proxy
 * instance inherited from {@code java.lang.Object} are not
 * overridden by a proxy class, so invocations of those methods behave
 * like they do for instances of {@code java.lang.Object}.
 * </ul>
 *
 * <h3>Methods Duplicated in Multiple Proxy Interfaces</h3>
 *
 * <p>When two or more interfaces of a proxy class contain a method with
 * the same name and parameter signature, the order of the proxy class's
 * interfaces becomes significant.  When such a <i>duplicate method</i>
 * is invoked on a proxy instance, the {@code Method} object passed
 * to the invocation handler will not necessarily be the one whose
 * declaring class is assignable from the reference type of the interface
 * that the proxy's method was invoked through.  This limitation exists
 * because the corresponding method implementation in the generated proxy
 * class cannot determine which interface it was invoked through.
 * Therefore, when a duplicate method is invoked on a proxy instance,
 * the {@code Method} object for the method in the foremost interface
 * that contains the method (either directly or inherited through a
 * superinterface) in the proxy class's list of interfaces is passed to
 * the invocation handler's {@code invoke} method, regardless of the
 * reference type through which the method invocation occurred.
 *
 * <p>If a proxy interface contains a method with the same name and
 * parameter signature as the {@code hashCode}, {@code equals},
 * or {@code toString} methods of {@code java.lang.Object},
 * when such a method is invoked on a proxy instance, the
 * {@code Method} object passed to the invocation handler will have
 * {@code java.lang.Object} as its declaring class.  In other words,
 * the public, non-final methods of {@code java.lang.Object}
 * logically precede all of the proxy interfaces for the determination of
 * which {@code Method} object to pass to the invocation handler.
 *
 * <p>Note also that when a duplicate method is dispatched to an
 * invocation handler, the {@code invoke} method may only throw
 * checked exception types that are assignable to one of the exception
 * types in the {@code throws} clause of the method in <i>all</i> of
 * the proxy interfaces that it can be invoked through.  If the
 * {@code invoke} method throws a checked exception that is not
 * assignable to any of the exception types declared by the method in one
 * of the proxy interfaces that it can be invoked through, then an
 * unchecked {@code UndeclaredThrowableException} will be thrown by
 * the invocation on the proxy instance.  This restriction means that not
 * all of the exception types returned by invoking
 * {@code getExceptionTypes} on the {@code Method} object
 * passed to the {@code invoke} method can necessarily be thrown
 * successfully by the {@code invoke} method.
 *
 * @author      Peter Jones
 * @see         InvocationHandler
 * @since       1.3
 */
public class Proxy implements java.io.Serializable {

    private static final long serialVersionUID = -2222568056686623797L;

    /** parameter types of a proxy class constructor */
    private static final Class<?>[] constructorParams =
        { InvocationHandler.class };

    /**
     * a cache of proxy classes
     */
    private static final WeakCache<ClassLoader, Class<?>[], Class<?>>
        proxyClassCache = new WeakCache<>(new KeyFactory(), new ProxyClassFactory());

    /**
     * the invocation handler for this proxy instance.
     * @serial
     */
    protected InvocationHandler h;

    /**
     * Prohibits instantiation.
     */
    private Proxy() {
    }

    /**
     * Constructs a new {@code Proxy} instance from a subclass
     * (typically, a dynamic proxy class) with the specified value
     * for its invocation handler.
     *
     * @param   h the invocation handler for this proxy instance
     */
    protected Proxy(InvocationHandler h) {
        doNewInstanceCheck();
        this.h = h;
    }

    private static class ProxyAccessHelper {
        // The permission is implementation specific.
        static final Permission PROXY_PERMISSION =
            new ReflectPermission("proxyConstructorNewInstance");
        // These system properties are defined to provide a short-term
        // workaround if customers need to disable the new security checks.
        static final boolean allowNewInstance;
        static final boolean allowNullLoader;
        static {
            allowNewInstance = getBooleanProperty("sun.reflect.proxy.allowsNewInstance");
            allowNullLoader = getBooleanProperty("sun.reflect.proxy.allowsNullLoader");
        }

        private static boolean getBooleanProperty(final String key) {
            String s = AccessController.doPrivileged(new PrivilegedAction<String>() {
                public String run() {
                    return System.getProperty(key);
                }
            });
            return Boolean.valueOf(s);
        }

        static boolean needsNewInstanceCheck(Class<?> proxyClass) {
            if (!Proxy.isProxyClass(proxyClass) || allowNewInstance) {
                return false;
            }

            if (ReflectUtil.isNonPublicProxyClass(proxyClass)) {
                for (Class<?> intf : proxyClass.getInterfaces()) {
                    if (!Modifier.isPublic(intf.getModifiers())) {
                        return true;
                    }
                }
            }
            return false;
        }
    }

