Android蓝牙实现设备间数据传输

这篇文章总结通过蓝牙实现两台pad间数据传输

文章基于传统蓝牙，而不是BLE。
蓝牙应该是移动设备经常用到的功能模块，Android Bluetooth API 是Android提供的用来实现点到点和多点无线功能。
使用 Bluetooth API，Android 应用可执行以下操作：

• 扫描其他蓝牙设备
• 查询本地蓝牙适配器的配对蓝牙设备
• 建立 RFCOMM 通道
• 通过服务发现连接到其他设备
• 与其他设备进行双向数据传输
• 管理多个连接

---

蓝牙权限

... >
  "android.permission.BLUETOOTH" />
  "android.permission.BLUETOOTH_ADMIN" />
  ...

---

1.设置蓝牙

您需要验证设备支持蓝牙，并且如果支持确保将其启用，然后您的应用才能通过蓝牙进行通信。

• 获取 BluetoothAdapter
  所有蓝牙 Activity 都需要 BluetoothAdapter。

  BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
  if (mBluetoothAdapter == null) {
  // Device does not support Bluetooth
  }

• 启用蓝牙
  下一步，您需要确保已启用蓝牙。

  if (!mBluetoothAdapter.isEnabled()) {
  Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
  startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
  }

---

2.搜索蓝牙设备

要开始发现设备，只需调用 startDiscovery()。该进程为异步进程，并且该方法会立即返回一个布尔值，指示是否已成功启动发现操作。 发现进程通常包含约 12 秒钟的查询扫描，之后对每台发现的设备进行页面扫描，以检索其蓝牙名称。

/**
     * 发现蓝牙的广播
     */
    private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {

            String action = intent.getAction();
            if(BluetoothDevice.ACTION_FOUND.equals(action)){
                BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
                //todo处理搜索到的蓝牙设备
            }
        }
    };

在Activity或者Fragment中注册广播

        IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND);
        registerReceiver(mReceiver, filter);

---

3.连接设备

要在两台设备上的应用之间创建连接，必须同时实现服务器端和客户端机制，因为其中一台设备必须开放服务器套接字，而另一台设备必须发起连接（使用服务器设备的 MAC 地址发起连接）。
服务器设备和客户端设备分别以不同的方法获得需要的 BluetoothSocket。服务器将在传入连接被接受时收到套接字。 客户端将在其打开到服务器的 RFCOMM 通道时收到该套接字。

注：如果两台设备之前尚未配对，则在连接过程中，Android 框架会自动向用户显示配对请求通知或对话框。因此，在尝试连接设备时，您的应用无需担心设备是否已配对。 您的 RFCOMM 连接尝试将被阻塞，直至用户成功完成配对或配对失败（包括用户拒绝配对、配对失败或超时）。

• 连接为服务器
  当您需要连接两台设备时，其中一台设备必须通过保持开放的 BluetoothServerSocket 来充当服务器。
  
  • 1.通过调用 listenUsingRfcommWithServiceRecord(String, UUID) 获取 BluetoothServerSocket。
    当客户端尝试连接此设备时，它会携带能够唯一标识其想要连接的服务的 UUID。 两个 UUID 必须匹配，在下一步中，连接才会被接受。
  • 通过调用 accept() 开始侦听连接请求。
  • 除非您想要接受更多连接，否则请调用 close()。
    这将释放服务器套接字及其所有资源，但不会关闭 accept() 所返回的已连接的 BluetoothSocket。 与 TCP/IP 不同，RFCOMM 一次只允许每个通道有一个已连接的客户端，因此大多数情况下，在接受已连接的套接字后立即在 BluetoothServerSocket 上调用 close() 是行得通的。

以下是一个用于接受传入连接的服务器组件的简化线程：

private class AcceptThread extends Thread {
    private final BluetoothServerSocket mmServerSocket;

    public AcceptThread() {
        // Use a temporary object that is later assigned to mmServerSocket,
        // because mmServerSocket is final
        BluetoothServerSocket tmp = null;
        try {
            // MY_UUID is the app's UUID string, also used by the client code
            tmp = mBluetoothAdapter.listenUsingRfcommWithServiceRecord(NAME, MY_UUID);
        } catch (IOException e) { }
        mmServerSocket = tmp;
    }

    public void run() {
        BluetoothSocket socket = null;
        // Keep listening until exception occurs or a socket is returned
        while (true) {
            try {
                socket = mmServerSocket.accept();
            } catch (IOException e) {
                break;
            }
            // If a connection was accepted
            if (socket != null) {
                // Do work to manage the connection (in a separate thread)
                manageConnectedSocket(socket);
                mmServerSocket.close();
                break;
            }
        }
    }

