public class MemoryCache {
  // 最大的緩存數(shù) 
  private static final int MAX_CACHE_CAPACITY = 30;
  //用Map軟引用的Bitmap對象, 保證內(nèi)存空間足夠情況下不會被垃圾回收
    private HashMap<String, SoftReference<Bitmap>> mCacheMap = 
      new LinkedHashMap<String, SoftReference<Bitmap>>() {
      private static final long serialVersionUID = 1L;
//當(dāng)緩存數(shù)量超過規(guī)定大?。ǚ祷豻rue）會清除最早放入緩存的  
      protected boolean removeEldestEntry(
Map.Entry<String,SoftReference<Bitmap>> eldest){
        return size() > MAX_CACHE_CAPACITY;};
  };
  /**
   * 從緩存里取出圖片
   * @param id
   * @return 如果緩存有，并且該圖片沒被釋放，則返回該圖片，否則返回null
   */
  public Bitmap get(String id){
    if(!mCacheMap.containsKey(id)) return null;
    SoftReference<Bitmap> ref = mCacheMap.get(id);
    return ref.get();
  }
  /**
   * 將圖片加入緩存
   * @param id
   * @param bitmap
   */
  public void put(String id, Bitmap bitmap){
    mCacheMap.put(id, new SoftReference<Bitmap>(bitmap));
  }
  /**
   * 清除所有緩存
   */
  public void clear() {
  try {
      for(Map.Entry<String,SoftReference<Bitmap>>entry :mCacheMap.entrySet()) 
{  SoftReference<Bitmap> sr = entry.getValue();
      if(null != sr) {
        Bitmap bmp = sr.get();
        if(null != bmp) bmp.recycle();
      }
    }
    mCacheMap.clear();
  } catch (Exception e) {
      e.printStackTrace();}
  }
}

public class FileCache { 
  //緩存文件目錄 
  private File mCacheDir;
  /**
   * 創(chuàng)建緩存文件目錄，如果有SD卡，則使用SD，如果沒有則使用系統(tǒng)自帶緩存目錄
   * @param context
   * @param cacheDir 圖片緩存的一級目錄
   */
public FileCache(Context context, File cacheDir, String dir){
if(android.os.Environment.getExternalStorageState().equals、(android.os.Environment.MEDIA_MOUNTED))
      mCacheDir = new File(cacheDir, dir);
   else
    mCacheDir = context.getCacheDir();// 如何獲取系統(tǒng)內(nèi)置的緩存存儲路徑
   if(!mCacheDir.exists()) mCacheDir.mkdirs();
  }
  public File getFile(String url){
    File f=null;
    try {
//對url進(jìn)行編輯，解決中文路徑問題
      String filename = URLEncoder.encode(url,"utf-8");
      f = new File(mCacheDir, filename);
    } catch (UnsupportedEncodingException e) {
      e.printStackTrace();
    }
    return f;
  }
  public void clear(){//清除緩存文件
    File[] files = mCacheDir.listFiles();
    for(File f:files)f.delete();
}
}

