md5 in java whitout reading file in a buffer

import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintStream;
import java.util.Scanner;


public class MD5 {

 /**
  * @param args
  * @throws Exception 
  */
 public static void main(String[] args) throws Exception {
    String[] cmd = new String[]{"md5sum","/home/user/workspace/project/buildfile"};
       ProcessBuilder pb = new ProcessBuilder(cmd);
       Process p = pb.start();
       BufferedReader br = new BufferedReader(new InputStreamReader(p.getInputStream()));  
       StringBuffer sb = new StringBuffer();  
       String line;  
       while ((line = br.readLine()) != null) {  
         sb.append(line).append("\n");  
       }  
       String answer = sb.toString();  
       
       int val = p.waitFor();
       String md5 ="";
       if(val == 0){
        Scanner s = new Scanner(answer);
        if(s.hasNext()){
         md5 = s.next();
         System.out.println(md5);
        }
       }else{
        System.out.println("Error executing command md5sum");
       }
      
 }
 

}