    /*
     * Access check on a proxy class that implements any non-public interface.
     *
     * @throws  SecurityException if a security manager exists, and
     *          the caller does not have the permission.
     */
    private void doNewInstanceCheck() {
        SecurityManager sm = System.getSecurityManager();
        Class<?> proxyClass = this.getClass();
        if (sm != null && ProxyAccessHelper.needsNewInstanceCheck(proxyClass)) {
            try {
                sm.checkPermission(ProxyAccessHelper.PROXY_PERMISSION);
            } catch (SecurityException e) {
                throw new SecurityException("Not allowed to construct a Proxy "
                        + "instance that implements a non-public interface", e);
            }
        }
    }

    /**
     * Returns the {@code java.lang.Class} object for a proxy class
     * given a class loader and an array of interfaces.  The proxy class
     * will be defined by the specified class loader and will implement
     * all of the supplied interfaces.  If a proxy class for the same
     * permutation of interfaces has already been defined by the class
     * loader, then the existing proxy class will be returned; otherwise,
     * a proxy class for those interfaces will be generated dynamically
     * and defined by the class loader.
     *
     * <p>There are several restrictions on the parameters that may be
     * passed to {@code Proxy.getProxyClass}:
     *
     * <ul>
     * <li>All of the {@code Class} objects in the
     * {@code interfaces} array must represent interfaces, not
     * classes or primitive types.
     *
     * <li>No two elements in the {@code interfaces} array may
     * refer to identical {@code Class} objects.
     *
     * <li>All of the interface types must be visible by name through the
     * specified class loader.  In other words, for class loader
     * {@code cl} and every interface {@code i}, the following
     * expression must be true:
     * <pre>
     *     Class.forName(i.getName(), false, cl) == i
     * </pre>
     *
     * <li>All non-public interfaces must be in the same package;
     * otherwise, it would not be possible for the proxy class to
     * implement all of the interfaces, regardless of what package it is
     * defined in.
     *
     * <li>For any set of member methods of the specified interfaces
     * that have the same signature:
     * <ul>
     * <li>If the return type of any of the methods is a primitive
     * type or void, then all of the methods must have that same
     * return type.
     * <li>Otherwise, one of the methods must have a return type that
     * is assignable to all of the return types of the rest of the
     * methods.
     * </ul>
     *
     * <li>The resulting proxy class must not exceed any limits imposed
     * on classes by the virtual machine.  For example, the VM may limit
     * the number of interfaces that a class may implement to 65535; in
     * that case, the size of the {@code interfaces} array must not
     * exceed 65535.
     * </ul>
     *
     * <p>If any of these restrictions are violated,
     * {@code Proxy.getProxyClass} will throw an
     * {@code IllegalArgumentException}.  If the {@code interfaces}
     * array argument or any of its elements are {@code null}, a
     * {@code NullPointerException} will be thrown.
     *
     * <p>Note that the order of the specified proxy interfaces is
     * significant: two requests for a proxy class with the same combination
     * of interfaces but in a different order will result in two distinct
     * proxy classes.
     *
     * @param   loader the class loader to define the proxy class
     * @param   interfaces the list of interfaces for the proxy class
     *          to implement
     * @return  a proxy class that is defined in the specified class loader
     *          and that implements the specified interfaces
     * @throws  IllegalArgumentException if any of the restrictions on the
     *          parameters that may be passed to {@code getProxyClass}
     *          are violated
     * @throws  NullPointerException if the {@code interfaces} array
     *          argument or any of its elements are {@code null}
     */
    @CallerSensitive
    public static Class<?> getProxyClass(ClassLoader loader,
                                         Class<?>... interfaces)
        throws IllegalArgumentException
    {
        final Class<?>[] intfs = interfaces.clone();
        final SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
        }

