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MiniThumbFile.javaAPI DocAndroid 5.1 API9877Thu Mar 12 22:22:30 GMT 2015android.media

MiniThumbFile

public class MiniThumbFile extends Object
This class handles the mini-thumb file. A mini-thumb file consists of blocks, indexed by id. Each block has BYTES_PER_MINTHUMB bytes in the following format: 1 byte status (0 = empty, 1 = mini-thumb available) 8 bytes magic (a magic number to match what's in the database) 4 bytes data length (LEN) LEN bytes jpeg data (the remaining bytes are unused)
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This file is shared between MediaStore and MediaProvider and should remained internal use only.

Fields Summary
private static final String
TAG
private static final int
MINI_THUMB_DATA_FILE_VERSION
public static final int
BYTES_PER_MINTHUMB
private static final int
HEADER_SIZE
private android.net.Uri
mUri
private RandomAccessFile
mMiniThumbFile
private FileChannel
mChannel
private ByteBuffer
mBuffer
private static final Hashtable
sThumbFiles
Constructors Summary
public MiniThumbFile(android.net.Uri uri)

        mUri = uri;
        mBuffer = ByteBuffer.allocateDirect(BYTES_PER_MINTHUMB);
Methods Summary
public synchronized voiddeactivate()

        if (mMiniThumbFile != null) {
            try {
                mMiniThumbFile.close();
                mMiniThumbFile = null;
            } catch (IOException ex) {
                // ignore exception
            }
        }
public synchronized longgetMagic(long id)

        // check the mini thumb file for the right data.  Right is
        // defined as having the right magic number at the offset
        // reserved for this "id".
        RandomAccessFile r = miniThumbDataFile();
        if (r != null) {
            long pos = id * BYTES_PER_MINTHUMB;
            FileLock lock = null;
            try {
                mBuffer.clear();
                mBuffer.limit(1 + 8);

                lock = mChannel.lock(pos, 1 + 8, true);
                // check that we can read the following 9 bytes
                // (1 for the "status" and 8 for the long)
                if (mChannel.read(mBuffer, pos) == 9) {
                    mBuffer.position(0);
                    if (mBuffer.get() == 1) {
                        return mBuffer.getLong();
                    }
                }
            } catch (IOException ex) {
                Log.v(TAG, "Got exception checking file magic: ", ex);
            } catch (RuntimeException ex) {
                // Other NIO related exception like disk full, read only channel..etc
                Log.e(TAG, "Got exception when reading magic, id = " + id +
                        ", disk full or mount read-only? " + ex.getClass());
            } finally {
                try {
                    if (lock != null) lock.release();
                }
                catch (IOException ex) {
                    // ignore it.
                }
            }
        }
        return 0;
public synchronized byte[]getMiniThumbFromFile(long id, byte[] data)
Gallery app can use this method to retrieve mini-thumbnail. Full size images share the same IDs with their corresponding thumbnails.

param
id the ID of the image (same of full size image).
param
data the buffer to store mini-thumbnail.

        RandomAccessFile r = miniThumbDataFile();
        if (r == null) return null;

        long pos = id * BYTES_PER_MINTHUMB;
        FileLock lock = null;
        try {
            mBuffer.clear();
            lock = mChannel.lock(pos, BYTES_PER_MINTHUMB, true);
            int size = mChannel.read(mBuffer, pos);
            if (size > 1 + 8 + 4) { // flag, magic, length
                mBuffer.position(0);
                byte flag = mBuffer.get();
                long magic = mBuffer.getLong();
                int length = mBuffer.getInt();

                if (size >= 1 + 8 + 4 + length && length != 0 && magic != 0 && flag == 1 &&
                        data.length >= length) {
                    mBuffer.get(data, 0, length);
                    return data;
                }
            }
        } catch (IOException ex) {
            Log.w(TAG, "got exception when reading thumbnail id=" + id + ", exception: " + ex);
        } catch (RuntimeException ex) {
            // Other NIO related exception like disk full, read only channel..etc
            Log.e(TAG, "Got exception when reading thumbnail, id = " + id +
                    ", disk full or mount read-only? " + ex.getClass());
        } finally {
            try {
                if (lock != null) lock.release();
            }
            catch (IOException ex) {
                // ignore it.
            }
        }
        return null;
public static synchronized android.media.MiniThumbFileinstance(android.net.Uri uri)

