Android 將圖片字節數組保存為文件：FileOutputStream 完整實現

場景

通過 MediaMetadataRetriever 獲取視頻縮略圖字節數組 byte[]，需保存為本地圖片文件。

標準保存方法

public static boolean saveImageToFile(byte[] imageData, File destination) {
    if (imageData == null || imageData.length == 0) return false;
    
    FileOutputStream fos = null;
    try {
        // 確保父目錄存在
        File parent = destination.getParentFile();
        if (parent != null && !parent.exists()) {
            parent.mkdirs();
        }
        
        fos = new FileOutputStream(destination);
        fos.write(imageData);
        fos.flush(); // 確保寫入磁盤
        return true;
    } catch (IOException e) {
        e.printStackTrace();
        return false;
    } finally {
        if (fos != null) {
            try { fos.close(); } catch (IOException ignored) {}
        }
    }
}

// 使用示例
MediaMetadataRetriever mmr = new MediaMetadataRetriever();
mmr.setDataSource(videoUrl);
byte[] thumbnail = mmr.getEmbeddedPicture();
mmr.release();

if (thumbnail != null) {
    File file = new File(getExternalFilesDir(Environment.DIRECTORY_PICTURES), "thumb_" + System.currentTimeMillis() + ".jpg");
    if (saveImageToFile(thumbnail, file)) {
        // 可選：發送媒體掃描廣播，讓相冊應用識別
        MediaScannerConnection.scanFile(this, new String[]{file.getAbsolutePath()}, null, null);
    }
}

關鍵點

Java 7+ try-with-resources 簡潔寫法

public static void saveImage(byte[] data, File file) throws IOException {
    File parent = file.getParentFile();
    if (parent != null) parent.mkdirs();
    try (FileOutputStream fos = new FileOutputStream(file)) {
        fos.write(data);
    }
}

完整流程：獲取視頻縮略圖並保存

public void extractAndSaveThumbnail(String videoPath) {
    Executors.newSingleThreadExecutor().execute(() -> {
        MediaMetadataRetriever mmr = new MediaMetadataRetriever();
        try {
            mmr.setDataSource(videoPath);
            byte[] data = mmr.getEmbeddedPicture();
            if (data != null) {
                File dir = getExternalFilesDir(Environment.DIRECTORY_PICTURES);
                File file = new File(dir, "video_thumb_" + System.currentTimeMillis() + ".jpg");
                saveImageToFile(data, file);
                runOnUiThread(() -> {
                    Toast.makeText(this, "縮略圖已保存: " + file.getAbsolutePath(), Toast.LENGTH_SHORT).show();
                    MediaScannerConnection.scanFile(this, new String[]{file.getAbsolutePath()}, null, null);
                });
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            mmr.release();
        }
    });
}

總結

FileOutputStream.write(byte[]) 是核心 API。注意**異步執行、目錄創建、資源關閉、媒體掃描**，即可可靠保存圖片字節數組到文件系統。