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藍牙（ Bluetooth? ）：是一種無線技術標準，可實現固定設備、移動設備和樓宇個人域網之間的短距離數據交換（使用2.4—2.485GHz的ISM波段的UHF無線電波）。藍牙技術最初由電信巨頭愛立信公司於1994年創制，當時是作為RS232數據線的替代方案。藍牙可連接多個設備，克服了數據同步的難題。 如今藍牙由藍牙技術聯盟（Bluetooth Special Interest Group，簡稱SIG）管理。藍牙技術聯盟在全球擁有超過25,000家成員公司，它們分布在電信、計算機、網絡、和消費電子等多重領域。IEEE將藍牙技術列為IEEE 802.15.1，但如今已不再維持該標準。藍牙技術聯盟負責監督藍牙規範的開發，管理認證項目，並維護商標權益。制造商的設備必須符合藍牙技術聯盟的標準才能以“藍牙設備”的名義進入市場。藍牙技術擁有一套專利網絡，可發放給符合標準的設備。 一、藍牙的分類

　　目前為止藍牙分為兩類：一是經典藍牙（傳統藍牙），二是低功耗藍牙（BLE）。顧名思義低功耗藍牙功耗要比傳統藍牙低，所以廣泛使用在智能穿戴設備上。要使安卓設備連接上智能穿戴設備（如智能手表），通過經典藍牙的socket連接一般是連接不上的（為什麽說一般呢，因為有些不良廠家和雜牌智能手環用的不是低功耗藍牙，這個可以使用經典藍牙連接上），必須要使用BLE的 GATT連接才能連接上。 二、GATT中的服務、特征值、描述、UUID 　　GATT連接涉及到四個比較陌生的名詞：服務（service）、特征值（Characteristic）、描述（discript）、UUID，下面以智能手環為例分別來解釋一下這些名詞是什麽意思。

• service：服務是包含了若幹個數據包（特征值）的集合，一個智能設備可能包含多個服務，使用之恩那個設備生產廠商提供的UUID碼來識別。比如之恩那個手環中有測心率的服務、步數的服務，心率和步數的數據包（特征值）都包含在服務中，通過指定的UUID來辨別到底是心率的服務還是步數的服務。
• characteristic：特征值包含在服務裏面，顧名思義就是一種數據值，特征值包含一個或者多個描述。如心率是多少，今天走了多少步都可以放進特征值裏面，服務中有多個特征值，也是通過UUID來識別
• discript：描述一般是對特征值的值進行描述，比如單位等等的描述，開發中一般用不到（我用不到）
• UUID：由藍牙設備廠商提供的UUID，UUID是在硬件編程裏已經確定了的，想要草所特定的服務、特征值都需要通過UUID來找。

三、安卓中GATT的操作

　　和經典藍牙最開始一樣，要檢測藍牙是否可用和藍牙是否打開，這部分代碼就不貼出來了。

　　一般操作GATT的教程都把操作放在安卓的server裏面，具體原因還請大神指教。下面的server代碼可以直接當作操作GATT的模板來使用，大部分都是些回調函數和對服務、特征值進行操作的方法：

public class UartService extends Service {
    private final static String TAG = UartService.class.getSimpleName();
    List<BluetoothGattService> serviceList = new ArrayList<BluetoothGattService>();//發現的服務列表

    private BluetoothAdapter mBluetoothAdapter;//本地藍牙適配器
    private String mBluetoothDeviceAddress;//本地藍牙MAC地址
    private BluetoothGatt mBluetoothGatt;//GTAA
    /**
     * 假設生產商提供了一個服務，該服務裏面有兩個特征值
     */
    private BluetoothGattService mBluetoothGattService;//gatt服務
    private BluetoothGattCharacteristic mBluetoothGattCharacteristic1;//gatt特征值1
    private BluetoothGattCharacteristic mBluetoothGattCharacteristic2;//gatt特征值2
    private int mConnectionState = STATE_DISCONNECTED;

    //連接狀態常量
    private static final int STATE_DISCONNECTED = 0;
    private static final int STATE_CONNECTING = 1;
    private static final int STATE_CONNECTED = 2;

    //藍牙廠商提供的UUID
    private static final UUID UUID_SERVICE = UUID.fromString("0000fff0-0000-1000-8000-00805f9b34fb"); //服務
    private static final UUID UUID_CHARA1 = UUID.fromString("0000fff1-0000-1000-8000-00805f9b34fb"); //特征值1
    private static final UUID UUID_CHARA2 = UUID.fromString("0000fff4-0000-1000-8000-00805f9b34fb"); //特征值2
    

