Примечание

Это не рекомендуется, так как оно все еще будет весьма неэффективным по сравнению с сохранением пути к файлу изображения.

Очевидный ответ - разделить изображение на управляемые части (чанки)

• (скажем, 256k чанков (14 таких чанков будут занимать около 3,5 Мб)) [1117 ]

, позволяя собирать отдельные блоки при необходимости.

Простой пример

• Этот пример иллюстрирует как сохранение, получение, сборку и отображение изображения, которое будет слишком большим (около 3,5 МБ).

• Чтобы сделать основное изображение легкодоступным, оно было помещено в папку ресурсов и затем скопировано приложением в данные приложения (data / data / myimages /) (вместо того, чтобы писать дополнительный код, скажем, использовать камеру).

  • 

• используются две таблицы

  • таблица с именем imagemaster , для данных единственного изображения, например это имя и
  • вторая таблица с именем imagechunk для блоков, каждый из которых ссылается на соответствующую строку в таблице imagemaster.

DatabaseHelper DBHelper.java: -

public class DBHelper extends SQLiteOpenHelper {

    public static final String DBNAME = "mydb";
    public static final int DBVERSION = 1;

    public static final String TBL_IMAGEMASTER = "image_matser";
    public static final String COL_IMAGEMASTER_ID = BaseColumns._ID;
    public static final String COL_IMAGEMASTER_DESCRIPTION = "description";
    public static final String COL_IMAGEMASTER_THUMBNAIL = "thumbnail";

    public static final String TBL_IMAGECHUNK = "imagechunk";
    public static final String COL_IMAGECHUNK_ID = BaseColumns._ID;
    public static final String COL_IMAGECHUNK_OWNER = "owner";
    public static final String COL_IMAGECHUNK_CHUNK = "chunk";
    public static final String COL_IMAGECHUNK_CHUNKORDER = "chunkorder";
    public static final String COL_IMAGECHUNK_CHUNKSIZE = "chunksize";

    public static final int MAXIMUM_CHUNK_SIZE = 256 * 1024; // 256k chunks

    // Some codes for when/if things go wrong
    public static final long NOSUCHFILE = -2;
    public static final long INPUT_ASSIGN_IO_ERROR = -3;
    public static final long INPUT_READ_IO_ERROR = -4;
    public static final long CHUNKCOUNTMISMATCH = -5;

    SQLiteDatabase mDB;

    public DBHelper(Context context) {
        super(context, DBNAME, null, DBVERSION);
        mDB = this.getWritableDatabase(); //Open the database
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        // The imagemaster table
        String mImageMasterCrtSQL = "CREATE TABLE IF NOT EXISTS " + TBL_IMAGEMASTER + "(" +
                COL_IMAGEMASTER_ID + " INTEGER PRIMARY KEY, " +
                COL_IMAGEMASTER_DESCRIPTION + " TEXT UNIQUE, " +
                COL_IMAGEMASTER_THUMBNAIL + " BLOB DEFAULT x'00' " +
                ")";
        db.execSQL(mImageMasterCrtSQL);

        // The imagechunk table
        String mImageChunkCrtSQL = "CREATE TABLE IF NOT EXISTS " + TBL_IMAGECHUNK + "(" +
                COL_IMAGECHUNK_ID + " INTEGER PRIMARY KEY, " +
                COL_IMAGECHUNK_OWNER + " INTEGER REFERENCES " + TBL_IMAGEMASTER + "(" +
                COL_IMAGEMASTER_ID +
                ")," +
                COL_IMAGECHUNK_CHUNKORDER + " INTEGER, " +
                COL_IMAGECHUNK_CHUNKSIZE + " INTEGER, " +
                COL_IMAGECHUNK_CHUNK + " BLOB DEFAULT x'00'" +
                ")";
        db.execSQL(mImageChunkCrtSQL);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }

