Android模拟器学framework和driver之battery & backlight-----2. battery in jni

上篇介绍了模拟器的内核goldfish中的battery模块，也介绍了power_supply是如何工作的，一般我自己写驱动也差不多是这个流程，驱动抄着抄着自己就熟悉了，呵呵，记得之前我问过一个前辈，驱动要怎么学习，她说：抄代码先！！！

废话不多扯，这里介绍android jni层是如何处理battery的信息的。

上一篇中讲到在driver中做的事情对我们user有用的就只有2件事情，一是当battery信息发生变化的时候会给用户层发送一个uevent，二是在在文件系统中生成了battery信息的文件，包括电池电量，电池状态灯信息。

这里介绍中间层jni，主要封装读取battery信息的函数，代码位置：android2.3.3/frameworks/base/services/jni/com_android_server_BatteryService.cpp

这里做的事情比较简单：

1. 找到文件系统中我们生成的battery信息的文件路径

2. 找到我们java文件中用到中battery信息相关的类

3. 得到我们java文件中定义的battery信息的变量的fieldID

4.  读取文件系统中相应的battery 信息的文件，通过fieldID给java中的变量赋值，进行battery状态的更新。

1. 找到文件系统中我们生成的battery信息的文件路径

    DIR* dir = opendir(POWER_SUPPLY_PATH);    if (dir == NULL) {        LOGE("Could not open %s\n", POWER_SUPPLY_PATH);        return -1;    }    while ((entry = readdir(dir))) {        const char* name = entry->d_name;        // ignore "." and ".."        if (name[0] == '.' && (name[1] == 0 || (name[1] == '.' && name[2] == 0))) {            continue;        }        char buf[20];        // Look for "type" file in each subdirectory        snprintf(path, sizeof(path), "%s/%s/type", POWER_SUPPLY_PATH, name);        int length = readFromFile(path, buf, sizeof(buf));        if (length > 0) {            if (buf[length - 1] == '\n')                buf[length - 1] = 0;            if (strcmp(buf, "Mains") == 0) {                snprintf(path, sizeof(path), "%s/%s/online", POWER_SUPPLY_PATH, name);                if (access(path, R_OK) == 0)                    gPaths.acOnlinePath = strdup(path);            }            else if (strcmp(buf, "USB") == 0) {                snprintf(path, sizeof(path), "%s/%s/online", POWER_SUPPLY_PATH, name);                if (access(path, R_OK) == 0)                    gPaths.usbOnlinePath = strdup(path);            }            else if (strcmp(buf, "Battery") == 0) {                snprintf(path, sizeof(path), "%s/%s/status", POWER_SUPPLY_PATH, name);                if (access(path, R_OK) == 0)                    gPaths.batteryStatusPath = strdup(path);                snprintf(path, sizeof(path), "%s/%s/health", POWER_SUPPLY_PATH, name);                if (access(path, R_OK) == 0)                    gPaths.batteryHealthPath = strdup(path);                snprintf(path, sizeof(path), "%s/%s/present", POWER_SUPPLY_PATH, name);                if (access(path, R_OK) == 0)                    gPaths.batteryPresentPath = strdup(path);                snprintf(path, sizeof(path), "%s/%s/capacity", POWER_SUPPLY_PATH, name);                if (access(path, R_OK) == 0)                    gPaths.batteryCapacityPath = strdup(path);                snprintf(path, sizeof(path), "%s/%s/voltage_now", POWER_SUPPLY_PATH, name);                if (access(path, R_OK) == 0) {                    gPaths.batteryVoltagePath = strdup(path);                    // voltage_now is in microvolts, not millivolts                    gVoltageDivisor = 1000;                } else {                    snprintf(path, sizeof(path), "%s/%s/batt_vol", POWER_SUPPLY_PATH, name);                    if (access(path, R_OK) == 0)                        gPaths.batteryVoltagePath = strdup(path);                }                snprintf(path, sizeof(path), "%s/%s/temp", POWER_SUPPLY_PATH, name);                if (access(path, R_OK) == 0) {                    gPaths.batteryTemperaturePath = strdup(path);                } else {                    snprintf(path, sizeof(path), "%s/%s/batt_temp", POWER_SUPPLY_PATH, name);                    if (access(path, R_OK) == 0)                        gPaths.batteryTemperaturePath = strdup(path);                }                snprintf(path, sizeof(path), "%s/%s/technology", POWER_SUPPLY_PATH, name);                if (access(path, R_OK) == 0)                    gPaths.batteryTechnologyPath = strdup(path);            }        }    }    closedir(dir);    if (!gPaths.acOnlinePath)        LOGE("acOnlinePath not found");    if (!gPaths.usbOnlinePath)        LOGE("usbOnlinePath not found");    if (!gPaths.batteryStatusPath)        LOGE("batteryStatusPath not found");    if (!gPaths.batteryHealthPath)        LOGE("batteryHealthPath not found");    if (!gPaths.batteryPresentPath)        LOGE("batteryPresentPath not found");    if (!gPaths.batteryCapacityPath)        LOGE("batteryCapacityPath not found");    if (!gPaths.batteryVoltagePath)        LOGE("batteryVoltagePath not found");    if (!gPaths.batteryTemperaturePath)        LOGE("batteryTemperaturePath not found");    if (!gPaths.batteryTechnologyPath)        LOGE("batteryTechnologyPath not found");

