Android中的缓存策略—拉取网络图片，缓存本地
一、前期基础知识储备
缓存策略在Android中有着广泛的使用场景，尤其在图片加载这个场景下，缓存策略更是尤为重要。加载图片是消耗流量的，如果用户加载图片，每次都要从网络中拉取，不但耗费更好的流量，同时加载速度也不是每次都可以接受的。如何避免过多的流量消耗呢？那就是Android中的缓存了。
当程序第一次从网络中加载图片之后，就将其缓存在存储设备上，这样下次使用这张图片就不用再从网络上获取了，这样就为用户节省了流量。很多时候为了提高用户的体验，往往还会把图片在内存中再缓存一份，这样当用户应用打算从网络上请求一张图片时，程序会首先从内存中去获取，如果内存中没有那就从存储设备中去获取，如果存储设备中没有，那就从网络中下载这张图片。因为从内存中加载扸比从存储设备中加载图片要快，所以这样既提高了程序的效率又为用户节约了不必要的流量开销。
上述的三级缓存策略不仅仅适用于图片，也适用于其他文件类型。
缓存策略：包括缓存的添加、获取和删除。不管是内存缓存还是存储设备缓存，它们的缓存大小都是有限制的，因此在使用缓存时总要为缓存指定一个最大的容量。如果当容量满了，但是程序还需要添加缓存，这个时候就需要删除一些旧的缓存并添加新的缓存，如何定义缓存的新旧这就是一种策略。
目前常用的一种缓存算法是LRU（Least Recently Used），LRU是近期最少使用算法，它的核心思想就是当缓存满时，会优先淘汰那些近期最少使用的缓存对象。采用LRU算法的缓存有两种：LruCache和DiskLruCache，LruCache用于实现内存缓存，而DiskLruCache则充当了存储设备缓存，通过三者的完美结合，就可以很方便的实现一个具有很高实用价值的ImageLoader。
二、上代码，具体实现
1.LruCache
LruCache是Android3.1所提供的一个缓存类。为了兼容Android低版本，在使用LruCache时建议使用support-v4兼容包下的LruCache，而不是直接使用Android3.1提供的LruCache。
LruCache是一个泛型类，它内部采用了一个LinkedHashMap以强引用的方式实现存储外界的缓存对象，其提供了get和put方法来完成缓存的获取和添加操作。
- 强引用：直接的对象引用；
- 软引用：当一个对象只有软引用存在时，系统内存不足时此对象会被gc回收；
- 弱引用：当一个对象只用弱引用存在时，此对象会随时被gc回收。
LruCache的实现比较简单，以下是使用LruCache来实现内存缓存：
1）LruCache的典型初始化过程：
int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);
int cacheSize = maxMemory / 8; // 总容量为当前进程的可用内存的1/8
mMemoryCache = new LruCache<String, Bitmap>(cacheSize) {
@Override
protected int sizeOf(String key, Bitmap bitmap) {
//sizeOf方法用以计算缓存对象的大小 比如Bitmap对象的大小
return bitmap.getRowBytes() * bitmap.getHeight() / 1024;
}
};上述代码中，只需要提供缓存的总容量大小并重写sizeOf方法即可。sizeOf方法的作用是计算缓存对象的大小，这里的大小单位和总容量的单位一致。对于上面的示例代码来说，总容量大小为当前进程可用内存的1/8，单位为KB。而sizeOf方法则完成了Bitmap对象的大小计算。
2）LruCache的添加、获取和删除：
从LruCache中获取一个缓存对象：mMemoryCache.get(key)
从LruCache中添加一个缓存对象：mMemoryCache.put(key, bitmap)
从LruCache中删除一个缓存对象：remove方法
从Android3.1开始，LruCache就是Android源码的一部分了。
2.DiskLruCache
DiskLruCache用于实现存储设备缓存，即磁盘缓存，它通过将缓存对象写入文件系统，从而实现缓存的效果。DiskLruCache得到了Android官方文档的推荐，但它不属于AndroidSDK的一部分，可以从网上找到它的源码，修改后添加到项目中。
1）DiskLruCache的创建：
DiskLruCache并不能通过构造方法来创建，它提供了open方法用于创建自身：
public static DiskLruCache open (File directory, int appVersion, int valueCount, long maxSize)open方法有四个参数，其中第一个参数表示磁盘缓存在文件系统中的存储路径。缓存路径可以选择SD卡上的缓存目录，具体是指/sdcard/Android/data/package_name/cache目录，其中package_name表示当前应用的包名，当应用被卸载后，此目录会一并被删除。这里给出一个建议：如果应用卸载后就希望删除缓存文件，那么就选择SD卡上的缓存目录，如果希望保留缓存数据那就应该选择SD卡上的其他特定目录；
第二个参数表示应用的版本号，设为1即可；
第三个参数表示单个节点所对应的数据个数大小，一般设为1即可；
第四个参数表示缓存的总大小，当缓存超过这个设定值后，DiskLruCache就会自行清除一些缓存。
private static final long DISK_CACHE_SIZE = 1024 * 1024 * 50; //50MB
File diskCacheDir = getDiskCacheDir(mContext, "bitmap");
if (!diskCacheDir.exists()) {
diskCacheDir.mkdirs();
}
if (getUsableSpace(diskCacheDir) > DISK_CACHE_SIZE) {
try {
mDiskLruCache = DiskLruCache.open(diskCacheDir, 1, 1,
DISK_CACHE_SIZE);
mIsDiskLruCacheCreated = true;
} catch (IOException e) {
e.printStackTrace();
}
}2）DiskLruCache的缓存添加：
DiskLruCache的缓存添加操作是通过Editor对象完成的，Editor表示一个缓存对象的编辑对象。这里以图片缓存为例，首先需要获取图片url对应的key，然后根据key就可以edit()来获取Editor对象，如果这个对象正在被编辑，那么edit()就会返回null。之所以把url转换成key，是因为图片的url中很可能有特殊字符，这将影响url在Android中的直接使用，一般采用url的md5值作为key。
//url转key DisLruCache 添加+读取
private String hashKeyFormUrl(String url) {
String cacheKey;
try {
final MessageDigest mDigest = MessageDigest.getInstance("MD5");
mDigest.update(url.getBytes());
cacheKey = bytesToHexString(mDigest.digest());
} catch (NoSuchAlgorithmException e) {
cacheKey = String.valueOf(url.hashCode());
}
return cacheKey;
}
private 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();
}将图片的url转为key之后，就可以获取Editor对象了。对于这个key来说，如果当前不存在其他Editor对象，那么edit()就会返回一个新的Editor对象，通过它就可以得到一个文件输出流。
String key = hashKeyFormUrl(url);
DiskLruCache.Editor editor = mDiskLruCache.edit(key);
if (editor != null) {
OutputStream outputStream = editor.newOutputStream(DISK_CACHE_INDEX);
}当从网络中下载图片时，图片就可以通过这个文件输出流写入到文件系统上:
public boolean downloadUrlToStream(String urlString,
OutputStream outputStream) {
HttpURLConnection urlConnection = null;
BufferedOutputStream out = null;
BufferedInputStream in = null;
try {
final URL url = new URL(urlString);
urlConnection = (HttpURLConnection) url.openConnection();
in = new BufferedInputStream(urlConnection.getInputStream(),
IO_BUFFER_SIZE);
out = new BufferedOutputStream(outputStream, IO_BUFFER_SIZE);
int b;
while ((b = in.read()) != -1) {
out.write(b);
}
return true;
} catch (IOException e) {
Log.e(TAG, "downloadBitmap failed." + e);
} finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
MyUtils.close(out);
MyUtils.close(in);
}
return false;
}经过上面的步骤，其实并没有真正将图片写入文件系统，还必须通过Editor的commit()来提交写入操作，如果图片下载过程发生了异常，那么还可以通过Editor的abort()来回退整个操作。
OutputStream outputStream = editor.newOutputStream(DISK_CACHE_INDEX);
if (downloadUrlToStream(url, outputStream)) {
// 图片下载正常
editor.commit();
} else {
// 图片下载异常
editor.abort();
}
mDiskLruCache.flush();经过上面几个步骤，图片就已经被正确地写入到文件系统中，接下来图片的获取操作就不需要请求网络了。
3）DiskLruCache的缓存查找：