    // Implements callback methods for GATT events that the app cares about.  For example,
    // connection change and services discovered.
    private final BluetoothGattCallback mGattCallback = new BluetoothGattCallback() {
        @Override
        public void onConnectionStateChange(BluetoothGatt gatt, int status, int newState) {
            if (newState == BluetoothProfile.STATE_CONNECTED) {
                mConnectionState = STATE_CONNECTED;
                Log.i(TAG, "Connected to GATT server.");
                // Attempts to discover services after successful connection.
                Log.i(TAG, "Attempting to start service discovery:" +
                        mBluetoothGatt.discoverServices());
            } else if (newState == BluetoothProfile.STATE_DISCONNECTED) {
                mConnectionState = STATE_DISCONNECTED;
                Log.i(TAG, "Disconnected from GATT server.");
            }
        }

        @Override
        public void onServicesDiscovered(BluetoothGatt gatt, int status) {//服務被發現
            if (status == BluetoothGatt.GATT_SUCCESS) {
                System.out.println("Service has bean discover.");
                mBluetoothGattService = gatt.getService(UUID_SERVICE);//發現服務
            } else {
                Log.w(TAG, "onServicesDiscovered received: " + status);
            }
        }

        @Override
        public void onCharacteristicRead(BluetoothGatt gatt,
                                         BluetoothGattCharacteristic characteristic,
                                         int status) {
            if (status == BluetoothGatt.GATT_SUCCESS) {
                Utiles.setData(characteristic);
            }
        }

        @Override
        public void onCharacteristicWrite(BluetoothGatt gatt,
                                          BluetoothGattCharacteristic characteristic,
                                          int status) {
        }

        @Override
        public void onCharacteristicChanged(BluetoothGatt gatt,
                                            BluetoothGattCharacteristic characteristic) {
        }
    };


    public class LocalBinder extends Binder {
        UartService getService() {
            return UartService.this;
        }
    }

    @Override
    public IBinder onBind(Intent intent) {
        return mBinder;
    }

    @Override
    public boolean onUnbind(Intent intent) {
        // After using a given device, you should make sure that BluetoothGatt.close() is called
        // such that resources are cleaned up properly.  In this particular example, close() is
        // invoked when the UI is disconnected from the Service.
        close();
        return super.onUnbind(intent);
    }

    private final IBinder mBinder = new LocalBinder();

    /**
     * Initializes a reference to the local Bluetooth adapter.
     *
     * @return Return true if the initialization is successful.
     */
    public boolean initialize() {//初始化
        // For API level 18 and above, get a reference to BluetoothAdapter through
        // BluetoothManager.
        mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
        if (mBluetoothAdapter == null) {
            Log.e(TAG, "Unable to obtain a BluetoothAdapter.");
            return false;
        }

        return true;
    }

    /**
     * Connects to the GATT server hosted on the Bluetooth LE device.
     *
     * @param address The device address of the destination device.
     *
     * @return Return true if the connection is initiated successfully. The connection result
     *         is reported asynchronously through the
     *         {@code BluetoothGattCallback#onConnectionStateChange(android.bluetooth.BluetoothGatt, int, int)}
     *         callback.
     */
    public boolean connect(final String address) {//連接服務
        if (mBluetoothAdapter == null || address == null) {
            Log.w(TAG, "BluetoothAdapter not initialized or unspecified address.");
            return false;
        }

        // Previously connected device.  Try to reconnect.
        if (mBluetoothDeviceAddress != null && address.equals(mBluetoothDeviceAddress)
                && mBluetoothGatt != null) {
            Log.d(TAG, "Trying to use an existing mBluetoothGatt for connection.");
            if (mBluetoothGatt.connect()) {
                mConnectionState = STATE_CONNECTING;
                return true;
            } else {
                return false;
            }
        }

        final BluetoothDevice device = mBluetoothAdapter.getRemoteDevice(address);
        if (device == null) {
            Log.w(TAG, "Device not found.  Unable to connect.");
            return false;
        }
        // We want to directly connect to the device, so we are setting the autoConnect
        // parameter to false.
        mBluetoothGatt = device.connectGatt(this, false, mGattCallback);
        Log.d(TAG, "Trying to create a new connection.");
        mBluetoothDeviceAddress = address;
        mConnectionState = STATE_CONNECTING;
        return true;
    }

    /**
     * Disconnects an existing connection or cancel a pending connection. The disconnection result
     * is reported asynchronously through the
     * {@code BluetoothGattCallback#onConnectionStateChange(android.bluetooth.BluetoothGatt, int, int)}
     * callback.
     */
    public void disconnect() {
        if (mBluetoothAdapter == null || mBluetoothGatt == null) {
            Log.w(TAG, "BluetoothAdapter not initialized");
            return;
        }
        mBluetoothGatt.disconnect();
    }

    /**
     * After using a given BLE device, the app must call this method to ensure resources are
     * released properly.
     */
    public void close() {
        if (mBluetoothGatt == null) {
            return;
        }
        mBluetoothGatt.close();
        mBluetoothGatt = null;
    }

