Android批量图片加载经典系列——使用二级缓存、异步网络负载形象

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 假设缓存有，而且该图片没被释放，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();
    }
    
    /**
     * 将图片增加缓存
     * @param id
     * @param bitmap
     */
    public void put(String id, Bitmap bitmap){
        mCacheMap.put(id, new SoftReference<Bitmap>(bitmap));
    }
    /**
     * 清除全部缓存
     */
   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 { 
    //缓存文件文件夹 
    private File mCacheDir;
    /**
     * 创建缓存文件文件夹，假设有SD卡。则使用SD，假设没有则使用系统自带缓存文件夹
     * @param context
     * @param cacheDir 图片缓存的一级文件夹
     */
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();// 怎样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
//记录已经载入图片的ImageView
    private Map<ImageView, String> mImageViews = Collections
            .synchronizedMap(new WeakHashMap<ImageView, String>());
//保存正在载入图片的url 
    private List<LoadPhotoTask> mTaskQueue = new ArrayList<LoadPhotoTask>();
    /**
     * 默认採用一个大小为5的线程池
     * @param context
     * @param memoryCache 所採用的快速缓存
     * @param fileCache 所採用的文件缓存
     */
    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（最大正在执行的线程数量）
    }
    /**
     * 依据url载入对应的图片
     * @param url
     * @return 先从一级缓存中取图片有则直接返回，假设没有则异步从文件（二级缓存）中取，假设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已经执行过图片载入了
        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) {
        //假设任务已经存在，则不又一次加入
        if(isTaskExisted(url))
            return;
        LoadPhotoTask task = new LoadPhotoTask(url, imageView);
        synchronized (mTaskQueue) {
            mTaskQueue.add(task);//将任务加入到队列中            
        }
        mExecutorService.execute(task);//向线程池中提交任务，假设没有达到上限(5),则执行否则被堵塞
    }
    
    /**
     * 推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
    }
    
    /**
     * 推断该ImageView是否已经载入过图片了（可用于推断是否须要进行载入图片）
     * @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)) {//推断ImageView是否已经被复用
                removeTask(this);//假设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控件载入图片
            }
            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里
     * @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.21-sun.com/UserFiles/x_Image/x_20150606083511_0.jpg",
"http://news.21-sun.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" );//缓存根文件夹
    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("标题信息測试———— "+position);
        vh.ivImg.setTag(data[position]);
        //异步载入图片。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();
    }
}