How can I get the console Output generated by a exe file

Question

when I am trying to use method getOutputSteam of Process to gain the outputStream,I got nothing!
I have also tried to use stream redirect,also no result!
please help me! Thank you in advance!
my main code are below:
Process ps=Runtime.getRuntime().exec("xxx.exe");/*xxx.exe is a executable program which will generate a console with the message I want to gain.*/
int exitVal= ps.waitFor();
if(exitVal==0){
BufferredReader br = new BufferedReader(new InputStreamReader(ps.getInputStream())); String st;
while((st = br.readLine()) !=null){
System.out.println("write:"+st);
}//my result show that I got nothing from the progam.

Answer 1

ok, this works (I tried) :
import java.lang.*;
import java.io.*;
public class ps {
        public ps() {
        public static void main(String[] args)
                try
                        Runtime rt=Runtime.getRuntime();
                        Process ps = rt.exec("ps");
                        BufferedReader br = new BufferedReader(new InputStreamReader(ps.getInputStream()));
                        String st;
                        while((st = br.readLine()) !=null){
                                    System.out.println("write:" + st);
                } catch (Exception e)
                        e.printStackTrace();
}But it's not the same that a simple ps :
[host@localhost java]$ ps
PID TTY TIME CMD
4065 pts/1 00:00:00 bash
4319 pts/1 00:00:00 ps
[host@localhost java]$java ps
write: PID TTY TIME CMD
write: 4065 pts/1 00:00:00 bash
write: 4320 pts/1 00:00:00 java
write: 4321 pts/1 00:00:00 java
write: 4322 pts/1 00:00:00 java
write: 4323 pts/1 00:00:00 java
write: 4324 pts/1 00:00:00 java
write: 4325 pts/1 00:00:00 java
write: 4326 pts/1 00:00:00 java
write: 4327 pts/1 00:00:00 java
write: 4328 pts/1 00:00:00 java
write: 4329 pts/1 00:00:00 java
write: 4330 pts/1 00:00:00 java
write: 4331 pts/1 00:00:00 ps
write: 4332 pts/1 00:00:00 java
write: 4333 pts/1 00:00:00 java
[paul@localhost java]$
And I don't know why...