public class ImageCacheUtil {
  private LruCache<String, Bitmap> lruCache;
  private File cacheDir;
  private ExecutorService newFixedThreadPool;
  private Handler handler;
  public static final int SUCCESS = 100;
  public static final int FAIL = 101;
  //當(dāng)我們獲取圖片的時候,分三步
  //1.從緩存中獲取圖片
  //2.從本地的緩存目錄中獲取圖片,并且獲取到之后,放到緩存中
  //3.從網(wǎng)絡(luò)去下載圖片,下載完成之后,保存到本地緩存目錄和放到緩存中
  public ImageCacheUtil(Context context,Handler handler){
    //獲取緩存的大小
    int maxsize = (int) (Runtime.getRuntime().maxMemory()/8);
    //maxSize : 設(shè)置緩存的最大空間
    lruCache = new LruCache<String, Bitmap>(maxsize){
      //獲取移出的圖片所占用的空間,當(dāng)圖片移出的時候,需要將圖片占用的緩存空間從緩存中移出
       @Override
      protected int sizeOf(String key, Bitmap value) {
         //計算圖片所占用的緩存大小
         //getRowBytes : 獲取圖片一行所占用的大小
         //getHeight :　獲取圖片所占用行數(shù)
        return value.getRowBytes()*value.getHeight();
      }
    };
    //獲取緩存目錄
    cacheDir = context.getCacheDir();
    //獲取線程池
    //nThreads : 線程池中的線程數(shù)量
    newFixedThreadPool = Executors.newFixedThreadPool(5);
    this.handler = handler;
  }
  /**
   * 獲取圖片的方法
   * @param url
   * @param positon
   * @return
   */
  public Bitmap getBitmap(String url,int position){
    Bitmap bitmap = null;
    //1.從緩存中獲取圖片 (LRUCache<k,v>) k:key 保存圖片的標(biāo)示,一般都是圖片的url地址,v:value 圖片
    bitmap = lruCache.get(url);//根據(jù)key從緩存中獲取相應(yīng)的圖片
    //lruCache.put(url, bitmap):保存圖片到緩存中
    if (bitmap!=null) {
      return bitmap;
    }
    //2.從本地的緩存目錄中獲取圖片,并且獲取到之后,放到緩存中
    bitmap = getFromLocal(url);
    if (bitmap!=null) {
      return bitmap;
    }
    //3.從網(wǎng)絡(luò)去下載圖片,下載完成之后,保存到本地緩存目錄和放到緩存中
    getFromNet(url,position);
    return null;
  }
  /**
   * 從網(wǎng)絡(luò)下載圖片,異步方式,線程池
   * @param url
   * @param position
   */
  private void getFromNet(String url, int position) {
    newFixedThreadPool.execute(new RunnableTask(url,position));
  }
  class RunnableTask implements Runnable{
    private String imageUrl;
    private int position;
    public RunnableTask(String url,int position){
      this.imageUrl = url;
      this.position = position;
    }

    @Override
    public void run() {
      Message message = Message.obtain();
      //下載圖片
      try {
        URL url = new URL(imageUrl);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setReadTimeout(3000);
        conn.setConnectTimeout(5000);
        conn.setRequestMethod("GET");
        InputStream inputStream = conn.getInputStream();
        Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
        //保存到本地緩存中
        wirteToLocal(imageUrl, bitmap);
        //保存到系統(tǒng)緩沖中
        lruCache.put(imageUrl, bitmap);
        //顯示圖片,給handler發(fā)送消息
        message.what = SUCCESS;
        message.obj = bitmap;
        message.arg1 = position;
        handler.sendMessage(message);
        return;
      } catch (Exception e) {
        e.printStackTrace();
      }
      message.what = FAIL;
      handler.sendMessage(message);
    }
  }
  /**
   * 從本地緩存目錄獲取圖片
   * @param url
   */
  private Bitmap getFromLocal(String url) {
    //根據(jù)圖片的名稱獲取圖片
    try {
      String fileName = MD5Encoder.encode(url).substring(10);
      File file = new File(cacheDir, fileName);
      Bitmap bitmap = BitmapFactory.decodeFile(file.getAbsolutePath());
      //防盜緩存當(dāng)中
      lruCache.put(url, bitmap);
      return bitmap;
    } catch (Exception e) {
      e.printStackTrace();
    }
    return null;
  }
  /**
   * 將圖片保存到本地緩存目錄中
   */
  public void wirteToLocal(String url,Bitmap bitmap){
    //url名稱,通過MD5加密,并且截取前10位作為名稱
    try {
      String fileName = MD5Encoder.encode(url).substring(10);
      File file = new File(cacheDir, fileName);
      FileOutputStream out = new FileOutputStream(file);
      //format :圖片的格式（android中用的png多，因為png質(zhì)量是不會改變的）
      //quality : 壓縮比例
      //stream : 流信息
      bitmap.compress(CompressFormat.JPEG, 100, out);//將圖片保存到那個位置
    } catch (Exception e) {
      e.printStackTrace();
    }
  }

}

public class MD5Encoder {

  public static String encode(String string) throws Exception {
    byte[] hash = MessageDigest.getInstance("MD5").digest(string.getBytes("UTF-8"));
    StringBuilder hex = new StringBuilder(hash.length * 2);
    for (byte b : hash) {
      if ((b & 0xFF) < 0x10) {
        hex.append("0");
      }
      hex.append(Integer.toHexString(b & 0xFF));
    }
    return hex.toString();
  }
}

ImageCacheUtil imageCacheUtil = new ImageCacheUtil(getApplicationContext, handler);

private Handler handler = new Handler(){
  public void handleMessage(android.os.Message msg) {
    switch (msg.what) {
    case ImageCacheUtil.SUCCESS:
      //給控件設(shè)置圖片
      Bitmap bitmap = (Bitmap) msg.obj;
      int position = msg.arg1;
      ImageView image= (ImageView) view.findViewWithTag(position);//就是根據(jù)條目的位置獲取相應(yīng)的控件
      if (image != null && bitmap != null) {
        image.setImageBitmap(bitmap);
      }
      break;
    case ImageCacheUtil.FAIL:
      Toast.makeText(getApplicationContext, "圖片下載失敗", 0).show();
      break;
    }
  };
};

Bitmap bitmap = imageCacheUtil.getBitmap(list.get(position).listimage, position);
if (bitmap != null) {
  viewHodler.image.setImageBitmap(bitmap);
}