How to retrieve db2 command output from within Java program

I am unable to retrieve the output of "db2 list db directory" command in my Java program. Basically, what I am trying to do is this:-

1. A combo box is populated with db2 instances in the local system
2. User selects a particular instance from the combo box
3. A new Process is run to list the database for that instance
4. Display the database as another combo box

This is the piece of code I have done:-

// dbinstances is a Combo box (Eclipse SWT widget)

this.dbInstances.addSelectionListener(new SelectionListener() {

    @Override
    public void widgetSelected(SelectionEvent arg0) {

        // get selected instance name 
        String instance = dbInstances.getText();

        // command invokes db2 command window, sets current instance and issues list db command
        String command = "db2cmd /c \"set DB2INSTANCE="+instance+" & db2 list db directory\""; 

        // execute command and read output
        try{
            Process p = Runtime.getRuntime().exec(command);
            BufferedReader br= new BufferedReader(new InputStreamReader(p.getInputStream()));
            String op = null;
            while((op=br.readLine())!=null){
                System.out.println(op);
            }
        }
        catch(IOException ioe){
             ioe.printStackTrace();
         }
     }

      public void widgetDefaultSelected(SelectionEvent arg0) {}
});

The problem is that the command executes, I am unable to retrieve the output. The window just opens and closes.

One solution I tried was to redirect the output to a temporary file and read it. It works, but is quite inefficient, since this piece of code runs each time the user selects an instance.

I am running DB2 9.7 Enterprise edition on Windows XP SP3 machine.

Any thoughts on how to retrieve the output in the Java program?

Thanks a lot in advance.