自写的ImageLoader用于缓存图片

public class MusicAdapter extends BaseAdapter{
	private Context context;
	private List musics;
	private LayoutInflater inflater;
	//声明图片下载任务集合
	private List tasks=new ArrayList();
	//声明用于轮循任务队列的工作线程
	private Thread workThread;
	private boolean isLoop=true;
	private ListView listView;
	//声明用于实现内存缓存的map
	private Map> cache = new HashMap>();
	
	//声明handler  显示图片
	private Handler handler = new Handler(){
		public void handleMessage(android.os.Message msg) {
			switch (msg.what) {
			case HANDLER_LOAD_IMAGE_SUCCESS: //图片下载成功
				ImageLoadTask task = (ImageLoadTask) msg.obj;
				Bitmap bitmap = task.bitmap;
				//通过listView.findViewWithTag()方法获取相应的imageView
				ImageView imageView=(ImageView) listView.findViewWithTag(task.path);
				if(imageView != null){
					if(bitmap!=null){
						imageView.setImageBitmap(bitmap);
					}else{
						imageView.setImageResource(R.drawable.ic_launcher);
					}
				}
				break;
			}
		}
	};
	
	public static final int HANDLER_LOAD_IMAGE_SUCCESS=1;
	
	public MusicAdapter(Context context, List musics, ListView listView) {
		this.context = context;
		this.listView = listView;
		this.musics = musics;
		this.inflater = LayoutInflater.from(context);
		//初始化并且启动workThread
		workThread = new Thread(){
			public void run() {
				//不断轮循任务集合  一旦有任务  则获取然后执行下载操作
				while(isLoop){
					if(!tasks.isEmpty()){ //有任务
						ImageLoadTask task=tasks.remove(0);
						String path = task.path;
						//下载图片
						Bitmap bitmap = loadBitmap(path);
						task.bitmap = bitmap;
						//给imageView 设置 Bitmap
						Message msg = new Message();
						msg.what = HANDLER_LOAD_IMAGE_SUCCESS;
						msg.obj = task;
						handler.sendMessage(msg);
						
					}else{ //没有任务  工作线程等待
						try {
							synchronized (workThread) {
								workThread.wait();
							}
						} catch (InterruptedException e) {
							e.printStackTrace();
						}
					}
				}
			}
		};
		workThread.start();
	}
	
	/**
	 * 通过path 下载图片
	 * @param path
	 * @return
	 */
	public Bitmap loadBitmap(String path){
		try {
			InputStream is = HttpUtils.get(path);
			Bitmap b = BitmapUtils.loadBitmap(is, 50, 50);
			//下载成功  把b存入内存缓存中
			cache.put(path, new SoftReference(b));
			//存入文件缓存目录中 
			String filename = path.substring(path.lastIndexOf("/")+1);
			// f --> /data/data/cn.tedu.music/cache/xxxxx.jpg
			File f = new File(context.getCacheDir(), filename);
			BitmapUtils.save(b, f.getAbsolutePath());


			return b;
		} catch (IOException e) {
			e.printStackTrace();
		}
		return null;
	}
	
	@Override
	public int getCount() {
		return musics.size();
	}


	@Override
	public Music getItem(int position) {
		return musics.get(position);
	}


	@Override
	public long getItemId(int position) {
		return position;
	}


	@Override
	public View getView(int position, View convertView, ViewGroup parent) {
		ViewHolder holder = null;
		if(convertView==null){
			convertView = inflater.inflate(R.layout.item_lv_music, null);
			holder = new ViewHolder();
			holder.ivPic = (ImageView) convertView.findViewById(R.id.ivPic);
			holder.tvName = (TextView) convertView.findViewById(R.id.tvName);
			holder.tvSinger = (TextView) convertView.findViewById(R.id.tvSinger);
			convertView.setTag(holder);
		}
		holder=(ViewHolder) convertView.getTag();
		//给holder中控件赋值
		Music m = getItem(position);
		holder.tvName.setText(m.getTitle());
		holder.tvSinger.setText(m.getArtist_name());
		//设置图片  从缓存中读取图片 
		SoftReference ref=cache.get(m.getPic_small());
		if(ref!=null){
			Log.i("info", "从内存中获取的图片...");
			Bitmap bitmap=ref.get();
			if(bitmap!=null){ //图片还没有被销毁
				holder.ivPic.setImageBitmap(bitmap);
				return convertView;
			}
		}
		//内存缓存中没有图片  则去文件缓存中读取
		String path = m.getPic_small();
		String filename = path.substring(path.lastIndexOf("/")+1);
		File f = new File(context.getCacheDir(), filename);
		Bitmap bitmap=BitmapUtils.loadBitmap(f.getAbsolutePath());
		if(bitmap!=null){
			Log.i("info", "从文件中获取的图片....");
			holder.ivPic.setImageBitmap(bitmap);
			//向内存缓存中再存一次
			cache.put(m.getPic_small(), new SoftReference(bitmap));
			return convertView;
		}
		// 向任务集合中添加一个图片下载任务
		//给imageView设置一个tag值  用于handler中通过tag值找到imageView
		holder.ivPic.setTag(m.getPic_small());
		ImageLoadTask task = new ImageLoadTask();
		task.path = m.getPic_small();
		tasks.add(task);
		//唤醒工作线程  赶紧起来干活
		synchronized (workThread) {
			workThread.notify();
		}
		return convertView;
	}
	
	/**
	 * 停止线程
	 */
	public void stopThread(){
		isLoop = false;
		synchronized (workThread) {
			//唤醒工作线程
			workThread.notify();
		}
	}


	class ViewHolder{
		ImageView ivPic;
		TextView tvName;
		TextView tvSinger;
	}


	/**
	 * 封装一个图片下载任务
	 */
	class ImageLoadTask {
		String path;   //图片路径
		Bitmap bitmap;  //通过路径下载成功的bitmap
	}
	
}