在Android 12中，当应用程序关闭时，系统不会自动断开蓝牙低功耗（Bluetooth LE）连接。这可能会产生一些负面影响，例如浪费电池寿命、占用带宽等。

为了解决此问题，可以使用新的Bluetooth GATT连接API。使用此API，应用程序可以请求系统在特定条件下保持连接。以下是一个示例代码，演示如何保持蓝牙低功耗连接：

private BluetoothGatt mBluetoothGatt;
private BluetoothGattCallback mGattCallback = new BluetoothGattCallback() {
    // 省略其他回调方法

    @Override
    public void onConnectionStateChange(BluetoothGatt gatt, int status, int newState) {
        super.onConnectionStateChange(gatt, status, newState);

        if (newState == BluetoothProfile.STATE_CONNECTED) {
            Log.d(TAG, "Connected to GATT server.");
            gatt.requestConnectionPriority(BluetoothGatt.CONNECTION_PRIORITY_HIGH);
            gatt.discoverServices();
        } else if (newState == BluetoothProfile.STATE_DISCONNECTED) {
            Log.d(TAG, "Disconnected from GATT server.");
            mBluetoothGatt.close();
            mBluetoothGatt = null;
        }
    }

    @Override
    public void onServicesDiscovered(BluetoothGatt gatt, int status) {
        super.onServicesDiscovered(gatt, status);

        if (status == BluetoothGatt.GATT_SUCCESS) {
            BluetoothGattService service = gatt.getService(SERVICE_UUID);
            BluetoothGattCharacteristic characteristic = service.getCharacteristic(CHARACTERISTIC_UUID);
            gatt.setCharacteristicNotification(characteristic, true);

            BluetoothGattDescriptor descriptor = characteristic.getDescriptor(CLIENT_CHARACTERISTIC_CONFIG_UUID);
            descriptor.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE);
            gatt.writeDescriptor(descriptor);

            // Request to keep the connection open even when app is closed
            BluetoothGattDescriptor keepAliveDescriptor = characteristic.getDescriptor(KEEP_ALIVE_UUID);
            keepAliveDescriptor.setValue(KEEP_ALIVE_VALUE);
            gatt.writeDescriptor(keepAliveDescriptor);
        }