android.os.FileUtils#readTextFile ( )源码实例Demo

/**
 * Hacky test to check if the device has an active USB connection, which is
 * a good proxy for someone doing local development work.
 */
private static boolean isUsbActive() {
    if (SystemProperties.getBoolean(PROP_VIRTUAL_DEVICE, false)) {
        Slog.v(TAG, "Assuming virtual device is connected over USB");
        return true;
    }
    try {
        final String state = FileUtils
                .readTextFile(new File("/sys/class/android_usb/android0/state"), 128, "");
        return "CONFIGURED".equals(state.trim());
    } catch (Throwable t) {
        Slog.w(TAG, "Failed to determine if device was on USB", t);
        return false;
    }
}
 

private static String readFileContents(String path) {
    final File file = new File(path);
    if (!file.exists()) {
        if (DEBUG_METRICS) Slog.i(TAG, path + " not found");
        return null;
    }

    try {
        return FileUtils.readTextFile(file, 0 /* max */, null /* ellipsis */);
    } catch (IOException e) {
        Slog.e(TAG, "Failed to read file:", e);
        return null;
    }
}
 

private void performPendingShutdown() {
    final String shutdownAction = SystemProperties.get(
            ShutdownThread.SHUTDOWN_ACTION_PROPERTY, "");
    if (shutdownAction != null && shutdownAction.length() > 0) {
        boolean reboot = (shutdownAction.charAt(0) == '1');

        final String reason;
        if (shutdownAction.length() > 1) {
            reason = shutdownAction.substring(1, shutdownAction.length());
        } else {
            reason = null;
        }

        // If it's a pending reboot into recovery to apply an update,
        // always make sure uncrypt gets executed properly when needed.
        // If '/cache/recovery/block.map' hasn't been created, stop the
        // reboot which will fail for sure, and get a chance to capture a
        // bugreport when that's still feasible. (Bug: 26444951)
        if (reason != null && reason.startsWith(PowerManager.REBOOT_RECOVERY_UPDATE)) {
            File packageFile = new File(UNCRYPT_PACKAGE_FILE);
            if (packageFile.exists()) {
                String filename = null;
                try {
                    filename = FileUtils.readTextFile(packageFile, 0, null);
                } catch (IOException e) {
                    Slog.e(TAG, "Error reading uncrypt package file", e);
                }

                if (filename != null && filename.startsWith("/data")) {
                    if (!new File(BLOCK_MAP_FILE).exists()) {
                        Slog.e(TAG, "Can't find block map file, uncrypt failed or " +
                                   "unexpected runtime restart?");
                        return;
                    }
                }
            }
        }
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                synchronized (this) {
                    ShutdownThread.rebootOrShutdown(null, reboot, reason);
                }
            }
        };

        // ShutdownThread must run on a looper capable of displaying the UI.
        Message msg = Message.obtain(UiThread.getHandler(), runnable);
        msg.setAsynchronous(true);
        UiThread.getHandler().sendMessage(msg);

    }
}