串口通讯的步骤：

1.打开串口。

2.串口处于监听状态

3.想串口写入数据，串口接收到数据返回数据

串口的一个基本结构：

SerialPort类所在的包一定要和上图包名一直，因为串口通讯需要使用jni中的函数。

SerialPort类：

package android_serialport_api;

import java.io.File;

import java.io.FileDescriptor;

import java.io.FileInputStream;

import java.io.FileOutputStream;

import java.io.IOException;

import com.fx.serialporttest.L;

public class SerialPort {

/*

* Do not remove or rename the field mFd: it is used by native method

* close();

*/

private FileDescriptor mFd;

private FileInputStream mFileInputStream;

private FileOutputStream mFileOutputStream;

/**

* 构造方法

* @param device 串口地址

* @param baurate 波特率

* @param flags

* @throws IOException

* @throws InterruptedException

*/

public SerialPort(File device,int baudrate,int flags) {

/*

* 检测是否有访问权限

*/

if(!device.canRead()||!device.canWrite()){

//如果没有读写权限，尝试chmod命令这个文件

L.tag("没有读写权限");

Process su;

try {

su = Runtime.getRuntime().exec("/system/bin/su");//获取root读写权限

String cmd = "chmod 777"+device.getAbsolutePath()+"\n"+"exit\n";

su.getOutputStream().write(cmd.getBytes()); //向此路径文件写入命令

if((su.waitFor()!=0||!device.canRead()||!device.canWrite())){

throw new SecurityException();

}

} catch (Exception e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

}

mFd = open(device.getAbsolutePath(),baudrate,flags);

if(mFd==null){

mFd = open(device.getAbsolutePath(),baudrate,flags);

L.tag("native open return null");

}

mFileInputStream = new FileInputStream(mFd);

mFileOutputStream = new FileOutputStream(mFd);

}

public FileInputStream getmFileInputStream() {

return mFileInputStream;

}

public void setmFileInputStream(FileInputStream mFileInputStream) {

this.mFileInputStream = mFileInputStream;

}

public FileOutputStream getmFileOutputStream() {

return mFileOutputStream;

}

public void setmFileOutputStream(FileOutputStream mFileOutputStream) {

this.mFileOutputStream = mFileOutputStream;

}

//JNI

private native static FileDescriptor open(String path,int baudrate,int flags);

public native void close();

static {

System.loadLibrary("serial_port");

}

}

SerialPortFinger类：

package android_serialport_api;

import java.io.File;

import java.io.FileInputStream;

import java.io.FileOutputStream;

import java.io.IOException;

import com.fx.serialporttest.L;

public  class SerialPortFinger {

private static ReadThread readThread;

private static FileInputStream mFileInputStream;

private static FileOutputStream mFileOutputStream;

static String path = "/dev/ttyS0";//设备主板的串口地址，地址有所不同

public  void startListener(){

SerialPort serialPort = new SerialPort(new File(path), 9600, 0);//9600是波特率，这个也是有所不同，具体要看设备

mFileInputStream = serialPort.getmFileInputStream();

mFileOutputStream = serialPort.getmFileOutputStream();//获取串口写入流

readThread  = new ReadThread();

readThread.start();//开启监听

}

/**

* 发送指令到串口

*

* @param cmd

* @return

*/

public boolean sendCmds(String cmd) {

boolean result = true;

byte[] mBuffer = (cmd+"\r\n").getBytes();

try {

if (mFileOutputStream != null) {

mFileOutputStream.write(mBuffer);

} else {

result = false;

}

} catch (IOException e) {

e.printStackTrace();

result = false;

}

return result;

}

static class ReadThread extends Thread{

@Override

public void run() {

// TODO Auto-generated method stub

super.run();

int len;

StringBuffer sb = new StringBuffer("");

while(true){ //循环监听串口，读取返回的数据

byte[] buffer = new byte[1024];

if(mFileInputStream==null){

return;

}

try {

len = mFileInputStream.read(buffer);

if(len>0){

sb.append(new String(buffer, 0, len));

}

if(!sb.toString().equals(""))

{

L.tag(sb.toString());//收到串口的返回数据，在日志中打印出来

}

} catch (IOException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

L.tag("接受完成");

}

}

}

}