    /** Will cancel the listening socket, and cause the thread to finish */
    public void cancel() {
        try {
            mmServerSocket.close();
        } catch (IOException e) { }
    }
}

注意上面是简化线程，也是网上搜索到最多的方法。但是其稳定性真的很差劲。

• 连接为客户端
  要发起与远程设备（保持开放的服务器套接字的设备）的连接，必须首先获取表示该远程设备的 BluetoothDevice 对象。（在前面有关查找设备的部分介绍了如何获取 BluetoothDevice）。 然后必须使用 BluetoothDevice 来获取 BluetoothSocket 并发起连接。
  
  • 1.使用 BluetoothDevice，通过调用 createRfcommSocketToServiceRecord(UUID) 获取 BluetoothSocket。
  • 2.通过调用 connect() 发起连接。

以下是发起蓝牙连接的线程的基本示例：

private class ConnectThread extends Thread {
    private final BluetoothSocket mmSocket;
    private final BluetoothDevice mmDevice;

    public ConnectThread(BluetoothDevice device) {
        // Use a temporary object that is later assigned to mmSocket,
        // because mmSocket is final
        BluetoothSocket tmp = null;
        mmDevice = device;

        // Get a BluetoothSocket to connect with the given BluetoothDevice
        try {
            // MY_UUID is the app's UUID string, also used by the server code
            tmp = device.createRfcommSocketToServiceRecord(MY_UUID);
        } catch (IOException e) { }
        mmSocket = tmp;
    }

    public void run() {
        // Cancel discovery because it will slow down the connection
        mBluetoothAdapter.cancelDiscovery();

        try {
            // Connect the device through the socket. This will block
            // until it succeeds or throws an exception
            mmSocket.connect();
        } catch (IOException connectException) {
            // Unable to connect; close the socket and get out
            try {
                mmSocket.close();
            } catch (IOException closeException) { }
            return;
        }

        // Do work to manage the connection (in a separate thread)
        manageConnectedSocket(mmSocket);
    }

    /** Will cancel an in-progress connection, and close the socket */
    public void cancel() {
        try {
            mmSocket.close();
        } catch (IOException e) { }
    }
}

代码很容易看懂，就不做过多解释了。

---

4.管理连接

在成功连接两台（或更多台）设备后，每台设备都会有一个已连接的 BluetoothSocket。 这一点非常有趣，因为这表示您可以在设备之间共享数据。 利用 BluetoothSocket，传输任意数据的一般过程非常简单：

• 获取 InputStream 和 OutputStream，二者分别通过套接字以及 getInputStream() 和 getOutputStream() 来处理数据传输。
• 使用 read(byte[]) 和 write(byte[]) 读取数据并写入到流式传输。

---

ok，至此，我们基本了解了传统蓝牙数据传输常用的API以及一些核心API的使用，接下来具体看我在项目中如何处理数据传输以及解决蓝牙Socket的稳定性。
在了解了上面一套机制以后，最开始我也是使用上面的简单实例进行蓝牙数据的传输与接受，但在传输过程中经常会出现连接异常，Socket断开等各种异常。经过不断的寻找解决方案，最后发现了官方一个通过蓝牙进行设备聊天的demo，仔细研究发现主要是通过一个自己封装的BluetoothChatService，其内部本质还是使用的我们上面介绍的知识，只不过这个Service对连接的处理更详细。

public class BluetoothChatService {
    // Debugging
    private static final String TAG = "BluetoothChatService";

    // Name for the SDP record when creating server socket
    private static final String NAME_SECURE = "BluetoothChatSecure";
    private static final String NAME_INSECURE = "BluetoothChatInsecure";

