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Rhino is an open-source implementation of JavaScript written entirely in Java. It is typically embedded into Java applications to provide scripting to end users.
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/* -*- Mode: java; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

package org.mozilla.javascript.jdk18;

import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import org.mozilla.javascript.Context;
import org.mozilla.javascript.ContextFactory;
import org.mozilla.javascript.InterfaceAdapter;
import org.mozilla.javascript.Scriptable;
import org.mozilla.javascript.VMBridge;

public class VMBridge_jdk18 extends VMBridge {
    private static final ThreadLocal contextLocal = new ThreadLocal<>();

    @Override
    protected Object getThreadContextHelper() {
        // To make subsequent batch calls to getContext/setContext faster
        // associate permanently one element array with contextLocal
        // so getContext/setContext would need just to read/write the first
        // array element.
        // Note that it is necessary to use Object[], not Context[] to allow
        // garbage collection of Rhino classes. For details see comments
        // by Attila Szegedi in
        // https://bugzilla.mozilla.org/show_bug.cgi?id=281067#c5

        Object[] storage = contextLocal.get();
        if (storage == null) {
            storage = new Object[1];
            contextLocal.set(storage);
        }
        return storage;
    }

    @Override
    protected Context getContext(Object contextHelper) {
        Object[] storage = (Object[]) contextHelper;
        return (Context) storage[0];
    }

    @Override
    protected void setContext(Object contextHelper, Context cx) {
        Object[] storage = (Object[]) contextHelper;
        storage[0] = cx;
    }

    @Override
    protected boolean tryToMakeAccessible(AccessibleObject accessible) {
        if (accessible.isAccessible()) {
            return true;
        }
        try {
            accessible.setAccessible(true);
        } catch (Exception ex) {
        }

        return accessible.isAccessible();
    }

    @Override
    protected Object getInterfaceProxyHelper(ContextFactory cf, Class[] interfaces) {
        // XXX: How to handle interfaces array withclasses from different
        // class loaders? Using cf.getApplicationClassLoader() ?
        ClassLoader loader = interfaces[0].getClassLoader();
        Class cl = Proxy.getProxyClass(loader, interfaces);
        Constructor c;
        try {
            c = cl.getConstructor(InvocationHandler.class);
        } catch (NoSuchMethodException ex) {
            // Should not happen
            throw new IllegalStateException(ex);
        }
        return c;
    }

    @Override
    protected Object newInterfaceProxy(
            Object proxyHelper,
            final ContextFactory cf,
            final InterfaceAdapter adapter,
            final Object target,
            final Scriptable topScope) {
        Constructor c = (Constructor) proxyHelper;

        InvocationHandler handler =
                new InvocationHandler() {
                    @Override
                    public Object invoke(Object proxy, Method method, Object[] args) {
                        // In addition to methods declared in the interface, proxies
                        // also route some java.lang.Object methods through the
                        // invocation handler.
                        if (method.getDeclaringClass() == Object.class) {
                            String methodName = method.getName();
                            if (methodName.equals("equals")) {
                                Object other = args[0];
                                // Note: we could compare a proxy and its wrapped function
                                // as equal here but that would break symmetry of equal().
                                // The reason == suffices here is that proxies are cached
                                // in ScriptableObject (see NativeJavaObject.coerceType())
                                return Boolean.valueOf(proxy == other);
                            }
                            if (methodName.equals("hashCode")) {
                                return Integer.valueOf(target.hashCode());
                            }
                            if (methodName.equals("toString")) {
                                return "Proxy[" + target.toString() + "]";
                            }
                        }
                        return adapter.invoke(cf, target, topScope, proxy, method, args);
                    }
                };
        Object proxy;
        try {
            proxy = c.newInstance(handler);
        } catch (InvocationTargetException ex) {
            throw Context.throwAsScriptRuntimeEx(ex);
        } catch (IllegalAccessException ex) {
            // Should not happen
            throw new IllegalStateException(ex);
        } catch (InstantiationException ex) {
            // Should not happen
            throw new IllegalStateException(ex);
        }
        return proxy;
    }
}