public class AsyncBitmapLoader 
{ 
 /** 
  * 内存图片软引用缓冲 
  */ 
 private HashMap<String, SoftReference<Bitmap>> imageCache = null; 
  
 public AsyncBitmapLoader() 
 { 
  imageCache = new HashMap<String, SoftReference<Bitmap>>(); 
 } 
  
 public Bitmap loadBitmap(final ImageView imageView, final String imageURL, final ImageCallBack imageCallBack) 
 { 
  //在内存缓存中，则返回Bitmap对象 
  if(imageCache.containsKey(imageURL)) 
  { 
   SoftReference<Bitmap> reference = imageCache.get(imageURL); 
   Bitmap bitmap = reference.get(); 
   if(bitmap != null) 
   { 
    return bitmap; 
   } 
  } 
  else 
  { 
   /** 
    * 加上一个对本地缓存的查找 
    */ 
   String bitmapName = imageURL.substring(imageURL.lastIndexOf("/") + 1); 
   File cacheDir = new File("/mnt/sdcard/test/"); 
   File[] cacheFiles = cacheDir.listFiles(); 
   int i = 0; 
   if(null!=cacheFiles){ 
   for(; i<cacheFiles.length; i++) 
   { 
    if(bitmapName.equals(cacheFiles[i].getName())) 
    { 
     break; 
    } 
   } 
    
   if(i < cacheFiles.length) 
   { 
    return BitmapFactory.decodeFile("/mnt/sdcard/test/" + bitmapName); 
   } 
   } 
  } 
   
  final Handler handler = new Handler() 
  { 
   /* (non-Javadoc) 
    * @see android.os.Handler#handleMessage(android.os.Message) 
    */ 
   @Override 
   public void handleMessage(Message msg) 
   { 
    // TODO Auto-generated method stub 
    imageCallBack.imageLoad(imageView, (Bitmap)msg.obj); 
   } 
  }; 
   
  //如果不在内存缓存中，也不在本地（被jvm回收掉），则开启线程下载图片 
  new Thread() 
  { 
   /* (non-Javadoc) 
    * @see java.lang.Thread#run() 
    */ 
   @Override 
   public void run() 
   { 
    // TODO Auto-generated method stub 
    InputStream bitmapIs = HttpUtils.getStreamFromURL(imageURL); 
     
    Bitmap bitmap = BitmapFactory.decodeStream(bitmapIs); 
    imageCache.put(imageURL, new SoftReference<Bitmap>(bitmap)); 
    Message msg = handler.obtainMessage(0, bitmap); 
    handler.sendMessage(msg); 
     
    File dir = new File("/mnt/sdcard/test/"); 
    if(!dir.exists()) 
    { 
     dir.mkdirs(); 
    } 
     
    File bitmapFile = new File("/mnt/sdcard/test/" +  
      imageURL.substring(imageURL.lastIndexOf("/") + 1)); 
    if(!bitmapFile.exists()) 
    { 
     try 
     { 
      bitmapFile.createNewFile(); 
     } 
     catch (IOException e) 
     { 
      // TODO Auto-generated catch block 
      e.printStackTrace(); 
     } 
    } 
    FileOutputStream fos; 
    try 
    { 
     fos = new FileOutputStream(bitmapFile); 
     bitmap.compress(Bitmap.CompressFormat.PNG,  
       100, fos); 
     fos.close(); 
    } 
    catch (FileNotFoundException e) 
    { 
     // TODO Auto-generated catch block 
     e.printStackTrace(); 
    } 
    catch (IOException e) 
    { 
     // TODO Auto-generated catch block 
     e.printStackTrace(); 
    } 
   } 
  }.start(); 
   
  return null; 
 } 
 
 public interface ImageCallBack 
 { 
  public void imageLoad(ImageView imageView, Bitmap bitmap); 
 } 
} 

public class HttpUtils { 
 
 public static InputStream getStreamFromURL(String imageURL) { 
  InputStream in=null; 
  try { 
   URL url=new URL(imageURL); 
   HttpURLConnection connection=(HttpURLConnection) url.openConnection(); 
   in=connection.getInputStream(); 
    
  } catch (Exception e) { 
   // TODO Auto-generated catch block 
   e.printStackTrace(); 
  } 
  return in; 
   
 } 
} 

public class ImageCacheActivity extends Activity { 
 /** Called when the activity is first created. */ 
 private ListView listview; 
 @Override 
 public void onCreate(Bundle savedInstanceState) { 
  super.onCreate(savedInstanceState); 
  setContentView(R.layout.main); 
   
  listview=(ListView) findViewById(R.id.listView_list); 
  MyAdapter adapter=new MyAdapter(); 
  listview.setAdapter(adapter); 
 } 
  
 private class MyAdapter extends BaseAdapter{ 
 
  private AsyncBitmapLoader asyncBitmapLoader; 
  public MyAdapter(){ 
   asyncBitmapLoader=new AsyncBitmapLoader(); 
  } 
  @Override 
  public int getCount() { 
   // TODO Auto-generated method stub 
   return 10; 
  } 
 
  @Override 
  public Object getItem(int position) { 
   // TODO Auto-generated method stub 
   return null; 
  } 
 
  @Override 
  public long getItemId(int position) { 
   // TODO Auto-generated method stub 
   return 0; 
  } 
 
  @Override 
  public View getView(int position, View convertView, ViewGroup parent) { 
   // TODO Auto-generated method stub 
   if(convertView==null){ 
    convertView=LayoutInflater.from(getApplicationContext()).inflate(R.layout.list_item, null); 
   } 
   ImageView image=(ImageView) convertView.findViewById(R.id.addexam_list_icon); 
   String imageURL="http://s.ata.net.cn/4f98db46908987a21a000003/logo/2012/04/114_80aaf295c083d07a496743699aac3193.png"; 
   Bitmap bitmap=asyncBitmapLoader.loadBitmap(image, imageURL, new ImageCallBack() { 
     
    @Override 
    public void imageLoad(ImageView imageView, Bitmap bitmap) { 
     // TODO Auto-generated method stub 
     imageView.setImageBitmap(bitmap); 
    } 
   }); 
    if(bitmap == null) 
    { 
     image.setImageResource(R.drawable.ic_launcher); 
    } 
    else 
    { 
     image.setImageBitmap(bitmap); 
    } 
     
   return convertView; 
  } 
   
 } 
}