How to supply sudo with root password from Java?

Question

I'm trying to write a small Java app that will overwrite my /etc/resolv.conf file (I'm on Ubuntu 12.04). To do so, I need to supply my root password:

myUser@myMachine:~$ sudo vim /etc/resolv.conf 
[sudo] password for myUser: *****

So the process for doing this has three steps:

1. Type sudo vim /etc/resolv.conf at terminal
2. Terminal asks me to type my root password
3. I enter the password and press [Enter]

From everything I've researched, I could use the following for performing step #1 above:

try {
    String installTrickledCmd = "sudo vim /etc/resolv.conf";
    Runtime runtime = Runtime.getRuntime();
    Process proc = runtime.exec(installTrickledCmd);
}
catch(Throwable throwable) {
    throw new RuntimeException(throwable);
}

But when this executes, the shell will want to prompt my Java process for the password. I'm not sure how to wait for this (step #2 above) and then to supply my password back to the shell (step #3 above). Thanks in advance.

Answer 1

Have you tried with -S ?

$echo mypassword | sudo -S vim /etc/resolv.conf

From man:

The -S (stdin) option causes sudo to read the password from the standard input 
instead of the terminal device.  The password must be followed by a newline 
character.

Answer 2

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;

public class Test1 {

  public static void main(String[] args) throws Exception {
    String[] cmd = {"sudo","-S", "ls"};
    System.out.println(runSudoCommand(cmd));
  }

  private static int runSudoCommand(String[] command) throws Exception {

    Runtime runtime =Runtime.getRuntime();
    Process process = runtime.exec(command);
    OutputStream os = process.getOutputStream();
    os.write("harekrishna\n".getBytes());
    os.flush();
    os.close();
    process.waitFor();
    String output = readFile(process.getInputStream());
    if (output != null && !output.isEmpty()) {
      System.out.println(output);
    }
    String error = readFile(process.getErrorStream());
    if (error != null && !error.isEmpty()) {
      System.out.println(error);
    }
    return process.exitValue();
  }

  private static String readFile(InputStream inputStream) throws Exception {
    if (inputStream == null) {
      return "";
    }
    StringBuilder sb = new StringBuilder();
    BufferedReader bufferedReader = null;
    try {
      bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
      String line = bufferedReader.readLine();
      while (line != null) {
        sb.append(line);
        line = bufferedReader.readLine();
      }
      return sb.toString();
    } finally {
      if (bufferedReader != null) {
        bufferedReader.close();
      }
    }
  }

}

Inspired from Viggiano answer.