和缓存的添加过程类似，缓存的查找过程也需要将url转化为key，然后通过DiskLruCache的get方法得到一个Snapshot对象，接着再通过Snapshot对象即可得到缓存的文件输入流，有了文件输出流，自然就可以得到Bitmap对象了。为了避免图片加载过程中导致的OOM问题，一般不建议直接加载原始图片。可以通过文件流来得到它所对应的文件描述符，然后再通过BitmapFactory.decodeFileDescriptor方法来加载一整缩放后的图片。实现如下：
Bitmap bitmap = null;
String key = hashKeyFormUrl(url);
DiskLruCache.Snapshot snapShot = mDiskLruCache.get(key);
if (snapShot != null) {
FileInputStream fileInputStream = (FileInputStream)snapShot.getInputStream(DISK_CACHE_INDEX);
FileDescriptor fileDescriptor = fileInputStream.getFD();
bitmap = mImageResizer.decodeSampledBitmapFromFileDescriptor(fileDescriptor,
reqWidth, reqHeight);
if (bitmap != null) {
addBitmapToMemoryCache(key, bitmap);
}
}除了上述方法之外，DiskLruCache还提供了remove和delete方法来用于磁盘缓存的删除操作。
三、ImageLoader的实现
一般来说，一个优秀的ImageLoader应该具备如下功能：
- 图片的同步加载
- 图片的异步加载
- 图片压缩
- 内存缓存
- 磁盘缓存
- 网络拉取
图片的同步加载是指能够以同步的方式向调用者提供所加载的图片；图片的异步加载是一个很有用的功能，很多时候调用者不想在单独的线程中以同步的方式来获取图片，这个时候ImageLoader内部就需要自己在线程中加载图片并将图片甚至所需的ImageView。图片压缩的作用更加毋庸置疑了，这是降低OOM概率的有效手段，ImageLoader必须合理地处理图片的压缩问题。
内存缓存和磁盘缓存时ImageLoader的核心。
以下为完整实现：
1）ImageLoader
/**
* 缓存：当应用第一次从网络加载图片之后，就将其缓存到内存和存储设备中，下次使用时就不必再从网络中获取；
* 三级缓存：再次请求时，先访问内存，没有就再去访问存储设备，如果两者都没有再从网络中进行下载；
* 缓存三要素：添加、读取、删除
* 缓存算法：LRU，近期使用最少算法，采用LRU算法的缓存有两种：LruCache和DisLruCache
* LruCache：Android3.1提供的缓存类，v4包下可以兼容到早期版本。线程安全，提供了get和put方法来完成获取和添加操作
* DisLruCache：没有加入源码，本项目中可以copy一份出来。将缓存对象写入文件系统，从而实现缓存的效果。
* 创建：open()①SD卡上的缓存目录(getDiskCacheDir(context,"name")getCacheDir/getExternalCacheDir)，②1；③1；④缓存的总容量。
* 添加：Editor缓存对象的编辑对象，url转为key，根据key通过edit()来获取Editor对象，通过后者可以获取到一个文件输出流(OutputStream)，然后写入到文件系统中。commit提交；abort回退。
* OutputStream outputStream = editor.newOutputStream(DISK_CACHE_INDEX);
* 查找：添加类似：url转为key，通过get方法获取Snapshot对象，通过后者获取一个文件输入流，有了文件输入流(FileInputStream)，自然可以得到Bitmap查找对象了。
* FileInputStream fileInputStream = (FileInputStream)snapShot.getInputStream(DISK_CACHE_INDEX);
* 为了避免加载图片过程中导致的OOM问题，一般不建议直接加载原始图片，磁盘缓存时使用BitmapFactory.decodeFileDescriptor(）方法来加载一张缩放后的图片。
*
* 加载的对象会优先缓存在磁盘缓存中，添加缓存成功后再往内存中缓存一份。读取的顺序是反过来的。
*/
public class ImageLoader {
private static final String TAG = "ImageLoader";
public static final int MESSAGE_POST_RESULT = 1;
private static final int CPU_COUNT = Runtime.getRuntime().availableProcessors();
private static final int CORE_POOL_SIZE = CPU_COUNT + 1;
private static final int MAXIMUM_POOL_SIZE = CPU_COUNT * 2 + 1;
private static final long KEEP_ALIVE = 10L;
private static final int TAG_KEY_URI = R.id.imageloader_uri;
private static final long DISK_CACHE_SIZE = 1024 * 1024 * 50; //50MB
private static final int IO_BUFFER_SIZE = 8 * 1024;
private static final int DISK_CACHE_INDEX = 0;
private boolean mIsDiskLruCacheCreated = false;
private static final ThreadFactory sThreadFactory = new ThreadFactory() {
private final AtomicInteger mCount = new AtomicInteger(1);
public Thread newThread(Runnable r) {
return new Thread(r, "ImageLoader#" + mCount.getAndIncrement());
}
};
//创建线程池 用于执行网络请求这一耗时操作
public static final Executor THREAD_POOL_EXECUTOR = new ThreadPoolExecutor(
CORE_POOL_SIZE, MAXIMUM_POOL_SIZE,
KEEP_ALIVE, TimeUnit.SECONDS,
new LinkedBlockingQueue<Runnable>(), sThreadFactory);
//创建Handler 用于发送消息 切回主线程执行UI操作
private Handler mMainHandler = new Handler(Looper.getMainLooper()) {
@Override
public void handleMessage(Message msg) {
LoaderResult result = (LoaderResult) msg.obj;
ImageView imageView = result.imageView;
String uri = (String) imageView.getTag(TAG_KEY_URI);
if (uri.equals(result.uri)) {
imageView.setImageBitmap(result.bitmap);
} else {
Log.w(TAG, "set image bitmap,but url has changed, ignored!");
}
};
};
private Context mContext;
private ImageResizer mImageResizer = new ImageResizer();
private LruCache<String, Bitmap> mMemoryCache; // 内存缓存
private DiskLruCache mDiskLruCache; // 磁盘缓存
private ImageLoader(Context context) {
mContext = context.getApplicationContext();
// 内存缓存 LruCache初始化
int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);
int cacheSize = maxMemory / 8; // 总容量为当前进程的可用内存的1/8
mMemoryCache = new LruCache<String, Bitmap>(cacheSize) {
@Override
protected int sizeOf(String key, Bitmap bitmap) {
//sizeOf方法用以计算缓存对象的大小 比如Bitmap对象的大小
return bitmap.getRowBytes() * bitmap.getHeight() / 1024;
}
};
// 磁盘缓存 DisLruCache初始化
File diskCacheDir = getDiskCacheDir(mContext, "bitmap");
if (!diskCacheDir.exists()) {
diskCacheDir.mkdirs();
}
if (getUsableSpace(diskCacheDir) > DISK_CACHE_SIZE) {
try {
mDiskLruCache = DiskLruCache.open(diskCacheDir, 1, 1,
DISK_CACHE_SIZE);
mIsDiskLruCacheCreated = true;
} catch (IOException e) {
e.printStackTrace();
}
}
}
/**
* build a new instance of ImageLoader
* @param context
* @return a new instance of ImageLoader
*/
public static ImageLoader build(Context context) {
return new ImageLoader(context);
}
// 添加进LruCache 添加缓存对象
private void addBitmapToMemoryCache(String key, Bitmap bitmap) {
if (getBitmapFromMemCache(key) == null) {
mMemoryCache.put(key, bitmap);
}
}
// LruCache读取出 获取缓存对象
private Bitmap getBitmapFromMemCache(String key) {
