lazilyloadedctor.java

java中比较著名的js引擎当属mozilla开源的rhino

/* -*- Mode: java; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 *
 * ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Rhino code, released
 * May 6, 1999.
 *
 * The Initial Developer of the Original Code is
 * Netscape Communications Corporation.
 * Portions created by the Initial Developer are Copyright (C) 1997-2000
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Norris Boyd
 *
 * Alternatively, the contents of this file may be used under the terms of
 * the GNU General Public License Version 2 or later (the "GPL"), in which
 * case the provisions of the GPL are applicable instead of those above. If
 * you wish to allow use of your version of this file only under the terms of
 * the GPL and not to allow others to use your version of this file under the
 * MPL, indicate your decision by deleting the provisions above and replacing
 * them with the notice and other provisions required by the GPL. If you do
 * not delete the provisions above, a recipient may use your version of this
 * file under either the MPL or the GPL.
 *
 * ***** END LICENSE BLOCK ***** */

package org.mozilla.javascript;

import java.lang.reflect.*;

/**
 * Avoid loading classes unless they are used.
 *
 * <p> This improves startup time and average memory usage.
 */
public final class LazilyLoadedCtor {

    public LazilyLoadedCtor(ScriptableObject scope,
                     String ctorName, String className, boolean sealed)
    {

        this.className = className;
        this.ctorName = ctorName;
        this.sealed = sealed;

        if (getter == null) {
            Method[] methods = FunctionObject.getMethodList(getClass());
            getter = FunctionObject.findSingleMethod(methods, "getProperty");
            setter = FunctionObject.findSingleMethod(methods, "setProperty");
        }

        scope.defineProperty(ctorName, this, getter, setter,
                             ScriptableObject.DONTENUM);
    }

    public Object getProperty(ScriptableObject obj) {
        synchronized (obj) {
            if (!isReplaced) {
                boolean removeOnError = false;
                Class cl = Kit.classOrNull(className);
                if (cl == null) {
                    removeOnError = true;
                } else {
                    try {
                        ScriptableObject.defineClass(obj, cl, sealed);
                        isReplaced = true;
                    } catch (InvocationTargetException ex) {
                        Throwable target = ex.getTargetException();
                        if (target instanceof RuntimeException) {
                            throw (RuntimeException)target;
                        }
                        removeOnError = true;
                    } catch (RhinoException ex) {
                        removeOnError = true;
                    } catch (InstantiationException ex) {
                        removeOnError = true;
                    } catch (IllegalAccessException ex) {
                        removeOnError = true;
                    } catch (SecurityException ex) {
                        // Treat security exceptions as absence of object.
                        // They can be due to the following reasons:
                        //  java.lang.RuntimePermission createClassLoader
                        removeOnError = true;
                    } catch (LinkageError ex) {
                        // No dependant classes
                        removeOnError = true;
                    }
                }
                if (removeOnError) {
                    obj.delete(ctorName);
                    return Scriptable.NOT_FOUND;
                }
            }
        }
        // Get just added object
        return obj.get(ctorName, obj);
    }

    public Object setProperty(ScriptableObject obj, Object val) {
        synchronized (obj) {
            isReplaced = true;
            return val;
        }
    }

    private static Method getter, setter;

    private String ctorName;
    private String className;
    private boolean sealed;
    private boolean isReplaced;
}