imagecache.java

来自「Mobile 应用程序使用 Java Micro Edition (Java M」· Java 代码 · 共 201 行

/*
 * @(#)ImageCache.java	1.3 08/02/04
 *
 * Copyright 2007 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */
package com.sun.java.swing.plaf.nimbus;

import java.awt.GraphicsConfiguration;
import java.awt.Image;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.util.Arrays;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * ImageCache - A fixed pixel count sized cache of Images keyed by arbitrary set of arguments. All images are held with
 * SoftReferences so they will be dropped by the GC if heap memory gets tight. When our size hits max pixel count least
 * recently requested images are removed first.
 *
 * @author Created by Jasper Potts (Aug 7, 2007)
 * @version 1.0
 */
class ImageCache {
    // Ordered Map keyed by args hash, ordered by most recent accessed entry.
    private final LinkedHashMap<Integer, PixelCountSoftReference> map =
            new LinkedHashMap<Integer, PixelCountSoftReference>(16, 0.75f, true);
    // Maximum number of pixels to cache, this is used if maxCount
    private final int maxPixelCount;
    // Maximum cached image size in pxiels
    private final int maxSingleImagePixelSize;
    // The current number of pixels stored in the cache
    private int currentPixelCount = 0;
    // Lock for concurrent access to map
    private ReadWriteLock lock = new ReentrantReadWriteLock();
    // Reference queue for tracking lost softreferences to images in the cache
    private ReferenceQueue<Image> referenceQueue = new ReferenceQueue<Image>();
    // Singleton Instance
    private static final ImageCache instance = new ImageCache();


    /** Get static singleton instance */
    static ImageCache getInstance() {
        return instance;
    }

    public ImageCache() {
        this.maxPixelCount = (8 * 1024 * 1024) / 4; // 8Mb of pixels
        this.maxSingleImagePixelSize = 300 * 300;
    }

    public ImageCache(int maxPixelCount, int maxSingleImagePixelSize) {
        this.maxPixelCount = maxPixelCount;
        this.maxSingleImagePixelSize = maxSingleImagePixelSize;
    }

    /** Clear the cache */
    public void flush() {
        lock.readLock().lock();
        try {
            map.clear();
        } finally {
            lock.readLock().unlock();
        }
    }

    /**
     * Check if the image size is to big to be stored in the cache
     *
     * @param w The image width
     * @param h The image height
     * @return True if the image size is less than max
     */
    public boolean isImageCachable(int w, int h) {
        return (w * h) < maxSingleImagePixelSize;
    }

    /**
     * Get the cached image for given keys
     *
     * @param config The graphics configuration, needed if cached image is a Volatile Image. Used as part of cache key
     * @param w      The image width, used as part of cache key
     * @param h      The image height, used as part of cache key
     * @param args   Other arguments to use as part of the cache key
     * @return Returns the cached Image, or null there is no cached image for key
     */
    public Image getImage(GraphicsConfiguration config, int w, int h, Object... args) {
        lock.readLock().lock();
        try {
            PixelCountSoftReference ref = map.get(hash(config, w, h, args));
            // check reference has not been lost and the key truly matches, in case of false positive hash match
            if (ref != null && ref.equals(config,w, h, args)) {
                return ref.get();
            } else {
                return null;
            }
        } finally {
            lock.readLock().unlock();
        }
    }

    /**
     * Sets the cached image for the specified constraints.
     *
     * @param image  The image to store in cache
     * @param config The graphics configuration, needed if cached image is a Volatile Image. Used as part of cache key
     * @param w      The image width, used as part of cache key
     * @param h      The image height, used as part of cache key
     * @param args   Other arguments to use as part of the cache key
     * @return true if the image could be cached or false if the image is too big
     */
    public boolean setImage(Image image, GraphicsConfiguration config, int w, int h, Object... args) {
        if (!isImageCachable(w, h)) return false;
        int hash = hash(config, w, h, args);
        lock.writeLock().lock();
        try {
            PixelCountSoftReference ref = map.get(hash);
            // check if currently in map
            if (ref != null && ref.get() == image) {
                return true;
            }
            // clear out old
            if (ref != null) {
                currentPixelCount -= ref.pixelCount;
                map.remove(hash);
            }
            // add new image to pixel count
            int newPixelCount = image.getWidth(null) * image.getHeight(null);
            currentPixelCount += newPixelCount;
            // clean out lost references if not enough space
            if (currentPixelCount > maxPixelCount) {
                while ((ref = (PixelCountSoftReference)referenceQueue.poll()) != null){
                    //reference lost
                    map.remove(ref.hash);
                    currentPixelCount -= ref.pixelCount;
                }
            }
            // remove old items till there is enough free space
            if (currentPixelCount > maxPixelCount) {
                Iterator<Map.Entry<Integer, PixelCountSoftReference>> mapIter = map.entrySet().iterator();
                while ((currentPixelCount > maxPixelCount) && mapIter.hasNext()) {
                    Map.Entry<Integer, PixelCountSoftReference> entry = mapIter.next();
                    mapIter.remove();
                    Image img = entry.getValue().get();
                    if (img != null) img.flush();
                    currentPixelCount -= entry.getValue().pixelCount;
                }
            }
            // finaly put new in map
            map.put(hash, new PixelCountSoftReference(image, referenceQueue, newPixelCount,hash, config, w, h, args));
            return true;
        } finally {
            lock.writeLock().unlock();
        }
    }

    /** Create a unique hash from all the input */
    private int hash(GraphicsConfiguration config, int w, int h, Object ... args) {
        int hash;
        hash = (config != null ? config.hashCode() : 0);
        hash = 31 * hash + w;
        hash = 31 * hash + h;
        hash = 31 * hash + Arrays.deepHashCode(args);
        return hash;
    }


    /** Extended SoftReference that stores the pixel count even after the image is lost */
    private static class PixelCountSoftReference extends SoftReference<Image> {
        private final int pixelCount;
        private final int hash;
        // key parts
        private final GraphicsConfiguration config;
        private final int w;
        private final int h;
        private final Object[] args;

        public PixelCountSoftReference(Image referent, ReferenceQueue<? super Image> q, int pixelCount, int hash,
                                       GraphicsConfiguration config, int w, int h, Object[] args) {
            super(referent, q);
            this.pixelCount = pixelCount;
            this.hash = hash;
            this.config = config;
            this.w = w;
            this.h = h;
            this.args = args;
        }

        public boolean equals (GraphicsConfiguration config, int w, int h, Object[] args){
            return config == this.config &&
                            w == this.w &&
                            h == this.h &&
                            Arrays.equals(args, this.args);
        }
    }
}