        return getProxyClass0(loader, intfs);
    }

    /*
     * Check permissions required to create a Proxy class.
     *
     * To define a proxy class, it performs the access checks as in
     * Class.forName (VM will invoke ClassLoader.checkPackageAccess):
     * 1. "getClassLoader" permission check if loader == null
     * 2. checkPackageAccess on the interfaces it implements
     *
     * To get a constructor and new instance of a proxy class, it performs
     * the package access check on the interfaces it implements
     * as in Class.getConstructor.
     *
     * If an interface is non-public, the proxy class must be defined by
     * the defining loader of the interface.  If the caller's class loader
     * is not the same as the defining loader of the interface, the VM
     * will throw IllegalAccessError when the generated proxy class is
     * being defined via the defineClass0 method.
     */
    private static void checkProxyAccess(Class<?> caller,
                                         ClassLoader loader,
                                         Class<?>... interfaces)
    {
        SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            ClassLoader ccl = caller.getClassLoader();
            if (loader == null && ccl != null) {
                if (!ProxyAccessHelper.allowNullLoader) {
                    sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
                }
            }
            ReflectUtil.checkProxyPackageAccess(ccl, interfaces);
        }
    }

    /**
     * Generate a proxy class.  Must call the checkProxyAccess method
     * to perform permission checks before calling this.
     */
    private static Class<?> getProxyClass0(ClassLoader loader,
                                           Class<?>... interfaces) {
        if (interfaces.length > 65535) {
            throw new IllegalArgumentException("interface limit exceeded");
        }

        // If the proxy class defined by the given loader implementing
        // the given interfaces exists, this will simply return the cached copy;
        // otherwise, it will create the proxy class via the ProxyClassFactory
        return proxyClassCache.get(loader, interfaces);
    }

    /*
     * a key used for proxy class with 0 implemented interfaces
     */
    private static final Object key0 = new Object();

    /*
     * Key1 and Key2 are optimized for the common use of dynamic proxies
     * that implement 1 or 2 interfaces.
     */

    /*
     * a key used for proxy class with 1 implemented interface
     */
    private static final class Key1 extends WeakReference<Class<?>> {
        private final int hash;

        Key1(Class<?> intf) {
            super(intf);
            this.hash = intf.hashCode();
        }

        @Override
        public int hashCode() {
            return hash;
        }

        @Override
        public boolean equals(Object obj) {
            Class<?> intf;
            return this == obj ||
                   obj != null &&
                   obj.getClass() == Key1.class &&
                   (intf = get()) != null &&
                   intf == ((Key1) obj).get();
        }
    }

    /*
     * a key used for proxy class with 2 implemented interfaces
     */
    private static final class Key2 extends WeakReference<Class<?>> {
        private final int hash;
        private final WeakReference<Class<?>> ref2;

        Key2(Class<?> intf1, Class<?> intf2) {
            super(intf1);
            hash = 31 * intf1.hashCode() + intf2.hashCode();
            ref2 = new WeakReference<Class<?>>(intf2);
        }

        @Override
        public int hashCode() {
            return hash;
        }

        @Override
        public boolean equals(Object obj) {
            Class<?> intf1, intf2;
            return this == obj ||
                   obj != null &&
                   obj.getClass() == Key2.class &&
                   (intf1 = get()) != null &&
                   intf1 == ((Key2) obj).get() &&
                   (intf2 = ref2.get()) != null &&
                   intf2 == ((Key2) obj).ref2.get();
        }
    }

    /*
     * a key used for proxy class with any number of implemented interfaces
     * (used here for 3 or more only)
     */
    private static final class KeyX {
        private final int hash;
        private final WeakReference<Class<?>>[] refs;

        KeyX(Class<?>[] interfaces) {
            hash = Arrays.hashCode(interfaces);
            refs = new WeakReference[interfaces.length];
            for (int i = 0; i < interfaces.length; i++) {
                refs[i] = new WeakReference(interfaces[i]);
            }
        }

        @Override
        public int hashCode() {
            return hash;
        }

        @Override
        public boolean equals(Object obj) {
            return this == obj ||
                   obj != null &&
                   obj.getClass() == KeyX.class &&
                   equals(refs, ((KeyX) obj).refs);
        }

        private static boolean equals(WeakReference<Class<?>>[] refs1,
                                      WeakReference<Class<?>>[] refs2) {
            if (refs1.length != refs2.length) {
                return false;
            }
            for (int i = 0; i < refs1.length; i++) {
                Class<?> intf = refs1[i].get();
                if (intf == null || intf != refs2[i].get()) {
                    return false;
                }
            }
            return true;
        }
    }

