Android串口通信可以实现设备与设备之间通过设备线连接进行数据（消息）传递
（一）导入so库

（二）在moudle的build中添加jniLibs

buildTypes {
        sourceSets {
            main { jni.srcDirs = [] }
        }
    }
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（三）添加Google的SerialPort
添加的是Google的所以必须创建android_serialport_api包
如需要更改SerialPort、SerialPortFinder位置需要重新生成so库

（四）创建串口通信工具类SerialPortUtils

package com.demo.serialport;

import android.util.Log;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import android_serialport_api.SerialPort;

/**
 * @author renquan
 */

public class SerialPortUtils {

    private final String TAG = "SerialPortUtils";
//    private String path = "/dev/ttyS1";
//    private int baudrate = 9600;
    public boolean serialPortStatus = false; //是否打开串口标志
    public String data_;
    public boolean threadStatus; //线程状态，为了安全终止线程

    public SerialPort serialPort = null;
    public InputStream inputStream = null;
    public OutputStream outputStream = null;
    public ChangeTool changeTool = new ChangeTool;


    /**
     * 打开串口
     * @return serialPort串口对象
     */
    public SerialPort openSerialPort(String path%2cint baudrate){
        try {
            serialPort = new SerialPort(new File(path)%2cbaudrate%2c0);
            this.serialPortStatus = true;
            threadStatus = false; //线程状态

            //获取打开的串口中的输入输出流，以便于串口数据的收发
            inputStream = serialPort.getInputStream;
            outputStream = serialPort.getOutputStream;

            new ReadThread.start; //开始线程监控是否有数据要接收
        } catch (IOException e) {
            Log.e(TAG%2c "openSerialPort: 打开串口异常：" + e.toString);
            return serialPort;
        }
        Log.d(TAG%2c "openSerialPort: 打开串口");
        return serialPort;
    }

    /**
     * 关闭串口
     */
    public void closeSerialPort{
        try {
            inputStream.close;
            outputStream.close;

            this.serialPortStatus = false;
            this.threadStatus = true; //线程状态
            serialPort.close;
        } catch (IOException e) {
            Log.e(TAG%2c "closeSerialPort: 关闭串口异常："+e.toString);
            return;
        }
        Log.d(TAG%2c "closeSerialPort: 关闭串口成功");
    }

    /**
     * 发送串口指令（字符串）
     * @param data String数据指令
     */
    public void sendSerialPort(String data){
        Log.d(TAG%2c "sendSerialPort: 发送数据");

        try {
            byte[] sendData = data.getBytes; //string转byte[]
            this.data_ = new String(sendData); //byte[]转string
            if (sendData.length > 0) {
                outputStream.write(sendData);
                outputStream.write('n');
                //outputStream.write('r'+'n');
                outputStream.flush;
                Log.d(TAG%2c "sendSerialPort: 串口数据发送成功");
            }
        } catch (IOException e) {
            Log.e(TAG%2c "sendSerialPort: 串口数据发送失败："+e.toString);
        }

    }

    /**
     * 单开一线程，来读数据
     */
    private class ReadThread extends Thread{
        @Override
        public void run {
            super.run;
            //判断进程是否在运行，更安全的结束进程
            while (!threadStatus){
                Log.d(TAG%2c "进入线程run");
                //64   1024
                byte[] buffer = new byte[64];
                int size; //读取数据的大小
                try {
                    size = inputStream.read(buffer);
                    if (size > 0){
                        Log.d(TAG%2c "run: 接收到了数据：" + changeTool.ByteArrToHex(buffer));
                        Log.d(TAG%2c "run: 接收到了数据大小：" + String.valueOf(size));
                        onDataReceiveListener.onDataReceive(buffer%2csize);
                    }
                } catch (IOException e) {
                    Log.e(TAG%2c "run: 数据读取异常：" +e.toString);
                }
            }

        }
    }

    //数据回调
    public OnDataReceiveListener onDataReceiveListener = null;
    public static interface OnDataReceiveListener {
        public void onDataReceive(byte[] buffer%2c int size);
    }
    public void setOnDataReceiveListener(OnDataReceiveListener dataReceiveListener) {
        onDataReceiveListener = dataReceiveListener;
    }

}

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package com.demo.serialport;

/**
 * @author renquan
 */

public class ChangeTool {

    /**
     * byte数组转16进制字符串
     *
     * @param bytes byte数组
     * @return 16进制字符串
     */
    public String ByteArrToHex(byte[] bytes) {
        String strHex;
        StringBuilder sb = new StringBuilder;
        for (byte aByte : bytes) {
            strHex = Integer.toHexString(aByte & 0xFF);
            sb.append(" ").append((strHex.length == 1) ? "0" : "").append(strHex); // 每个字节由两个字符表示，位数不够，高位补0
        }
        return sb.toString.trim;
    }

    /**
     * byte字节转int
     *
     * @param b byte字节
     * @return int
     */
    public static int byteToInt(byte b) {
        int x = b & 0xff;
        if (x == 127) {
            return 0;
        }
        return x;
    }
}

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package com.demo.serialport;

import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

import androidx.appcompat.app.AppCompatActivity;

/**
 * @author renquan
 */

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
    private EditText mMessage;
    private Button mOpen;
    private Button mSend;
    private Button mClose;
    private SerialPortUtils serialPortUtils;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        init;


        //串口数据监听事件
        serialPortUtils.setOnDataReceiveListener(new SerialPortUtils.OnDataReceiveListener {
            @Override
            public void onDataReceive(byte[] buffer%2c int size) {
                Log.d("TAG"%2c "进入数据监听事件中。。。" + new String(buffer));

            }
        });

    }

    private void init {
        initView;
        serialPortUtils = new SerialPortUtils;
    }

    private void initView {
        mMessage = (EditText) findViewById(R.id.message);
        mOpen = (Button) findViewById(R.id.open);
        mOpen.setOnClickListener(this);
        mSend = (Button) findViewById(R.id.send);
        mSend.setOnClickListener(this);
        mClose = (Button) findViewById(R.id.close);
        mClose.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        switch (v.getId) {
            case R.id.open:
                // TODO 20/12/28
                serialPortUtils.openSerialPort("/dev/ttyS9"%2c9600);
                break;
            case R.id.send:
                // TODO 20/12/28
                serialPortUtils.sendSerialPort(mSend.getText.toString);
                break;
            case R.id.close:
                serialPortUtils.closeSerialPort;
                // TODO 20/12/28
                break;
            default:
                break;
        }
    }
}
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Demo——github地址