这是我正在关注的磁盘缓存教程。我已将源代码下载到 DiskLruCache，但源代码中不存在此示例中使用的方法。
http://developer.android.com/training/displaying-bitmaps/cache-bitmap.html#disk-cache
我是否需要自己实现这些方法，或者是否有我在某处缺少的 DiskLruCache 版本？
问问题
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2 回答
2
这里是完整的实现DiskLruCache。
首先从 AOSP下载DiskLruCache.java 。
这是我DiskCache.java的基本缓存操作的辅助类。
/**
* Created by Babar on 12-Aug-15.
*/
public class DiskCache
{
private Context context;
private static DiskCache diskCache;
public DiskLruCache mDiskLruCache;
private final Object mDiskCacheLock = new Object();
private BitmapProcessor bitmapProcessor;
private static final int DISK_CACHE_INDEX = 0;
public static boolean mDiskCacheStarting = true;
private static final String DISK_CACHE_SUBDIR = "ooredoo_thumbnails";
private static final int DISK_CACHE_SIZE = 1024 * 1024 * 100; // 100MB
public static DiskCache getInstance()
{
if(diskCache == null)
{
diskCache = new DiskCache();
}
return diskCache;
}
private DiskCache() {}
public void requestInit(Context context)
{
this.context = context;
bitmapProcessor = new BitmapProcessor();
new DiskCacheTask(this).execute(DiskCacheTask.INIT);
}
public void init() throws IOException {
synchronized (mDiskCacheLock)
{
if(mDiskLruCache == null || mDiskLruCache.isClosed())
{
File cacheDir = FileUtils.getDiskCacheDir(context, DISK_CACHE_SUBDIR);
if(!cacheDir.exists())
{
cacheDir.mkdir();
}
if(FileUtils.getUsableSpace(cacheDir) > DISK_CACHE_SIZE)
{
mDiskLruCache = DiskLruCache.open(cacheDir, 1, 1, DISK_CACHE_SIZE);
}
else
{
Logger.print("InitDiskCache failed: NOT enough space on disk");
}
}
mDiskCacheStarting = false; // Finished initialization
mDiskCacheLock.notifyAll(); // Wake any waiting threads
}
}
public void addBitmapToDiskCache(final String key, final Bitmap value) {
if (key == null || value == null) {
return;
}
synchronized (mDiskCacheLock)
{
if (mDiskLruCache != null) {
OutputStream out = null;
String encryptedKey = CryptoUtils.encryptToMD5(key);
Logger.print("addBitmapToDiskCache encryptToMD5: " + encryptedKey);
try {
DiskLruCache.Snapshot snapshot = mDiskLruCache.get(encryptedKey);
if (snapshot == null) {
final DiskLruCache.Editor editor = mDiskLruCache.edit(encryptedKey);
if (editor != null) {
out = editor.newOutputStream(DISK_CACHE_INDEX);
value.compress(Bitmap.CompressFormat.JPEG, 100, out);
editor.commit();
out.close();
}
} else {
snapshot.getInputStream(DISK_CACHE_INDEX).close();
}
} catch (IOException e) {
e.printStackTrace();
} finally {
if (out != null) {
try {
out.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
}
/**
* Get from disk cache.
*
* @param key Unique identifier for which item to get
* @return The bitmap if found in cache, null otherwise
*/
public Bitmap getBitmapFromDiskCache(final String key)
{
Bitmap bitmap = null;
String encryptedKey = CryptoUtils.encryptToMD5(key);
Logger.print("getBitmapFromDiskCache encryptToMD5: " + encryptedKey);
synchronized (mDiskCacheLock)
{
Logger.print("mDiskcachestarting: "+mDiskCacheStarting);
// Wait while disk cache is started from background thread
while (mDiskCacheStarting)
{
try
{
mDiskCacheLock.wait();
}
catch (InterruptedException e)
{
e.printStackTrace();
}
}
if(mDiskLruCache != null)
{
InputStream inputStream = null;
try
{
final DiskLruCache.Snapshot snapshot = mDiskLruCache.get(encryptedKey);
if(snapshot != null)
{
Logger.print("Disk cache hit");
inputStream = snapshot.getInputStream(DISK_CACHE_INDEX);
if(inputStream != null)
{
FileDescriptor fd = ((FileInputStream) inputStream).getFD();
// Decode bitmap, but we don't want to sample so give
// MAX_VALUE as the target dimensions
bitmap = bitmapProcessor.decodeSampledBitmapFromDescriptor(fd);
}
}
}
catch (IOException e)
{
e.printStackTrace();
}
finally
{
if(inputStream != null)
{
try
{
inputStream.close();
}
catch (IOException e)
{
e.printStackTrace();
}
}
}
}
Logger.print("dCache getBitmapFromDiskCache synchronized completed");
}
Logger.print("dCache getBitmapFromDiskCache returning Bitmap");
return bitmap;
}
public void requestFlush()
{
new DiskCacheTask(this).execute(DiskCacheTask.FLUSH);
}
/**
* Flushes the disk cache associated with this ImageCache object. Note that this includes
* disk access so this should not be executed on the main/UI thread.