return mMemoryCache.get(key);
}
/**
* 异步加载图片
* load bitmap from memory cache or disk cache or network async, then bind imageView and bitmap.
* NOTE THAT: should run in UI Thread
* @param uri http url
* @param imageView bitmap's bind object
*/
public void bindBitmap(final String uri, final ImageView imageView) {
bindBitmap(uri, imageView, 0, 0);
}
public void bindBitmap(final String uri, final ImageView imageView,
final int reqWidth, final int reqHeight) {
imageView.setTag(TAG_KEY_URI, uri);
Bitmap bitmap = loadBitmapFromMemCache(uri);
if (bitmap != null) {
imageView.setImageBitmap(bitmap);
return;
}
Runnable loadBitmapTask = new Runnable() {
@Override
public void run() {
Bitmap bitmap = loadBitmap(uri, reqWidth, reqHeight);
if (bitmap != null) {
LoaderResult result = new LoaderResult(imageView, uri, bitmap);
mMainHandler.obtainMessage(MESSAGE_POST_RESULT, result).sendToTarget();
}
}
};
THREAD_POOL_EXECUTOR.execute(loadBitmapTask);
}
/**
* 同步加载图片
* load bitmap from memory cache or disk cache or network.
* @param uri http url
* @param reqWidth the width ImageView desired
* @param reqHeight the height ImageView desired
* @return bitmap, maybe null.
*/
public Bitmap loadBitmap(String uri, int reqWidth, int reqHeight) {
Bitmap bitmap = loadBitmapFromMemCache(uri); // 内存缓存中读取
if (bitmap != null) {
Log.d(TAG, "loadBitmapFromMemCache,url:" + uri);
return bitmap;
}
try {
bitmap = loadBitmapFromDiskCache(uri, reqWidth, reqHeight); // 磁盘缓存的查找 即读取
if (bitmap != null) {
Log.d(TAG, "loadBitmapFromDisk,url:" + uri);
return bitmap;
}
bitmap = loadBitmapFromHttp(uri, reqWidth, reqHeight); // 磁盘缓存的添加 当磁盘缓存查找失败时调用该方法
Log.d(TAG, "loadBitmapFromHttp,url:" + uri);
} catch (IOException e) {
e.printStackTrace();
}
if (bitmap == null && !mIsDiskLruCacheCreated) {
Log.w(TAG, "encounter error, DiskLruCache is not created.");
bitmap = downloadBitmapFromUrl(uri); // 前面两次读取缓存Bitmap失败 重现调用网络拉取
}
return bitmap;
}
// LruCache加载图片 调用上面的方法
private Bitmap loadBitmapFromMemCache(String url) {
final String key = hashKeyFormUrl(url);
return getBitmapFromMemCache(key);
}
//DisLruCache 添加 Editor -耗时操作
//添加的方法最终会在最后调用一次磁盘查找的方法，返回一个Bitmap，所以这是一个有返回值的方法
private Bitmap loadBitmapFromHttp(String url, int reqWidth, int reqHeight)
throws IOException {
// 写入磁盘的操作是耗时操作 不能在主线程中执行 利用主线程Looper进行判断是否为主线程
if (Looper.myLooper() == Looper.getMainLooper()) {
throw new RuntimeException("can not visit network from UI Thread.");
}
if (mDiskLruCache == null) {
return null;
}
String key = hashKeyFormUrl(url);
DiskLruCache.Editor editor = mDiskLruCache.edit(key);
if (editor != null) {
OutputStream outputStream = editor.newOutputStream(DISK_CACHE_INDEX);
if (downloadUrlToStream(url, outputStream)) {
// 图片下载正常
editor.commit();
} else {
// 图片下载异常
editor.abort();
}
mDiskLruCache.flush();
}
return loadBitmapFromDiskCache(url, reqWidth, reqHeight);
}
//DisLruCache 缓存查找 Snapshot -耗时操作
//磁盘缓存的查找方法，得到查找对象后，会调用内存缓存的添加方法，将对象添加进内存中
private Bitmap loadBitmapFromDiskCache(String url, int reqWidth,
int reqHeight) throws IOException {
// 读取磁盘的操作是耗时操作 不能在主线程中执行 利用主线程Looper进行判断是否为主线程
if (Looper.myLooper() == Looper.getMainLooper()) {
Log.w(TAG, "load bitmap from UI Thread, it's not recommended!");
}
if (mDiskLruCache == null) {
return null;
}
Bitmap bitmap = null;
String key = hashKeyFormUrl(url);
DiskLruCache.Snapshot snapShot = mDiskLruCache.get(key);
if (snapShot != null) {
FileInputStream fileInputStream = (FileInputStream)snapShot.getInputStream(DISK_CACHE_INDEX);
FileDescriptor fileDescriptor = fileInputStream.getFD();
bitmap = mImageResizer.decodeSampledBitmapFromFileDescriptor(fileDescriptor,
reqWidth, reqHeight);
if (bitmap != null) {
addBitmapToMemoryCache(key, bitmap);
}
}
return bitmap;
}
//外界调用该方法时传入文件输出流对象，和Url，就可以直接将下载好的图片写入到文件系统上
//DisLruCache判断下载是否异常 写入是否成功 最后决定是com_mit() 还是ab_ort()
//通过Editor对象获取文件输出流之后，当从网络中下载图片之后，再利用这个输出流将图片写入到文件系统上
// OutputStream输出流 write()写入方法
// 注意这里已经执行了从网络中拉取图片的方法，所以调用磁盘添加方法时，实际已经进行了网络图片的拉取
public boolean downloadUrlToStream(String urlString,
OutputStream outputStream) {
HttpURLConnection urlConnection = null;
BufferedOutputStream out = null;
BufferedInputStream in = null;
try {
final URL url = new URL(urlString);
urlConnection = (HttpURLConnection) url.openConnection();
in = new BufferedInputStream(urlConnection.getInputStream(),
IO_BUFFER_SIZE);
out = new BufferedOutputStream(outputStream, IO_BUFFER_SIZE);
int b;
while ((b = in.read()) != -1) {
out.write(b);
}
return true;
} catch (IOException e) {
Log.e(TAG, "downloadBitmap failed." + e);
} finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
MyUtils.close(out);
MyUtils.close(in);
}
return false;
}
// HttpURL_Connection 网络拉取图片
private Bitmap downloadBitmapFromUrl(String urlString) {
Bitmap bitmap = null;
HttpURLConnection urlConnection = null;
BufferedInputStream in = null;
try {
final URL url = new URL(urlString);
urlConnection = (HttpURLConnection) url.openConnection();
