Android的蓝牙部分暂且分为2.0,4.0，虽然苹果已经出了5.0版本了，咱先不说这个。
简单讲解一下，4.0是兼容2.0的功能的，今天讲的bluetoothSocket通信是在2.0上面就已经有了。

Android手机蓝牙跟硬件蓝牙交互一般都是用的bluetoothGatt.
Android手机跟手机蓝牙通信一般用的是bluetoothSocket.

这里我暂且把要连接的设备叫客户端，扫描以及请求配对都由客户端操作，被连接的设备叫做服务端。

流程：(双方蓝牙都在打开并且服务端在可检测的情况下)

客户端–>扫描到服务端–>通过扫描到bluetoothDevice获取bluetoothSocket(UUID);再用
bluetoothSocket.connect();连接服务端，这里的UUID是服务端指定的UUID

服务端–>通过蓝牙适配器获取BluetoothServerSocket(Name，UUID);–Name跟UUID都有自己指定；客户端通过这个UUID连接服务端，建立双方通信。

服务端:

OutputStream outputStream;BluetoothServerSocket serverSocket;private void startServer(){//新建线程，并且使服务端做好接收准备new Thread(new Runnable() {@Overridepublic void run() {try {//name以及UUID由服务端指定serverSocket= bluetoothAdapter.listenUsingRfcommWithServiceRecord("Server" ,UUID.fromString("00001101-0000-1000-8000-00805F9B34FB"));Log.i("bluetooth" , "蓝牙服务器开始等待...");BluetoothSocket socket = serverSocket.accept();Log.i("bluetooth" , "蓝牙客户端连接上来了!");outputStream = socket.getOutputStream();InputStream inputStream = socket.getInputStream();byte[] bytes = new byte[1024];int n ;while((n = inputStream.read(bytes)) != -1) {String b = new String(bytes , 0 , n , "UTF-8");Log.i("bluetooth" , "蓝牙服务器接收到数据" + b);}outputStream.close();inputStream.close();socket.close();} catch (IOException e) {e.printStackTrace();}}}).start();}/*** 发送数据给客户端*/private void sendSocketData(){if (outputStream !=null) {Log.i("bluetooth" , "蓝牙服务器发送数据!");try {//指定发送的数据已经数据编码，编码统一，不然会乱码outputStream.write("数据".getBytes("UTF-8"));outputStream.flush();} catch (IOException e) {e.printStackTrace();}}

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客户端：

BluetoothAdapter adapter;BluetoothDevice device;private BluetoothSocket socket;private OutputStream outputStream;private InputStream inputStream;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_operator_login);sendBroadcast();adapter = BluetoothAdapter.getDefaultAdapter();}/*** 发送数据给服务端*/private void sendData(){if (outputStream != null) {try {outputStream.write("数据".getBytes("UTF-8"));outputStream.flush();} catch (IOException e) {e.printStackTrace();}}}//发出蓝牙扫描的接受广播private void sendBroadcast(){BluetoothReceiver receiver = new BluetoothReceiver();IntentFilter filter = new IntentFilter();filter.addAction(BluetoothDevice.ACTION_FOUND);filter.addAction(BluetoothDevice.ACTION_BOND_STATE_CHANGED);//状态改变filter.addAction(BluetoothAdapter.ACTION_SCAN_MODE_CHANGED);//行动扫描模式改变了filter.addAction(BluetoothAdapter.ACTION_STATE_CHANGED);//动作状态发生了变化registerReceiver(receiver , filter);}class BluetoothReceiver extends BroadcastReceiver{@RequiresApi(api = Build.VERSION_CODES.KITKAT)@Overridepublic void onReceive(Context context, Intent intent) {if (intent.getAction().equals(BluetoothDevice.ACTION_FOUND)){//获取蓝牙设备device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);if (device.getName().equals("OPPO A31")){adapter.cancelDiscovery();LogUtils.i("bluetoothInfo"  , "扫描到的蓝牙设备名称" + device.getName());try {//这里的UUID必须跟服务端的UUID一样socket = device.createRfcommSocketToServiceRecord(UUID.fromString("00001101-0000-1000-8000-00805F9B34FB"));socket.connect();LogUtils.i("bluetoothInfo"  , "连接服务器成功");outputStream = socket.getOutputStream();inputStream = socket.getInputStream();new Thread(new Runnable() {@Overridepublic void run() {try {byte[] b = new byte[1024];int n;while ((n = inputStream.read(b)) != -1) {String s = new String(b,0 , n ,"UTF-8");LogUtils.i("bluetoothInfo" , "客户端收到服务器的数据了" + s);}} catch (IOException e) {e.printStackTrace();}}}).start();} catch (IOException e) {e.printStackTrace();}}} //状态改变时else if (BluetoothDevice.ACTION_BOND_STATE_CHANGED.equals(intent.getAction())) {BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);switch (device.getBondState()) {case BluetoothDevice.BOND_BONDING://正在配对LogUtils.i("bluetoothInfo", "正在配对......");break;case BluetoothDevice.BOND_BONDED://配对结束LogUtils.i("bluetoothInfo", "完成配对");break;case BluetoothDevice.BOND_NONE://取消配对/未配对LogUtils.i("bluetoothInfo", "取消配对");default:break;}}}}

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最后:

别忘了加权限

<uses-permission android:name="android.permission.BLUETOOTH" />
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />

最后大家回想，你这个都没有配对啊，只是扫描了一下啊；其实在客户端扫描到服务端的时候；
bluetoothSocket.connect();的时候这步操作就已经包含了配对操作，会提前提示双方手机配对，当然已经配对过的就不会有。

操作基本上跟平时的tcp的Socket的用法都差不多。