How to execute more than one command in a Process

Question

Hello all,
I would like to change the user in my application by
using the unix command su user and then execute some commands as this user.My code is the following, my problem is to execute other commands after execute the su command.
public static void main(String [] args)
try
Runtime r = Runtime.getRuntime();
String msg = "";
String emsg = "";
int len = 0;
byte buffer [] = new byte[100];
Process p1 = r.exec(new String [] "su","user"});
InputStream input = p1.getErrorStream();
len = input.read(buffer);
System.out.println(new String(buffer,0,len));
OutputStream out = p1.getOutputStream(); String password = "password";     
out.write(password.getBytes());
out.flush();
out.close();
System.out.println(password);
p1.destroy();
catch(Exception e)
System.out.println(e.toString());

Answer 1

For those of you who are "shell challenged", here's a Java program that will tell you how the shell interprets the command and argument you give it:
public class RuntimeHelper {
    public static void main(String[] args) {
        for (int i = 0; i < args.length; i++)
            System.out.println(args);
When you run the program with
java RuntimeHelper su username -c "cmd arg1 arg2"
the output is:
su
username
-c
cmd arg1 arg2
Each line shows one argument that the shell passed to the java command.