*/
public void flush()
{
synchronized (mDiskCacheLock)
{
if(mDiskLruCache != null)
{
try
{
mDiskLruCache.flush();
Logger.print("flush: disk cache flushed");
}
catch (IOException e)
{
e.printStackTrace();
}
}
}
}
public void requestClose()
{
new DiskCacheTask(this).execute(DiskCacheTask.CLOSE);
}
/**
* Closes the disk cache associated with this ImageCache object. Note that this includes
* disk access so this should not be executed on the main/UI thread.
*/
public void close()
{
synchronized (mDiskCacheLock)
{
if(mDiskLruCache != null)
{
if(!mDiskLruCache.isClosed())
{
try
{
mDiskLruCache.close();
mDiskLruCache = null;
Logger.print("disk cache closed");
}
catch (IOException e)
{
e.printStackTrace();
}
}
}
}
}
/**
* Do not call this method unless you need to explicitly clear disk cache
*/
public void requestTearDown()
{
new DiskCacheTask(this).execute(DiskCacheTask.TEAR_DOWN);
}
public final void tearDown()
{
synchronized (mDiskCacheLock)
{
mDiskCacheStarting = true;
if(mDiskLruCache != null && !mDiskLruCache.isClosed())
{
try
{
mDiskLruCache.delete();
Logger.print("disk cache cleared");
}
catch (IOException e)
{
e.printStackTrace();
}
mDiskLruCache = null;
}
}
}
}
这是BitmapProcesser.java
/**
* @author Babar
* @since 15-Jun-15.
*/
public class BitmapProcessor
{
public Bitmap decodeSampledBitmapFromStream(InputStream inputStream, URL url,
int reqWidth, int reqHeight) throws IOException {
Bitmap bitmap;
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeStream(inputStream, null, options);
int width = options.outWidth;
int height = options.outHeight;
Logger.print("@Req Width: "+reqWidth);
Logger.print("@Req Height: " + reqHeight);
Logger.print("@Actual Width: "+width);
Logger.print("@Actual Height: " + height);
int sampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
options.inJustDecodeBounds = false;
options.inSampleSize = sampleSize;
inputStream = url.openStream();
bitmap = BitmapFactory.decodeStream(inputStream, null, options);
if(bitmap != null)
{
width = bitmap.getWidth();
height = bitmap.getHeight();
Logger.print("@inSample:"+sampleSize);
Logger.print("@Modified Width: "+width);
Logger.print("@Modified Height: " + height);
}
return bitmap;
}
public Bitmap decodeSampledBitmapFromDescriptor(FileDescriptor fd)
{
/*final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeFileDescriptor(fd, null, options);
options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
options.inJustDecodeBounds = false;*/
return BitmapFactory.decodeFileDescriptor(fd);
}
public Bitmap decodeSampledBitmapFromFile(String pathName, int reqWidth, int reqHeight) throws IOException {
Bitmap bitmap;
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeFile(pathName, options);
int width = options.outWidth;
int height = options.outHeight;
Logger.print("@Req Width: "+reqWidth);
Logger.print("@Req Height: " + reqHeight);
Logger.print("@Actual Width: "+width);
Logger.print("@Actual Height: " + height);
int sampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
options.inJustDecodeBounds = false;
options.inSampleSize = sampleSize;
bitmap = BitmapFactory.decodeFile(pathName, options);
if(bitmap != null)
{
width = bitmap.getWidth();
height = bitmap.getHeight();
Logger.print("@inSample:"+sampleSize);
Logger.print("@Modified Width: "+width);
Logger.print("@Modified Height: " + height);
}
return bitmap != null ? rotateBitmapIfNeeded(pathName, bitmap) : null;
}
public int calculateInSampleSize(BitmapFactory.Options options,
int requiredWidth, int requiredHeight)
{
final int width = options.outWidth;
final int height = options.outHeight;
int inSampleSize = 1;
if(width > requiredWidth || height > requiredHeight)
{
final int halfWidth = width / 2;
final int halfHeight = height / 2;
// Calculate the largest inSampleSize value that is a power of 2 and keeps both
// height and width larger than the requested height and width.
