Android读写串口的时候需要jni调用c代码来实现，在开始之前需要下载ndk并配置好环境变量，也就是path里面加上ndk的bin路径。下面是具体的步骤
1、建一个包含jni方法的串口操作类：
package com.luoye.frigo.device;
public class SerialPortReaderWriter {
protected native int open(String path, int baudrate, int parity,int stopBites,int dataBites);
protected native void close(int fd);
protected native int read(int fd,byte[] bytes,int len);
protected native int write(int fd,byte[] bytes,int len);
}
2、在java目录下编译SerialPortReaderWriter这个类：
D:\myprojects\android\LibTestApp\device\src\main\java>javac -d ../jni com/luoye/frigo/device/SerialPortReaderWriter.java
3、在jni目录下生成c头文件SerialPortReaderWriter.h:
D:\myprojects\android\LibTestApp\device\src\main\jni>javah -o SerialPortReaderWriter.h -jni com.luoye.frigo.device.SerialPortReaderWriter
4、在jni目录下添加c文件SerialPortReaderWriter.c，在这个文件中实现串口操作的逻辑：
//
// Created by dave on 2020/4/28.
//
#include <termios.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <jni.h>
#include "SerialPortReaderWriter.h"
#include "android/log.h"
static const char *TAG="serial_port_reader_writer";
#define LOGI(fmt, args...) __android_log_print(ANDROID_LOG_INFO, TAG, fmt, ##args)
#define LOGD(fmt, args...) __android_log_print(ANDROID_LOG_DEBUG, TAG, fmt, ##args)
#define LOGE(fmt, args...) __android_log_print(ANDROID_LOG_ERROR, TAG, fmt, ##args)
static speed_t getBaudrate(jint baudrate)
{
switch(baudrate) {
case 0: return B0;
case 50: return B50;
case 75: return B75;
case 110: return B110;
case 134: return B134;
case 150: return B150;
case 200: return B200;
case 300: return B300;
case 600: return B600;
case 1200: return B1200;
case 1800: return B1800;
case 2400: return B2400;
case 4800: return B4800;
case 9600: return B9600;
case 19200: return B19200;
case 38400: return B38400;
case 57600: return B57600;
case 115200: return B115200;
case 230400: return B230400;
case 460800: return B460800;
case 500000: return B500000;
case 576000: return B576000;
case 921600: return B921600;
case 1000000: return B1000000;
case 1152000: return B1152000;
case 1500000: return B1500000;
case 2000000: return B2000000;
case 2500000: return B2500000;
case 3000000: return B3000000;
case 3500000: return B3500000;
case 4000000: return B4000000;
default: return -1;
}
}
/*
* Class: com_tricent_frigo_device_SerialPortReaderWriter
* Method: open
* Signature: (Ljava/lang/String;IIII)I
*/
JNIEXPORT jint JNICALL Java_com_luoye_frigo_device_SerialPortReaderWriter_open
(JNIEnv *env, jobject thiz, jstring path, jint baudrate, jint parity, jint stop_bites, jint data_bites){
int fd=0;
speed_t speed;
jobject mFileDescriptor;
/* Check arguments */
{
speed = getBaudrate(baudrate);
if (speed == -1) {
/* TODO: throw an exception */
LOGE("Invalid baudrate");
return -1;
}
if(parity>5||parity<1){
LOGE("Invalid parity");
return -2;
}
if(stop_bites>3||stop_bites<1){
LOGE("Invalid stop_bites");
return -3;
}
if(data_bites>8||data_bites<5){
LOGE("Invalid data_bites");
return -4;
}
}
/* Opening device */
{
jboolean iscopy;
const char *path_utf = (*env)->GetStringUTFChars(env, path, &iscopy);
LOGD("Opening serial port %s with flags 0x%x", path_utf, O_RDWR | O_NOCTTY | O_NDELAY);
fd = open(path_utf, O_RDWR | O_NOCTTY | O_NDELAY);
LOGD("open() fd = %d", fd);
(*env)->ReleaseStringUTFChars(env, path, path_utf);
if (fd == -1)
{
