双缓存实例
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下载DiskLruCache.java
google认证的第三方
https://android.googlesource.com/platform/libcore/+/android-4.1.1_r1/luni/src/main/java/libcore/io/DiskLruCache.java -
新建LruCacheUtils进行操作
该类设计为单例模式。public class LruCacheUtils { private static LruCacheUtils lruCacheUtils; private DiskLruCache diskLruCache; //LRU磁盘缓存 private LruCache<String, Bitmap> lruCache; //LRU内存缓存 private Context context; private LruCacheUtils() { } public static LruCacheUtils getInstance() { if (lruCacheUtils == null) { lruCacheUtils = new LruCacheUtils(); } return lruCacheUtils; } }``` -
首先需要获得采样比例
//获得采样比例 public int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) { //获取位图的圆宽高 int width = options.outWidth; int height = options.outHeight; System.out.println("outWidth=" + width + "outHeight" + height); int inSampleSize = 1; if (width > reqWidth || height > reqHeight) { //判断原图的宽高,再进行匹配,按照小的来求采样比例 if (width > height) { inSampleSize = Math.round((float) height / (float) reqHeight); } else { inSampleSize = Math.round((float) width / (float) reqWidth); } } System.out.println("inSampleSize" + inSampleSize); return inSampleSize; } -
再实现一个方法，通过字节转换成位图
public Bitmap decodeSampleBitmapFromStream(byte[] bytes, int reqWidth, int reqHeight) { BitmapFactory.Options options = new BitmapFactory.Options(); options.inJustDecodeBounds = true; BitmapFactory.decodeByteArray(bytes,0,bytes.length,options); options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight); options.inJustDecodeBounds = false; return BitmapFactory.decodeByteArray(bytes,0,bytes.length,options); } -
还需要两个方法，获取AppVersion以及缓存目录
//在清单文件中定义的versionCode private int getAppVersion() { try { return context.getPackageManager().getPackageInfo(context.getPackageName(), 0).versionCode; } catch (PackageManager.NameNotFoundException e) { e.printStackTrace(); } return 1; } //获取缓存目录 private File getCacheDir(String name) { //判断是不是SD卡 或者外部存储已经被删掉 前面一个是有SD卡(mnt/sdcard/Android/data/包名/cache) 后面一个没有SD卡(缓存在私有目录下data/data/包名/cache) String cachePath = Environment.getExternalStorageState() == Environment.MEDIA_MOUNTED || !Environment.isExternalStorageRemovable() ? context.getExternalCacheDir().getPath() : context.getCacheDir().getPath(); return new File(cachePath + File.separator + name); } -
下面是两个方法，计算MD5的字符串摘要
//计算MD5的字符串摘要 public String hashKeyForDisk(String key) { String cacheKey; try { final MessageDigest mDigest = MessageDigest.getInstance("MD5"); mDigest.update(key.getBytes()); cacheKey = bytesToHexString(mDigest.digest()); } catch (NoSuchAlgorithmException e) { cacheKey = String.valueOf(key.hashCode()); } return cacheKey;
}
public String bytesToHexString(byte[] bytes) {
StringBuilder sb = new StringBuilder();
for (int i = 0; i < bytes.length; i++) {
String hex = Integer.toHexString(0xFF & bytes[i]);
if (hex.length() == 1) {
sb.append('0');
}
sb.append(hex);
}
return sb.toString();
}
* 然后是两个添加和删除内存缓存的方法
//添加缓存
public void addBitmapToCache(String url, Bitmap bitmap) {
String key = hashKeyForDisk(url);
if (getBitmapFromCache(key) == null) {
System.out.println("key=====" + key);
System.out.println("bitmap====" + bitmap);
lruCache.put(key, bitmap);
}
}
//读取缓存
public Bitmap getBitmapFromCache(String url) {
String key = hashKeyForDisk(url);
return lruCache.get(key);
}
* 还需要打开缓存的方法
public void open(Context context, String disk_cache_subdir, int disk_cache_size) {
this.context = context;
ActivityManager am = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
int memoryClass = am.getMemoryClass();
final int cacheSize = memoryClass / 8 * 1024 * 1024; //单位大小为字节 八分之一的内存作为缓存大小
lruCache = new LruCache<>(cacheSize);
try {
diskLruCache = DiskLruCache.open(getCacheDir(disk_cache_subdir), getAppVersion(), 1, disk_cache_size);
} catch (IOException e) {
e.printStackTrace();
}
}