public class AsyncImageLoader{
  private MemoryCache mMemoryCache;//內(nèi)存緩存
  private FileCache mFileCache;//文件緩存
  private ExecutorService mExecutorService;//線程池
//記錄已經(jīng)加載圖片的ImageView
  private Map<ImageView, String> mImageViews = Collections
      .synchronizedMap(new WeakHashMap<ImageView, String>());
//保存正在加載圖片的url 
  private List<LoadPhotoTask> mTaskQueue = new ArrayList<LoadPhotoTask>();
  /**
   * 默認(rèn)采用一個(gè)大小為5的線程池
   * @param context
   * @param memoryCache 所采用的高速緩存
   * @param fileCache 所采用的文件緩存
   */
  public AsyncImageLoader(Context context, MemoryCache memoryCache, FileCache fileCache) {
    mMemoryCache = memoryCache;
    mFileCache = fileCache;
    mExecutorService = Executors.newFixedThreadPool(5);//建立一個(gè)容量為5的固定尺寸的線程池（最大正在運(yùn)行的線程數(shù)量）
  }
  /**
   * 根據(jù)url加載相應(yīng)的圖片
   * @param url
   * @return 先從一級緩存中取圖片有則直接返回，如果沒有則異步從文件（二級緩存）中取，如果沒有再從網(wǎng)絡(luò)端獲取
   */
  public Bitmap loadBitmap(ImageView imageView, String url) {
    //先將ImageView記錄到Map中,表示該ui已經(jīng)執(zhí)行過圖片加載了
    mImageViews.put(imageView, url);
    Bitmap bitmap = mMemoryCache.get(url);//先從一級緩存中獲取圖片
    if(bitmap == null) {
      enquequeLoadPhoto(url, imageView);//再從二級緩存和網(wǎng)絡(luò)中獲取
    }
    return bitmap;
  }
  /**
   * 加入圖片下載隊(duì)列
   * @param url
   */
  private void enquequeLoadPhoto(String url, ImageView imageView) {
    //如果任務(wù)已經(jīng)存在，則不重新添加
    if(isTaskExisted(url))
      return;
    LoadPhotoTask task = new LoadPhotoTask(url, imageView);
    synchronized (mTaskQueue) {
      mTaskQueue.add(task);//將任務(wù)添加到隊(duì)列中      
    }
    mExecutorService.execute(task);//向線程池中提交任務(wù)，如果沒有達(dá)到上限(5),則運(yùn)行否則被阻塞
  }
  /**
   * 判斷下載隊(duì)列中是否已經(jīng)存在該任務(wù)
   * @param url
   * @return
   */
  private boolean isTaskExisted(String url) {
    if(url == null)
      return false;
    synchronized (mTaskQueue) {
      int size = mTaskQueue.size();
      for(int i=0; i<size; i++) {
        LoadPhotoTask task = mTaskQueue.get(i);
        if(task != null && task.getUrl().equals(url))
          return true;
      }
    }
    return false;
  }
  /**
   * 從緩存文件或者網(wǎng)絡(luò)端獲取圖片
   * @param url
   */
  private Bitmap getBitmapByUrl(String url) {
    File f = mFileCache.getFile(url);//獲得緩存圖片路徑
    Bitmap b = ImageUtil.decodeFile(f);//獲得文件的Bitmap信息
    if (b != null)//不為空表示獲得了緩存的文件
      return b;
    return ImageUtil.loadBitmapFromWeb(url, f);//同網(wǎng)絡(luò)獲得圖片
  }
  /**
   * 判斷該ImageView是否已經(jīng)加載過圖片了（可用于判斷是否需要進(jìn)行加載圖片）
   * @param imageView
   * @param url
   * @return
   */
  private boolean imageViewReused(ImageView imageView, String url) {
    String tag = mImageViews.get(imageView);
    if (tag == null || !tag.equals(url))
      return true;
    return false;
  }
  private void removeTask(LoadPhotoTask task) {
    synchronized (mTaskQueue) {
      mTaskQueue.remove(task);
    }
  }
  class LoadPhotoTask implements Runnable {
    private String url;
    private ImageView imageView;  
    LoadPhotoTask(String url, ImageView imageView) {
      this.url = url;
      this.imageView = imageView;
    }
    @Override
    public void run() {
      if (imageViewReused(imageView, url)) {//判斷ImageView是否已經(jīng)被復(fù)用
        removeTask(this);//如果已經(jīng)被復(fù)用則刪除任務(wù)
        return;
      }
      Bitmap bmp = getBitmapByUrl(url);//從緩存文件或者網(wǎng)絡(luò)端獲取圖片
      mMemoryCache.put(url, bmp);// 將圖片放入到一級緩存中
      if (!imageViewReused(imageView, url)) {//若ImageView未加圖片則在ui線程中顯示圖片
      BitmapDisplayer bd = new BitmapDisplayer(bmp, imageView, url);            Activity a = (Activity) imageView.getContext();
      a.runOnUiThread(bd);//在UI線程調(diào)用bd組件的run方法，實(shí)現(xiàn)為ImageView控件加載圖片
      }
      removeTask(this);//從隊(duì)列中移除任務(wù)
    }
    public String getUrl() {
      return url;
    }
  }
  /**
   * 
   *由UI線程中執(zhí)行該組件的run方法
   */
  class BitmapDisplayer implements Runnable {
    private Bitmap bitmap;
    private ImageView imageView;
    private String url;
    public BitmapDisplayer(Bitmap b, ImageView imageView, String url) {
      bitmap = b;
      this.imageView = imageView;
      this.url = url;
    }
    public void run() {
      if (imageViewReused(imageView, url))
        return;
      if (bitmap != null)
        imageView.setImageBitmap(bitmap);
    }
  }
  /**
   * 釋放資源
   */
  public void destroy() {
    mMemoryCache.clear();
    mMemoryCache = null;
    mImageViews.clear();
    mImageViews = null;
    mTaskQueue.clear();
    mTaskQueue = null;
    mExecutorService.shutdown();
    mExecutorService = null;
  }
}