/* Throw an exception */
LOGE("Cannot open port");
/* TODO: throw an exception */
return -5;
}
}
/* Configure device */
{
struct termios cfg;
LOGD("Configuring serial port");
if (tcgetattr(fd, &cfg))
{
LOGE("tcgetattr() failed");
close(fd);
/* TODO: throw an exception */
return -6;
}
//cfmakeraw(&cfg);
/*设置波特率*/
//tcflush(fd,TCIOFLUSH);
cfsetispeed(&cfg,speed);
/*设置数据位*/
cfg.c_cflag &= ~CSIZE;
switch (data_bites) /*设置数据位数*/
{
case 5:
cfg.c_cflag |= CS5;
break;
case 6:
cfg.c_cflag |= CS6;
break;
case 7:
cfg.c_cflag |= CS7;
break;
case 8:
cfg.c_cflag |= CS8;
break;
}
/*设置奇偶校验率*/
switch (parity)
{
case 1:
cfg.c_cflag &= ~PARENB; /* Clear parity enable */
cfg.c_iflag &= ~INPCK; /* Enable parity checking */
break;
case 2:
cfg.c_cflag |= (PARODD | PARENB); /* 设置为奇效验*/
cfg.c_iflag |= INPCK; /* Disnable parity checking */
break;
case 3:
cfg.c_cflag |= PARENB; /* Enable parity */
cfg.c_cflag &= ~PARODD; /* 转换为偶效验*/
cfg.c_iflag |= INPCK; /* Disnable parity checking */
break;
case 4: /*as no parity*/
cfg.c_cflag &= ~PARENB;
cfg.c_cflag &= ~CSTOPB;
break;
case 5:
cfg.c_cflag &= ~PARENB;
cfg.c_cflag &= CSTOPB;
break;
}
/* 设置停止位*/
switch (stop_bites)
{
case 1:
cfg.c_cflag &= ~CSTOPB;
break;
case 2:
cfg.c_cflag |= CSTOPB;
break;
}
cfg.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
//屏蔽软件流控，让X-ON X-OFF可以发送出去
cfg.c_iflag &= ~ (IXON | IXOFF | IXANY | ICRNL);
cfg.c_oflag &= ~OPOST;
cfg.c_cc[VTIME] = 150; /* 设置超时15 seconds*/
cfg.c_cc[VMIN] = 0;
tcflush(fd,TCIFLUSH);/* Update the cfg and do it NOW */
//立即将新属性赋予串口
if (tcsetattr(fd, TCSANOW, &cfg))
{
LOGE("tcsetattr() failed");
close(fd);
/* TODO: throw an exception */
return -7;
}
}
return fd;
}
/*
* Class: com_tricent_frigo_device_SerialPortReaderWriter
* Method: close
* Signature: (I)V
*/
JNIEXPORT void JNICALL Java_com_luoye_frigo_device_SerialPortReaderWriter_close
(JNIEnv *env, jobject thiz, jint fd){
LOGD("close(fd = %d)", fd);
close(fd);
}
/*
* Class: com_tricent_frigo_device_SerialPortReaderWriter
* Method: read
* Signature: (I[BI)I
*/
JNIEXPORT jint JNICALL Java_com_luoye_frigo_device_SerialPortReaderWriter_read
(JNIEnv *env, jobject thiz, jint fd, jbyteArray byteArray, jint len){
//方式1
jbyte* byte = (*env)->GetByteArrayElements(env,byteArray, 0);
//jbyte* byte = env->GetByteArrayElements(byteArray, 0);//c++写法
int nRet = read(fd,byte,len);
LOGD("read(nRet = %d)", nRet);
//方式2
//char chTmp[len];
//memset(chTmp, 0, len);
//int nRet = read(fd,chTmp,len);
//LOGD("read(nRet = %d)", nRet);
//(*env)->SetByteArrayRegion(env,byteArray, 0, len, chTmp);
return nRet;
}
/*
* Class: com_tricent_frigo_device_SerialPortReaderWriter
* Method: write
* Signature: (I[BI)I
*/
JNIEXPORT jint JNICALL Java_com_luoye_frigo_device_SerialPortReaderWriter_write
(JNIEnv *env, jobject thiz, jint fd, jbyteArray byteArray, jint len){
jbyte* byte = (*env)->GetByteArrayElements(env,byteArray, 0);
int nRet = write(fd,byte,len);
LOGD("write(nRet = %d)", nRet);
(*env)->ReleaseByteArrayElements(env, byteArray, byte, 0);
return nRet;
}
5、在jni目录下添加makefile文件Android.mk:
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := dev-jni
LOCAL_SRC_FILES := SerialPortReaderWriter.c
LOCAL_LDLIBS := -llog
include $(BUILD_SHARED_LIBRARY)
6、在jni目录下执行ndk-build命令：
D:\myprojects\android\LibTestApp\device\src\main\jni>ndk-build
