要向蓝牙设备发送命令，您可以使用Android的BluetoothAdapter和BluetoothSocket类。以下是一个示例代码，演示如何向蓝牙设备发送命令：

import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothSocket;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.UUID;

public class BluetoothCommandSender {
    private final BluetoothAdapter bluetoothAdapter;
    private final Handler handler;
    private ConnectThread connectThread;
    private ConnectedThread connectedThread;
    private static final UUID MY_UUID = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");

    private static final int STATE_NONE = 0; // 无连接
    private static final int STATE_CONNECTING = 1; // 连接中
    private static final int STATE_CONNECTED = 2; // 已连接
    private int state;

    public BluetoothCommandSender(Handler handler) {
        bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
        state = STATE_NONE;
        this.handler = handler;
    }

    public synchronized void connect(BluetoothDevice device) {
        if (state == STATE_CONNECTING) {
            if (connectThread != null) {
                connectThread.cancel();
                connectThread = null;
            }
        }
        if (connectedThread != null) {
            connectedThread.cancel();
            connectedThread = null;
        }

        connectThread = new ConnectThread(device);
        connectThread.start();
        setState(STATE_CONNECTING);
    }

    public synchronized void sendCommand(String command) {
        if (state != STATE_CONNECTED) {
            return;
        }

        connectedThread.write(command.getBytes());
    }

    private void connectionFailed() {
        setState(STATE_NONE);
        Message message = handler.obtainMessage(0);
        Bundle bundle = new Bundle();
        bundle.putString("error", "连接失败");
        message.setData(bundle);
        handler.sendMessage(message);
    }

    private void connectionLost() {
        setState(STATE_NONE);
        Message message = handler.obtainMessage(0);
        Bundle bundle = new Bundle();
        bundle.putString("error", "连接断开");
        message.setData(bundle);
        handler.sendMessage(message);
    }

    private void setState(int state) {
        this.state = state;
        handler.obtainMessage(0, state, -1).sendToTarget();
    }

    private class ConnectThread extends Thread {
        private final BluetoothSocket socket;
        private final BluetoothDevice device;

        public ConnectThread(BluetoothDevice device) {
            this.device = device;
            BluetoothSocket temp = null;
            try {
                temp = device.createRfcommSocketToServiceRecord(MY_UUID);
            } catch (IOException e) {
                e.printStackTrace();
            }
            socket = temp;
        }

        public void run() {
            bluetoothAdapter.cancelDiscovery();

            try {
                socket.connect();
            } catch (IOException e) {
                e.printStackTrace();
                try {
                    socket.close();
                } catch (IOException e2) {
                    e2.printStackTrace();
                }
                connectionFailed();
                return;
            }

            synchronized (BluetoothCommandSender.this) {
                connectThread = null;
            }

            connected(socket, device);
        }

        public void cancel() {
            try {
                socket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    private class ConnectedThread extends Thread {
        private final BluetoothSocket socket;
        private final InputStream inputStream;
        private final OutputStream outputStream;

        public ConnectedThread(BluetoothSocket socket) {
            this.socket = socket;
            InputStream tempIn = null;
            OutputStream tempOut = null;

            try {
                tempIn = socket.getInputStream();
                tempOut = socket.getOutputStream();
            } catch (IOException e) {
                e.printStackTrace();
            }

            inputStream = tempIn;
            outputStream = tempOut;
        }

        public void run() {
            byte[] buffer = new byte[1024];
            int bytes;
            while (true) {
                try {
                    bytes = inputStream.read(buffer);
                    handler.obtainMessage(1, bytes, -1, buffer).sendToTarget();
                } catch (IOException e) {
                    e.printStackTrace();
                    connectionLost();
                    break;
                }
            }
        }

        public void write(byte[] buffer) {
            try {
                outputStream.write(buffer);
                handler.obtainMessage(2, -1, -1, buffer).sendToTarget();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        public void cancel() {
            try {
                socket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

这是一个简