while ((halfWidth / inSampleSize) > requiredWidth
&&
(halfHeight / inSampleSize) > requiredHeight)
{
inSampleSize *= 2;
}
}
return inSampleSize;
}
public static Bitmap rotateBitmapIfNeeded(String pathName, Bitmap bitmap) throws IOException {
ExifInterface exifInterface = new ExifInterface(pathName);
int orientation = exifInterface.getAttributeInt(ExifInterface.TAG_ORIENTATION,
ExifInterface.ORIENTATION_NORMAL);
Logger.logI("BITMAP_ORIENTATION: " + orientation, pathName);
switch (orientation)
{
case ExifInterface.ORIENTATION_ROTATE_90:
return rotateBitmap(bitmap, 90);
case ExifInterface.ORIENTATION_ROTATE_180:
return rotateBitmap(bitmap, 180);
case ExifInterface.ORIENTATION_ROTATE_270:
return rotateBitmap(bitmap, 270);
}
return bitmap;
}
public Bitmap makeBitmapRound(Bitmap src)
{
int width = src.getWidth();
int height = src.getHeight();
Bitmap bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
// Canvas canvas = new Canvas(bitmap);
BitmapShader shader = new BitmapShader(src, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);
Paint paint = new Paint();
paint.setAntiAlias(true);
paint.setShader(shader);
RectF rectF = new RectF(0.0f, 0.0f, width, height);
// rect contains the bounds of the shape
// radius is the radius in pixels of the rounded corners
// paint contains the shader that will texture the shape
Canvas canvas = new Canvas(src);
canvas.drawRoundRect(rectF, 30, 30, paint);
return src;
}
public static Bitmap rotateBitmap(Bitmap bitmap, int degree) {
Matrix matrix = new Matrix();
matrix.postRotate(degree);
return Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), matrix, true);
}
}
这是CryptoUtils.java
/**
* @author Babar
* @since 29-Jun-15.
*/
public class CryptoUtils
{
private static final String MD5_ALGO = "MD5";
public static String encryptToMD5(String text)
{
try
{
java.security.MessageDigest md = java.security.MessageDigest.getInstance(MD5_ALGO);
md.update(text.getBytes());
byte[] bytes = md.digest();
String hex = bytesToHexString(bytes);
return hex;
}
catch (NoSuchAlgorithmException e)
{
e.printStackTrace();
return String.valueOf(text.hashCode());
}
}
private static String bytesToHexString(byte[] bytes)
{
StringBuffer sb = new StringBuffer();
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();
}
public static String encodeToBase64(String str) {
String tmp = "";
if(isNotNullOrEmpty(str)) {
try {
tmp = new String(Base64.encode(str.getBytes(), Base64.DEFAULT)).trim();
} catch(Throwable e) {
e.printStackTrace();
}
}
return tmp;
}
}
这是DiskCacheTask.java
/**
* Created by Babar on 12-Aug-15.
*/
public class DiskCacheTask extends BaseAsyncTask<Integer, Void, Void>
{
private DiskCache diskCache;
public static final int INIT = 1;
public static final int FLUSH = 2;
public static final int CLOSE = 3;
public static final int TEAR_DOWN = 4;
public static final int REMOVE = 5;
public DiskCacheTask(DiskCache diskCache)
{
this.diskCache = diskCache;
}
@Override
protected Void doInBackground(Integer... params)
{
switch (params[0])
{
case INIT:
try
{
diskCache.init();
}
catch (IOException e)
{
e.printStackTrace();
}
break;
case FLUSH:
diskCache.flush();
break;
case CLOSE:
diskCache.close();
break;
case TEAR_DOWN:
diskCache.tearDown();
break;
case REMOVE:
diskCache.remove();
break;
}
return null;
}
}
要初始化缓存，只需new DiskCache().getInstance().requestInit();从 MainActivity 的onCreate(). 另请注意，磁盘操作应在单独的线程中完成，Handler例如AsyncTask. 因此，当您想向/从磁盘缓存添加/获取位图时，请从工作线程执行此操作。
于 2015-09-11T06:06:09.253 回答
1
您将需要使用您自己的提供更高级别抽象的缓存来包装 DiskLruCache。有人已经为位图做到了这一点，请参阅Using DiskLruCache in android 4.0 does not provide for openCache method
或者，您可以使用开源库，例如 Picasso。
于 2014-02-16T20:09:01.363 回答