Android编程图片加载类ImageLoader定义与用法实例分析

/**
 * @描述 图片加载类
 * @项目名称 App_News
 * @包名 com.android.news.tools
 * @类名 ImageLoader
 * @author chenlin
 * @date 2015-3-7 下午7:35:28
 * @version 1.0
 */
public class ImageLoader {
  private static ImageLoader mInstance;
  /**
   * 图片缓存的核心对象
   */
  private LruCache<String, Bitmap> mLruCache;
  /**
   * 线程池
   */
  private ExecutorService mThreadPool;
  private static final int DEAFULT_THREAD_COUNT = 1;
  /**
   * 队列的调度方式
   */
  private Type mType = Type.LIFO;
  /**
   * 任务队列
   */
  private LinkedList<Runnable> mTaskQueue;
  /**
   * 后台轮询线程
   */
  private Thread mPoolThread;
  private Handler mPoolThreadHandler;
  /**
   * UI线程中的Handler
   */
  private Handler mUIHandler;
  private Semaphore mSemaphorePoolThreadHandler = new Semaphore(0);
  private Semaphore mSemaphoreThreadPool;
  private boolean isDiskCacheEnable = true;
  private static final String TAG = "ImageLoader";
  public enum Type {
    FIFO, LIFO;
  }
  private ImageLoader(int threadCount, Type type) {
    init(threadCount, type);
  }
  /**
   * 初始化
   *
   * @param threadCount
   * @param type
   */
  private void init(int threadCount, Type type) {
    initBackThread();
    // 获取我们应用的最大可用内存
    int maxMemory = (int) Runtime.getRuntime().maxMemory();
    int cacheMemory = maxMemory / 8;
    mLruCache = new LruCache<String, Bitmap>(cacheMemory) {
      @Override
      protected int sizeOf(String key, Bitmap value) {
        return value.getRowBytes() * value.getHeight();
      }
    };
    // 创建线程池
    mThreadPool = Executors.newFixedThreadPool(threadCount);
    mTaskQueue = new LinkedList<Runnable>();
    mType = type;
    mSemaphoreThreadPool = new Semaphore(threadCount);
  }
  /**
   * 初始化后台轮询线程
   */
  private void initBackThread() {
    // 后台轮询线程
    mPoolThread = new Thread() {
      @Override
      public void run() {
        Looper.prepare();
        mPoolThreadHandler = new Handler() {
          @Override
          public void handleMessage(Message msg) {
            // 线程池去取出一个任务进行执行
            mThreadPool.execute(getTask());
            try {
              mSemaphoreThreadPool.acquire();
            } catch (InterruptedException e) {
            }
          }
        };
        // 释放一个信号量
        mSemaphorePoolThreadHandler.release();
        Looper.loop();
      };
    };
    mPoolThread.start();
  }
  public static ImageLoader getInstance() {
    if (mInstance == null) {
      synchronized (ImageLoader.class) {
        if (mInstance == null) {
          mInstance = new ImageLoader(DEAFULT_THREAD_COUNT, Type.LIFO);
        }
      }
    }
    return mInstance;
  }
  public static ImageLoader getInstance(int threadCount, Type type) {
    if (mInstance == null) {
      synchronized (ImageLoader.class) {
        if (mInstance == null) {
          mInstance = new ImageLoader(threadCount, type);
        }
      }
    }
    return mInstance;
  }
  /**
   * 根据path为imageview设置图片
   *
   * @param path
   * @param imageView
   */
  public void loadImage(final String path, final ImageView imageView, final boolean isFromNet) {
    imageView.setTag(path);
    if (mUIHandler == null) {
      mUIHandler = new Handler() {
        public void handleMessage(Message msg) {
          // 获取得到图片，为imageview回调设置图片
          ImgBeanHolder holder = (ImgBeanHolder) msg.obj;
          Bitmap bm = holder.bitmap;
          ImageView imageview = holder.imageView;
          String path = holder.path;
          // 将path与getTag存储路径进行比较
          if (imageview.getTag().toString().equals(path)) {
            imageview.setImageBitmap(bm);
          }
        };
      };
    }
    // 根据path在缓存中获取bitmap
    Bitmap bm = getBitmapFromLruCache(path);
    if (bm != null) {
      refreashBitmap(path, imageView, bm);
    } else {
      addTask(buildTask(path, imageView, isFromNet));
