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.VeVB.COm/UserFiles/x_Image/x_20150606083511_0.jpg","http://news.VeVB.COm/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();  }}