Android Bluetooth Low Energy Using a Gatt Server
Example
In order for your device to act as a peripheral, first you need to open a BluetoothGattServer and populate it with at least one BluetoothGattService and one BluetoothGattCharacteristic:
BluetoothGattServer server=bluetoothManager.openGattServer(context, bluetoothGattServerCallback);
BluetoothGattService service = new BluetoothGattService(SERVICE_UUID, BluetoothGattService.SERVICE_TYPE_PRIMARY);
This is an example of a BluetoothGattCharacteristic with full write,read and notify permissions. According to your needs, you might want to fine tune the permissions that you grant this characteristic:
BluetoothGattCharacteristic characteristic = new BluetoothGattCharacteristic(CHARACTERISTIC_UUID,
BluetoothGattCharacteristic.PROPERTY_READ | BluetoothGattCharacteristic.PROPERTY_WRITE |
BluetoothGattCharacteristic.PROPERTY_NOTIFY,
BluetoothGattCharacteristic.PERMISSION_READ | BluetoothGattCharacteristic.PERMISSION_WRITE);
characteristic.addDescriptor(new BluetoothGattDescriptor(UUID.fromString("00002902-0000-1000-8000-00805f9b34fb"), BluetoothGattCharacteristic.PERMISSION_WRITE));
service.addCharacteristic(characteristic);
server.addService(service);
The BluetoothGattServerCallback is responsible for receiving all events related to your BluetoothGattServer:
BluetoothGattServerCallback bluetoothGattServerCallback= new BluetoothGattServerCallback() {
@Override
public void onConnectionStateChange(BluetoothDevice device, int status, int newState) {
super.onConnectionStateChange(device, status, newState);
}
@Override
public void onCharacteristicReadRequest(BluetoothDevice device, int requestId, int offset, BluetoothGattCharacteristic characteristic) {
super.onCharacteristicReadRequest(device, requestId, offset, characteristic);
}
@Override
public void onCharacteristicWriteRequest(BluetoothDevice device, int requestId, BluetoothGattCharacteristic characteristic, boolean preparedWrite, boolean responseNeeded, int offset, byte[] value) {
super.onCharacteristicWriteRequest(device, requestId, characteristic, preparedWrite, responseNeeded, offset, value);
}
@Override
public void onDescriptorReadRequest(BluetoothDevice device, int requestId, int offset, BluetoothGattDescriptor descriptor) {
super.onDescriptorReadRequest(device, requestId, offset, descriptor);
}
@Override
public void onDescriptorWriteRequest(BluetoothDevice device, int requestId, BluetoothGattDescriptor descriptor, boolean preparedWrite, boolean responseNeeded, int offset, byte[] value) {
super.onDescriptorWriteRequest(device, requestId, descriptor, preparedWrite, responseNeeded, offset, value);
}
Whenever you receive a request for a write/read to a characteristic or descriptor you must send a response to it in order for the request to be completed succesfully :
@Override
public void onCharacteristicReadRequest(BluetoothDevice device, int requestId, int offset, BluetoothGattCharacteristic characteristic) {
super.onCharacteristicReadRequest(device, requestId, offset, characteristic);
server.sendResponse(device, requestId, BluetoothGatt.GATT_SUCCESS, offset, YOUR_RESPONSE);
}
