Handling an external (Windows) process from Java.

Question

There is an example program in the 3rd edition of "The Java Language" by Gosling, et. al. The example is a simplified shell to handle an external executable. This is the code:
public static Process userProg(String cmd) {
    Process child = Runtime.getRuntime().exec(cmd);
    plugTogether(System.in, child.getOutputStream());
    plugTogether(System.out, child.getInputStream());
    plugTogether(System.err, child.getErrorStream());
}I have tried various means to make this skeleton work but to no avail. Is anybody aware of an example that would show how to not only startup an external executable but manage it with I/O? I have plenty of examples that startup something like:
String[] cmdLine = {"ls", "-l" "dir"};
Runtime.getRuntime().exec(cmdLine);
...But none of them control an external application like ftp that require an interactive session. If anyone can point me towards a book, website url, example here at Sun, I'd appreciate it but it needs to be an example that controls an external executable through input and output. Thanks.
-John

Answer 1

OK.
This is not exactly an "example"; it is actual code from a production program. Names have been changed to protect proprietary info, so it is not clear that this will even compile. (Also: I would write this differently today, so please don't show this to anyone:-)
Key limitations as an example:
o The server is proprietary, so you can't see it.
o The scripting language is proprietary, so you can't see it.
This is a fragment of the interface between a large java application and a session-based server. The server was fed scripts - lines of interpreted code; the server executed the script. Key points:
o If the script terminated with an "execute"command, then the server would hang around waiting for more scripts.
o If the script terminated with an end, then the server process would exit.
o What the server "said" in response was controlled by print statements in the script it was fed.
Note the goofy print statements that allow my client to detect when the server completed a given transmission.
import java.util.Enumeration;
import java.util.Vector;
import java.io.*;
import Logger;
* Provides data from proprietary server.
public class ServerAccess {
      * Class to write script to server.
     private class Writer implements Runnable {
          Vector script;
          PrintStream p;
           * Constructor - establish a print stream to server.
          Writer(OutputStream s) {
               p = new PrintStream(s);
           * Save the script to be written and start the writer.
          public void init( Vector script) {
               this.script = script;
               new Thread(this).start();
           * Thread to write script lines.
          public void run() {
               for (Enumeration e = script.elements(); e.hasMoreElements(); ) {
                    p.println((String)e.nextElement());
               // Make sure everything gets written out.
               p.flush();
          public void finalize() {
               // Shut down the print stream.
               p.close();
     public boolean init() {
          // Access runtime so process can be created.
          Runtime r = Runtime.getRuntime();
          // Execute server.
          try {
               p = r.exec("server.exe");
               return true;
          catch(Exception e) {
               Logger.logAlways("ServerAccess: Couldn't execute server. " + e.toString());
               return false;
      * Terminate access to server.
     public void terminate() {
          Vector script = new Vector();
          script.add("end");
          // Write script to server process.
          Writer w = new Writer(p.getOutputStream());
          w.init(script);
          BufferedReader b = new BufferedReader(new InputStreamReader(p.getInputStream()));
          try {
               String line;
               while ((line = b.readLine()) != null) {
          catch (Exception e) {
               Logger.logAlways("ServerAccess: Couldn't terminate server. " + e.toString());
          return;
      * Test method.
     public void runTest() {
          // Create test script.
          Vector script = new Vector();
          script.add(....);
          script.add("print END_OF_OUTPUT %RET");
          script.add("execute");
          // Write script to server process.
          Writer w = new Writer(p.getOutputStream());
          w.init(script);
          BufferedReader b = new BufferedReader(new InputStreamReader(p.getInputStream()));
          try {
               String line;
               while (true) {
               line = b.readLine();
               if (line.equals("END_OF_OUTPUT"))
                    break;
                    System.out.println(line);
          catch (Exception e) {
               System.err.println(e.toString());
     * Test.
    public static void main(String[] args) {
        ServerAccess a = new ServerAccess();
          try {
               a.init();
          catch(Exception e) {
            System.err.println(e.toString());
            return;
        a.runTest();
        a.terminate();
     // Object attributes.
    private Process p = null;
     String END_OF_PACKAGE = "END_OF_CONTENT";
     String END_OF_OUTPUT = "END_OF_OUTPUT";