原版程序出处未知，不知道是谁写的了，我在原有的基础上现在做一些改进优化

1.增加线程池功能，限制通知下载的线程数，

但是还有一些缺陷，

public class AsyncImageLoader {    private static final String TAG = "AsyncImageLoader";    private ThreadPoolExecutor mPoolExecutor;    private HashMap
    
     > imageCache;    private Handler mMainThreadHandler;    /**     * 创建一个异步图片加载器，默认最大5个工作线程，最大等待队列20     */    public AsyncImageLoader() {        this(5, 20);    }    /**     * 创建一个异步图片加载器，当等待下载的图片超过设置的最大等待数量之后，会从等待队列中放弃一个最早加入队列的任务     *      * @param maxPoolSize 最大工作线程数     * @param queueSize 最大等待数     */    public AsyncImageLoader(int maxPoolSize, int queueSize) {        this(2, maxPoolSize, 3, TimeUnit.SECONDS, new LinkedBlockingQueue
     
      (queueSize),                new ThreadPoolExecutor.DiscardOldestPolicy());    }    /**     * 自定义线程池的加载器,请参考:{@link ThreadPoolExecutor}     *      * @param corePoolSize     * @param maximumPoolSize     * @param keepAliveTime     * @param unit     * @param workQueue     * @param handler     */    public AsyncImageLoader(int corePoolSize, int maximumPoolSize, long keepAliveTime,            TimeUnit unit, BlockingQueue
      
        workQueue, RejectedExecutionHandler handler) {        imageCache = new HashMap
       
        >();        mPoolExecutor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, unit,                workQueue, handler);        mMainThreadHandler = new Handler(Looper.getMainLooper());    }    /**     * 异步加载一张图片     *      * @param imageUrl     * @param imageCallback     */    public void loadDrawable(final String imageUrl, final ImageCallback imageCallback) {        if (imageCache.containsKey(imageUrl)) {            SoftReference
        
          softReference = imageCache.get(imageUrl);            Drawable drawable = softReference.get();            if (drawable != null) {                LogUtils.d(TAG, "load image from cache url:" + imageUrl);                imageCallback.onLoaded(drawable);                return;            }        }        LoadImageTask task = new LoadImageTask(imageUrl, this, mMainThreadHandler, imageCallback);        mPoolExecutor.execute(task);    }    /**     * 停止线程池运行，停止之后，将不能在继续调用 {@link #loadDrawable(String, ImageCallback)}     */    public void shutdown() {        mPoolExecutor.shutdown();        imageCache.clear();    }    private void cache(String url, Drawable drawable) {        imageCache.put(url, new SoftReference
         
          (drawable)); } /** * 下载任务 * */ private static final class LoadImageTask implements Runnable { private Handler mHandler; private ImageCallback mCallback; private AsyncImageLoader mLoader; private String mPath; /** * @param imgPath 要下载的图片地址 * @param loader 图片加载器 * @param handler 主线程Handler * @param imageCallback 图片加载回调 */ public LoadImageTask(String imgPath, AsyncImageLoader loader, Handler handler, ImageCallback imageCallback) { LogUtils.d(TAG, "start a task for load image:" + imgPath); this.mHandler = handler; this.mPath = imgPath; this.mLoader = loader; this.mCallback = imageCallback; } @Override public void run() { URL url; InputStream is = null; try { url = new URL(mPath); URLConnection conn = url.openConnection(); conn.connect(); is = conn.getInputStream(); final Drawable drawable = Drawable.createFromStream(is, "src"); mLoader.cache(mPath, drawable); mHandler.post(new Runnable() { @Override public void run() { LogUtils.d(TAG, "load image success:" + mPath); mCallback.onLoaded(drawable); } }); } catch (final Exception e) { LogUtils.e(TAG, e.getMessage() + "", e); mHandler.post(new Runnable() { @Override public void run() { LogUtils.d(TAG, "load image failed:" + mPath); mCallback.onError(e); } }); } } } /** * 回调接口,在主线程中运行 * */ public static interface ImageCallback { /** * 加载成功 * * @param imageDrawable 下载下来的图片 */ public void onLoaded(Drawable drawable); /** * 加载失败 * * @param e 异常 */ public void onError(Exception e); }}