7、将生成的libs目录拷贝到项目根目录
8、在Java类SerialPortReaderWriter中添加：
static {
System.loadLibrary("dev-jni");
}
完善后的完整代码：
package com.luoye.frigo.device;
public class SerialPortReaderWriter {
static {
System.loadLibrary("dev-jni");
}
protected native int open(String path, int baudrate, int parity,int stopBites,int dataBites);
protected native void close(int fd);
protected native int read(int fd,byte[] bytes,int len);
protected native int write(int fd,byte[] bytes,int len);
private int fd=-1;
public void openSerialPort(String path, int baudrate, int parity,int stopBites,int dataBites){
fd=open(path,baudrate,parity,stopBites,dataBites);
}
public void openSerialPort(String path, int baudrate){
openSerialPort(path,baudrate,1,1,8);
}
public void closeSerialPort(){
close(fd);
fd=-1;
}
public int read(byte[] bytes){
if(bytes==null||fd==-1){
return 0;
}
int len=bytes.length;
return read(fd,bytes,len);
}
public int write(byte[] bytes){
if(bytes==null||fd==-1){
return 0;
}
int len=bytes.length;
return write(fd,bytes,len);
}
}
9、使用示例：
SerialPortReaderWriter serialPortReaderWriter=new SerialPortReaderWriter();
serialPortReaderWriter.openSerialPort("/dev/ttymxc3",9600);
serialPortReaderWriter.write("hello world".getBytes());
byte bs[]=new byte[32];
int r=serialPortReaderWriter.read(bs);
etr.setText(r+":"+new String(bs));
serialPortReaderWriter.closeSerialPort();
补充（另一种方式：通过在Java类中保留文件描述符，然后基于此获取java的输入输出流来对串口进行读写）：
package com.luoye.frigo.device;
import java.io.File;
import java.io.FileDescriptor;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import android.util.Log;
public class SerialPort {
private static final String TAG = "SerialPort";
public interface SerialPath{
String TTYMXC1="/dev/ttymxc1";
String TTYMXC2="/dev/ttymxc2";
String TTYMXC3="/dev/ttymxc3";
String TTYMXC4="/dev/ttymxc4";
}
public interface SerialPortParity {
int None=1; //没有校验位 无校验（8bit)
int Odd=2; //每个字节穿送整个过程中bit为1的个数是奇数个（校验位调整个数）奇校验（7bit)
int ComEvent=3; //每个字节传送整个过程中bit为1的个数是偶数个（校验位调整个数）偶校验（7bit)
int Mark=4; //校验位总为1(8bit)
int Space=5; //校验位总为0 Space校验（7bit)
}
//定义停止位
public interface SerialPortStopBits{
int STOP_1 = 1;
int STOP_2=2;
}
//数据位
public interface SerialPortDataBits{
int BITS_5 = 5;
int BITS_6 = 6;
int BITS_7 = 7;
int BITS_8 = 8;
}
//
//
// /*
// * Do not remove or rename the field mFd: it is used by native method close();
// */
private FileDescriptor mFd;
private FileInputStream mFileInputStream;
private FileOutputStream mFileOutputStream;
protected SerialPort(File device, int baudrate, int parity, int stopBites, int dataBites) throws SecurityException, IOException {
/* Check access permission */
if (!device.canRead() || !device.canWrite()) {
try {
/* Missing read/write permission, trying to chmod the file */
Process su;
su = Runtime.getRuntime().exec("/system/bin/su");
String cmd = "chmod 666 " + device.getAbsolutePath() + "\n"
+ "exit\n";
su.getOutputStream().write(cmd.getBytes());
if ((su.waitFor() != 0) || !device.canRead()
|| !device.canWrite()) {
throw new SecurityException();
}
} catch (Exception e) {
e.printStackTrace();
throw new SecurityException();
}
}
mFd = open(device.getAbsolutePath(), baudrate, parity,stopBites,dataBites);
if (mFd == null) {
Log.e(TAG, "native open returns null");
throw new IOException();
