android的HAL第一种调用hal方法中的JNI代码的实现：

 （2）JNI层
文件：mokoid-read-only/frameworks/base/service/jni/com_mokoid_server_LedService.cpp
 
struct led_control_device_t *sLedDevice = NULL;    
static jboolean mokoid_setOn(JNIEnv* env, jobject thiz, jint led)   
{  
    LOGI("LedService JNI: mokoid_setOn() is invoked.");  
    if (sLedDevice == NULL) {  
        LOGI("LedService JNI: sLedDevice was not fetched correctly.");  
        return -1;  
    } else {  
        return sLedDevice->set_on(sLedDevice, led);//调用hal层的注册的方法  
    }  
}  
  
static jboolean mokoid_setOff(JNIEnv* env, jobject thiz, jint led)   
{  
    LOGI("LedService JNI: mokoid_setOff() is invoked.");  
  
  
    if (sLedDevice == NULL) {  
        LOGI("LedService JNI: sLedDevice was not fetched correctly.");  
        return -1;  
    } else {  
        return sLedDevice->set_off(sLedDevice, led); //调用hal层的注册的方法  
    }  
}  
  
/** helper APIs */  
static inline int led_control_open(const struct hw_module_t* module,  
        struct led_control_device_t** device) {  
            return module->methods->open(module,LED_HARDWARE_MODULE_ID, (struct hw_device_t**)device);  
            //这个过程非常重要，jni通过LED_HARDWARE_MODULE_ID找到对应的stub  
}  
  
static jboolean mokoid_init(JNIEnv *env, jclass clazz)  
{  
    led_module_t* module;  
     LOGI("jni init-----------------------.");  
     if (hw_get_module(LED_HARDWARE_MODULE_ID, (const hw_module_t**)&module) == 0) {  
        //根据LED_HARDWARE_MODULE_ID找到hw_module_t，参考hal层的实现  
        LOGI("LedService JNI: LED Stub found.");  
        if (led_control_open(&module->common, &sLedDevice) == 0) {    
        //通过hw_module_t找到led_control_device_t  
            LOGI("LedService JNI: Got Stub operations.");  
            return 0;  
        }  
    }  
  
    LOGE("LedService JNI: Get Stub operations failed.");  
    return -1;  
}  
  
/* 
 * Array of methods. 
* Each entry has three fields: the name of the method, the method
* signature, and a pointer to the native implementation. 
 */  
static const JNINativeMethod gMethods[] = {  
    { "_init",      "()Z",  (void *)mokoid_init },//Framework层调用_init时促发  
    { "_set_on",    "(I)Z", (void *)mokoid_setOn },  
    { "_set_off",   "(I)Z", (void *)mokoid_setOff },  
};  
/* 
*JNINativeMethod是jni层注册的方法，Framework层可以使用这些方法 
*_init 、_set_on、_set_off是在Framework中调用的方法名称，函数的类型及返回值如下： 
*（）Z   无参数    返回值为bool型 
* (I)Z   整型参数  返回值为bool型 
*/  
static int registerMethods(JNIEnv* env) {  
        static const char* const kClassName =  
        "com/mokoid/server/LedService";//注意：必须和你Framework层的service类名相同  
        jclass clazz;   
      /* look up the class */  
        clazz = env->FindClass(kClassName);  
        if (clazz == NULL) {  
                    LOGE("Can't find class %s\n", kClassName);  
                    return -1;  
        }  
    /* register all the methods */  
        if (env->RegisterNatives(clazz, gMethods,  
                        sizeof(gMethods) / sizeof(gMethods[0])) != JNI_OK)  
        {  
            LOGE("Failed registering methods for %s\n", kClassName);  
            return -1;  
        }  
    /* fill out the rest of the ID cache */  
        return 0;  
}   
jint JNI_OnLoad(JavaVM* vm, void* reserved) {//Framework层加载jni库时调用   
        JNIEnv* env = NULL;  
        jint result = -1;  
        LOGI("JNI_OnLoad LED");  
            if (vm->GetEnv((void**) &env, JNI_VERSION_1_4) != JNI_OK) {  
            LOGE("ERROR: GetEnv failed\n");  
            goto fail;  
        }  
            assert(env != NULL);  
        if (registerMethods(env) != 0) { //注册你的JNINativeMethod  
            LOGE("ERROR: PlatformLibrary native registration failed\n");  
            goto fail;  
        }  
        /* success -- return valid version number */      
        result = JNI_VERSION_1_4;  
fail:  
        return result;  
}