Android APP通过JNI直接访问硬件框架

1 APP应用程序调用HardControl.java类中的方法

2.1 HardControl.java类中的方法通过系统调用System.loadLibrary("hardcontrol")来加载C库

public class HardControl {
    static {
        try {
            System.loadLibrary("hardcontrol");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

2.2 HardControl.java类申明native本地方法供app java应用程序调用

public class HardControl {
    public static native int ledCtrl(int which, int status);
    public static native int ledOpen();
    public static native void ledClose();
}

3 C库实现对应硬件的控制（open，read，write）

HardControl.java类中申明的native本地方法通过JNI将HardControl.c中实现的本地函数关联起来

HardControl.java                      《==========》               HardControl.c

申明native本地方法                                                          实现并注册对应的native函数

 

App应用程序

1.将申明本地方法的java类导入进来

import com.thisway.hardlibrary.*;

2.new申明native的类

一旦该类被使用，则该类的静态块static{}就会被调用

HardControl.java类中静态块代码通过系统调用System.loadLibrary("hardcontrol")来加载C库

如何加载C库：

2.1 将HardControl.c编译成so动态库

2.2 将生产的动态库HardControl.so编译进apk，或者放到/vendor/lib或者/system/lib路径下

如何将动态库编译进apk

2.2.1 将动态库HardControl.so文件放到app工程路径下的app/libs/armeabi/路径下

2.2.2 然后编译生成apk文件

HardControl hardcontorl = new HardControl();

3.调用类里面申明的native方法

MainActivityApp.java

import xxx.xx.x

 

HardControl.java

package com.thisway.hardlibrary;

public class HardControl {
    public static native int ledCtrl(int which, int status);
    public static native int ledOpen();
    public static native void ledClose();

    static {
        try {
            System.loadLibrary("hardcontrol");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

 

HardControl.c

在系统调用加载C库的时候会调用JNI_OnLoad(JavaVM *jvm, void *reserved)

通过(*env)->FindClass(env, "com/thisway/hardlibrary/HardControl")找到对应加载它的类

通过(*env)->RegisterNatives(env, cls, methods, sizeof(methods)/sizeof(methods[0])

将类中申明的方法同C库中实现的函数关联起来

#include <jni.h>  /* /usr/lib/jvm/java-1.7.0-openjdk-amd64/include/ */
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>

#include <android/log.h>  /* liblog */

//__android_log_print(ANDROID_LOG_DEBUG, "JNIDemo", "native add ...");

 
#if 0
typedef struct {
    char *name;          /* Java里调用的函数名 */
    char *signature;    /* JNI字段描述符, 用来表示Java里调用的函数的参数和返回值类型 */
    void *fnPtr;          /* C语言实现的本地函数 */
} JNINativeMethod;
#endif

static jint fd;

jint ledOpen(JNIEnv *env, jobject cls)
{
	fd = open("/dev/leds", O_RDWR);
	__android_log_print(ANDROID_LOG_DEBUG, "LEDDemo", "native ledOpen : %d", fd);
	if (fd >= 0)
		return 0;
	else
		return -1;
}

void ledClose(JNIEnv *env, jobject cls)
{
	__android_log_print(ANDROID_LOG_DEBUG, "LEDDemo", "native ledClose ...");
	close(fd);
}


jint ledCtrl(JNIEnv *env, jobject cls, jint which, jint status)
{
	int ret = ioctl(fd, status, which);
	__android_log_print(ANDROID_LOG_DEBUG, "LEDDemo", "native ledCtrl : %d, %d, %d", which, status, ret);
	return ret;
}


static const JNINativeMethod methods[] = {
	{"ledOpen", "()I", (void *)ledOpen},
	{"ledClose", "()V", (void *)ledClose},
	{"ledCtrl", "(II)I", (void *)ledCtrl},
};




/* System.loadLibrary */
JNIEXPORT jint JNICALL
JNI_OnLoad(JavaVM *jvm, void *reserved)
{
	JNIEnv *env;
	jclass cls;

	if ((*jvm)->GetEnv(jvm, (void **)&env, JNI_VERSION_1_4)) {
		return JNI_ERR; /* JNI version not supported */
	}
	cls = (*env)->FindClass(env, "com/thisway/hardlibrary/HardControl");
	if (cls == NULL) {
		return JNI_ERR;
	}

	/* 2. map java hello <-->c c_hello */
	if ((*env)->RegisterNatives(env, cls, methods, sizeof(methods)/sizeof(methods[0])) < 0)
		return JNI_ERR;

	return JNI_VERSION_1_4;
}