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Android example source code file (MiniThumbFile.java)

This example Android source code file (MiniThumbFile.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Android by Example" TM.

Java - Android tags/keywords

android, bytes_per_minthumb, filechannel, filelock, got, hashtable, header_size, io, ioexception, mini_thumb_data_file_version, minithumbfile, net, network, os, randomaccessfile, runtimeexception, securityexception, string, uri, util

The MiniThumbFile.java Android example source code

/*
 * Copyright (C) 2009 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 android.media;

import android.graphics.Bitmap;
import android.net.Uri;
import android.os.Environment;
import android.util.Log;

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
import java.util.Hashtable;

/**
 * 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)
 *
 * @hide This file is shared between MediaStore and MediaProvider and should remained internal use
 *       only.
 */
public class MiniThumbFile {
    private static final String TAG = "MiniThumbFile";
    private static final int MINI_THUMB_DATA_FILE_VERSION = 3;
    public static final int BYTES_PER_MINTHUMB = 10000;
    private static final int HEADER_SIZE = 1 + 8 + 4;
    private Uri mUri;
    private RandomAccessFile mMiniThumbFile;
    private FileChannel mChannel;
    private ByteBuffer mBuffer;
    private static Hashtable<String, MiniThumbFile> sThumbFiles =
        new Hashtable<String, MiniThumbFile>();

    /**
     * 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.
     */
    public static synchronized void reset() {
        for (MiniThumbFile file : sThumbFiles.values()) {
            file.deactivate();
        }
        sThumbFiles.clear();
    }

    public static synchronized MiniThumbFile instance(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 String randomAccessFilePath(int version) {
        String directoryName =
                Environment.getExternalStorageDirectory().toString()
                + "/DCIM/.thumbnails";
        return directoryName + "/.thumbdata" + version + "-" + mUri.hashCode();
    }

    private void removeOldFile() {
        String oldPath = randomAccessFilePath(MINI_THUMB_DATA_FILE_VERSION - 1);
        File oldFile = new File(oldPath);
        if (oldFile.exists()) {
            try {
                oldFile.delete();
            } catch (SecurityException ex) {
                // ignore
            }
        }
    }

    private RandomAccessFile miniThumbDataFile() {
        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;
    }

    public MiniThumbFile(Uri uri) {
        mUri = uri;
        mBuffer = ByteBuffer.allocateDirect(BYTES_PER_MINTHUMB);
    }

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

    // Get the magic number for the specified id in the mini-thumb file.
    // Returns 0 if the magic is not available.
    public synchronized long getMagic(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 void saveMiniThumbToFile(byte[] data, long id, long magic)
            throws IOException {
        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.
            }
        }
    }

    /**
     * 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.
     */
    public synchronized byte [] getMiniThumbFromFile(long id, byte [] data) {
        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 && 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;
    }
}

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