    // Need to turn on FOREIGN KEY support
    @Override
    public void onConfigure(SQLiteDatabase db) {
        super.onConfigure(db);
        db.setForeignKeyConstraintsEnabled(true);
    }

    // Add an imagemaster row (private as imagemaster row and imagechunk rows are to be added together)
    private long addImageMaster(String description, byte[] thumbnail) {
        ContentValues cv = new ContentValues();
        cv.put(COL_IMAGEMASTER_DESCRIPTION,description);
        if (thumbnail.length > 0) {
            cv.put(COL_IMAGEMASTER_THUMBNAIL,thumbnail);
        }
        return mDB.insert(TBL_IMAGEMASTER,null,cv);
    }

    // Add an imagechunk row (private as imagemaster and imagechucks will be added togther)
    private long addImageChunk(long owningImage, long order, byte[] image) {
        ContentValues cv = new ContentValues();
        cv.put(COL_IMAGECHUNK_OWNER,owningImage);
        cv.put(COL_IMAGECHUNK_CHUNKORDER,order);
        cv.put(COL_IMAGECHUNK_CHUNKSIZE,image.length);
        cv.put(COL_IMAGECHUNK_CHUNK,image);
        return mDB.insert(TBL_IMAGECHUNK,null,cv);
    }

    // Add imagemaster and all imagechunk rows from a File
    public long storeImageFromFile(String description, File image, byte[] thumbnail, boolean printstacktrace) {
        long rv = NOSUCHFILE;
        long master_id;
        if (!image.exists()) {
            return rv;
        }

        //Get image info from file
        long chunkcount = (image.length() / (long) MAXIMUM_CHUNK_SIZE);
        if ((image.length() - (chunkcount * (long) MAXIMUM_CHUNK_SIZE)) > 0) {
            chunkcount++;
        }
        // Add the image master row
        rv = addImageMaster(description, thumbnail);
        if (rv < 1) {
            return rv;
        }
        master_id = rv;
        // Prepare to save chunks
        byte[] buffer = new byte[MAXIMUM_CHUCK_SIZE];
        int currentchunk = 0;
        int readlength = 0;
        rv = INPUT_ASSIGN_IO_ERROR;
        long chunksavedcount = 0;
        try {
            InputStream is = new FileInputStream(image);
            rv = INPUT_READ_IO_ERROR;
            while ((readlength = is.read(buffer)) > 0) {
                if (readlength == MAXIMUM_CHUNK_SIZE) {
                    if (addImageChunk(master_id, currentchunk++, buffer) > 0) {
                        chunksavedcount++;
                    }
                } else {
                    byte[] lastbuffer = new byte[readlength];
                    for (int i = 0; i < readlength; i++) {
                        lastbuffer[i] = buffer[i];
                    }
                    if (addImageChunk(master_id, currentchunk, lastbuffer) > 0) {
                        chunksavedcount++;
                    }
                }
            }
            is.close();
        } catch (IOException ioe) {
            if (printstacktrace) {
                ioe.printStackTrace();
            }
            return rv;
        }
        if (chunksavedcount != chunkcount) {
            rv = CHUNKCOUNTMISMATCH;
        }
        return rv;
    }

    //Get the image as a byte array (could easily return a BitMap) according to the image description
    public byte[] getAllChunksAsByteArray(String imageDescription) {
        String column_chucksize_sum = "chuck_size_sum";
        long master_id = -1;
        int imagesize = 0;

        //Stage 1 get the image master id according to the description
        String[] columns = new String[]{COL_IMAGEMASTER_ID};
        String whereclause = COL_IMAGEMASTER_DESCRIPTION  + "=?";
        String[] whereargs = new String[]{imageDescription};
        Cursor csr = mDB.query(TBL_IMAGEMASTER,columns,whereclause,whereargs,null,null,null,null);
        if (csr.moveToFirst()) {
            master_id = csr.getLong(csr.getColumnIndex(COL_IMAGEMASTER_ID));
        }
        //If no such image then return empty byte array
        if (master_id < 1) {
            csr.close();
            return new byte[0];
        }

