Java example source code file (NashornStaticClassLinker.java)

This example Java source code file (NashornStaticClassLinker.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

callsitedescriptor, class, exception, guardedinvocation, linkerservices, linkrequest, nashorn, nashornstaticclasslinker, object, override, staticclass, typebasedguardingdynamiclinker

The NashornStaticClassLinker.java Java example source code

/*
 * Copyright (c) 2010, 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 jdk.nashorn.internal.runtime.linker;

import jdk.internal.dynalink.CallSiteDescriptor;
import jdk.internal.dynalink.beans.BeansLinker;
import jdk.internal.dynalink.beans.StaticClass;
import jdk.internal.dynalink.linker.GuardedInvocation;
import jdk.internal.dynalink.linker.GuardingDynamicLinker;
import jdk.internal.dynalink.linker.LinkRequest;
import jdk.internal.dynalink.linker.LinkerServices;
import jdk.internal.dynalink.linker.TypeBasedGuardingDynamicLinker;
import jdk.internal.dynalink.support.Guards;
import jdk.nashorn.internal.runtime.Context;
import jdk.nashorn.internal.runtime.ECMAErrors;

/**
 * Internal linker for {@link StaticClass} objects, only ever used by Nashorn engine and not exposed to other engines.
 * It is used for extending the "new" operator on StaticClass in order to be able to instantiate interfaces and abstract
 * classes by passing a ScriptObject or ScriptFunction as their implementation, e.g.:
 * <pre>
 *   var r = new Runnable() { run: function() { print("Hello World" } }
 * </pre>
 * or for SAM types, even just passing a function:
 * <pre>
 *   var r = new Runnable(function() { print("Hello World" })
 * </pre>
 */
final class NashornStaticClassLinker implements TypeBasedGuardingDynamicLinker {
    private static final GuardingDynamicLinker staticClassLinker = BeansLinker.getLinkerForClass(StaticClass.class);

    @Override
    public boolean canLinkType(Class<?> type) {
        return type == StaticClass.class;
    }

    @Override
    public GuardedInvocation getGuardedInvocation(LinkRequest linkRequest, LinkerServices linkerServices) throws Exception {
        final LinkRequest request = linkRequest.withoutRuntimeContext(); // Nashorn has no runtime context
        final Object self = request.getReceiver();
        if (self.getClass() != StaticClass.class) {
            return null;
        }
        final Class<?> receiverClass = ((StaticClass) self).getRepresentedClass();
        Bootstrap.checkReflectionAccess(receiverClass, true);
        final CallSiteDescriptor desc = request.getCallSiteDescriptor();
        // We intercept "new" on StaticClass instances to provide additional capabilities
        if ("new".equals(desc.getNameToken(CallSiteDescriptor.OPERATOR))) {
            // make sure new is on accessible Class
            Context.checkPackageAccess(receiverClass);

            // Is the class abstract? (This includes interfaces.)
            if (NashornLinker.isAbstractClass(receiverClass)) {
                // Change this link request into a link request on the adapter class.
                final Object[] args = request.getArguments();
                args[0] = JavaAdapterFactory.getAdapterClassFor(new Class<?>[] { receiverClass }, null,
                        linkRequest.getCallSiteDescriptor().getLookup());
                final LinkRequest adapterRequest = request.replaceArguments(request.getCallSiteDescriptor(), args);
                final GuardedInvocation gi = checkNullConstructor(delegate(linkerServices, adapterRequest), receiverClass);
                // Finally, modify the guard to test for the original abstract class.
                return gi.replaceMethods(gi.getInvocation(), Guards.getIdentityGuard(self));
            }
            // If the class was not abstract, just delegate linking to the standard StaticClass linker. Make an
            // additional check to ensure we have a constructor. We could just fall through to the next "return"
            // statement, except we also insert a call to checkNullConstructor() which throws an ECMAScript TypeError
            // with a more intuitive message when no suitable constructor is found.
            return checkNullConstructor(delegate(linkerServices, request), receiverClass);
        }
        // In case this was not a "new" operation, just delegate to the the standard StaticClass linker.
        return delegate(linkerServices, request);
    }

    private static GuardedInvocation delegate(LinkerServices linkerServices, final LinkRequest request) throws Exception {
        return NashornBeansLinker.getGuardedInvocation(staticClassLinker, request, linkerServices);
    }

    private static GuardedInvocation checkNullConstructor(final GuardedInvocation ctorInvocation, final Class<?> receiverClass) {
        if(ctorInvocation == null) {
            throw ECMAErrors.typeError("no.constructor.matches.args", receiverClass.getName());
        }
        return ctorInvocation;
    }
}