Android批量图片加载经典系列——采取二级缓存、异步加载网络图片

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.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();    }}