    /**
     * A function that maps an array of interfaces to an optimal key where
     * Class objects representing interfaces are weakly referenced.
     */
    private static final class KeyFactory
        implements BiFunction<ClassLoader, Class<?>[], Object>
    {
        @Override
        public Object apply(ClassLoader classLoader, Class<?>[] interfaces) {
            switch (interfaces.length) {
                case 1: return new Key1(interfaces[0]); // the most frequent
                case 2: return new Key2(interfaces[0], interfaces[1]);
                case 0: return key0;
                default: return new KeyX(interfaces);
            }
        }
    }

    /**
     * A factory function that generates, defines and returns the proxy class given
     * the ClassLoader and array of interfaces.
     */
    private static final class ProxyClassFactory
        implements BiFunction<ClassLoader, Class<?>[], Class<?>>
    {
        // prefix for all proxy class names
        private static final String proxyClassNamePrefix = "$Proxy";

        // next number to use for generation of unique proxy class names
        private static final AtomicLong nextUniqueNumber = new AtomicLong();

        @Override
        public Class<?> apply(ClassLoader loader, Class<?>[] interfaces) {

            Map<Class<?>, Boolean> interfaceSet = new IdentityHashMap<>(interfaces.length);
            for (Class<?> intf : interfaces) {
                /*
                 * Verify that the class loader resolves the name of this
                 * interface to the same Class object.
                 */
                Class<?> interfaceClass = null;
                try {
                    interfaceClass = Class.forName(intf.getName(), false, loader);
                } catch (ClassNotFoundException e) {
                }
                if (interfaceClass != intf) {
                    throw new IllegalArgumentException(
                        intf + " is not visible from class loader");
                }
                /*
                 * Verify that the Class object actually represents an
                 * interface.
                 */
                if (!interfaceClass.isInterface()) {
                    throw new IllegalArgumentException(
                        interfaceClass.getName() + " is not an interface");
                }
                /*
                 * Verify that this interface is not a duplicate.
                 */
                if (interfaceSet.put(interfaceClass, Boolean.TRUE) != null) {
                    throw new IllegalArgumentException(
                        "repeated interface: " + interfaceClass.getName());
                }
            }

            String proxyPkg = null;     // package to define proxy class in

            /*
             * Record the package of a non-public proxy interface so that the
             * proxy class will be defined in the same package.  Verify that
             * all non-public proxy interfaces are in the same package.
             */
            for (Class<?> intf : interfaces) {
                int flags = intf.getModifiers();
                if (!Modifier.isPublic(flags)) {
                    String name = intf.getName();
                    int n = name.lastIndexOf('.');
                    String pkg = ((n == -1) ? "" : name.substring(0, n + 1));
                    if (proxyPkg == null) {
                        proxyPkg = pkg;
                    } else if (!pkg.equals(proxyPkg)) {
                        throw new IllegalArgumentException(
                            "non-public interfaces from different packages");
                    }
                }
            }

            if (proxyPkg == null) {
                // if no non-public proxy interfaces, use com.sun.proxy package
                proxyPkg = ReflectUtil.PROXY_PACKAGE + ".";
            }

            /*
             * Choose a name for the proxy class to generate.
             */
            long num = nextUniqueNumber.getAndIncrement();
            String proxyName = proxyPkg + proxyClassNamePrefix + num;

            /*
             * Generate the specified proxy class.
             */
            byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
                proxyName, interfaces);
            try {
                return defineClass0(loader, proxyName,
                                    proxyClassFile, 0, proxyClassFile.length);
            } catch (ClassFormatError e) {
                /*
                 * A ClassFormatError here means that (barring bugs in the
                 * proxy class generation code) there was some other
                 * invalid aspect of the arguments supplied to the proxy
                 * class creation (such as virtual machine limitations
                 * exceeded).
                 */
                throw new IllegalArgumentException(e.toString());
            }
        }
    }

