How to take a screenshot using android service in rooted device

Question

I tried the following code but it is not working for me.

I heard about Library call ASL, but I never found anything about that library.

How can I take a screenshot from the service ? I want to take it using a background service.

try {
    sh = Runtime.getRuntime().exec("su", null,null);
} catch (IOException e) {
    e.printStackTrace();
}

OutputStream os = sh.getOutputStream();
try {
    os.write(("/system/bin/screencap -p " + "/sdcard/img.png").getBytes("ASCII"));
} catch (IOException e) {
    e.printStackTrace();
}
try {
    os.flush();
} catch (IOException e) {
    e.printStackTrace();
}

try {
    os.close();
} catch (IOException e) {
    e.printStackTrace();
}
try {
    sh.waitFor();
} catch (InterruptedException e) {
    e.printStackTrace();
}



Bitmap screen = BitmapFactory.decodeFile(Environment.getExternalStorageDirectory()+ File.separator +"abcb");


ByteArrayOutputStream bytes = new ByteArrayOutputStream();
screen.compress(Bitmap.CompressFormat.JPEG, 15, bytes);

File f = new File(Environment.getExternalStorageDirectory()+ File.separator + timeStamp()+".jpg");
try {
    f.createNewFile();
    Log.e("TimeStamp : true ","file created ");
} catch (IOException e) {
    e.printStackTrace();
}

FileOutputStream fo = null;
try {
    fo = new FileOutputStream(f);
} catch (FileNotFoundException e) {
    e.printStackTrace();
}
try {
    fo.write(bytes.toByteArray());
} catch (IOException e) {
    e.printStackTrace();
}


try {
    fo.close();
} catch (IOException e) {
    e.printStackTrace();