class CPUUsage {
private static final String TAG = "CpuUsage";
private RandomAccessFile statFile;
private CpuInfo mCpuInfoTotal;
private ArrayList<CpuInfo> mCpuInfoList;

CPUUsage() {
}

private void update() {
    try {
        createFile();
        parseFile();
        closeFile();
    } catch (FileNotFoundException e) {
        statFile = null;
        Log.e(TAG, "cannot open /proc/stat: " + e);
    } catch (IOException e) {
        Log.e(TAG, "cannot close /proc/stat: " + e);
    }
}

private void createFile() throws FileNotFoundException {
    statFile = new RandomAccessFile("/proc/stat", "r");
}

private void closeFile() throws IOException {
    if (statFile != null)
        statFile.close();
}

private void parseFile() {
    if (statFile != null) {
        try {
            statFile.seek(0);
            String cpuLine;
            int cpuId = -1;
            do {
                cpuLine = statFile.readLine();
                parseCpuLine(cpuId, cpuLine);
                cpuId++;
            } while (cpuLine != null);
        } catch (IOException e) {
            Log.e(TAG, "Ops: " + e);
        }
    }
}

private void parseCpuLine(int cpuId, String cpuLine) {
    if (cpuLine != null && cpuLine.length() > 0) {
        String[] parts = cpuLine.split("[ ]+");
        String cpuLabel = "cpu";
        if (parts[0].contains(cpuLabel)) {
            createCpuInfo(cpuId, parts);
        }
    } else {
        Log.e(TAG, "unable to get cpu line");
    }
}

private void createCpuInfo(int cpuId, String[] parts) {
    if (cpuId == -1) {
        if (mCpuInfoTotal == null)
            mCpuInfoTotal = new CpuInfo();
        mCpuInfoTotal.update(parts);
    } else {
        if (mCpuInfoList == null)
            mCpuInfoList = new ArrayList<>();
        if (cpuId < mCpuInfoList.size())
            mCpuInfoList.get(cpuId).update(parts);
        else {
            CpuInfo info = new CpuInfo();
            info.update(parts);
            mCpuInfoList.add(info);
        }
    }
}

int getTotalCpuUsage() {
    update();
    int usage = 0;
    if (mCpuInfoTotal != null)
        usage = mCpuInfoTotal.getUsage();
    return usage;
}


public String toString() {
    update();
    StringBuilder buf = new StringBuilder();
    if (mCpuInfoTotal != null) {
        buf.append("Cpu Total : ");
        buf.append(mCpuInfoTotal.getUsage());
        buf.append("%");
    }
    if (mCpuInfoList != null) {
        for (int i = 0; i < mCpuInfoList.size(); i++) {
            CpuInfo info = mCpuInfoList.get(i);
            buf.append(" Cpu Core(").append(i).append(") : ");
            buf.append(info.getUsage());
            buf.append("%");
            info.getUsage();
        }
    }
    return buf.toString();
}

private class CpuInfo {
    private int mUsage;
    private long mLastTotal;
    private long mLastIdle;

    CpuInfo() {
        mUsage = 0;
        mLastTotal = 0;
        mLastIdle = 0;
    }

    private int getUsage() {
        return mUsage;
    }

    void update(String[] parts) {
        long idle = Long.parseLong(parts[4], 10);
        long total = 0;
        boolean head = true;
        for (String part : parts) {
            if (head) {
                head = false;
                continue;
            }
            total += Long.parseLong(part, 10);
        }
        long diffIdle = idle - mLastIdle;
        long diffTotal = total - mLastTotal;
        mUsage = (int) ((float) (diffTotal - diffIdle) / diffTotal * 100);
        mLastTotal = total;
        mLastIdle = idle;
        Log.i(TAG, "CPU total=" + total + "; idle=" + idle + "; usage=" + mUsage);
    }
}

cpu  32875 8617 24283 55887 1700 1288 1280 0 0 0
cpu0 9055 2312 8395 34225 1281 643 625 0 0 0
cpu1 7098 2263 5864 121 1 219 203 0 0 0
cpu2 7526 2176 4967 141 0 219 186 0 0 0
cpu3 5462 1593 3823 134 0 156 162 0 0 0
cpu4 1284 91 440 5692 72 20 16 0 0 0
cpu5 473 44 211 2588 125 6 67 0 0 0
cpu6 516 47 210 3047 49 10 3 0 0 0
cpu7 1461 91 373 9939 172 15 18 0 0 0