* 下面是最重要的部分,加入缓存，这里用到了AsyncTask，而且还需要定义一个回调接口来做出完成的响应
public void putCache(final String url, final CallBack callBack) {
new AsyncTask<String, Void, Bitmap>() {
@Override
protected Bitmap doInBackground(String... params) {
String key = hashKeyForDisk(params[0]);
System.out.println("key=" + key);
DiskLruCache.Editor editor = null;
Bitmap bitmap = null;
try {
URL url = new URL(params[0]);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setReadTimeout(1000 * 30);
conn.setConnectTimeout(1000 * 30);
ByteArrayOutputStream baos = null;
if (conn.getResponseCode() == HttpURLConnection.HTTP_OK) {
BufferedInputStream bis = new BufferedInputStream(conn.getInputStream());
baos = new ByteArrayOutputStream();
byte[] bytes = new byte[1024];
int len = -1;
while ((len = bis.read(bytes)) != -1) {
baos.write(bytes, 0, len);
}
bis.close();
baos.close();
conn.disconnect();
}
if (baos != null) {
bitmap = decodeSampleBitmapFromStream(baos.toByteArray(), 100, 100);
//加入缓存
addBitmapToCache(params[0], bitmap);
//加入磁盘缓存
editor = diskLruCache.edit(key);
System.out.println(url.getFile());
//位图压缩后输出(参数:压缩格式,质量(100表示不压缩,30表示压缩70%),输出流)
bitmap.compress(Bitmap.CompressFormat.JPEG, 100, editor.newOutputStream(0));
editor.commit();
}
} catch (IOException e) {
try {
editor.abort(); //放弃写入
} catch (IOException e1) {
e1.printStackTrace();
}
e.printStackTrace();
}
return bitmap;
}
@Override
protected void onPostExecute(Bitmap bitmap) {
super.onPostExecute(bitmap);
callBack.response(bitmap);
}
}.execute(url);
}
//回调接口
public interface CallBack<T> {
public void response(T entity);
}
* 最后还需要实现获取磁盘缓存，关闭磁盘缓存以及刷新磁盘缓存三个方法
//获取磁盘缓存
public InputStream getDiskCache(String url) {
String key = hashKeyForDisk(url);
System.out.println("getDiskCache=" + key);
try {
//快照
DiskLruCache.Snapshot snapshot = diskLruCache.get(key);
System.out.println(snapshot);
if (snapshot != null) {
return snapshot.getInputStream(0);
}
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
//关闭磁盘缓存
public void close() {
if (diskLruCache != null && !diskLruCache.isClosed()) {
try {
diskLruCache.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
//刷新磁盘缓存
public void flush() {
if (diskLruCache != null) {
try {
diskLruCache.flush();
} catch (IOException e) {
e.printStackTrace();
}
}
}
* 上面都是我们在LruCacheUtils.java的工具类中完成的方法，下面我们看看在MainActivity中的内容
private DiskLruCacheUtils diskLruCacheUtils;
private static final String DISK_CACHE_SUBDIR = "temp";//目录名
private static final int DISK_CACHE_SIZE = 1024 * 1024 * 10; //定义磁盘缓存大小,10MB
点击按钮时我们开始实现双缓存加载图片
public void show2Click(View view) {
String url = "http://p3.image.hiapk.com/uploads/allimg/141124/7730-141124100258.jpg";
loadBitmap(url, iv2);
}
* 我们需要在onResume方法中打开磁盘缓存，在onPause时刷新缓存，并在onStop时关闭缓存
@Override
protected void onResume() {
super.onResume();
lruCacheUtils = LruCacheUtils.getInstance();
lruCacheUtils.open(this, DISK_CACHE_SUBDIR, DISK_CACHE_SIZE);
}
//刷新把缓存写好
@Override
protected void onPause() {
super.onPause();
lruCacheUtils.flush();
}
@Override
protected void onStop() {
super.onStop();
lruCacheUtils.close();
}
* 最后我们需要实现loadBitmap方法，加载图片
public void loadBitmap(String url, final ImageView imageView) {
//从内存缓存中取图片
Bitmap bitmap = lruCacheUtils.getBitmapFromCache(url);
if (bitmap == null) {
//再从磁盘缓存中取
InputStream in = lruCacheUtils.getDiskCache(url);
if (in == null) {
//去网上取
lruCacheUtils.putCache(url, new LruCacheUtils.CallBack<Bitmap>() {
@Override
public void response(Bitmap entity) {
System.out.println("http load");
imageView.setImageBitmap(entity);
}
});
} else {
System.out.println("disk cache");
bitmap = BitmapFactory.decodeStream(in);
//取完添加到内存缓存中
lruCacheUtils.addBitmapToCache(url, bitmap);
imageView.setImageBitmap(bitmap);
}
} else {
System.out.println("memory cache");
imageView.setImageBitmap(bitmap);
}
}
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