galler3d的源码分析——数据来源
我们这里主要讲本地sd卡的数据，pisaca看情况后续再作分析。
数据操作设计的类包括：CacheService，MediaFeed，LocalDataSource，DiskCache，MediaItem， MediaSet，MediaClustering。
数据操作包括几个方面：寻找媒体源（图片、视频），cache媒体源，将cache数据导出，将cache的媒体渲染到屏幕。
首先是找图片或者视频：
1. 如果当前cache文件不存在，或者当前cache文件记录的语言、国家和变量代码与系统的不一致的场景时，首先将所有cache文件(index和chunk文件）删除，接着将语言、国家和变量代码写入local-album-cachechunk0的文件中。
2. 启动一个线程，寻找图片或者视频，并将相册信息cache。
3. 再启动一个线程，将图片缩略图化，并cache。
4. 如果上一次还有一部分数据cache，执行步骤2和3。
5. 如果这一次有新的媒体文件需要cache，启动一个线程，将新的媒体文件cache。再执行步骤3。
关键的代码如下：
@Override
protected void onHandleIntent(final Intent intent) {
Log.i(TAG, "CacheService, onHandleIntent, Starting CacheService");
if (Environment.getExternalStorageState() == Environment.MEDIA_BAD_REMOVAL) {
sAlbumCache.deleteAll();
putLocaleForAlbumCache(Locale.getDefault());
}
Locale locale = getLocaleForAlbumCache();
if (locale != null && locale.equals(Locale.getDefault())) {
// The cache is in the same locale as the system locale.
if (!isCacheReady(false)) {
// The albums and their items have not yet been cached, we need
// to run the service.
Log.i(TAG, "CacheService, onHandleIntent, start new cache thread");
startNewCacheThread();
} else {
Log.i(TAG, "CacheService, onHandleIntent, start new cache thread for dirty sets");
startNewCacheThreadForDirtySets();
}
} else {
// The locale has changed, we need to regenerate the strings.
Log.i(TAG, "CacheService, onHandleIntent, delete all");
sAlbumCache.deleteAll();
putLocaleForAlbumCache(Locale.getDefault());
startNewCacheThread();
}
if (intent.getBooleanExtra("checkthumbnails", false)) {
Log.i(TAG, "CacheService, onHandleIntent, start new thumbnail thread");
startNewThumbnailThread(this);
} else {
final Thread existingThread = THUMBNAIL_THREAD.getAndSet(null);
if (existingThread != null) {
existingThread.interrupt();
}
}
}
先看这个函数：
private static final Locale getLocaleForAlbumCache() {
Log.i(TAG, "CacheService, getLocaleForAlbumCache");
final byte[] data = sAlbumCache.get(ALBUM_CACHE_LOCALE_INDEX, 0);
if (data != null && data.length > 0) {
ByteArrayInputStream bis = new ByteArrayInputStream(data);
DataInputStream dis = new DataInputStream(bis);
try {
String country = Utils.readUTF(dis);
if (country == null)
country = "";
String language = Utils.readUTF(dis);
if (language == null)
language = "";
String variant = Utils.readUTF(dis);
if (variant == null)
variant = "";
final Locale locale = new Locale(language, country, variant);
dis.close();
bis.close();
return locale;
} catch (IOException e) {
// Could not read locale in cache.
Log.i(TAG, "Error reading locale from cache.");
return null;
}
}
return null;
}
我们看到 sAlbumCache这个变量，这个变量的定义是这样的：
public static final DiskCache sAlbumCache = new DiskCache("local-album-cache");
我们来看看DiskCache的构造函数做了什么？
public DiskCache(String cacheDirectoryName) {
String cacheDirectoryPath = CacheService.getCachePath(cacheDirectoryName);
// Create the cache directory if needed.
File cacheDirectory = new File(cacheDirectoryPath);
if (!cacheDirectory.isDirectory() && !cacheDirectory.mkdirs()) {
Log.e(TAG, "Unable to create cache directory " + cacheDirectoryPath);
}
mCacheDirectoryPath = cacheDirectoryPath;
loadIndex();
}
public static final String getCachePath(final String subFolderName) {
return Environment.getExternalStorageDirectory() + "/Android/data/com.luowei.media/cache/" + subFolderName;
}
原来如此，在sd卡建立了一个目录/Android/data/com.luowei.media/cache/local-album-cache。
建立目录后呢？
private void loadIndex() {
final String indexFilePath = getIndexFilePath();
try {
// Open the input stream.
final FileInputStream fileInput = new FileInputStream(indexFilePath);
final BufferedInputStream bufferedInput = new BufferedInputStream(fileInput, 1024);
final DataInputStream dataInput = new DataInputStream(bufferedInput);
// Read the header.
final int magic = dataInput.readInt();//4
final int version = dataInput.readInt();//4
boolean valid = true;
if (magic != INDEX_HEADER_MAGIC) {
Log.e(TAG, "Index file appears to be corrupt (" + magic + " != " + INDEX_HEADER_MAGIC + "), " + indexFilePath);
valid = false;
}
if (valid && version != INDEX_HEADER_VERSION) {
// Future versions can implement upgrade in this case.