in = new BufferedInputStream(urlConnection.getInputStream(),
IO_BUFFER_SIZE);
bitmap = BitmapFactory.decodeStream(in);
} catch (final IOException e) {
Log.e(TAG, "Error in downloadBitmap: " + e);
} finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
MyUtils.close(in);
}
return bitmap;
}
//url转key DisLruCache 添加+读取
private String hashKeyFormUrl(String url) {
String cacheKey;
try {
final MessageDigest mDigest = MessageDigest.getInstance("MD5");
mDigest.update(url.getBytes());
cacheKey = bytesToHexString(mDigest.digest());
} catch (NoSuchAlgorithmException e) {
cacheKey = String.valueOf(url.hashCode());
}
return cacheKey;
}
private 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();
}
public File getDiskCacheDir(Context context, String uniqueName) {
boolean externalStorageAvailable = Environment
.getExternalStorageState().equals(Environment.MEDIA_MOUNTED);
final String cachePath;
if (externalStorageAvailable) {
cachePath = context.getExternalCacheDir().getPath();
// -/storage/emulated/0/Android/data/com.camera.fhuji.camera/cache 应用数据目录下的外部存储目录，优先使用
} else {
cachePath = context.getCacheDir().getPath();
// -/data/user/0/com.camera.fhuji.camera/cache 应用数据目录下的内部存储目录，尽量少用
}
// -/storage/emulated/0/Android/data/com.camera.fhuji.camera/cache/bitmap
return new File(cachePath + File.separator + uniqueName);
}
@TargetApi(VERSION_CODES.GINGERBREAD)
private long getUsableSpace(File path) {
if (Build.VERSION.SDK_INT >= VERSION_CODES.GINGERBREAD) {
return path.getUsableSpace();
}
final StatFs stats = new StatFs(path.getPath());
return (long) stats.getBlockSize() * (long) stats.getAvailableBlocks();
}
private static class LoaderResult {
public ImageView imageView;
public String uri;
public Bitmap bitmap;
public LoaderResult(ImageView imageView, String uri, Bitmap bitmap) {
this.imageView = imageView;
this.uri = uri;
this.bitmap = bitmap;
}
}
}
2）图片压缩ImageResizer
public class ImageResizer {
private static final String TAG = "ImageResizer";
public ImageResizer() {
}
public Bitmap decodeSampledBitmapFromResource(Resources res,
int resId, int reqWidth, int reqHeight) {
// First decode with inJustDecodeBounds=true to check dimensions
final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeResource(res, resId, options);
// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, reqWidth,
reqHeight);
// Decode bitmap with inSampleSize set
options.inJustDecodeBounds = false;
return BitmapFactory.decodeResource(res, resId, options);
}
public Bitmap decodeSampledBitmapFromFileDescriptor(FileDescriptor fd, int reqWidth, int reqHeight) {
// First decode with inJustDecodeBounds=true to check dimensions
final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeFileDescriptor(fd, null, options);
// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, reqWidth,
reqHeight);
// Decode bitmap with inSampleSize set
options.inJustDecodeBounds = false;
return BitmapFactory.decodeFileDescriptor(fd, null, options);
}
public int calculateInSampleSize(BitmapFactory.Options options,
int reqWidth, int reqHeight) {
if (reqWidth == 0 || reqHeight == 0) {
return 1;
}
// Raw height and width of image
final int height = options.outHeight;
final int width = options.outWidth;
Log.d(TAG, "origin, w= " + width + " h=" + height);
int inSampleSize = 1;
if (height > reqHeight || width > reqWidth) {
final int halfHeight = height / 2;
final int halfWidth = width / 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 ((halfHeight / inSampleSize) >= reqHeight
&& (halfWidth / inSampleSize) >= reqWidth) {
inSampleSize *= 2;
}
}
Log.d(TAG, "sampleSize:" + inSampleSize);
return inSampleSize;
}
}
3）Activity中使用ImageLoader
mImageLoader.bindBitmap(uri, imageView, mImageWidth, mImageWidth);4）附录：DiskLruCache源码（自主添加进项目）
/*
* Copyright (C) 2011 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.camera.fhuji.camera.art.loader;
import java.io.BufferedInputStream;
import java.io.BufferedWriter;
import java.io.Closeable;
import java.io.EOFException;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Reader;
import java.io.StringWriter;
import java.io.Writer;
import java.lang.reflect.Array;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
/**
******************************************************************************
* Taken from the JB source code, can be found in:
* libcore/luni/src/main/java/libcore/io/DiskLruCache.java
* or direct link:
* https://android.googlesource.com/platform/libcore/+/android-4.1.1_r1/luni/src/main/java/libcore/io/DiskLruCache.java
******************************************************************************
*
* A cache that uses a bounded amount of space on a filesystem. Each cache
* entry has a string key and a fixed number of values. Values are byte
* sequences, accessible as streams or files. Each value must be between {@code
* 0} and {@code Integer.MAX_VALUE} bytes in length.