    /**
     * Returns an instance of a proxy class for the specified interfaces
     * that dispatches method invocations to the specified invocation
     * handler.  This method is equivalent to:
     * <pre>
     *     Proxy.getProxyClass(loader, interfaces).
     *         getConstructor(new Class[] { InvocationHandler.class }).
     *         newInstance(new Object[] { handler });
     * </pre>
     *
     * <p>{@code Proxy.newProxyInstance} throws
     * {@code IllegalArgumentException} for the same reasons that
     * {@code Proxy.getProxyClass} does.
     *
     * @param   loader the class loader to define the proxy class
     * @param   interfaces the list of interfaces for the proxy class
     *          to implement
     * @param   h the invocation handler to dispatch method invocations to
     * @return  a proxy instance with the specified invocation handler of a
     *          proxy class that is defined by the specified class loader
     *          and that implements the specified interfaces
     * @throws  IllegalArgumentException if any of the restrictions on the
     *          parameters that may be passed to {@code getProxyClass}
     *          are violated
     * @throws  NullPointerException if the {@code interfaces} array
     *          argument or any of its elements are {@code null}, or
     *          if the invocation handler, {@code h}, is
     *          {@code null}
     */
    @CallerSensitive
    public static Object newProxyInstance(ClassLoader loader,
                                          Class<?>[] interfaces,
                                          InvocationHandler h)
        throws IllegalArgumentException
    {
        if (h == null) {
            throw new NullPointerException();
        }

        final Class<?>[] intfs = interfaces.clone();
        final SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
        }

        /*
         * Look up or generate the designated proxy class.
         */
        Class<?> cl = getProxyClass0(loader, intfs);

        /*
         * Invoke its constructor with the designated invocation handler.
         */
        try {
            final Constructor<?> cons = cl.getConstructor(constructorParams);
            final InvocationHandler ih = h;
            if (sm != null && ProxyAccessHelper.needsNewInstanceCheck(cl)) {
                // create proxy instance with doPrivilege as the proxy class may
                // implement non-public interfaces that requires a special permission
                return AccessController.doPrivileged(new PrivilegedAction<Object>() {
                    public Object run() {
                        return newInstance(cons, ih);
                    }
                });
            } else {
                return newInstance(cons, ih);
            }
        } catch (NoSuchMethodException e) {
            throw new InternalError(e.toString());
        }
    }

    private static Object newInstance(Constructor<?> cons, InvocationHandler h) {
        try {
            return cons.newInstance(new Object[] {h} );
        } catch (IllegalAccessException | InstantiationException e) {
            throw new InternalError(e.toString());
        } catch (InvocationTargetException e) {
            Throwable t = e.getCause();
            if (t instanceof RuntimeException) {
                throw (RuntimeException) t;
            } else {
                throw new InternalError(t.toString());
            }
        }
    }

    /**
     * Returns true if and only if the specified class was dynamically
     * generated to be a proxy class using the {@code getProxyClass}
     * method or the {@code newProxyInstance} method.
     *
     * <p>The reliability of this method is important for the ability
     * to use it to make security decisions, so its implementation should
     * not just test if the class in question extends {@code Proxy}.
     *
     * @param   cl the class to test
     * @return  {@code true} if the class is a proxy class and
     *          {@code false} otherwise
     * @throws  NullPointerException if {@code cl} is {@code null}
     */
    public static boolean isProxyClass(Class<?> cl) {
        return Proxy.class.isAssignableFrom(cl) && proxyClassCache.containsValue(cl);
    }

    /**
     * Returns the invocation handler for the specified proxy instance.
     *
     * @param   proxy the proxy instance to return the invocation handler for
     * @return  the invocation handler for the proxy instance
     * @throws  IllegalArgumentException if the argument is not a
     *          proxy instance
     */
    @CallerSensitive
    public static InvocationHandler getInvocationHandler(Object proxy)
        throws IllegalArgumentException
    {
        /*
         * Verify that the object is actually a proxy instance.
         */
        if (!isProxyClass(proxy.getClass())) {
            throw new IllegalArgumentException("not a proxy instance");
        }

        final Proxy p = (Proxy) proxy;
        final InvocationHandler ih = p.h;
        if (System.getSecurityManager() != null) {
            Class<?> ihClass = ih.getClass();
            Class<?> caller = Reflection.getCallerClass();
            if (ReflectUtil.needsPackageAccessCheck(caller.getClassLoader(),
                                                    ihClass.getClassLoader()))
            {
                ReflectUtil.checkPackageAccess(ihClass);
            }
        }

        return ih;
    }

    private static native Class defineClass0(ClassLoader loader, String name,
                                             byte[] b, int off, int len);
}