    /**
     * Request a read on a given {@code BluetoothGattCharacteristic}. The read result is reported
     * asynchronously through the {@code BluetoothGattCallback#onCharacteristicRead(android.bluetooth.BluetoothGatt, android.bluetooth.BluetoothGattCharacteristic, int)}
     * callback.
     *
     * @param characteristic The characteristic to read from.
     */
    public void readCharacteristic(BluetoothGattCharacteristic characteristic) {
        if (mBluetoothAdapter == null || mBluetoothGatt == null) {
            Log.w(TAG, "BluetoothAdapter not initialized");
            return;
        }
        mBluetoothGatt.readCharacteristic(characteristic);
    }

    /**
     * Request a read on a given {@code BluetoothGattCharacteristic}. The read result is reported
     * asynchronously through the {@code BluetoothGattCallback#onCharacteristicRead(android.bluetooth.BluetoothGatt, android.bluetooth.BluetoothGattCharacteristic, int)}
     * callback.
     *
     * @param characteristic The characteristic to read from.
     */
    public void writeCharacteristic(BluetoothGattCharacteristic characteristic) {
        if (mBluetoothAdapter == null || mBluetoothGatt == null) {
            Log.w(TAG, "BluetoothAdapter not initialized");
            return;
        }
        mBluetoothGatt.writeCharacteristic(characteristic);
    }
    
    public boolean writeCharacteristic1Info(String s){
        if(mBluetoothGattService==null){
            return false;
        }
        mBluetoothGattCharacteristic1 = mBluetoothGattService.getCharacteristic(UUID_CHARA1);//獲得特征值1
        mBluetoothGattCharacteristic1.setValue(s.getBytes());
        writeCharacteristic(mBluetoothGattCharacteristic1);
        return true;
    }

    /**
     * Enables or disables notification on a give characteristic.
     *
     * @param characteristic Characteristic to act on.
     * @param enabled If true, enable notification.  False otherwise.
     */
    public void setCharacteristicNotification(BluetoothGattCharacteristic characteristic,
                                              boolean enabled) {
        if (mBluetoothAdapter == null || mBluetoothGatt == null) {
            Log.w(TAG, "BluetoothAdapter not initialized");
            return;
        }
        mBluetoothGatt.setCharacteristicNotification(characteristic, enabled);
    }
    

    /**
     * Retrieves a list of supported GATT services on the connected device. This should be
     * invoked only after {@code BluetoothGatt#discoverServices()} completes successfully.
     *
     * @return A {@code List} of supported services.
     */
    public List<BluetoothGattService> getSupportedGattServices() {
        if (mBluetoothGatt == null) return null;

        return mBluetoothGatt.getServices();
    }
    
    @Override//使用startService啟動服務時回調
    public int onStartCommand(Intent intent, int flags, int startId) {
        System.out.println("UartService Start");
        return super.onStartCommand(intent, flags, startId);
    }
}

ps：在發現服務後，最好把特征值取出來成一個列表，然後使用 setCharacteristicNotification(BluetoothGattCharacteristic characteristic,boolean enabled)方法對所有特征值進行設置，確保服務的特征值都可讀可寫。

 mBluetoothGattService = gatt.getService(UUID_SERVICE);//發現服務
 List<BluetoothGattCharacteristic> characteristics = mBluetoothGattService.getCharacteristics();
 if(characteristics.size()!=2){return;}//如果此服務不是有2個特征值，說明不是我們要的服務
 for (BluetoothGattCharacteristic bluetoothGattCharacteristic : characteristics) {
      setCharacteristicNotification(bluetoothGattCharacteristic, true);
 }
 mBluetoothGattCharacteristic1 = characteristics.get(0);
 mBluetoothGattCharacteristic2 = characteristics.get(1);

寫完Service之後就可以用Service了

四、Service的使用

1. 在activity中綁定服務或者開啟服務。綁定服務時，當activity銷毀時服務跟著銷毀；開啟服務時，activity銷毀，service不會跟著銷毀
2. 初始化本地藍牙設備

   mUartService.initialize();//初始化本地設備

3. 連接

   mUartService.connect(String MacAddress);//通過遠程設備地址鏈接到遠程設備

4. 鏈接後，回掉service中的onConnectionStateChange方法，其他的回掉方法也是字面意思，非常簡單
5. 給設備發送數據

   writeCharacteristic1Info(String s);

---

總結

1. 要使用service
2. 拿到服務之後馬上設置特征值為可讀可寫，否則有可能導致收發數據不正常
3. UUID不一定是我的這個，是藍牙廠商提供的，找硬件編程的小夥伴要UUID
4. 有什麽問題望各位指教

Android BLE （低功耗藍牙）應用