I am been trying to copy a apk from assets of another apk to /system.

Here is what I have done,it was working in my previous app but not in this.I have added permission for wrtiting external storage. It is successfully copying to internal storage,not not to /system. Is there any way to directly copy to /system?

copyStream("y.apk","/sdcard/x.apk");

Process mSuProcess;

mSuProcess = Runtime.getRuntime().exec("su");

new DataOutputStream(mSuProcess.getOutputStream()).writeBytes("mount -o remount rw /system");

DataOutputStream mSuDataOutputStream = new DataOutputStream(mSuProcess.getOutputStream());

mSuDataOutputStream.writeBytes("cp /sdcard/x.apk /system/app/x.apk"); 

mSuDataOutputStream.writeBytes("exit\n");