        String type = uri.getPathSegments().get(1);
        MiniThumbFile file = sThumbFiles.get(type);
        // Log.v(TAG, "get minithumbfile for type: "+type);
        if (file == null) {
            file = new MiniThumbFile(
                    Uri.parse("content://media/external/" + type + "/media"));
            sThumbFiles.put(type, file);
        }

        return file;
private java.io.RandomAccessFileminiThumbDataFile()

        if (mMiniThumbFile == null) {
            removeOldFile();
            String path = randomAccessFilePath(MINI_THUMB_DATA_FILE_VERSION);
            File directory = new File(path).getParentFile();
            if (!directory.isDirectory()) {
                if (!directory.mkdirs()) {
                    Log.e(TAG, "Unable to create .thumbnails directory "
                            + directory.toString());
                }
            }
            File f = new File(path);
            try {
                mMiniThumbFile = new RandomAccessFile(f, "rw");
            } catch (IOException ex) {
                // Open as read-only so we can at least read the existing
                // thumbnails.
                try {
                    mMiniThumbFile = new RandomAccessFile(f, "r");
                } catch (IOException ex2) {
                    // ignore exception
                }
            }
            if (mMiniThumbFile != null) {
                mChannel = mMiniThumbFile.getChannel();
            }
        }
        return mMiniThumbFile;
private java.lang.StringrandomAccessFilePath(int version)

        String directoryName =
                Environment.getExternalStorageDirectory().toString()
                + "/DCIM/.thumbnails";
        return directoryName + "/.thumbdata" + version + "-" + mUri.hashCode();
private voidremoveOldFile()

        String oldPath = randomAccessFilePath(MINI_THUMB_DATA_FILE_VERSION - 1);
        File oldFile = new File(oldPath);
        if (oldFile.exists()) {
            try {
                oldFile.delete();
            } catch (SecurityException ex) {
                // ignore
            }
        }
public static synchronized voidreset()
We store different types of thumbnails in different files. To remain backward compatibility, we should hashcode of content://media/external/images/media remains the same.


                              
         
        for (MiniThumbFile file : sThumbFiles.values()) {
            file.deactivate();
        }
        sThumbFiles.clear();
public synchronized voidsaveMiniThumbToFile(byte[] data, long id, long magic)

        RandomAccessFile r = miniThumbDataFile();
        if (r == null) return;

        long pos = id * BYTES_PER_MINTHUMB;
        FileLock lock = null;
        try {
            if (data != null) {
                if (data.length > BYTES_PER_MINTHUMB - HEADER_SIZE) {
                    // not enough space to store it.
                    return;
                }
                mBuffer.clear();
                mBuffer.put((byte) 1);
                mBuffer.putLong(magic);
                mBuffer.putInt(data.length);
                mBuffer.put(data);
                mBuffer.flip();

                lock = mChannel.lock(pos, BYTES_PER_MINTHUMB, false);
                mChannel.write(mBuffer, pos);
            }
        } catch (IOException ex) {
            Log.e(TAG, "couldn't save mini thumbnail data for "
                    + id + "; ", ex);
            throw ex;
        } catch (RuntimeException ex) {
            // Other NIO related exception like disk full, read only channel..etc
            Log.e(TAG, "couldn't save mini thumbnail data for "
                    + id + "; disk full or mount read-only? " + ex.getClass());
        } finally {
            try {
                if (lock != null) lock.release();
            }
            catch (IOException ex) {
                // ignore it.
            }
        }