2. 找到我们java文件中用到中battery信息相关的类

    jclass clazz = env->FindClass("com/android/server/BatteryService");    if (clazz == NULL) {        LOGE("Can't find com/android/server/BatteryService");        return -1;    }

3. 得到我们java文件中定义的battery信息的变量的fieldID

    gFieldIds.mAcOnline = env->GetFieldID(clazz, "mAcOnline", "Z");    gFieldIds.mUsbOnline = env->GetFieldID(clazz, "mUsbOnline", "Z");    gFieldIds.mBatteryStatus = env->GetFieldID(clazz, "mBatteryStatus", "I");    gFieldIds.mBatteryHealth = env->GetFieldID(clazz, "mBatteryHealth", "I");    gFieldIds.mBatteryPresent = env->GetFieldID(clazz, "mBatteryPresent", "Z");    gFieldIds.mBatteryLevel = env->GetFieldID(clazz, "mBatteryLevel", "I");    gFieldIds.mBatteryTechnology = env->GetFieldID(clazz, "mBatteryTechnology", "Ljava/lang/String;");    gFieldIds.mBatteryVoltage = env->GetFieldID(clazz, "mBatteryVoltage", "I");    gFieldIds.mBatteryTemperature = env->GetFieldID(clazz, "mBatteryTemperature", "I");

4.  读取文件系统中相应的battery 信息的文件，通过fieldID给java中的变量赋值，进行battery状态的更新。

static void android_server_BatteryService_update(JNIEnv* env, jobject obj){    setBooleanField(env, obj, gPaths.acOnlinePath, gFieldIds.mAcOnline);    setBooleanField(env, obj, gPaths.usbOnlinePath, gFieldIds.mUsbOnline);    setBooleanField(env, obj, gPaths.batteryPresentPath, gFieldIds.mBatteryPresent);        setIntField(env, obj, gPaths.batteryCapacityPath, gFieldIds.mBatteryLevel);    setVoltageField(env, obj, gPaths.batteryVoltagePath, gFieldIds.mBatteryVoltage);    setIntField(env, obj, gPaths.batteryTemperaturePath, gFieldIds.mBatteryTemperature);        const int SIZE = 128;    char buf[SIZE];        if (readFromFile(gPaths.batteryStatusPath, buf, SIZE) > 0)        env->SetIntField(obj, gFieldIds.mBatteryStatus, getBatteryStatus(buf));    else        env->SetIntField(obj, gFieldIds.mBatteryStatus,                         gConstants.statusUnknown);        if (readFromFile(gPaths.batteryHealthPath, buf, SIZE) > 0)        env->SetIntField(obj, gFieldIds.mBatteryHealth, getBatteryHealth(buf));    if (readFromFile(gPaths.batteryTechnologyPath, buf, SIZE) > 0)        env->SetObjectField(obj, gFieldIds.mBatteryTechnology, env->NewStringUTF(buf));}

具体代码自行分析，这边我推荐我的一个关于JNI的专栏，那里我写的比较详细，在jni是如何调用java中的成员变量和成员函数的。

http://blog.csdn.net/column/details/jnijni.html

jni层介绍到这边，比较简单。