BlueNRG2 - which call back? for write characteristic

i am writing an andriod app, i am wondering which call back of BlueNRG2 will respond after the following codes of app?

BluetoothGattService gattService =

bluetooth_gatt.getService(java.util.UUID.fromString(serviceUuid));

BluetoothGattCharacteristic gattChar = gattService

.getCharacteristic(java.util.UUID.fromString(characteristicUuid));

gattChar.setValue(value);

bluetooth_gatt.writeCharacteristic(gattChar);