}
mFileInputStream = new FileInputStream(mFd);
mFileOutputStream = new FileOutputStream(mFd);
}
// Getters and setters
protected InputStream getInputStream() {
return mFileInputStream;
}
protected OutputStream getOutputStream() {
return mFileOutputStream;
}
// JNI:设备文件路径，波特率，奇偶校验位，停止位，数据位
private native static FileDescriptor open(String path, int baudrate, int parity,int stopBites,int dataBites);
protected native void close();
static {
System.loadLibrary("serial_port");
}
}
SerialPort.h
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/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_luoye_frigo_device_SerialPort */
#ifndef _Included_com_tricent_frigo_device_SerialPort
#define _Included_com_tricent_frigo_device_SerialPort
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: com_luoye_frigo_device_SerialPort
* Method: open
* Signature: (Ljava/lang/String;IIII)Ljava/io/FileDescriptor;
*/
JNIEXPORT jobject JNICALL Java_com_luoye_frigo_device_SerialPort_open
(JNIEnv *, jclass, jstring, jint, jint, jint, jint);
/*
* Class: com_tricent_frigo_device_SerialPort
* Method: close
* Signature: ()V
*/
JNIEXPORT void JNICALL Java_com_luoye_frigo_device_SerialPort_close
(JNIEnv *, jobject);
#ifdef __cplusplus
}
#endif
#endif
SerialPort.c
/*
* Copyright 2009-2011 Cedric Priscal
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <termios.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <jni.h>
#include "SerialPort.h"
#include "android/log.h"
static const char *TAG="serial_port";
#define LOGI(fmt, args...) __android_log_print(ANDROID_LOG_INFO, TAG, fmt, ##args)
#define LOGD(fmt, args...) __android_log_print(ANDROID_LOG_DEBUG, TAG, fmt, ##args)
#define LOGE(fmt, args...) __android_log_print(ANDROID_LOG_ERROR, TAG, fmt, ##args)
static speed_t getBaudrate(jint baudrate)
{
switch(baudrate) {
case 0: return B0;
case 50: return B50;
case 75: return B75;
case 110: return B110;
case 134: return B134;
case 150: return B150;
case 200: return B200;
case 300: return B300;
case 600: return B600;
case 1200: return B1200;
case 1800: return B1800;
case 2400: return B2400;
case 4800: return B4800;
case 9600: return B9600;
case 19200: return B19200;
case 38400: return B38400;
case 57600: return B57600;
case 115200: return B115200;
case 230400: return B230400;
case 460800: return B460800;
case 500000: return B500000;
case 576000: return B576000;
case 921600: return B921600;
case 1000000: return B1000000;
case 1152000: return B1152000;
case 1500000: return B1500000;
case 2000000: return B2000000;
case 2500000: return B2500000;
case 3000000: return B3000000;
case 3500000: return B3500000;
case 4000000: return B4000000;
default: return -1;
}
}
/*
* Class: android_serialport_SerialPort
* Method: open
* Signature: (Ljava/lang/String;II)Ljava/io/FileDescriptor;
*/
JNIEXPORT jobject JNICALL Java_com_luoye_frigo_device_SerialPort_open
(JNIEnv *env, jclass thiz, jstring path, jint baudrate, jint parity, jint stop_bites, jint data_bites)
{
int fd;
speed_t speed;
jobject mFileDescriptor;
/* Check arguments */
{
speed = getBaudrate(baudrate);
if (speed == -1) {
/* TODO: throw an exception */
LOGE("Invalid baudrate");
return NULL;
}
if(parity>5||parity<1){
LOGE("Invalid parity");
return NULL;
}
if(stop_bites>3||stop_bites<1){
