jdk/src/share/classes/com/sun/imageio/stream/StreamFinalizer.java

/*
 * Copyright 2005 Sun Microsystems, Inc.  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.  Sun designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 */

package com.sun.imageio.stream;

import java.io.IOException;
import javax.imageio.stream.ImageInputStream;

/**
 * Small class to assist in properly closing an ImageInputStream instance
 * prior to garbage collection.  The ImageInputStreamImpl class defines a
 * finalize() method, but in a number of its public subclasses
 * (e.g. FileImageInputStream) we override the finalize() method to be
 * empty for performance reasons, and instead rely on the Disposer mechanism
 * for closing/disposing resources.  This is fine when one of these classes
 * is instantiated directly (e.g. new FileImageInputStream()) but in the
 * unlikely case where a user defines their own subclass of one of those
 * streams, we need some way to get back to the behavior of
 * ImageInputStreamImpl, which will call close() as part of finalization.
 *
 * Typically an Image{Input,Output}Stream will construct an instance of
 * StreamFinalizer in its constructor if it detects that it has been
 * subclassed by the user.  The ImageInputStream instance will hold a
 * reference to the StreamFinalizer, and the StreamFinalizer will hold a
 * reference back to the ImageInputStream from which it was created.  When
 * both are no longer reachable, the StreamFinalizer.finalize() method will
 * be called, which will take care of closing down the ImageInputStream.
 *
 * Clearly this is a bit of a hack, but it will likely only be used in the
 * rarest of circumstances: when a user has subclassed one of the public
 * stream classes.  (It should be no worse than the old days when the public
 * stream classes had non-empty finalize() methods.)
 */
public class StreamFinalizer {
    private ImageInputStream stream;

    public StreamFinalizer(ImageInputStream stream) {
        this.stream = stream;
    }

    protected void finalize() throws Throwable {
        try {
            stream.close();
        } catch (IOException e) {
        } finally {
            stream = null;
            super.finalize();
        }
    }
}