使用新式LruCache取代SoftReference缓存图片，Android异步加载图片

import java.io.InputStream;
import java.net.URL;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Handler;
import android.os.Message;
import android.support.v4.util.LruCache;
import android.util.Log;

public class AsyncImageLoader {
 
 /**
  * 使用新式的LruCache取代SoftReference缓存图片，异步加载图片。
  * 
  * 备注：图片的URL作为缓存图片时LruCache的 Key
  * */
 
 private final int CACHE_SIZE = 4 * 1024 * 1024; // 4MiB
 private final int MESSAGE_WHAT = 201;
 
 private LruCache mMemoryCache;

    public AsyncImageLoader() {     
       mMemoryCache = new LruCache(CACHE_SIZE) {
        @Override
              protected int sizeOf(String key, Bitmap value) {
                  return value.getRowBytes() * value.getHeight();
               }};
    }
        
    
        public Bitmap loadBitmap(final String imageUrl, final ImageLoadedListener imageLoadedListener) 
        {
         final Handler handler = new Handler() {
          
             @Override
                public void handleMessage(Message message) {
              
              switch(message.what)
              {
               case MESSAGE_WHAT:
                imageLoadedListener.imageLoaded((Bitmap) message.obj, imageUrl);
              }
                }
            };
         
            if (mMemoryCache.get(imageUrl)!=null) {
             Log.d(this.getClass().getName(),"发现图片缓存，从缓存中读取！");
             
             Bitmap bmp = mMemoryCache.get(imageUrl);
                
                Message message = handler.obtainMessage();
                message.what=MESSAGE_WHAT;
                message.obj=bmp;
                handler.sendMessage(message);
                
                return bmp;
            }
           
            Log.d(this.getClass().getName(),"图片没有缓存，从网络加载！");
            
            new Thread() {
                @Override
                public void run() {
                    Bitmap bmp = loadBitmapFromUrl(imageUrl);
                    mMemoryCache.put(imageUrl, bmp);
                    
                    Message message = handler.obtainMessage();
                    message.what=MESSAGE_WHAT;
                    message.obj=bmp;
                    handler.sendMessage(message);
                }
            }.start();
            
            return null;
        }
     
        
       public static Bitmap loadBitmapFromUrl(String url) {
        
        Log.d("AsyncImageLoader.loadBitmapFromUrl()","Loading -> "+url);
        
           InputStream is = null;
           try {
               is = (InputStream) new URL(url).getContent();
           } catch (Exception e) {
               e.printStackTrace();
           } 
           
           Bitmap bmp=BitmapFactory.decodeStream(is); 
           return bmp;
       }
     
        public interface ImageLoadedListener {
            public void imageLoaded(Bitmap bitmap, String url);
        }
}