*
* <p>The cache stores its data in a directory on the filesystem. This
* directory must be exclusive to the cache; the cache may delete or overwrite
* files from its directory. It is an error for multiple processes to use the
* same cache directory at the same time.
*
* <p>This cache limits the number of bytes that it will store on the
* filesystem. When the number of stored bytes exceeds the limit, the cache will
* remove entries in the background until the limit is satisfied. The limit is
* not strict: the cache may temporarily exceed it while waiting for files to be
* deleted. The limit does not include filesystem overhead or the cache
* journal so space-sensitive applications should set a conservative limit.
*
* <p>Clients call {@link #edit} to create or update the values of an entry. An
* entry may have only one editor at one time; if a value is not available to be
* edited then {@link #edit} will return null.
* <ul>
* <li>When an entry is being <strong>created</strong> it is necessary to
* supply a full set of values; the empty value should be used as a
* placeholder if necessary.
* <li>When an entry is being <strong>edited</strong>, it is not necessary
* to supply data for every value; values default to their previous
* value.
* </ul>
* Every {@link #edit} call must be matched by a call to {@link Editor#commit}
* or {@link Editor#abort}. Committing is atomic: a read observes the full set
* of values as they were before or after the commit, but never a mix of values.
*
* <p>Clients call {@link #get} to read a snapshot of an entry. The read will
* observe the value at the time that {@link #get} was called. Updates and
* removals after the call do not impact ongoing reads.
*
* <p>This class is tolerant of some I/O errors. If files are missing from the
* filesystem, the corresponding entries will be dropped from the cache. If
* an error occurs while writing a cache value, the edit will fail silently.
* Callers should handle other problems by catching {@code IOException} and
* responding appropriately.
*/
public final class DiskLruCache implements Closeable {
static final String JOURNAL_FILE = "journal";
static final String JOURNAL_FILE_TMP = "journal.tmp";
static final String MAGIC = "libcore.io.DiskLruCache";
static final String VERSION_1 = "1";
static final long ANY_SEQUENCE_NUMBER = -1;
private static final String CLEAN = "CLEAN";
private static final String DIRTY = "DIRTY";
private static final String REMOVE = "REMOVE";
private static final String READ = "READ";
private static final Charset UTF_8 = Charset.forName("UTF-8");
private static final int IO_BUFFER_SIZE = 8 * 1024;
/*
* This cache uses a journal file named "journal". A typical journal file
* looks like this:
* libcore.io.DiskLruCache
* 1
* 100
* 2
*
* CLEAN 3400330d1dfc7f3f7f4b8d4d803dfcf6 832 21054
* DIRTY 335c4c6028171cfddfbaae1a9c313c52
* CLEAN 335c4c6028171cfddfbaae1a9c313c52 3934 2342
* REMOVE 335c4c6028171cfddfbaae1a9c313c52
* DIRTY 1ab96a171faeeee38496d8b330771a7a
* CLEAN 1ab96a171faeeee38496d8b330771a7a 1600 234
* READ 335c4c6028171cfddfbaae1a9c313c52
* READ 3400330d1dfc7f3f7f4b8d4d803dfcf6
*
* The first five lines of the journal form its header. They are the
* constant string "libcore.io.DiskLruCache", the disk cache's version,
* the application's version, the value count, and a blank line.
*
* Each of the subsequent lines in the file is a record of the state of a
* cache entry. Each line contains space-separated values: a state, a key,
* and optional state-specific values.
* o DIRTY lines track that an entry is actively being created or updated.
* Every successful DIRTY action should be followed by a CLEAN or REMOVE
* action. DIRTY lines without a matching CLEAN or REMOVE indicate that
* temporary files may need to be deleted.
* o CLEAN lines track a cache entry that has been successfully published
* and may be read. A publish line is followed by the lengths of each of
* its values.
* o READ lines track accesses for LRU.
* o REMOVE lines track entries that have been deleted.
*
* The journal file is appended to as cache operations occur. The journal may
* occasionally be compacted by dropping redundant lines. A temporary file named
* "journal.tmp" will be used during compaction; that file should be deleted if
* it exists when the cache is opened.
*/
private final File directory;
private final File journalFile;
private final File journalFileTmp;
private final int appVersion;
private final long maxSize;
private final int valueCount;
private long size = 0;
private Writer journalWriter;
private final LinkedHashMap<String, Entry> lruEntries
= new LinkedHashMap<String, Entry>(0, 0.75f, true);
private int redundantOpCount;
/**
* To differentiate between old and current snapshots, each entry is given
* a sequence number each time an edit is committed. A snapshot is stale if
* its sequence number is not equal to its entry's sequence number.
*/
private long nextSequenceNumber = 0;
/* From java.util.Arrays */
@SuppressWarnings("unchecked")
private static <T> T[] copyOfRange(T[] original, int start, int end) {
final int originalLength = original.length; // For exception priority compatibility.
if (start > end) {
throw new IllegalArgumentException();
}
if (start < 0 || start > originalLength) {
throw new ArrayIndexOutOfBoundsException();
}
final int resultLength = end - start;
final int copyLength = Math.min(resultLength, originalLength - start);
final T[] result = (T[]) Array
.newInstance(original.getClass().getComponentType(), resultLength);
System.arraycopy(original, start, result, 0, copyLength);
return result;
}
/**
* Returns the remainder of 'reader' as a string, closing it when done.