Log.e(TAG, "Index file version " + version + " not supported");
valid = false;
}
if (valid) {
mTailChunk = dataInput.readShort();//2
}
// Read the entries.
if (valid) {
// Parse the index file body into the in-memory map.
final int numEntries = dataInput.readInt();//4
mIndexMap = new LongSparseArray<Record>(numEntries);
synchronized (mIndexMap) {
for (int i = 0; i < numEntries; ++i) {
final long key = dataInput.readLong();//8
final int chunk = dataInput.readShort();//2
final int offset = dataInput.readInt();//4
final int size = dataInput.readInt();//4
final int sizeOnDisk = dataInput.readInt();//4
final long timestamp = dataInput.readLong();//8
mIndexMap.append(key, new Record(chunk, offset, size, sizeOnDisk, timestamp));
}
}
}
dataInput.close();
if (!valid) {
deleteAll();
}
} catch (FileNotFoundException e) {
// If the file does not exist the cache is empty, so just continue.
} catch (IOException e) {
Log.e(TAG, "Unable to read the index file " + indexFilePath);
} finally {
if (mIndexMap == null) {
mIndexMap = new LongSparseArray<Record>();
}
}
}
首先找索引文件，索引文件路径是什么？
private String getIndexFilePath() {
return mCacheDirectoryPath + INDEX_FILE_NAME;
}
具体路径是 sd卡下/Android/data/com.luowei.media/cache/local-album-cacheindex。如果文件不存在，就只做一件事，将mIndexMap初始化；如果文件存在，读取文件头，如果文件头是00 00 CA FE 00 00 00 02这个格式，说明是标准的索引文件，继续分析此文件，将数据写入mIndexMap映射表。
接着继续分析getLocaleForAlbumCache函数，sAlbumCache.get做了什么？
public byte[] get(long key, long timestamp) {
// Look up the record for the given key.
Record record = null;
synchronized (mIndexMap) {
record = mIndexMap.get(key);
}
if (record != null) {
// Read the chunk from the file.
if (record.timestamp != timestamp) {
return null;
}
try {
RandomAccessFile chunkFile = getChunkFile(record.chunk);
if (chunkFile != null) {
byte[] data = new byte[record.size];
chunkFile.seek(record.offset);
chunkFile.readFully(data);
return data;
}
} catch (Exception e) {
Log.e(TAG, "Unable to read from chunk file");
}
}
return null;
}
如果mIndexMap没有ALBUM_CACHE_LOCALE_INDEX这个key的数据，返回null；如果有，接着比较。如果记录的时间戳也不一致，返回null。那getChunkFile又有什么呢？
private RandomAccessFile getChunkFile(int chunk) {
RandomAccessFile chunkFile = null;
synchronized (mChunkFiles) {
chunkFile = mChunkFiles.get(chunk);
}
if (chunkFile == null) {
final String chunkFilePath = mCacheDirectoryPath + CHUNK_FILE_PREFIX + chunk;
Log.i(TAG, "DiskCache, chunkFilePath:"+chunkFilePath);
try {
chunkFile = new RandomAccessFile(chunkFilePath, "rw");
} catch (FileNotFoundException e) {
Log.e(TAG, "Unable to create or open the chunk file " + chunkFilePath);
}
synchronized (mChunkFiles) {
mChunkFiles.put(chunk, chunkFile);
}
}
return chunkFile;
}
mChunkFiles也是一个chunk映射表，local-album-cache对应的chunk文件路径对应为/Android/data/com.luowei.media/cache/local-album-cachechunk0。如果chunk文件不存在，需要建立这个文件，同时将这个文件加入mChunkFiles映射表。
回到getLocaleForAlbumCache这个函数，发现这个chunk文件的头记录语言、地区和变量代码。再返回onHandleIntent函数，如果getLocaleForAlbumCache取回的代码是空的或者跟本机的代码不一致，就需要做三件事情：
1. 将/Android/data/com.luowei.media/cache/local-album-cache目录下所有文件，其实这里面有个bug，请读者自行发现；
2. 创建chunk和index文件，并将语言、地区和变量代码写入chunk文件，这就是putLocaleForAlbumCache函数所作的事情；
3. 开启新的cache线程：startNewCacheThread。