    // Unique UUID for this application
    private static final UUID MY_UUID_SECURE =
            UUID.fromString("fa87c0d0-afac-11de-8a39-0800200c9a66");
    private static final UUID MY_UUID_INSECURE =
            UUID.fromString("8ce255c0-200a-11e0-ac64-0800200c9a66");

    // Member fields
    private final BluetoothAdapter mAdapter;
    private final Handler mHandler;
    private AcceptThread mSecureAcceptThread;
    private AcceptThread mInsecureAcceptThread;
    private ConnectThread mConnectThread;
    private ConnectedThread mConnectedThread;
    private int mState;
    private int mNewState;

    // Constants that indicate the current connection state
    public static final int STATE_NONE = 0;       // we're doing nothing
    public static final int STATE_LISTEN = 1;     // now listening for incoming connections
    public static final int STATE_CONNECTING = 2; // now initiating an outgoing connection
    public static final int STATE_CONNECTED = 3;  // now connected to a remote device

    /**
     * Constructor. Prepares a new BluetoothChat session.
     *
     * @param context The UI Activity Context
     * @param handler A Handler to send messages back to the UI Activity
     */
    public BluetoothChatService(Context context, Handler handler) {
        mAdapter = BluetoothAdapter.getDefaultAdapter();
        mState = STATE_NONE;
        mNewState = mState;
        mHandler = handler;
    }

    /**
     * Update UI title according to the current state of the chat connection
     */
    private synchronized void updateUserInterfaceTitle() {
        mState = getState();
        Log.d(TAG, "updateUserInterfaceTitle() " + mNewState + " -> " + mState);
        mNewState = mState;

        // Give the new state to the Handler so the UI Activity can update
        mHandler.obtainMessage(Constants.MESSAGE_STATE_CHANGE, mNewState, -1).sendToTarget();
    }

    /**
     * Return the current connection state.
     */
    public synchronized int getState() {
        return mState;
    }

    /**
     * Start the chat service. Specifically start AcceptThread to begin a
     * session in listening (server) mode. Called by the Activity onResume()
     */
    public synchronized void start() {
        Log.d(TAG, "start");

        // Cancel any thread attempting to make a connection
        if (mConnectThread != null) {
            mConnectThread.cancel();
            mConnectThread = null;
        }

        // Cancel any thread currently running a connection
        if (mConnectedThread != null) {
            mConnectedThread.cancel();
            mConnectedThread = null;
        }

        // Start the thread to listen on a BluetoothServerSocket
        if (mSecureAcceptThread == null) {
            mSecureAcceptThread = new AcceptThread(true);
            mSecureAcceptThread.start();
        }
        if (mInsecureAcceptThread == null) {
            mInsecureAcceptThread = new AcceptThread(false);
            mInsecureAcceptThread.start();
        }
        // Update UI title
        updateUserInterfaceTitle();
    }

    /**
     * Start the ConnectThread to initiate a connection to a remote device.
     *
     * @param device The BluetoothDevice to connect
     * @param secure Socket Security type - Secure (true) , Insecure (false)
     */
    public synchronized void connect(BluetoothDevice device, boolean secure) {
        Log.d(TAG, "connect to: " + device);

        // Cancel any thread attempting to make a connection
        if (mState == STATE_CONNECTING) {
            if (mConnectThread != null) {
                mConnectThread.cancel();
                mConnectThread = null;
            }
        }

        // Cancel any thread currently running a connection
        if (mConnectedThread != null) {
            mConnectedThread.cancel();
            mConnectedThread = null;
        }

        // Start the thread to connect with the given device
        mConnectThread = new ConnectThread(device, secure);
        mConnectThread.start();
        // Update UI title
        updateUserInterfaceTitle();
    }

    /**
     * Start the ConnectedThread to begin managing a Bluetooth connection
     *
     * @param socket The BluetoothSocket on which the connection was made
     * @param device The BluetoothDevice that has been connected
     */
    public synchronized void connected(BluetoothSocket socket, BluetoothDevice
            device, final String socketType) {
        Log.d(TAG, "connected, Socket Type:" + socketType);

        // Cancel the thread that completed the connection
        if (mConnectThread != null) {
            mConnectThread.cancel();
            mConnectThread = null;
        }

