文件上传获取文件编码格式

文件上传获取文件编码格式：

private static String getFilecharset(InputStream inputStream) {
    //默认GBK
    String charset = "GBK";
    byte[] first3Bytes = new byte[3];
    try(BufferedInputStream bis = new BufferedInputStream(inputStream)) {
        bis.mark(0);
        int read = bis.read(first3Bytes, 0, 3);
        // 文件编码为 ANSI
        if (read == -1) {
            return charset;
        }
        // 文件编码为 Unicode
        if (first3Bytes[0] == (byte) 0xFF && first3Bytes[1] == (byte) 0xFE) {
            return  "UTF-16LE";
        }
        // 文件编码为 Unicode big endian
        if (first3Bytes[0] == (byte) 0xFE && first3Bytes[1] == (byte) 0xFF) {
            return "UTF-16BE";
        }
        // 文件编码为 UTF-8
        if (first3Bytes[0] == (byte) 0xEF && first3Bytes[1] == (byte) 0xBB && first3Bytes[2] == (byte) 0xBF) {
            return "UTF-8";
        }
        bis.reset();

        int loc = 0;
        while ((read = bis.read()) != -1) {
            loc++;
            if (read >= 0xF0) {
                break;
            }
            // 单独出现BF以下的，也算是GBK
            if (0x80 <= read && read <= 0xBF) {
                break;
            }
            if (0xC0 <= read && read <= 0xDF) {
                read = bis.read();
                // 双字节 (0xC0 - 0xDF)
                if (0x80 <= read && read <= 0xBF) {
                    // (0x80
                    // - 0xBF),也可能在GB编码内
                    continue;
                }
                break;
            }
            // 也有可能出错，但是几率较小
            if (0xE0 <= read && read <= 0xEF) {
                read = bis.read();
                if (0x80 <= read && read <= 0xBF) {
                    read = bis.read();
                    if (0x80 <= read && read <= 0xBF) {
                        charset = "UTF-8";
                    }
                }
                break;
            }
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
    return charset;
}