    }
  }
  /**
   * 根据传入的参数，新建一个任务
   *
   * @param path
   * @param imageView
   * @param isFromNet
   * @return
   */
  private Runnable buildTask(final String path, final ImageView imageView, final boolean isFromNet) {
    return new Runnable() {
      @Override
      public void run() {
        Bitmap bm = null;
        if (isFromNet) {
          File file = getDiskCacheDir(imageView.getContext(), md5(path));
          if (file.exists())// 如果在缓存文件中发现
          {
            Log.e(TAG, "find image :" + path + " in disk cache .");
            bm = loadImageFromLocal(file.getAbsolutePath(), imageView);
          } else {
            if (isDiskCacheEnable)// 检测是否开启硬盘缓存
            {
              boolean downloadState = DownloadImgUtils.downloadImgByUrl(path, file);
              if (downloadState)// 如果下载成功
              {
                Log.e(TAG,
                    "download image :" + path + " to disk cache . path is "
                        + file.getAbsolutePath());
                bm = loadImageFromLocal(file.getAbsolutePath(), imageView);
              }
            } else
            // 直接从网络加载
            {
              Log.e(TAG, "load image :" + path + " to memory.");
              bm = DownloadImgUtils.downloadImgByUrl(path, imageView);
            }
          }
        } else {
          bm = loadImageFromLocal(path, imageView);
        }
        // 3、把图片加入到缓存
        addBitmapToLruCache(path, bm);
        refreashBitmap(path, imageView, bm);
        mSemaphoreThreadPool.release();
      }
    };
  }
  private Bitmap loadImageFromLocal(final String path, final ImageView imageView) {
    Bitmap bm;
    // 加载图片
    // 图片的压缩
    // 1、获得图片需要显示的大小
    ImageSize imageSize = ImageSizeUtil.getImageViewSize(imageView);
    // 2、压缩图片
    bm = decodeSampledBitmapFromPath(path, imageSize.width, imageSize.height);
    return bm;
  }
  /**
   * 从任务队列取出一个方法
   *
   * @return
   */
  private Runnable getTask() {
    if (mType == Type.FIFO) {
      return mTaskQueue.removeFirst();
    } else if (mType == Type.LIFO) {
      return mTaskQueue.removeLast();
    }
    return null;
  }
  /**
   * 利用签名辅助类，将字符串字节数组
   *
   * @param str
   * @return
   */
  public String md5(String str) {
    byte[] digest = null;
    try {
      MessageDigest md = MessageDigest.getInstance("md5");
      digest = md.digest(str.getBytes());
      return bytes2hex02(digest);
    } catch (NoSuchAlgorithmException e) {
      e.printStackTrace();
    }
    return null;
  }
  /**
   * 方式二
   *
   * @param bytes
   * @return
   */
  public String bytes2hex02(byte[] bytes) {
    StringBuilder sb = new StringBuilder();
    String tmp = null;
    for (byte b : bytes) {
      // 将每个字节与0xFF进行与运算，然后转化为10进制，然后借助于Integer再转化为16进制
      tmp = Integer.toHexString(0xFF & b);
      if (tmp.length() == 1)// 每个字节8为，转为16进制标志，2个16进制位
      {
        tmp = "0" + tmp;
      }
      sb.append(tmp);
    }
    return sb.toString();
  }
  private void refreashBitmap(final String path, final ImageView imageView, Bitmap bm) {
    Message message = Message.obtain();
    ImgBeanHolder holder = new ImgBeanHolder();
    holder.bitmap = bm;
    holder.path = path;
    holder.imageView = imageView;
    message.obj = holder;
    mUIHandler.sendMessage(message);
  }
  /**
   * 将图片加入LruCache
   *
   * @param path
   * @param bm
   */
  protected void addBitmapToLruCache(String path, Bitmap bm) {
    if (getBitmapFromLruCache(path) == null) {
      if (bm != null)
        mLruCache.put(path, bm);
    }
  }
  /**
   * 根据图片需要显示的宽和高对图片进行压缩
   *
   * @param path
   * @param width
   * @param height
   * @return
   */
  protected Bitmap decodeSampledBitmapFromPath(String path, int width, int height) {
    // 获得图片的宽和高，并不把图片加载到内存中
    BitmapFactory.Options options = new BitmapFactory.Options();
    options.inJustDecodeBounds = true;
