[Android jni开发系列(四)]利用jni开发生成Android串口开发的so库

1、定义包含native方法的java类

package android.serialport.api;

import android.util.Log;

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;


/**
 * Create by Jason.Yin 2018/4/24.
 */
public class SerialPort {
    private static final String TAG = "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;

    public SerialPort(File device, int baudrate, int flags) throws SecurityException, IOException {
        /* Check access permission, the serial port must can be write and read */
        if (!device.canRead() || !device.canWrite()) {
            try {
                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, flags);
        if (mFd == null) {
            Log.e(TAG, "native open returns null");
            throw new IOException();
        }
        mFileInputStream = new FileInputStream(mFd);
        mFileOutputStream = new FileOutputStream(mFd);
    }


    public InputStream getInputStream() {
        return mFileInputStream;
    }

    public OutputStream getOutputStream() {
        return mFileOutputStream;
    }

    //Definition jni method
    private native static FileDescriptor open(String path, int baudrate, int flags);

    public native void close();

    static {
        System.loadLibrary("serial_port");
    }
}

2、利用《[Android jni开发系列(二)]AndroidStudio移植eclipse NDK项目开发》中定义的javah命令生成jni的头文件

android_serialport_api_SerialPort.h
/* DO NOT EDIT THIS FILE - it is machine generated */
#include 
/* Header for class android_serialport_api_SerialPort */

#ifndef _Included_android_serialport_api_SerialPort
#define _Included_android_serialport_api_SerialPort
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     android_serialport_api_SerialPort
 * Method:    open
 * Signature: (Ljava/lang/String;II)Ljava/io/FileDescriptor;
 */
JNIEXPORT jobject JNICALL Java_android_serialport_api_SerialPort_open
  (JNIEnv *, jclass, jstring, jint, jint);

/*
 * Class:     android_serialport_api_SerialPort
 * Method:    close
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_android_serialport_api_SerialPort_close
  (JNIEnv *, jobject);

#ifdef __cplusplus
}
#endif
#endif

3、实现android_serialport_api_SerialPort.h中的方法

//
// Created by Jason.Yin on 2018/4/11.
//

/* DO NOT EDIT THIS FILE - it is machine generated */
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include"android_serialport_api_SerialPort.h"
#include 

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_api_SerialPort
 * Method:    open
 * Signature: (Ljava/lang/String;II)Ljava/io/FileDescriptor;
 */
JNIEXPORT jobject JNICALL Java_android_serialport_api_SerialPort_open
        (JNIEnv *env, jclass thiz, jstring path, jint baudrate, jint flags) {

    int fd;
    speed_t speed;
    jobject mFileDescriptor;

    /* Check arguments */
    speed = getBaudrate(baudrate);
    if (speed == -1) {
        /* TODO: throw an exception */
        LOGE("Invalid baudrate");
        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 | flags);
        fd = open(path_utf, O_RDWR | flags);
        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);
        cfsetispeed(&cfg, speed);
        cfsetospeed(&cfg, speed);

        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, "", "()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:     android_serialport_api_SerialPort
 * Method:    close
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_android_serialport_api_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);
}

4、配置gradle.properties和build.gradle文件

gradle.properties
android.useDeprecatedNdk=true //添加这行

build.gradle
    defaultConfig {
       ...
        ndk {
            moduleName "serial_port"
            ldLibs "log", "z", "m"  //log依赖
//           abiFilters "armeabi", "armeabi-v7a", "x86"  //ndk 版本不能用最新的，本人测试android-ndk-r15c可以，其它的没试
//            abiFilters "armeabi-v7a", "x86" //ndk版本17.0.4640043 rc1不支持armeabi，否则编译会出错
        }
    }

5、编译工程后会在下图所示目录生成对应so库