在Android中，可以使用BluetoothGattServer类来实现一个BLE服务器，并通过使用BluetoothDevice对象和MAC地址来确定允许连接的设备。以下是实现这个功能的示例代码：

首先，在你的Android项目中创建一个新的Java类，名为BleServerManager，并添加以下代码：

public class BleServerManager {
    private BluetoothGattServer mGattServer;
    private BluetoothManager mBluetoothManager;
    private BluetoothAdapter mBluetoothAdapter;
    private Context mContext;

    public BleServerManager(Context context) {
        mContext = context;
        mBluetoothManager = (BluetoothManager) mContext.getSystemService(Context.BLUETOOTH_SERVICE);
        mBluetoothAdapter = mBluetoothManager.getAdapter();
    }

    public void startServer() {
        BluetoothGattServerCallback gattServerCallback = new BluetoothGattServerCallback() {
            @Override
            public void onConnectionStateChange(BluetoothDevice device, int status, int newState) {
                if (newState == BluetoothProfile.STATE_CONNECTED) {
                    // 检查设备是否是你允许连接的设备
                    if (isAllowedDevice(device)) {
                        // 设备是允许连接的设备，执行你的操作
                    } else {
                        // 设备不是允许连接的设备，断开连接
                        mGattServer.cancelConnection(device);
                    }
                }
            }
        };

        mGattServer = mBluetoothManager.openGattServer(mContext, gattServerCallback);
        if (mGattServer == null) {
            // 无法打开Gatt服务器
            return;
        }

        // 添加Gatt服务和特征
        BluetoothGattService service = new BluetoothGattService(YOUR_SERVICE_UUID, BluetoothGattService.SERVICE_TYPE_PRIMARY);
        BluetoothGattCharacteristic characteristic = new BluetoothGattCharacteristic(YOUR_CHARACTERISTIC_UUID, BluetoothGattCharacteristic.PROPERTY_READ | BluetoothGattCharacteristic.PROPERTY_WRITE, BluetoothGattCharacteristic.PERMISSION_READ | BluetoothGattCharacteristic.PERMISSION_WRITE);
        service.addCharacteristic(characteristic);
        mGattServer.addService(service);

        // 开启Gatt服务器
        advertiseGattServer();
    }

    private boolean isAllowedDevice(BluetoothDevice device) {
        // 根据设备的MAC地址或其他标识来确定是否允许连接
        String allowedDeviceMacAddress = "00:00:00:00:00:00";
        return device.getAddress().equals(allowedDeviceMacAddress);
    }

    private void advertiseGattServer() {
        BluetoothLeAdvertiser advertiser = mBluetoothAdapter.getBluetoothLeAdvertiser();
        if (advertiser == null) {
            // 无法获取广播器
            return;
        }

        AdvertiseSettings settings = new AdvertiseSettings.Builder()
                .setAdvertiseMode(AdvertiseSettings.ADVERTISE_MODE_LOW_LATENCY)
                .setConnectable(true)
                .build();

        AdvertiseData data = new AdvertiseData.Builder()
                .setIncludeDeviceName(true)
                .setIncludeTxPowerLevel(true)
                .addServiceUuid(new ParcelUuid(YOUR_SERVICE_UUID))
                .build();

        advertiser.startAdvertising(settings, data, mAdvertiseCallback);
    }

    private AdvertiseCallback mAdvertiseCallback = new AdvertiseCallback() {
        @Override
        public void onStartSuccess(AdvertiseSettings settingsInEffect) {
            // 广播成功开始
        }

        @Override
        public void onStartFailure(int errorCode) {
            // 广播开始失败
        }
    };
}

请注意，上面的代码示例中使用了YOUR_SERVICE_UUID和YOUR_CHARACTERISTIC_UUID，你需要将其替换为你自己的服务和特征的UUID。

然后，在你的Activity或Fragment中实例化BleServerManager类并调用startServer()方法来启动BLE服务器：

BleServerManager bleServerManager = new BleServerManager(this);
bleServerManager.startServer();

以上代码将启动BLE服务器，并在设备连接时检查设备的MAC地址是否是允许连接的设备。如果设备是允许连接的设备，你可以在onConnectionStateChange()方法中执行你的操作。如果设备不是允许连接的设备，服务器将断开与设备的连接。