    BitmapFactory.decodeFile(path, options);
    options.inSampleSize = ImageSizeUtil.caculateInSampleSize(options, width, height);
    // 使用获得到的InSampleSize再次解析图片
    options.inJustDecodeBounds = false;
    Bitmap bitmap = BitmapFactory.decodeFile(path, options);
    return bitmap;
  }
  private synchronized void addTask(Runnable runnable) {
    mTaskQueue.add(runnable);
    // if(mPoolThreadHandler==null)wait();
    try {
      if (mPoolThreadHandler == null)
        mSemaphorePoolThreadHandler.acquire();
    } catch (InterruptedException e) {
    }
    mPoolThreadHandler.sendEmptyMessage(0x110);
  }
  /**
   * 获得缓存图片的地址
   *
   * @param context
   * @param uniqueName
   * @return
   */
  public File getDiskCacheDir(Context context, String uniqueName) {
    String cachePath;
    if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) {
      cachePath = context.getExternalCacheDir().getPath();
    } else {
      cachePath = context.getCacheDir().getPath();
    }
    return new File(cachePath + File.separator + uniqueName);
  }
  /**
   * 根据path在缓存中获取bitmap
   *
   * @param key
   * @return
   */
  private Bitmap getBitmapFromLruCache(String key) {
    return mLruCache.get(key);
  }
  private class ImgBeanHolder {
    Bitmap bitmap;
    ImageView imageView;
    String path;
  }
}

/**
 * @描述 获取图片大小工具类s
 * @项目名称 App_News
 * @包名 com.android.news.util
 * @类名 ImageSizeUtil
 * @author chenlin
 * @date 2014-3-7 下午7:37:50
 * @version 1.0
 */
public class ImageSizeUtil {
  /**
   * 根据需求的宽和高以及图片实际的宽和高计算SampleSize
   *
   * @param options
   * @param width
   * @param height
   * @return
   */
  public static int caculateInSampleSize(Options options, int reqWidth, int reqHeight) {
    int width = options.outWidth;
    int height = options.outHeight;
    int inSampleSize = 1;
    if (width > reqWidth || height > reqHeight) {
      int widthRadio = Math.round(width * 1.0f / reqWidth);
      int heightRadio = Math.round(height * 1.0f / reqHeight);
      inSampleSize = Math.max(widthRadio, heightRadio);
    }
    return inSampleSize;
  }
  /**
   * 根据ImageView获适当的压缩的宽和高
   *
   * @param imageView
   * @return
   */
  public static ImageSize getImageViewSize(ImageView imageView) {
    ImageSize imageSize = new ImageSize();
    DisplayMetrics displayMetrics = imageView.getContext().getResources().getDisplayMetrics();
    LayoutParams lp = imageView.getLayoutParams();
    int width = imageView.getWidth();// 获取imageview的实际宽度
    if (lp != null) {
      if (width <= 0) {
        width = lp.width;// 获取imageview在layout中声明的宽度
      }
    }
    if (width <= 0) {
      // width = imageView.getMaxWidth();// 检查最大值
      width = getImageViewFieldValue(imageView, "mMaxWidth");
    }
    if (width <= 0) {
      width = displayMetrics.widthPixels;
    }
    int height = imageView.getHeight();// 获取imageview的实际高度
    if (lp != null) {
      if (height <= 0) {
        height = lp.height;// 获取imageview在layout中声明的宽度
      }
    }
    if (height <= 0) {
      height = getImageViewFieldValue(imageView, "mMaxHeight");// 检查最大值
    }
    if (height <= 0) {
      height = displayMetrics.heightPixels;
    }
    imageSize.width = width;
    imageSize.height = height;
    return imageSize;
  }
  public static class ImageSize {
    public int width;
    public int height;
  }
  /**
   * 通过反射获取imageview的某个属性值
   *
   * @param object
   * @param fieldName
   * @return
   */
  private static int getImageViewFieldValue(Object object, String fieldName) {
    int value = 0;
    try {
      Field field = ImageView.class.getDeclaredField(fieldName);
      field.setAccessible(true);
      int fieldValue = field.getInt(object);
      if (fieldValue > 0 && fieldValue < Integer.MAX_VALUE) {
        value = fieldValue;
      }
    } catch (Exception e) {
    }
    return value;
  }
}