Java: Execute process and prefix output lines with 'o' or 'e'

Exec.java

import java.lang.*;
import java.io.*;

public class Exec {
  public static void main(String[] args) {
    try {
      Process process = Runtime.getRuntime().exec("ls /vmlinuz /mvlinuz");

      try {
        process.waitFor();
      } catch(InterruptedException e) {
        e.printStackTrace();
      }

      BufferedReader ir = new BufferedReader(new InputStreamReader(process.getInputStream(), "utf8"));
      BufferedReader er = new BufferedReader(new InputStreamReader(process.getErrorStream(), "utf8"));
      String s = null;

      while((s = ir.readLine()) != null) {
        s = "o: " + s;
        System.out.println(s);
      }

      while((s = er.readLine()) != null) {
        s = "e: " + s;
        System.out.println(s);
      }
    } catch(IOException e) {
      e.printStackTrace();
    }
  }
}