*/
public static String readFully(Reader reader) throws IOException {
try {
StringWriter writer = new StringWriter();
char[] buffer = new char[1024];
int count;
while ((count = reader.read(buffer)) != -1) {
writer.write(buffer, 0, count);
}
return writer.toString();
} finally {
reader.close();
}
}
/**
* Returns the ASCII characters up to but not including the next "\r\n", or
* "\n".
*
* @throws EOFException if the stream is exhausted before the next newline
* character.
*/
public static String readAsciiLine(InputStream in) throws IOException {
// TODO: support UTF-8 here instead
StringBuilder result = new StringBuilder(80);
while (true) {
int c = in.read();
if (c == -1) {
throw new EOFException();
} else if (c == '\n') {
break;
}
result.append((char) c);
}
int length = result.length();
if (length > 0 && result.charAt(length - 1) == '\r') {
result.setLength(length - 1);
}
return result.toString();
}
/**
* Closes 'closeable', ignoring any checked exceptions. Does nothing if 'closeable' is null.
*/
public static void closeQuietly(Closeable closeable) {
if (closeable != null) {
try {
closeable.close();
} catch (RuntimeException rethrown) {
throw rethrown;
} catch (Exception ignored) {
}
}
}
/**
* Recursively delete everything in {@code dir}.
*/
// TODO: this should specify paths as Strings rather than as Files
public static void deleteContents(File dir) throws IOException {
File[] files = dir.listFiles();
if (files == null) {
throw new IllegalArgumentException("not a directory: " + dir);
}
for (File file : files) {
if (file.isDirectory()) {
deleteContents(file);
}
if (!file.delete()) {
throw new IOException("failed to delete file: " + file);
}
}
}
/** This cache uses a single background thread to evict entries. */
private final ExecutorService executorService = new ThreadPoolExecutor(0, 1,
60L, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());
private final Callable<Void> cleanupCallable = new Callable<Void>() {
@Override public Void call() throws Exception {
synchronized (DiskLruCache.this) {
if (journalWriter == null) {
return null; // closed
}
trimToSize();
if (journalRebuildRequired()) {
rebuildJournal();
redundantOpCount = 0;
}
}
return null;
}
};
private DiskLruCache(File directory, int appVersion, int valueCount, long maxSize) {
this.directory = directory;
this.appVersion = appVersion;
this.journalFile = new File(directory, JOURNAL_FILE);
this.journalFileTmp = new File(directory, JOURNAL_FILE_TMP);
this.valueCount = valueCount;
this.maxSize = maxSize;
}
/**
* Opens the cache in {@code directory}, creating a cache if none exists
* there.
*
* @param directory a writable directory
* @param appVersion
* @param valueCount the number of values per cache entry. Must be positive.
* @param maxSize the maximum number of bytes this cache should use to store
* @throws IOException if reading or writing the cache directory fails
*/
public static DiskLruCache open(File directory, int appVersion, int valueCount, long maxSize)
throws IOException {
if (maxSize <= 0) {
throw new IllegalArgumentException("maxSize <= 0");
}
if (valueCount <= 0) {
throw new IllegalArgumentException("valueCount <= 0");
}
// prefer to pick up where we left off
DiskLruCache cache = new DiskLruCache(directory, appVersion, valueCount, maxSize);
if (cache.journalFile.exists()) {
try {
cache.readJournal();
cache.processJournal();
cache.journalWriter = new BufferedWriter(new FileWriter(cache.journalFile, true),
IO_BUFFER_SIZE);
return cache;
} catch (IOException journalIsCorrupt) {
// System.logW("DiskLruCache " + directory + " is corrupt: "
// + journalIsCorrupt.getMessage() + ", removing");
cache.delete();
}
}
// create a new empty cache
directory.mkdirs();
cache = new DiskLruCache(directory, appVersion, valueCount, maxSize);
cache.rebuildJournal();
return cache;
}
private void readJournal() throws IOException {
InputStream in = new BufferedInputStream(new FileInputStream(journalFile), IO_BUFFER_SIZE);
try {
String magic = readAsciiLine(in);
String version = readAsciiLine(in);
String appVersionString = readAsciiLine(in);
String valueCountString = readAsciiLine(in);
String blank = readAsciiLine(in);
if (!MAGIC.equals(magic)
|| !VERSION_1.equals(version)
|| !Integer.toString(appVersion).equals(appVersionString)
|| !Integer.toString(valueCount).equals(valueCountString)
|| !"".equals(blank)) {
throw new IOException("unexpected journal header: ["
+ magic + ", " + version + ", " + valueCountString + ", " + blank + "]");
}
while (true) {
try {
readJournalLine(readAsciiLine(in));
} catch (EOFException endOfJournal) {
break;
}
}
} finally {
closeQuietly(in);
}
}
private void readJournalLine(String line) throws IOException {
String[] parts = line.split(" ");
if (parts.length < 2) {
throw new IOException("unexpected journal line: " + line);
}
String key = parts[1];
if (parts[0].equals(REMOVE) && parts.length == 2) {
lruEntries.remove(key);
return;
}
Entry entry = lruEntries.get(key);
if (entry == null) {
entry = new Entry(key);
lruEntries.put(key, entry);
}
if (parts[0].equals(CLEAN) && parts.length == 2 + valueCount) {
entry.readable = true;
entry.currentEditor = null;
entry.setLengths(copyOfRange(parts, 2, parts.length));
} else if (parts[0].equals(DIRTY) && parts.length == 2) {
entry.currentEditor = new Editor(entry);
} else if (parts[0].equals(READ) && parts.length == 2) {
// this work was already done by calling lruEntries.get()
} else {
throw new IOException("unexpected journal line: " + line);
}
}
/**
* Computes the initial size and collects garbage as a part of opening the
* cache. Dirty entries are assumed to be inconsistent and will be deleted.
*/
private void processJournal() throws IOException {
deleteIfExists(journalFileTmp);
for (Iterator<Entry> i = lruEntries.values().iterator(); i.hasNext(); ) {
Entry entry = i.next();
if (entry.currentEditor == null) {
for (int t = 0; t < valueCount; t++) {
size += entry.lengths[t];
}
} else {
entry.currentEditor = null;
for (int t = 0; t < valueCount; t++) {
deleteIfExists(entry.getCleanFile(t));
deleteIfExists(entry.getDirtyFile(t));
}
i.remove();
}
}
}
/**
* Creates a new journal that omits redundant information. This replaces the
* current journal if it exists.