LOGE("Invalid stop_bites");
return NULL;
}
if(data_bites>8||data_bites<5){
LOGE("Invalid data_bites");
return NULL;
}
}
/* Opening device */
{
jboolean iscopy;
const char *path_utf = (*env)->GetStringUTFChars(env, path, &iscopy);
LOGD("Opening serial port %s with flags 0x%x", path_utf, O_RDWR | O_NOCTTY | O_NDELAY);
fd = open(path_utf, O_RDWR | O_NOCTTY | O_NDELAY);
LOGD("open() fd = %d", fd);
(*env)->ReleaseStringUTFChars(env, path, path_utf);
if (fd == -1)
{
/* Throw an exception */
LOGE("Cannot open port");
/* TODO: throw an exception */
return NULL;
}
}
/* Configure device */
{
struct termios cfg;
LOGD("Configuring serial port");
if (tcgetattr(fd, &cfg))
{
LOGE("tcgetattr() failed");
close(fd);
/* TODO: throw an exception */
return NULL;
}
//cfmakeraw(&cfg);
/*设置波特率*/
//tcflush(fd,TCIOFLUSH);
cfsetispeed(&cfg,speed);
/*设置数据位*/
cfg.c_cflag &= ~CSIZE;
switch (data_bites) /*设置数据位数*/
{
case 5:
cfg.c_cflag |= CS5;
break;
case 6:
cfg.c_cflag |= CS6;
break;
case 7:
cfg.c_cflag |= CS7;
break;
case 8:
cfg.c_cflag |= CS8;
break;
}
/*设置奇偶校验率*/
switch (parity)
{
case 1:
cfg.c_cflag &= ~PARENB; /* Clear parity enable */
cfg.c_iflag &= ~INPCK; /* Enable parity checking */
break;
case 2:
cfg.c_cflag |= (PARODD | PARENB); /* 设置为奇效验*/
cfg.c_iflag |= INPCK; /* Disnable parity checking */
break;
case 3:
cfg.c_cflag |= PARENB; /* Enable parity */
cfg.c_cflag &= ~PARODD; /* 转换为偶效验*/
cfg.c_iflag |= INPCK; /* Disnable parity checking */
break;
case 4: /*as no parity*/
cfg.c_cflag &= ~PARENB;
cfg.c_cflag &= ~CSTOPB;
break;
case 5:
cfg.c_cflag &= ~PARENB;
cfg.c_cflag &= CSTOPB;
break;
}
/* 设置停止位*/
switch (stop_bites)
{
case 1:
cfg.c_cflag &= ~CSTOPB;
break;
case 2:
cfg.c_cflag |= CSTOPB;
break;
}
cfg.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
//屏蔽软件流控，让X-ON X-OFF可以发送出去
cfg.c_iflag &= ~ (IXON | IXOFF | IXANY | ICRNL);
cfg.c_oflag &= ~OPOST;
cfg.c_cc[VTIME] = 150; /* 设置超时15 seconds*/
cfg.c_cc[VMIN] = 0;
tcflush(fd,TCIFLUSH);/* Update the cfg and do it NOW */
//立即将新属性赋予串口
if (tcsetattr(fd, TCSANOW, &cfg))
{
LOGE("tcsetattr() failed");
close(fd);
/* TODO: throw an exception */
return NULL;
}
}
/* Create a corresponding file descriptor */
{
jclass cFileDescriptor = (*env)->FindClass(env, "java/io/FileDescriptor");
jmethodID iFileDescriptor = (*env)->GetMethodID(env, cFileDescriptor, "<init>", "()V");
jfieldID descriptorID = (*env)->GetFieldID(env, cFileDescriptor, "descriptor", "I");
mFileDescriptor = (*env)->NewObject(env, cFileDescriptor, iFileDescriptor);
(*env)->SetIntField(env, mFileDescriptor, descriptorID, (jint)fd);
}
return mFileDescriptor;
}
/*
* Class: cedric_serial_SerialPort
* Method: close
* Signature: ()V
*/
JNIEXPORT void JNICALL Java_com_luoye_frigo_device_SerialPort_close
(JNIEnv *env, jobject thiz)
{
jclass SerialPortClass = (*env)->GetObjectClass(env, thiz);
jclass FileDescriptorClass = (*env)->FindClass(env, "java/io/FileDescriptor");
jfieldID mFdID = (*env)->GetFieldID(env, SerialPortClass, "mFd", "Ljava/io/FileDescriptor;");
jfieldID descriptorID = (*env)->GetFieldID(env, FileDescriptorClass, "descriptor", "I");
jobject mFd = (*env)->GetObjectField(env, thiz, mFdID);
jint descriptor = (*env)->GetIntField(env, mFd, descriptorID);
LOGD("close(fd = %d)", descriptor);
close(descriptor);
}