systemApp.java

static public boolean runCommandWait(String cmd, boolean needsu) {
  try {
    String su = "sh";
    if (needsu) { su = "su"; }

    Process process = Runtime.getRuntime().exec(new String[]{su, "-c", cmd});
    int result = process.waitFor();

    return (result == 0);

  } catch (IOException e) {
    throw new RuntimeException(e);
  } catch (InterruptedException e) {
    throw new RuntimeException(e);
  }
}

static public void makeAppSystem(String appName) {
  String systemPrivAppDir = "/system/priv-app/";
  String systemAppDir = "/system/app/";

  String appPath = "/data/app/" + appName;

  if (!runCommandWait("mount -o remount,rw /system", true)) {
    Log.e(TAG, "makeAppSystem: Can't mount /system");
    return;
  }

  int api = Build.VERSION.SDK_INT;
  String appDir = systemPrivAppDir;

  if (api >= 21) {
    runCommandWait("cp -R " + appPath + "* " + appDir, true);
    runCommandWait("chown -R 0:0 " + appDir + appName + "*", true);
    runCommandWait("rm -Rf " + appPath + "*", true);
  } else {
    if (api < 20) { appDir = systemAppDir; }
    runCommandWait("cp " + appPath + "* " + appDir, true);
    runCommandWait("chown 0:0 " + appDir + appName + "*", true);
    runCommandWait("rm -f " + appPath + "*", true);
  }

  Shell.runCommand("am restart", true);
}