*/
private synchronized void rebuildJournal() throws IOException {
if (journalWriter != null) {
journalWriter.close();
}
Writer writer = new BufferedWriter(new FileWriter(journalFileTmp), IO_BUFFER_SIZE);
writer.write(MAGIC);
writer.write("\n");
writer.write(VERSION_1);
writer.write("\n");
writer.write(Integer.toString(appVersion));
writer.write("\n");
writer.write(Integer.toString(valueCount));
writer.write("\n");
writer.write("\n");
for (Entry entry : lruEntries.values()) {
if (entry.currentEditor != null) {
writer.write(DIRTY + ' ' + entry.key + '\n');
} else {
writer.write(CLEAN + ' ' + entry.key + entry.getLengths() + '\n');
}
}
writer.close();
journalFileTmp.renameTo(journalFile);
journalWriter = new BufferedWriter(new FileWriter(journalFile, true), IO_BUFFER_SIZE);
}
private static void deleteIfExists(File file) throws IOException {
// try {
// Libcore.os.remove(file.getPath());
// } catch (ErrnoException errnoException) {
// if (errnoException.errno != OsConstants.ENOENT) {
// throw errnoException.rethrowAsIOException();
// }
// }
if (file.exists() && !file.delete()) {
throw new IOException();
}
}
/**
* Returns a snapshot of the entry named {@code key}, or null if it doesn't
* exist is not currently readable. If a value is returned, it is moved to
* the head of the LRU queue.
*/
public synchronized Snapshot get(String key) throws IOException {
checkNotClosed();
validateKey(key);
Entry entry = lruEntries.get(key);
if (entry == null) {
return null;
}
if (!entry.readable) {
return null;
}
/*
* Open all streams eagerly to guarantee that we see a single published
* snapshot. If we opened streams lazily then the streams could come
* from different edits.
*/
InputStream[] ins = new InputStream[valueCount];
try {
for (int i = 0; i < valueCount; i++) {
ins[i] = new FileInputStream(entry.getCleanFile(i));
}
} catch (FileNotFoundException e) {
// a file must have been deleted manually!
return null;
}
redundantOpCount++;
journalWriter.append(READ + ' ' + key + '\n');
if (journalRebuildRequired()) {
executorService.submit(cleanupCallable);
}
return new Snapshot(key, entry.sequenceNumber, ins);
}
/**
* Returns an editor for the entry named {@code key}, or null if another
* edit is in progress.
*/
public Editor edit(String key) throws IOException {
return edit(key, ANY_SEQUENCE_NUMBER);
}
private synchronized Editor edit(String key, long expectedSequenceNumber) throws IOException {
checkNotClosed();
validateKey(key);
Entry entry = lruEntries.get(key);
if (expectedSequenceNumber != ANY_SEQUENCE_NUMBER
&& (entry == null || entry.sequenceNumber != expectedSequenceNumber)) {
return null; // snapshot is stale
}
if (entry == null) {
entry = new Entry(key);
lruEntries.put(key, entry);
} else if (entry.currentEditor != null) {
return null; // another edit is in progress
}
Editor editor = new Editor(entry);
entry.currentEditor = editor;
// flush the journal before creating files to prevent file leaks
journalWriter.write(DIRTY + ' ' + key + '\n');
journalWriter.flush();
return editor;
}
/**
* Returns the directory where this cache stores its data.
*/
public File getDirectory() {
return directory;
}
/**
* Returns the maximum number of bytes that this cache should use to store
* its data.
*/
public long maxSize() {
return maxSize;
}
/**
* Returns the number of bytes currently being used to store the values in
* this cache. This may be greater than the max size if a background
* deletion is pending.
*/
public synchronized long size() {
return size;
}
private synchronized void completeEdit(Editor editor, boolean success) throws IOException {
Entry entry = editor.entry;
if (entry.currentEditor != editor) {
throw new IllegalStateException();
}
// if this edit is creating the entry for the first time, every index must have a value
if (success && !entry.readable) {
for (int i = 0; i < valueCount; i++) {
if (!entry.getDirtyFile(i).exists()) {
editor.abort();
throw new IllegalStateException("edit didn't create file " + i);
}
}
}
for (int i = 0; i < valueCount; i++) {
File dirty = entry.getDirtyFile(i);
if (success) {
if (dirty.exists()) {
File clean = entry.getCleanFile(i);
dirty.renameTo(clean);
long oldLength = entry.lengths[i];
long newLength = clean.length();
entry.lengths[i] = newLength;
size = size - oldLength + newLength;
}
} else {
deleteIfExists(dirty);
}
}
redundantOpCount++;
entry.currentEditor = null;
if (entry.readable | success) {
entry.readable = true;
journalWriter.write(CLEAN + ' ' + entry.key + entry.getLengths() + '\n');
if (success) {
entry.sequenceNumber = nextSequenceNumber++;
}
} else {
lruEntries.remove(entry.key);
journalWriter.write(REMOVE + ' ' + entry.key + '\n');
}
if (size > maxSize || journalRebuildRequired()) {
executorService.submit(cleanupCallable);
}
}
/**
* We only rebuild the journal when it will halve the size of the journal
* and eliminate at least 2000 ops.
*/
private boolean journalRebuildRequired() {
final int REDUNDANT_OP_COMPACT_THRESHOLD = 2000;
return redundantOpCount >= REDUNDANT_OP_COMPACT_THRESHOLD
&& redundantOpCount >= lruEntries.size();
}
/**
* Drops the entry for {@code key} if it exists and can be removed. Entries
* actively being edited cannot be removed.
*
* @return true if an entry was removed.
*/
public synchronized boolean remove(String key) throws IOException {
checkNotClosed();
validateKey(key);
Entry entry = lruEntries.get(key);
if (entry == null || entry.currentEditor != null) {
return false;
}
for (int i = 0; i < valueCount; i++) {
File file = entry.getCleanFile(i);
if (!file.delete()) {
throw new IOException("failed to delete " + file);
}
size -= entry.lengths[i];
entry.lengths[i] = 0;
}
redundantOpCount++;
journalWriter.append(REMOVE + ' ' + key + '\n');
lruEntries.remove(key);
if (journalRebuildRequired()) {
executorService.submit(cleanupCallable);
}
return true;
}
/**
* Returns true if this cache has been closed.