public class ImageUtil {
  /**
   * 從網(wǎng)絡(luò)獲取圖片，并緩存在指定的文件中
   * @param url 圖片url
   * @param file 緩存文件
   * @return
   */
  public static Bitmap loadBitmapFromWeb(String url, File file) {
    HttpURLConnection conn = null;
    InputStream is = null;
    OutputStream os = null;
    try {
      Bitmap bitmap = null;
      URL imageUrl = new URL(url);
      conn = (HttpURLConnection) imageUrl.openConnection();
      conn.setConnectTimeout(30000);
      conn.setReadTimeout(30000);
      conn.setInstanceFollowRedirects(true);
      is = conn.getInputStream();
      os = new FileOutputStream(file);
      copyStream(is, os);//將圖片緩存到磁盤中
      bitmap = decodeFile(file);
      return bitmap;
    } catch (Exception ex) {
      ex.printStackTrace();
      return null;
    } finally {
      try {
        if(os != null) os.close();
        if(is != null) is.close();
        if(conn != null) conn.disconnect();
      } catch (IOException e) {  }
    }
  }
  public static Bitmap decodeFile(File f) {
    try {
      return BitmapFactory.decodeStream(new FileInputStream(f), null, null);
    } catch (Exception e) { } 
    return null;
  }
  private static void copyStream(InputStream is, OutputStream os) {
    final int buffer_size = 1024;
    try {
      byte[] bytes = new byte[buffer_size];
      for (;;) {
        int count = is.read(bytes, 0, buffer_size);
        if (count == -1)
          break;
        os.write(bytes, 0, count);
      }
    } catch (Exception ex) {
      ex.printStackTrace();
    }
  }
}

public class MainActivity extends Activity { 
  ListView list;
  ListViewAdapter adapter;
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    list=(ListView)findViewById(R.id.list);
    adapter=new ListViewAdapter(this, mStrings);
    list.setAdapter(adapter);
  }
  public void onDestroy(){
    list.setAdapter(null);
    super.onDestroy();
    adapter.destroy();
  } 
 private String[] mStrings={
 "http://news.jb51.net/UserFiles/x_Image/x_20150606083511_0.jpg",
"http://news.jb51.net/UserFiles/x_Image/x_20150606082847_0.jpg",
…..};

public class ListViewAdapter extends BaseAdapter {
  private Activity mActivity;
  private String[] data;
  private static LayoutInflater inflater=null;
  private AsyncImageLoader imageLoader;//異步組件
  public ListViewAdapter(Activity mActivity, String[] d) {
    this.mActivity=mActivity;
    data=d;
    inflater = (LayoutInflater)mActivity.getSystemService(
Context.LAYOUT_INFLATER_SERVICE);
    MemoryCache mcache=new MemoryCache();//內(nèi)存緩存
 File sdCard = android.os.Environment.getExternalStorageDirectory();//獲得SD卡
    File cacheDir = new File(sdCard, "jereh_cache" );//緩存根目錄
  FileCache fcache=new FileCache(mActivity, cacheDir, "news_img");//文件緩存
    imageLoader = new AsyncImageLoader(mActivity, mcache,fcache);
  }
  public int getCount() {
    return data.length;
  }
  public Object getItem(int position) {
    return position;
  }
  public long getItemId(int position) {
    return position;
  }
  public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder vh=null;
    if(convertView==null){
      convertView = inflater.inflate(R.layout.item, null);
      vh=new ViewHolder();
      vh.tvTitle=(TextView)convertView.findViewById(R.id.text);
      vh.ivImg=(ImageView)convertView.findViewById(R.id.image);
      convertView.setTag(vh);    
    }else{
      vh=(ViewHolder)convertView.getTag();
    }
    vh.tvTitle.setText("標(biāo)題信息測試———— "+position);
    vh.ivImg.setTag(data[position]);
    //異步加載圖片，先從一級緩存、再二級緩存、最后網(wǎng)絡(luò)獲取圖片
    Bitmap bmp = imageLoader.loadBitmap(vh.ivImg, data[position]);
    if(bmp == null) {
      vh.ivImg.setImageResource(R.drawable.default_big);
    } else {
      vh.ivImg.setImageBitmap(bmp);
    }
    return convertView;
  }
  private class ViewHolder{
    TextView tvTitle;
    ImageView ivImg;
  }
  public void destroy() {
    imageLoader.destroy();
  }
}