        // Cancel any thread currently running a connection
        if (mConnectedThread != null) {
            mConnectedThread.cancel();
            mConnectedThread = null;
        }

        // Cancel the accept thread because we only want to connect to one device
        if (mSecureAcceptThread != null) {
            mSecureAcceptThread.cancel();
            mSecureAcceptThread = null;
        }
        if (mInsecureAcceptThread != null) {
            mInsecureAcceptThread.cancel();
            mInsecureAcceptThread = null;
        }

        // Start the thread to manage the connection and perform transmissions
        mConnectedThread = new ConnectedThread(socket, socketType);
        mConnectedThread.start();

        // Send the name of the connected device back to the UI Activity
        Message msg = mHandler.obtainMessage(Constants.MESSAGE_DEVICE_NAME);
        Bundle bundle = new Bundle();
        bundle.putString(Constants.DEVICE_NAME, device.getName());
        msg.setData(bundle);
        mHandler.sendMessage(msg);
        // Update UI title
        updateUserInterfaceTitle();
    }

    /**
     * Stop all threads
     */
    public synchronized void stop() {
        Log.d(TAG, "stop");

        if (mConnectThread != null) {
            mConnectThread.cancel();
            mConnectThread = null;
        }

        if (mConnectedThread != null) {
            mConnectedThread.cancel();
            mConnectedThread = null;
        }

        if (mSecureAcceptThread != null) {
            mSecureAcceptThread.cancel();
            mSecureAcceptThread = null;
        }

        if (mInsecureAcceptThread != null) {
            mInsecureAcceptThread.cancel();
            mInsecureAcceptThread = null;
        }
        mState = STATE_NONE;
        // Update UI title
        updateUserInterfaceTitle();
    }

    /**
     * Write to the ConnectedThread in an unsynchronized manner
     *
     * @param out The bytes to write
     * @see ConnectedThread#write(byte[])
     */
    public void write(byte[] out) {
        // Create temporary object
        ConnectedThread r;
        // Synchronize a copy of the ConnectedThread
        synchronized (this) {
            if (mState != STATE_CONNECTED) return;
            r = mConnectedThread;
        }
        // Perform the write unsynchronized
        r.write(out);
    }

    /**
     * Indicate that the connection attempt failed and notify the UI Activity.
     */
    private void connectionFailed() {
        // Send a failure message back to the Activity
        Message msg = mHandler.obtainMessage(Constants.MESSAGE_TOAST);
        Bundle bundle = new Bundle();
        bundle.putString(Constants.TOAST, "无法连接蓝牙设备...");
        msg.setData(bundle);
        mHandler.sendMessage(msg);

        mState = STATE_NONE;
        // Update UI title
        updateUserInterfaceTitle();

        // Start the service over to restart listening mode
        BluetoothChatService.this.start();
    }

    /**
     * Indicate that the connection was lost and notify the UI Activity.
     */
    private void connectionLost() {
        // Send a failure message back to the Activity
        Message msg = mHandler.obtainMessage(Constants.MESSAGE_TOAST);
        Bundle bundle = new Bundle();
        bundle.putString(Constants.TOAST, "Device connection was lost");
        msg.setData(bundle);
        mHandler.sendMessage(msg);

        mState = STATE_NONE;
        // Update UI title
        updateUserInterfaceTitle();

        // Start the service over to restart listening mode
        BluetoothChatService.this.start();
    }

    /**
     * This thread runs while listening for incoming connections. It behaves
     * like a server-side client. It runs until a connection is accepted
     * (or until cancelled).
     */
    private class AcceptThread extends Thread {
        // The local server socket
        private final BluetoothServerSocket mmServerSocket;
        private String mSocketType;

        public AcceptThread(boolean secure) {
            BluetoothServerSocket tmp = null;
            mSocketType = secure ? "Secure" : "Insecure";

            // Create a new listening server socket
            try {
                if (secure) {
                    tmp = mAdapter.listenUsingRfcommWithServiceRecord(NAME_SECURE,
                            MY_UUID_SECURE);
                } else {
                    tmp = mAdapter.listenUsingInsecureRfcommWithServiceRecord(
                            NAME_INSECURE, MY_UUID_INSECURE);
                }
            } catch (IOException e) {
                Log.e(TAG, "Socket Type: " + mSocketType + "listen() failed", e);
            }
            mmServerSocket = tmp;
            mState = STATE_LISTEN;
        }

        public void run() {
            Log.d(TAG, "Socket Type: " + mSocketType +
                    "BEGIN mAcceptThread" + this);
            setName("AcceptThread" + mSocketType);

