public interface Cache {public void put(String key,Bitmap bitmap);//存入public Bitmap get(String key);//取出public boolean isExist(String key);//是否存在public void clear();//清空}

/*** 内存缓存，设置大小限制，当超过限制，将最近最久未使用的一项移出* @author huangbei**/
public class MemoryCache implements Cache {private  Map<String, Bitmap> cache ;private Cache softCache;//内存缓存所占的字节，初始为0private long size ;// 内存缓存当中所占字节的最大限制private long limit ;public MemoryCache(Cache softCache){//设置默认限制为最大运行内存的八分之一setLimit(Runtime.getRuntime().maxMemory() / 8);  size=0;this.softCache= softCache;// 放入缓存时是个同步操作  // LinkedHashMap构造方法的最后一个参数true代表这个map里的元素将按照最近使用次数由少到多排列，即LRU  // 这样的好处是如果要将缓存中的元素替换，则先遍历出最近最少使用的元素来替换以提高效率  cache = Collections.synchronizedMap(new LinkedHashMap<String, Bitmap>(10, 1.5f, true));}public void setLimit(long limit){this.limit=limit;}@Overridepublic void put(String key, Bitmap bitmap) {this.cache.put(key, bitmap);if(!checkSize(bitmap)){remove();}}@Overridepublic Bitmap get(String key) {return cache.get(key);}@Overridepublic boolean isExist(String key) {return cache.containsKey(key);}@Overridepublic void clear() {cache.clear(); }//检查添加的图片是否会超过限制private boolean checkSize(Bitmap bitmap){long bitsize=BitmapUtil.getSizeInBytes(bitmap);if((size+bitsize)<=limit){return true;}else{return false;}}//移除掉超过内存限制的图片private void remove(){Iterator<Entry<String, Bitmap>> iter = cache.entrySet().iterator();  while (iter.hasNext()) {  Entry<String, Bitmap> entry = iter.next();  size -= BitmapUtil.getSizeInBytes(entry.getValue());softCache.put(entry.getKey(), entry.getValue());iter.remove();if (size <= limit)  break;  }}}

/*** 软引用缓存，不设置大小限制，内存不够，系统自动释放* @author huangbei**/
public class SoftReferenceCache implements Cache {//软引用缓存private  Map<String, SoftReference<Bitmap>> cache;public SoftReferenceCache(){cache = new HashMap<String, SoftReference<Bitmap>>();}@Overridepublic void put(String key, Bitmap bitmap) {cache.put(key, new SoftReference<Bitmap>(bitmap));}@Overridepublic Bitmap get(String key) {return cache.get(key).get();}@Overridepublic boolean isExist(String key) {if(cache.containsKey(key)&&cache.get(key).get()!=null)return true;elsereturn false;}@Overridepublic void clear() {cache.clear(); }}

/*** 文件缓存，图片存于文件当中，不设置大小限制，避免重复下载，节省流量* @author huangbei**/
public class FileCache implements Cache{private String cashe_dir="";private File cacheDir;  //图片存储的路径public FileCache(Context context) {if (android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED)){cacheDir = new File(android.os.Environment.getExternalStorageDirectory(), cashe_dir);}else{cacheDir = context.getCacheDir();}if (!cacheDir.exists())cacheDir.mkdirs();}@Overridepublic void put(String key, Bitmap bitmap) {File f = new File(cacheDir, key);if(!f.exists()){try {f.createNewFile();} catch (IOException e) {e.printStackTrace();}}BitmapUtil.saveBitmap(f, bitmap);}@Overridepublic Bitmap get(String key) {File f = new File(cacheDir, key);if (f.exists()){return BitmapUtil.decodeFile(f);}else{return null;} }@Overridepublic boolean isExist(String key) {File f = new File(cacheDir, key);if (f.exists()){return true;}else{return false;} }@Overridepublic void clear() {File[] files = cacheDir.listFiles();for (File f : files)f.delete();}}

public class ThreeLevelCache implements Cache{private Cache memoryCache;private Cache softCache;private Cache fileCache;private ThreeLevelCache cache; private ThreeLevelCache(Context context){this.softCache=new SoftReferenceCache();this.fileCache=new FileCache(context);this.memoryCache=new MemoryCache(softCache);}public ThreeLevelCache newInstance(Context context){if(cache==null){cache=new ThreeLevelCache(context);}return cache;}@Overridepublic void put(String key, Bitmap bitmap) {this.fileCache.put(key, bitmap);this.memoryCache.put(key, bitmap);}@Overridepublic Bitmap get(String key) {if(memoryCache.isExist(key)){return memoryCache.get(key);}else if(softCache.isExist(key)){return softCache.get(key);}else if(fileCache.isExist(key)){return fileCache.get(key);}else{return null;}}@Overridepublic boolean isExist(String key) {return memoryCache.isExist(key)||softCache.isExist(key)||fileCache.isExist(key);}@Overridepublic void clear() {memoryCache.clear();softCache.clear();fileCache.clear();}
}

public class BitmapUtil {//图片所占的内存大小public static long getSizeInBytes(Bitmap bitmap) {  if (bitmap == null){ return 0;  }return bitmap.getRowBytes() * bitmap.getHeight();  }//将图片存入文件当中public static boolean saveBitmap(File file, Bitmap bitmap){if(file == null || bitmap == null)return false;try {BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(file));return bitmap.compress(CompressFormat.JPEG, 100, out);} catch (FileNotFoundException e) {e.printStackTrace();return false;}}// decode这个图片并且按比例缩放以减少内存消耗，虚拟机对每张图片的缓存大小也是有限制的  public static Bitmap decodeFile(File f) {  try {  // decode image size  BitmapFactory.Options option = new BitmapFactory.Options();  option.inJustDecodeBounds = true;  BitmapFactory.decodeStream(new FileInputStream(f), null, option);  // Find the correct scale value. It should be the power of 2.  final int REQUIRED_SIZE = 100;  int width_tmp = option.outWidth, height_tmp = option.outHeight;  int scale = 1;  while (true) {  if (width_tmp / 2 < REQUIRED_SIZE  || height_tmp / 2 < REQUIRED_SIZE){break;  }width_tmp /= 2;  height_tmp /= 2;  scale *= 2;  }  // decode with inSampleSize  BitmapFactory.Options option2 = new BitmapFactory.Options();  option2.inSampleSize = scale;  return BitmapFactory.decodeStream(new FileInputStream(f), null, option2);  } catch (FileNotFoundException e) {  e.printStackTrace();return null;}  }}