stealthcopter.com

This snippet shows how root access can be requested inside an application in order to write a file into a place we do not have permission to access usually. Requesting root access will only work if your phone allows it, or it has been ‘rooted’ (hacked to allow superuser permissions).

Process p;
try {
   // Preform su to get root privledges
   p = Runtime.getRuntime().exec("su"); 

   // Attempt to write a file to a root-only
   DataOutputStream os = new DataOutputStream(p.getOutputStream());
   os.writeBytes("echo \"Do I have root?\" >/system/sd/temporary.txt\n");

   // Close the terminal
   os.writeBytes("exit\n");
   os.flush();
   try {
      p.waitFor();
           if (p.exitValue() != 255) {
        	  // TODO Code to run on success
              toastMessage("root");
           }
           else {
        	   // TODO Code to run on unsuccessful
        	   toastMessage("not root");
           }
   } catch (InterruptedException e) {
      // TODO Code to run in interrupted exception
	   toastMessage("not root");
   }
} catch (IOException e) {
   // TODO Code to run in input/output exception
	toastMessage("not root");
}

Where my “toastMessage” is just a function which creates a toast to display on the screen. On phones with superuser permissions installed (root access) this will display a dialog asking the user to allow or deny the application permission to have root access:

android request root access dialog

Ref
anddev.org