            BluetoothSocket socket = null;

            // Listen to the server socket if we're not connected
            while (mState != STATE_CONNECTED) {
                try {
                    // This is a blocking call and will only return on a
                    // successful connection or an exception
                    socket = mmServerSocket.accept();
                } catch (IOException e) {
                    Log.e(TAG, "Socket Type: " + mSocketType + "accept() failed", e);
                    break;
                }

                // If a connection was accepted
                if (socket != null) {
                    synchronized (BluetoothChatService.this) {
                        switch (mState) {
                            case STATE_LISTEN:
                            case STATE_CONNECTING:
                                // Situation normal. Start the connected thread.
                                connected(socket, socket.getRemoteDevice(),
                                        mSocketType);
                                break;
                            case STATE_NONE:
                            case STATE_CONNECTED:
                                // Either not ready or already connected. Terminate new socket.
                                try {
                                    socket.close();
                                } catch (IOException e) {
                                    Log.e(TAG, "Could not close unwanted socket", e);
                                }
                                break;
                        }
                    }
                }
            }
            Log.i(TAG, "END mAcceptThread, socket Type: " + mSocketType);

        }

        public void cancel() {
            Log.d(TAG, "Socket Type" + mSocketType + "cancel " + this);
            try {
                mmServerSocket.close();
            } catch (IOException e) {
                Log.e(TAG, "Socket Type" + mSocketType + "close() of server failed", e);
            }
        }
    }


    /**
     * This thread runs while attempting to make an outgoing connection
     * with a device. It runs straight through; the connection either
     * succeeds or fails.
     */
    private class ConnectThread extends Thread {
        private final BluetoothSocket mmSocket;
        private final BluetoothDevice mmDevice;
        private String mSocketType;

        public ConnectThread(BluetoothDevice device, boolean secure) {
            mmDevice = device;
            BluetoothSocket tmp = null;
            mSocketType = secure ? "Secure" : "Insecure";

            // Get a BluetoothSocket for a connection with the
            // given BluetoothDevice
            try {
                if (secure) {
                    tmp = device.createRfcommSocketToServiceRecord(
                            MY_UUID_SECURE);
                } else {
                    tmp = device.createInsecureRfcommSocketToServiceRecord(
                            MY_UUID_INSECURE);
                }
            } catch (IOException e) {
                Log.e(TAG, "Socket Type: " + mSocketType + "create() failed", e);
            }
            mmSocket = tmp;
            mState = STATE_CONNECTING;
        }

        public void run() {
            Log.i(TAG, "BEGIN mConnectThread SocketType:" + mSocketType);
            setName("ConnectThread" + mSocketType);

            // Always cancel discovery because it will slow down a connection
            mAdapter.cancelDiscovery();

            // Make a connection to the BluetoothSocket
            try {
                // This is a blocking call and will only return on a
                // successful connection or an exception
                mmSocket.connect();
            } catch (IOException e) {
                // Close the socket
                try {
                    mmSocket.close();
                } catch (IOException e2) {
                    Log.e(TAG, "unable to close() " + mSocketType +
                            " socket during connection failure", e2);
                }
                connectionFailed();
                return;
            }

            // Reset the ConnectThread because we're done
            synchronized (BluetoothChatService.this) {
                mConnectThread = null;
            }

            // Start the connected thread
            connected(mmSocket, mmDevice, mSocketType);
        }

        public void cancel() {
            try {
                mmSocket.close();
            } catch (IOException e) {
                Log.e(TAG, "close() of connect " + mSocketType + " socket failed", e);
            }
        }
    }

    /**
     * This thread runs during a connection with a remote device.
     * It handles all incoming and outgoing transmissions.
     */
    private class ConnectedThread extends Thread {
        private final BluetoothSocket mmSocket;
        private final InputStream mmInStream;
        private final OutputStream mmOutStream;

        public ConnectedThread(BluetoothSocket socket, String socketType) {
            Log.d(TAG, "create ConnectedThread: " + socketType);
            mmSocket = socket;
            InputStream tmpIn = null;
            OutputStream tmpOut = null;

