java 通過圖片的Base64字符串判斷文件格式

	/** * base64字符串轉寫為文件 * * @param base64ImgData * @param filePath * @throws IOException */
	public static void convertBase64DataToImage(String base64ImgData, String filePath) throws IOException {
		Files.write(Paths.get(filePath), Base64.getDecoder().decode(base64ImgData), StandardOpenOption.CREATE);
	}

	/** * 將文件轉寫為base64字符串 * * @param filePath * @return * @throws IOException */
	public static String convertImageToBase64Data(String filePath) throws IOException {
		byte[] b = Files.readAllBytes(Paths.get(filePath));
		return Base64.getEncoder().encodeToString(b);
	}

	/** * 判斷圖片base64字符串的文件格式 * * @param base64ImgData * @return */
	public static String checkImageBase64Format(String base64ImgData) {
		byte[] b = Base64.getDecoder().decode(base64ImgData);
		String type = "";
		if (0x424D == ((b[0] & 0xff) << 8 | (b[1] & 0xff))) {
			type = "bmp";
		} else if (0x8950 == ((b[0] & 0xff) << 8 | (b[1] & 0xff))) {
			type = "png";
		} else if (0xFFD8 == ((b[0] & 0xff) << 8 | (b[1] & 0xff))) {
			type = "jpg";
		}
		return type;
	}