        // Stage 2 get the total size of the image
        columns = new String[]{"sum(" + COL_IMAGECHUNK_CHUNKSIZE + ") AS " + column_chucksize_sum};
        whereclause = COL_IMAGECHUNK_OWNER + "=?";
        whereargs = new String[]{String.valueOf(master_id)};
        csr = mDB.query(TBL_IMAGECHUNK,columns,whereclause,whereargs,null,null,COL_IMAGECHUNK_CHUNKORDER + " ASC");
        if (csr.moveToFirst()) {
            imagesize = csr.getInt(csr.getColumnIndex(column_chucksize_sum));
        }
        //If no chunks or all chunks are empty return empty byte array
        if (imagesize < 1) {
            csr.close();
            return new byte[0];
        }

        //Stage 3 combine all the chunks into a single byte array
        columns = new String[]{COL_IMAGECHUNK_CHUNK, COL_IMAGECHUNK_CHUNKSIZE};
        csr = mDB.query(TBL_IMAGECHUNK,columns,whereclause,whereargs,null,null,COL_IMAGECHUNK_CHUNKORDER + " ASC");
        if (csr.getCount() < 1) {
            csr.close();
            return new byte[0];
        }
        int rv_offset = 0;
        byte[] rv = new byte[imagesize];
        while (csr.moveToNext()) {
            int currentsize = csr.getInt(csr.getColumnIndex(COL_IMAGECHUNK_CHUNKSIZE));
            byte[] thischunk = csr.getBlob(csr.getColumnIndex(COL_IMAGECHUNK_CHUNK));
            for (int i = 0; i < thischunk.length; i++) {
                rv[rv_offset + i] = thischunk[i];
            }
            rv_offset = rv_offset + currentsize;
        }
        csr.close();
        return rv;
    }
}

Активность MainActivity.java

public class MainActivity extends AppCompatActivity {

    DBHelper mDBHlpr; //The database helper
    ImageView mMyImageView; //For displaying the image (initially nothing shown)
    Button mTestIt; //Button that will retrieve the image from the DB and display it
    String mSaveDirectory = "myimages"; //The directory in which to save the image file
    byte[] extracted_image; //For the retrieved image


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mMyImageView = this.findViewById(R.id.myimageview);
        mTestIt = this.findViewById(R.id.testit);
        mTestIt.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                showimage(extracted_image); //<<<<<<<<<< extract the image and display it.
            }
        });

        mDBHlpr = new DBHelper(this); //<<<<<<<<<< instantiate the Database Helper

        String testfilename = "20141107 1924 SCC Bedroom.JPG"; //The file to get from the assets folder
        String testdescription = "MyTestImage"; //The description to give the image

        //1. copy the file from the assets folder e.g. akin to taking photo from camera
        File testfile = new File(saveAssetAsFile(testfilename));

        //2. Add the image and the chucks to the DB
        mDBHlpr.storeImageFromFile(testdescription,testfile,new byte[]{0,1,2,3,4,5,6},true);

        //3. Extract the rows and write them to the log
        Cursor csr = mDBHlpr.getWritableDatabase().query(DBHelper.TBL_IMAGEMASTER,null,null,null,null,null,null);
        DatabaseUtils.dumpCursor(csr);
        csr = mDBHlpr.getWritableDatabase().query(DBHelper.TBL_IMAGECHUNK,null,null,null,null,null,null);
        DatabaseUtils.dumpCursor(csr);
        csr.close();

        //4. extract the byte array for the image display the length of the byte array
        extracted_image = mDBHlpr.getAllChunksAsByteArray(testdescription);
        Log.d("EXTRACTED","The extracted image size is " + String.valueOf(extracted_image.length));
    }