*/
public boolean isClosed() {
return journalWriter == null;
}
private void checkNotClosed() {
if (journalWriter == null) {
throw new IllegalStateException("cache is closed");
}
}
/**
* Force buffered operations to the filesystem.
*/
public synchronized void flush() throws IOException {
checkNotClosed();
trimToSize();
journalWriter.flush();
}
/**
* Closes this cache. Stored values will remain on the filesystem.
*/
public synchronized void close() throws IOException {
if (journalWriter == null) {
return; // already closed
}
for (Entry entry : new ArrayList<Entry>(lruEntries.values())) {
if (entry.currentEditor != null) {
entry.currentEditor.abort();
}
}
trimToSize();
journalWriter.close();
journalWriter = null;
}
private void trimToSize() throws IOException {
while (size > maxSize) {
// Map.Entry<String, Entry> toEvict = lruEntries.eldest();
final Map.Entry<String, Entry> toEvict = lruEntries.entrySet().iterator().next();
remove(toEvict.getKey());
}
}
/**
* Closes the cache and deletes all of its stored values. This will delete
* all files in the cache directory including files that weren't created by
* the cache.
*/
public void delete() throws IOException {
close();
deleteContents(directory);
}
private void validateKey(String key) {
if (key.contains(" ") || key.contains("\n") || key.contains("\r")) {
throw new IllegalArgumentException(
"keys must not contain spaces or newlines: \"" + key + "\"");
}
}
private static String inputStreamToString(InputStream in) throws IOException {
return readFully(new InputStreamReader(in, UTF_8));
}
/**
* A snapshot of the values for an entry.
*/
public final class Snapshot implements Closeable {
private final String key;
private final long sequenceNumber;
private final InputStream[] ins;
private Snapshot(String key, long sequenceNumber, InputStream[] ins) {
this.key = key;
this.sequenceNumber = sequenceNumber;
this.ins = ins;
}
/**
* Returns an editor for this snapshot's entry, or null if either the
* entry has changed since this snapshot was created or if another edit
* is in progress.
*/
public Editor edit() throws IOException {
return DiskLruCache.this.edit(key, sequenceNumber);
}
/**
* Returns the unbuffered stream with the value for {@code index}.
*/
public InputStream getInputStream(int index) {
return ins[index];
}
/**
* Returns the string value for {@code index}.
*/
public String getString(int index) throws IOException {
return inputStreamToString(getInputStream(index));
}
@Override public void close() {
for (InputStream in : ins) {
closeQuietly(in);
}
}
}
/**
* Edits the values for an entry.
*/
public final class Editor {
private final Entry entry;
private boolean hasErrors;
private Editor(Entry entry) {
this.entry = entry;
}
/**
* Returns an unbuffered input stream to read the last committed value,
* or null if no value has been committed.
*/
public InputStream newInputStream(int index) throws IOException {
synchronized (DiskLruCache.this) {
if (entry.currentEditor != this) {
throw new IllegalStateException();
}
if (!entry.readable) {
return null;
}
return new FileInputStream(entry.getCleanFile(index));
}
}
/**
* Returns the last committed value as a string, or null if no value
* has been committed.
*/
public String getString(int index) throws IOException {
InputStream in = newInputStream(index);
return in != null ? inputStreamToString(in) : null;
}
/**
* Returns a new unbuffered output stream to write the value at
* {@code index}. If the underlying output stream encounters errors
* when writing to the filesystem, this edit will be aborted when
* {@link #commit} is called. The returned output stream does not throw
* IOExceptions.
*/
public OutputStream newOutputStream(int index) throws IOException {
synchronized (DiskLruCache.this) {
if (entry.currentEditor != this) {
throw new IllegalStateException();
}
return new FaultHidingOutputStream(new FileOutputStream(entry.getDirtyFile(index)));
}
}
/**
* Sets the value at {@code index} to {@code value}.
*/
public void set(int index, String value) throws IOException {
Writer writer = null;
try {
writer = new OutputStreamWriter(newOutputStream(index), UTF_8);
writer.write(value);
} finally {
closeQuietly(writer);
}
}
/**
* Commits this edit so it is visible to readers. This releases the
* edit lock so another edit may be started on the same key.
*/
public void commit() throws IOException {
if (hasErrors) {
completeEdit(this, false);
remove(entry.key); // the previous entry is stale
} else {
completeEdit(this, true);
}
}
/**
* Aborts this edit. This releases the edit lock so another edit may be
* started on the same key.
*/
public void abort() throws IOException {
completeEdit(this, false);
}
private class FaultHidingOutputStream extends FilterOutputStream {
private FaultHidingOutputStream(OutputStream out) {
super(out);
}
@Override public void write(int oneByte) {
try {
out.write(oneByte);
} catch (IOException e) {
hasErrors = true;
}
}
@Override public void write(byte[] buffer, int offset, int length) {
try {
out.write(buffer, offset, length);
} catch (IOException e) {
hasErrors = true;
}
}
@Override public void close() {
try {
out.close();
} catch (IOException e) {
hasErrors = true;
}
}
@Override public void flush() {
try {
out.flush();
} catch (IOException e) {
hasErrors = true;
}
}
}
}
private final class Entry {
private final String key;
/** Lengths of this entry's files. */
private final long[] lengths;
/** True if this entry has ever been published */
private boolean readable;
/** The ongoing edit or null if this entry is not being edited. */
private Editor currentEditor;
/** The sequence number of the most recently committed edit to this entry. */
private long sequenceNumber;
private Entry(String key) {
this.key = key;
this.lengths = new long[valueCount];
}
public String getLengths() throws IOException {
StringBuilder result = new StringBuilder();
for (long size : lengths) {
result.append(' ').append(size);
}
return result.toString();
}
/**
* Set lengths using decimal numbers like "10123".
*/
private void setLengths(String[] strings) throws IOException {
if (strings.length != valueCount) {
throw invalidLengths(strings);
}
try {
for (int i = 0; i < strings.length; i++) {
lengths[i] = Long.parseLong(strings[i]);
}
} catch (NumberFormatException e) {
throw invalidLengths(strings);
}
}
private IOException invalidLengths(String[] strings) throws IOException {
throw new IOException("unexpected journal line: " + Arrays.toString(strings));
}
public File getCleanFile(int i) {
return new File(directory, key + "." + i);
}
public File getDirtyFile(int i) {
return new File(directory, key + "." + i + ".tmp");
}
}
}