Android中使用二级缓存、异步加载批量加载图片完整案例

public class MemoryCache {
  // 最大的缓存数 
  private static final int MAX_CACHE_CAPACITY = 30;
  //用Map软引用的Bitmap对象, 保证内存空间足够情况下不会被垃圾回收
    private HashMap<String, SoftReference<Bitmap>> mCacheMap = 
      new LinkedHashMap<String, SoftReference<Bitmap>>() {
      private static final long serialVersionUID = 1L;
//当缓存数量超过规定大小（返回true）会清除最早放入缓存的  
      protected boolean removeEldestEntry(
Map.Entry<String,SoftReference<Bitmap>> eldest){
        return size() > MAX_CACHE_CAPACITY;};
  };
  /**
   * 从缓存里取出图片
   * @param id
   * @return 如果缓存有，并且该图片没被释放，则返回该图片，否则返回null
   */
  public Bitmap get(String id){
    if(!mCacheMap.containsKey(id)) return null;
    SoftReference<Bitmap> ref = mCacheMap.get(id);
    return ref.get();
  }
  /**
   * 将图片加入缓存
   * @param id
   * @param bitmap
   */
  public void put(String id, Bitmap bitmap){
    mCacheMap.put(id, new SoftReference<Bitmap>(bitmap));
  }
  /**
   * 清除所有缓存
   */
  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 { 
  //缓存文件目录 
  private File mCacheDir;
  /**
   * 创建缓存文件目录，如果有SD卡，则使用SD，如果没有则使用系统自带缓存目录
   * @param context
   * @param cacheDir 图片缓存的一级目录
   */
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();// 如何获取系统内置的缓存存储路径
   if(!mCacheDir.exists()) mCacheDir.mkdirs();
  }
  public File getFile(String url){
    File f=null;
    try {
//对url进行编辑，解决中文路径问题
      String filename = URLEncoder.encode(url,"utf-8");
      f = new File(mCacheDir, filename);
    } catch (UnsupportedEncodingException e) {
      e.printStackTrace();
    }
    return f;
  }
  public void clear(){//清除缓存文件
    File[] files = mCacheDir.listFiles();
    for(File f:files)f.delete();
}
}

public class AsyncImageLoader{
  private MemoryCache mMemoryCache;//内存缓存
  private FileCache mFileCache;//文件缓存
  private ExecutorService mExecutorService;//线程池
//记录已经加载图片的ImageView
  private Map<ImageView, String> mImageViews = Collections
      .synchronizedMap(new WeakHashMap<ImageView, String>());
//保存正在加载图片的url 
  private List<LoadPhotoTask> mTaskQueue = new ArrayList<LoadPhotoTask>();
  /**
   * 默认采用一个大小为5的线程池
   * @param context
   * @param memoryCache 所采用的高速缓存
   * @param fileCache 所采用的文件缓存
   */
  public AsyncImageLoader(Context context, MemoryCache memoryCache, FileCache fileCache) {
    mMemoryCache = memoryCache;
    mFileCache = fileCache;
    mExecutorService = Executors.newFixedThreadPool(5);//建立一个容量为5的固定尺寸的线程池（最大正在运行的线程数量）
  }
  /**
   * 根据url加载相应的图片
   * @param url
   * @return 先从一级缓存中取图片有则直接返回，如果没有则异步从文件（二级缓存）中取，如果没有再从网络端获取
   */
  public Bitmap loadBitmap(ImageView imageView, String url) {
    //先将ImageView记录到Map中,表示该ui已经执行过图片加载了
    mImageViews.put(imageView, url);
    Bitmap bitmap = mMemoryCache.get(url);//先从一级缓存中获取图片
    if(bitmap == null) {
      enquequeLoadPhoto(url, imageView);//再从二级缓存和网络中获取
    }
    return bitmap;
  }
  /**
   * 加入图片下载队列
   * @param url
   */
  private void enquequeLoadPhoto(String url, ImageView imageView) {
    //如果任务已经存在，则不重新添加
    if(isTaskExisted(url))
      return;
    LoadPhotoTask task = new LoadPhotoTask(url, imageView);
    synchronized (mTaskQueue) {
      mTaskQueue.add(task);//将任务添加到队列中      
    }
    mExecutorService.execute(task);//向线程池中提交任务，如果没有达到上限(5),则运行否则被阻塞
  }
  /**
   * 判断下载队列中是否已经存在该任务
   * @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;
  }
  /**
   * 从缓存文件或者网络端获取图片
   * @param url
   */
  private Bitmap getBitmapByUrl(String url) {
    File f = mFileCache.getFile(url);//获得缓存图片路径
    Bitmap b = ImageUtil.decodeFile(f);//获得文件的Bitmap信息
    if (b != null)//不为空表示获得了缓存的文件
      return b;
    return ImageUtil.loadBitmapFromWeb(url, f);//同网络获得图片
  }
  /**
   * 判断该ImageView是否已经加载过图片了（可用于判断是否需要进行加载图片）
   * @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)) {//判断ImageView是否已经被复用
        removeTask(this);//如果已经被复用则删除任务
        return;
      }
      Bitmap bmp = getBitmapByUrl(url);//从缓存文件或者网络端获取图片
      mMemoryCache.put(url, bmp);// 将图片放入到一级缓存中
      if (!imageViewReused(imageView, url)) {//若ImageView未加图片则在ui线程中显示图片
      BitmapDisplayer bd = new BitmapDisplayer(bmp, imageView, url);            Activity a = (Activity) imageView.getContext();
      a.runOnUiThread(bd);//在UI线程调用bd组件的run方法，实现为ImageView控件加载图片
      }
      removeTask(this);//从队列中移除任务
    }
    public String getUrl() {
      return url;
    }
  }
  /**
   * 
   *由UI线程中执行该组件的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);
    }
  }
  /**
   * 释放资源
   */
  public void destroy() {
    mMemoryCache.clear();
    mMemoryCache = null;
    mImageViews.clear();
    mImageViews = null;
    mTaskQueue.clear();
    mTaskQueue = null;
    mExecutorService.shutdown();
    mExecutorService = null;
  }
}

public class ImageUtil {
  /**
   * 从网络获取图片，并缓存在指定的文件中
   * @param url 图片url
   * @param file 缓存文件
   * @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);//将图片缓存到磁盘中
      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;//异步组件
  public ListViewAdapter(Activity mActivity, String[] d) {
    this.mActivity=mActivity;
    data=d;
    inflater = (LayoutInflater)mActivity.getSystemService(
Context.LAYOUT_INFLATER_SERVICE);
    MemoryCache mcache=new MemoryCache();//内存缓存
 File sdCard = android.os.Environment.getExternalStorageDirectory();//获得SD卡
    File cacheDir = new File(sdCard, "jereh_cache" );//缓存根目录
  FileCache fcache=new FileCache(mActivity, cacheDir, "news_img");//文件缓存
    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("标题信息测试―――― "+position);
    vh.ivImg.setTag(data[position]);
    //异步加载图片，先从一级缓存、再二级缓存、最后网络获取图片
    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();
  }
}