在写Android应用程序时经常会用到图片缓存，对于网络请求使用Android平台上的网络通信库Volley，能使网络通信更快，更简单，更健壮，而且Volley特别适合数据量不大但是通信频繁的场景，所以可以使用volley来请求网络图片。接下来就将本人在一个项目中的图片缓存模块拿出来跟大家分享，欢迎批评指正。
/** * @author * @date 2015/4/14 * 利用文件缓存图片 */public class ImageFileCacheUtils {private static final String CHCHEDIR = "ImageChace";//缓存目录private static final String WHOLESALE_CONV = ".cache";//缓存文件后缀名private static final int MB = 1024 * 1024;private static final int CACHE_SIZE = 80;//缓存最大容量（超过就会利用lru算法删除最近最少使用的缓存文件）private static final int FREE_SD_SPACE_NEEDED_TO_CACHE = 100;//缓存所需SD卡所剩的最小容量private static ImageFileCacheUtils instance = null; //单例模式public static ImageFileCacheUtils getInstance(){if (instance == null) {synchronized (ImageFileCacheUtils.class) {if (instance == null) {instance = new ImageFileCacheUtils();}}}return instance;}public ImageFileCacheUtils(){removeCache(getDirectory());}/** * 从文件缓存中获取图片 * @param url * @return */public Bitmap getImage(final String url){final String path = getDirectory() + "/" +convertUrlToFileName(url);File file = new File(path);if(file.exists()){Bitmap bitmap = BitmapFactory.decodeFile(path);if(bitmap == null){file.delete();return null;}else {updateFileTime(path);//更新文件最新访问时间return bitmap;}}else {return null;}}/** * 获得缓存目录 * @return */private String getDirectory() {String dir = getSDPath() + "/" + CHCHEDIR;return dir;}private String getSDPath(){File sdDir = null;boolean adCardExit = Environment.getExternalStorageState().endsWith(Environment.MEDIA_MOUNTED);//判断SD卡是否挂载if (adCardExit) {sdDir = Environment.getExternalStorageDirectory();//获取根目录}if (sdDir != null) {return sdDir.toString();}else {return "";}}/** * 修改文件的最后修改时间 * @param path */private void updateFileTime(String path) {File file = new File(path);long newModeifyTime = System.currentTimeMillis();file.setLastModified(newModeifyTime);}public void saveBitmap(Bitmap bitmap,String url){if (bitmap == null) {return ;}//判断SD卡上的空间if(FREE_SD_SPACE_NEEDED_TO_CACHE > freeSpaceOnSd()){return;}String fileName = convertUrlToFileName(url);String dir = getDirectory();File dirFile = new File(dir);if (!dirFile.exists()) {dirFile.mkdirs();}File file = new File(dir + "/" +fileName);try {file.createNewFile();OutputStream outputStream = new FileOutputStream(file);bitmap.compress(Bitmap.CompressFormat.JPEG, 100, outputStream);outputStream.flush();outputStream.close();} catch (IOException e) {e.printStackTrace();}}/** * 计算sd卡上的剩余空间 * @return */private int freeSpaceOnSd() {StatFs statFs = new StatFs(Environment.getExternalStorageDirectory().getPath());double sdFreeMB = ((double)statFs.getAvailableBlocks() * (double)statFs.getBlockSize()) / MB;Log.i("test", "剩余空间为："+sdFreeMB);return (int)sdFreeMB;}/** * 将url转成文件名 * @param url * @return */private String convertUrlToFileName(String url) {String[] strs = url.split("/");return strs[strs.length – 1] + WHOLESALE_CONV;}/** * 计算存储目录下的文件大小 * 当文件总大小大于规定的大小或者sd卡剩余空间小于FREE_SD_SPACE_NEEDED_TO_CACHE的规定时 * ，那么删除40%最近没有被使用的文件 * @param dirPath * @return */private boolean removeCache(String dirPath){File dirFile = new File(dirPath);File[] files = dirFile.listFiles();if (files == null || files.length <= 0) {return true;}//如果sd卡没有挂载if (!Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {return false;}int dirSize = 0;for (int i = 0; i < files.length; i++) {if (files[i].getName().contains(WHOLESALE_CONV)) {dirSize += files[i].length();}}if (dirSize > CACHE_SIZE * MB || FREE_SD_SPACE_NEEDED_TO_CACHE > freeSpaceOnSd()) {int removeFactor = (int)((0.4 * files.length) + 1);Arrays.sort(files, new FileLastModifySoft());for (int i = 0; i < removeFactor; i++) {if (files[i].getName().contains(WHOLESALE_CONV)) {files[i].delete();}}}if (freeSpaceOnSd() <= CACHE_SIZE) {return false;}return true; }//比较器类private class FileLastModifySoft implements Comparator<File>{@Overridepublic int compare(File arg0, File arg1) {if (arg0.lastModified() > arg1.lastModified()) {return 1;}else if (arg0.lastModified() == arg1.lastModified()) {return 0;}else {return -1;}}}}利用volley的networkImageview加载图片时需要传入一个ImageLoader，在构造ImageLoader时需要一个实现ImageCache接口的类，所以先构造此类：public class ImageFileCache implements ImageCache{@Overridepublic Bitmap getBitmap(String url) {return ImageFileCacheUtils.getInstance().getImage(url);}@Overridepublic void putBitmap(String url, Bitmap bitmap) {ImageFileCacheUtils.getInstance().saveBitmap(bitmap, url);}}接下来使用networkImageview加载网络图片：选择逃避，选择被动的去面对生活。
