1.从应用中获取图片

Bitmap bitmap = BitmapFactory.decodeResource(getResources(), imageId);

2.从本地缓存中获取图片

BitmapFactory.Options bmOptions = new BitmapFactory.Options();
Bitmap bitmap = BitmapFactory.decodeFile(imagePath, bmOptions);

3.将图片写入相册

 /**
     * 保存图片至相册
     */
    public static void saveImageToGallery(Context context, Bitmap bmp) {
        // 首先保存图片
        File appDir = new File(Environment.getExternalStorageDirectory(), "云阅相册");
        if (!appDir.exists()) {
            appDir.mkdirs();
        }

        String fileName = System.currentTimeMillis() + ".jpg";
        File file = new File(appDir, fileName);
        try {
            FileOutputStream fos = new FileOutputStream(file);
            bmp.compress(Bitmap.CompressFormat.JPEG, 100, fos);

            fos.flush();
            fos.close();
        } catch (IOException e) {

            e.printStackTrace();
        }

        // 其次把文件插入到系统图库
        try {
            MediaStore.Images.Media.insertImage(context.getContentResolver(),
                    file.getAbsolutePath(), fileName, null);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        // 最后通知图库更新
        context.sendBroadcast(new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE, Uri.parse("file://" + file.getAbsoluteFile())));
    }