            // Get the BluetoothSocket input and output streams
            try {
                tmpIn = socket.getInputStream();
                tmpOut = socket.getOutputStream();
            } catch (IOException e) {
                Log.e(TAG, "temp sockets not created", e);
            }

            mmInStream = tmpIn;
            mmOutStream = tmpOut;
            mState = STATE_CONNECTED;
        }

        public void run() {
            Log.i(TAG, "BEGIN mConnectedThread");
            byte[] buffer = new byte[1024];
            int bytes;

            // Keep listening to the InputStream while connected
            while (mState == STATE_CONNECTED) {
                try {
                    // Read from the InputStream
                    bytes = mmInStream.read(buffer);

                    // Send the obtained bytes to the UI Activity
                    mHandler.obtainMessage(Constants.MESSAGE_READ, bytes, -1, buffer)
                            .sendToTarget();
                } catch (IOException e) {
                    Log.e(TAG, "disconnected", e);
                    connectionLost();
                    break;
                }
            }
        }

        /**
         * Write to the connected OutStream.
         *
         * @param buffer The bytes to write
         */
        public void write(byte[] buffer) {
            try {
                mmOutStream.write(buffer);

                // Share the sent message back to the UI Activity
                mHandler.obtainMessage(Constants.MESSAGE_WRITE, -1, -1, buffer)
                        .sendToTarget();
            } catch (IOException e) {
                Log.e(TAG, "Exception during write", e);
            }
        }

        public void cancel() {
            try {
                mmSocket.close();
            } catch (IOException e) {
                Log.e(TAG, "close() of connect socket failed", e);
            }
        }
    }
}

看似很长的一段代码，其实仔细阅读并不难。提供了三个线程:

• AcceptThread 用来处理接收数据;
• ConnectThread 用来处理蓝牙设备连接；
• ConnectedThread 用来管理连接，进行数据传输。

接下来看具体的使用：

发送方：

private final Handler mHandler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what){
                case Constants.MESSAGE_WRITE:
                    T.showLong(MshipWaterTankActivity.this,"蓝牙数据发送成功!");
                    break;
                case Constants.MESSAGE_READ:
                    //处理接收到的数据
                    break;
                case Constants.MESSAGE_DEVICE_NAME:
                    try {
                        // save the connected device's name
                        mConnectedDeviceName = msg.getData().getString(Constants.DEVICE_NAME);
                        if (null != mContext) {
                            Toast.makeText(mContext, "蓝牙已成功连接到: "
                                    + mConnectedDeviceName, Toast.LENGTH_SHORT).show();
                        }
                        //连接成功发送数据
                        sendMsg();
                    } catch (Exception e) {
                        e.printStackTrace();
                        Log.e("wj","压缩数据异常");
                    }
                    break;
                case Constants.MESSAGE_TOAST:
                    if (null != mContext) {
                        Toast.makeText(mContext, msg.getData().getString(Constants.TOAST),
                                Toast.LENGTH_SHORT).show();
                    }
                    break;
            }
        }
    };
@Override
    protected void onStart() {
        super.onStart();
        // If BT is not on, request that it be enabled.
        // setupChat() will then be called during onActivityResult
        if (!mBluetoothAdapter.isEnabled()) {
            Intent enableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
            startActivityForResult(enableIntent, REQUEST_ENABLE_BT);
            // Otherwise, setup the chat session
        } else if (mChatService == null) {
            setupChat();
        }
    }

     @Override
    protected void onResume() {
        super.onResume();

        // Performing this check in onResume() covers the case in which BT was
        // not enabled during onStart(), so we were paused to enable it...
        // onResume() will be called when ACTION_REQUEST_ENABLE activity returns.
        if (mChatService != null) {
            // Only if the state is STATE_NONE, do we know that we haven't started already
            if (mChatService.getState() == BluetoothChatService.STATE_NONE) {
                // Start the Bluetooth chat services
                mChatService.start();
            }
        }

@Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        switch (requestCode){
            case REQUEST_ENABLE_BT:
                // When the request to enable Bluetooth returns
                if (resultCode == Activity.RESULT_OK) {
                    // Bluetooth is now enabled, so set up a chat session
                    setupChat();
                } else {
                    // User did not enable Bluetooth or an error occurred
                    Log.d("wj", "BT not enabled");
                    Toast.makeText(this, "蓝牙会话已关闭",
                            Toast.LENGTH_SHORT).show();
                }
                break;
        }
    }
@Override
    protected void onDestroy() {
        super.onDestroy();
        unregisterReceiver(mReceiver);
        if (mChatService != null) {
            mChatService.stop();
        }
    }
private void setupChat(){
        // Initialize the BluetoothChatService to perform bluetooth connections
        mChatService = new BluetoothChatService(this, mHandler);
        // Initialize the buffer for outgoing messages
        mOutStringBuffer = new StringBuffer("");
    }

private void connectDevice(BluetoothDevice device, boolean secure) {
        // Attempt to connect to the device
        mChatService.connect(device, secure);
    }
private void sendBluetoothMessage(String message) {
        // Check that we're actually connected before trying anything
        if (mChatService.getState() != BluetoothChatService.STATE_CONNECTED) {
            Toast.makeText(this, "蓝牙未连接...", Toast.LENGTH_SHORT).show();
            return;
        }

        // Check that there's actually something to send
        if (message.length() > 0) {
            // Get the message bytes and tell the BluetoothChatService to write
            byte[] send = message.getBytes();
            mChatService.write(send);

            // Reset out string buffer to zero and clear the edit text field
            mOutStringBuffer.setLength(0);
        }
    }
    ...

代码并不是很全，但是可以看到关键的Service的初始化，设备连接的方法以及传输数据的方法。

接收方：

其实跟上面的类似，只不过BluetoothChatService处理的handler不同，这里就不再继续赘述上面各种Service的初始化，看下核心handler的处理：

private final Handler mHandler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            FragmentActivity activity = getActivity();
            switch (msg.what) {
                case Constants.MESSAGE_READ:
                    byte[] readBuf = (byte[]) msg.obj;
                    // construct a string from the valid bytes in the buffer
                    String readMessage = new String(readBuf, 0, msg.arg1);
                    dealContent(readMessage);//处理返回的数据
                    break;
                case Constants.MESSAGE_DEVICE_NAME:
                    // save the connected device's name
                    mConnectedDeviceName = msg.getData().getString(Constants.DEVICE_NAME);
                    if (null != activity) {
                        Toast.makeText(activity, "已成功连接到 "
                                + mConnectedDeviceName, Toast.LENGTH_SHORT).show();
                    }
                    break;
                case Constants.MESSAGE_TOAST:
                    if (null != activity) {
                        Toast.makeText(activity, msg.getData().getString(Constants.TOAST),
                                Toast.LENGTH_SHORT).show();
                    }
                    break;
            }
        }
    };

可以看到dealContent(readMessage)方法就是处理接收到的数据。

细心的你可能发现了，我在进行蓝牙数据传输的时候对字符串进行了压缩处理，因为我传输的json字符串超过了蓝牙数据传输的最大限制，导致接收到的数据不完整，因此我对数据进行了压缩和解压缩处理。

---

通过使用BluetoothChatService，可以很好的解决两台设备间数据传输的问题。具体可以参考官方蓝牙聊天的demo：https://github.com/googlesamples/android-BluetoothChat/#readme

这篇文章使用的是传统蓝牙的技术，Android4.0以后推出了BLE蓝牙机制。开始我也下尝试使用BLE实现两台平板间数据传输。但是仔细深入了解以后，BLE分外围设备和中央设备，通常我们手机连接手表或者一些智能设备都使用BLE的方式进行的数据传输。但是手机和手机通过BLE方式传输会有一个问题，需要我们自己将其中一台设备通过API处理成模拟外围设备，但是我在将一台设备模拟成外围设备进行数据传输的时候还是无法成功发送数据，网上很多地方说Android自身不支持手机和手机间通过BLE传输数据，但我也没有在官网找到明确的说法，总之 最终我放弃了BLE，还是用传统蓝牙实现了设备间数据传输。

接下来有时间我会继续对BLE的机制进行总结。欢迎大家留言交流。