    //Copy the asset to a file
    private String saveAssetAsFile(String asset) {

        //For ease use data/data//myimages to save the image as a file
        //Note a bit of a cheat as getDatabasePath will return  data/data//databases/xxx (or equivalent)
        //GetDatabasepath available for all Android versions
        String filepath = this.getDatabasePath("xxx").getParentFile().getParent() + File.separator + mSaveDirectory + File.separator + asset;
        File savelocation = new File(filepath);

        //If the file exists then no need to copy again so return
        if (savelocation.exists()) return savelocation.getPath();
        //Create the myimages directory if needed (will be required first run)
        if (!savelocation.getParentFile().exists()) {
            savelocation.getParentFile().mkdirs();
        }
        byte[] buffer = new byte[DBHelper.MAXIMUM_CHUNK_SIZE]; //Use 256k buffer as size is defined
        int buffer_length;
        try {
            InputStream is = this.getAssets().open(asset);
            FileOutputStream os = new FileOutputStream(savelocation);
            while ((buffer_length = is.read(buffer)) > 0) {
                os.write(buffer,0,buffer_length);
            }
            os.flush();
            os.close();
            is.close();

        } catch (IOException ioe) {
            ioe.printStackTrace();
        }
        return savelocation.getPath();
    }

    private void showimage(byte[] imagetoshow) {
        Bitmap bmp = BitmapFactory.decodeByteArray(imagetoshow, 0, imagetoshow.length);
        mMyImageView.setImageBitmap(bmp);
    }
}

Результат

Когда Приложение запускается (без изображения): -

После нажатия кнопки: -

Изображение извлекается из БД

Журнал: -

........
03-24 16:44:36.416 22859-22859/aaa.so55276671hiddenimages I/System.out: 13 {
03-24 16:44:36.416 22859-22859/aaa.so55276671hiddenimages I/System.out:    _id=14
03-24 16:44:36.416 22859-22859/aaa.so55276671hiddenimages I/System.out:    owner=1
03-24 16:44:36.416 22859-22859/aaa.so55276671hiddenimages I/System.out:    chunkorder=13
03-24 16:44:36.416 22859-22859/aaa.so55276671hiddenimages I/System.out:    chunksize=97210
03-24 16:44:36.416 22859-22859/aaa.so55276671hiddenimages I/System.out:    chunk=
03-24 16:44:36.416 22859-22859/aaa.so55276671hiddenimages I/System.out: }
03-24 16:44:36.416 22859-22859/aaa.so55276671hiddenimages I/System.out: <<<<<
03-24 16:44:36.423 22859-22859/aaa.so55276671hiddenimages W/CursorWindow: Window is full: requested allocation 262144 bytes, free space 261532 bytes, window size 2097152 bytes
03-24 16:44:36.441 22859-22859/aaa.so55276671hiddenimages W/CursorWindow: Window is full: requested allocation 262144 bytes, free space 261532 bytes, window size 2097152 bytes
03-24 16:44:36.453 22859-22859/aaa.so55276671hiddenimages D/EXTRACTED: The extracted image size is 3505082

........... click the button

03-24 16:50:09.565 22859-22859/aaa.so55276671hiddenimages D/BEFOREEXTRACT: Button clicked so extracting image.
03-24 16:50:09.583 22859-22872/aaa.so55276671hiddenimages I/art: Background sticky concurrent mark sweep GC freed 1882(116KB) AllocSpace objects, 7(1631KB) LOS objects, 0% free, 65MB/65MB, paused 6.779ms total 17.678ms
03-24 16:50:09.765 22859-22859/aaa.so55276671hiddenimages D/AFTEREXTRACT: Finished extracting the image.

• Обратите внимание, полные сообщения CursorWindow не являются сбои, скорее просто сказать, что была сделана попытка добавить строку, но она была полной.
• ПРЕДУПРЕЖДЕНИЕ Как видно, для 5 таких изображений потребуется 1 секунда на извлечение и отображение