详解Android 图片的三级缓存及图片压缩

 public class NetCacheUtils {

    private LocalCacheUtils mLocalCacheUtils;
    private MemoryCacheUtils mMemoryCacheUtils;

    public NetCacheUtils(LocalCacheUtils localCacheUtils,
        MemoryCacheUtils memoryCacheUtils) {
      mLocalCacheUtils = localCacheUtils;
      mMemoryCacheUtils = memoryCacheUtils;
    }

    /**
     * 从网络下载图片
     * 
     * @param ivPic
     * @param url
     */
    public void getBitmapFromNet(ImageView ivPic, String url) {
      new BitmapTask().execute(ivPic, url);// 启动AsyncTask,
                          // 参数会在doInbackground中获取
    }

    /**
     * Handler和线程池的封装
     * 
     * 第一个泛型: 参数类型 第二个泛型: 更新进度的泛型, 第三个泛型是onPostExecute的返回结果
     * 
     * 
     */
    class BitmapTask extends AsyncTask<Object, Void, Bitmap> {

      private ImageView ivPic;
      private String url;

      /**
       * 后台耗时方法在此执行, 子线程
       */
      @Override
      protected Bitmap doInBackground(Object... params) {
        ivPic = (ImageView) params[0];
        url = (String) params[1];

        ivPic.setTag(url);// 将url和imageview绑定

        return downloadBitmap(url);
      }

      /**
       * 更新进度, 主线程
       */
      @Override
      protected void onProgressUpdate(Void... values) {
        super.onProgressUpdate(values);
      }

      /**
       * 耗时方法结束后,执行该方法, 主线程
       */
      @Override
      protected void onPostExecute(Bitmap result) {
        if (result != null) {
          String bindUrl = (String) ivPic.getTag();

          if (url.equals(bindUrl)) {// 确保图片设定给了正确的imageview
            ivPic.setImageBitmap(result);
            mLocalCacheUtils.setBitmapToLocal(url, result);// 将图片保存在本地
            mMemoryCacheUtils.setBitmapToMemory(url, result);// 将图片保存在内存
            System.out.println("从网络缓存读取图片啦...");
          }
        }
      }
    }

    /**
     * 下载图片
     * 
     * @param url
     * @return
     */
    private Bitmap downloadBitmap(String url) {

      HttpURLConnection conn = null;
      try {
        conn = (HttpURLConnection) new URL(url).openConnection();

        conn.setConnectTimeout(5000);
        conn.setReadTimeout(5000);
        conn.setRequestMethod("GET");
        conn.connect();

        int responseCode = conn.getResponseCode();
        if (responseCode == 200) {
          InputStream inputStream = conn.getInputStream();

          //图片压缩处理
          BitmapFactory.Options option = new BitmapFactory.Options();
          option.inSampleSize = 2;//宽高都压缩为原来的二分之一, 此参数需要根据图片要展示的大小来确定
          option.inPreferredConfig = Bitmap.Config.RGB_565;//设置图片格式

          Bitmap bitmap = BitmapFactory.decodeStream(inputStream, null, option);
          return bitmap;
        }

      } catch (Exception e) {
        e.printStackTrace();
      } finally {
        conn.disconnect();
      }

      return null;
    }
  }

  public class LocalCacheUtils {

    public static final String CACHE_PATH = Environment
        .getExternalStorageDirectory().getAbsolutePath() + "/local_cache";

    /**
     * 从本地sdcard读图片
     */
    public Bitmap getBitmapFromLocal(String url) {
      try {
        String fileName = MD5Encoder.encode(url);
        File file = new File(CACHE_PATH, fileName);

        if (file.exists()) {
          Bitmap bitmap = BitmapFactory.decodeStream(new FileInputStream(
              file));
          return bitmap;
        }

      } catch (Exception e) {
        e.printStackTrace();
      }

      return null;
    }

    /**
     * 向sdcard写图片
     * 
     * @param url
     * @param bitmap
     */
    public void setBitmapToLocal(String url, Bitmap bitmap) {
      try {
        String fileName = MD5Encoder.encode(url);

        File file = new File(CACHE_PATH, fileName);

        File parentFile = file.getParentFile();
        if (!parentFile.exists()) {// 如果文件夹不存在, 创建文件夹
          parentFile.mkdirs();
        }

        // 将图片保存在本地
        bitmap.compress(CompressFormat.JPEG, 100,
            new FileOutputStream(file));
      } catch (Exception e) {
        e.printStackTrace();
      }

    }
  }

    public class MemoryCacheUtils {

      // private HashMap<String, SoftReference<Bitmap>> mMemoryCache = new
      // HashMap<String, SoftReference<Bitmap>>();
      private LruCache<String, Bitmap> mMemoryCache;

      public MemoryCacheUtils() {
        long maxMemory = Runtime.getRuntime().maxMemory() / 8;// 模拟器默认是16M
        mMemoryCache = new LruCache<String, Bitmap>((int) maxMemory) {
          @Override
          protected int sizeOf(String key, Bitmap value) {
            int byteCount = value.getRowBytes() * value.getHeight();// 获取图片占用内存大小
            return byteCount;
          }
        };
      }

      /**
       * 从内存读
       * 
       * @param url
       */
      public Bitmap getBitmapFromMemory(String url) {
        // SoftReference<Bitmap> softReference = mMemoryCache.get(url);
        // if (softReference != null) {
        // Bitmap bitmap = softReference.get();
        // return bitmap;
        // }
        return mMemoryCache.get(url);
      }

      /**
       * 写内存
       * 
       * @param url
       * @param bitmap
       */
      public void setBitmapToMemory(String url, Bitmap bitmap) {
        // SoftReference<Bitmap> softReference = new
        // SoftReference<Bitmap>(bitmap);
        // mMemoryCache.put(url, softReference);
        mMemoryCache.put(url, bitmap);
      }
    }

  //图片压缩处理（在从网络获取图片的时候就进行压缩）
  BitmapFactory.Options option = new BitmapFactory.Options();
  option.inSampleSize = 2;//宽高都压缩为原来的二分之一, 此参数需要根据图片要展示的大小来确定
  option.inPreferredConfig = Bitmap.Config.RGB_565;//设置图片格式
  Bitmap bitmap = BitmapFactory.decodeStream(inputStream, null, option);