一、.java生成.class文件
可以有两种方式:
1、直接使用javac 类名(进入到类所在目录)
注意:如果提示'javac' 不是内部或外部命令,也不是可运行的程序的话,需要在环境变量里面的用户变量(不是系统变量哦)中的Path变量,新增%JAVA_HOME%\bin;
2、新增了JNI类以后,rebuild project,这样.class文件会在项目的\app\build\intermediates\classes\debug目录下生成。
二、.class生成.h文件(最坑的一步了)
我在这一步卡了半天,一直不行,总是提示:找不到“xxx.xxx.xxx”的类文件。内心接近崩溃~
最终还是摸索出来了,生成了.h文件。先进入classes目录下,然后执行了如下命令就可以了!(注意有一点.的)
E:\android_workspace\JNITest\app\build\intermediates\classes\debug>javah -classpath . -jni com.river.jnitest.SerialPort
参考博客:https://www.cnblogs.com/xieyuan/p/3787297.html
补充:
我的环境变量里面的系统变量 CLASSPATH的值为:
.;%JAVA_HOME%\lib;%JAVA_HOME%\lib\tools.jar;%JAVA_HOME%\jre\lib\rt.jar;%JAVA_HOME%\lib\dt.jar;
JAVA_HOME的值是jdk的路径:D:\river\jdk1.8
为了证明我是成功了的!粘贴一下代码:
//SerialPort.java
package com.river.jnitest;
import java.io.FileDescriptor;
public class SerialPort {
private native static FileDescriptor open(String path, int baudrate, int flags);
public native void close();
}
下面是生成的.h文件,文件名为:com_river_jnitest_SerialPort.h
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_river_jnitest_SerialPort */
#ifndef _Included_com_river_jnitest_SerialPort
#define _Included_com_river_jnitest_SerialPort
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: com_river_jnitest_SerialPort
* Method: open
* Signature: (Ljava/lang/String;II)Ljava/io/FileDescriptor;
*/
JNIEXPORT jobject JNICALL Java_com_river_jnitest_SerialPort_open
(JNIEnv *, jclass, jstring, jint, jint);
/*
* Class: com_river_jnitest_SerialPort
* Method: close
* Signature: ()V
*/
JNIEXPORT void JNICALL Java_com_river_jnitest_SerialPort_close
(JNIEnv *, jobject);
#ifdef __cplusplus
}
#endif
#endif
三、生成.so文件
1、准备Android.mk、Application.mk文件
2、将.h、.c和两个.mk文件放到同一个目录下
3、进入到2中的目录下,输入ndk-build.cmd的目录,回车,即可生成so文件 (我已经测试过了,可以成功和串口通讯!)
E:\android_workspace\JNITest\app\src\main\jni>D:\river\android\sdk\ndk-bundle\ndk-build.cmd
生成的so会在lib下,如下图:
下面是代码:
Android.mk
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
TARGET_PLATFORM := android-19
LOCAL_MODULE := serial_port
LOCAL_SRC_FILES := SerialPort.c
LOCAL_LDLIBS := -llog
#加了下面这句,可以避免relocation的问题
LOCAL_LDFLAGS += -fPIC
include $(BUILD_SHARED_LIBRARY)
Application.mk
APP_ABI := armeabi-v7a x86
SerialPort.c(源码来自:https://github.com/cepr/android-serialport-api,我修改了两个函数的命名,因为包名被我改了)
#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"/* 生成的com_river_jnitest_SerialPort.h,重命名了 */
#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_river_jnitest_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, "<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_river_jnitest_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);
}
觉得有用的老铁赞一下呗,谢谢!