Calling Java application from servlet

Hi !
I'm trying to run a Java application from within a servlet with Tomcat 4. I'm using the Runtime.getRuntime ().exec () method. So the application is run in a different JVM as a subprocess of the servlet. I use ObjectInputStream and ObjectOutputStream and a serializable object to enable communication between the servlet and the application.
I tested the application and the serializable object with another Java application that works as the caller and it works fine. However, replacing the caller application with the servlet I get a StreamCorruptedException. The structure of the caller application and the servlet is the same.
My questions are:
- Is there something I should configure in Tomcat to create a subprocess ?
- What is the cause of the StreamCorruptedException ? How do I get it with the servlet and not with the application ?
- Should I use an environment with the call to Runtime.getRuntime ().exec () ? How do I use it ?
- Is the called application forced to run in my servlet's context ?
- Is there a better way to do this ?
Thanks to all

Here's my code:
1. The serializable object:
// Object Obj
import java.io.*;
public class Obj implements Serializable
public int n;
public Obj ()
n = 0;
public Obj (int n)
this.n = n;
public String toString ()
return getClass ().getName () + " -> (n = " + n + ")";
2. The application Sub (subprogram)
// Application Sub
import java.io.*;
public class Sub
private static File f;
private static FileWriter fw;
public static void main (String [] args)
throws IOException, InterruptedException, ClassNotFoundException
ObjectInputStream ois;
ObjectOutputStream oos;
Obj obj;
ois = new ObjectInputStream (System.in);
obj = (Obj) ois.readObject ();
f = new File ("Sub.txt");
fw = new FileWriter (f);
fw.write (obj.toString ());
fw.close ();
oos = new ObjectOutputStream (System.out);
oos.writeObject (obj);
ois.close ();
oos.close ();
3. The application AMain (caller application)
// Application AMain
import java.io.*;
class AMain
private static File f;
private static FileWriter fw;
public static void main (String [] args)
throws IOException, ClassNotFoundException
Runtime r;
Process p;
ObjectInputStream ois;
ObjectOutputStream oos;
Obj obj, obj2;
r = Runtime.getRuntime ();
p = r.exec ("java Sub");
oos = new ObjectOutputStream (p.getOutputStream ());
obj = new Obj (5);
oos.writeObject (obj);
oos.flush ();
B.comunica (obj);
System.out.println ("AMain sends to Sub: " + obj.toString ());
try
p.waitFor ();
catch (InterruptedException e)
System.out.println ("Subprogram was interrupted");
System.out.println (e.toString ());
ois = new ObjectInputStream (p.getInputStream ());
System.out.print ("Sub sends to AMain: ");
obj2 = (Obj) ois.readObject ();
System.out.println (" " + obj2.toString ());
oos.close ();
ois.close ();
p.destroy ();
4. The servlet SMain (the calling servlet)
// Servlet SMain
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;
import java.io.*;
import java.util.*;
public class SMain extends HttpServlet
public void doPost (HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException
Runtime r;
Process p;
ObjectInputStream ois;
ObjectOutputStream oos;
Obj obj, obj2;
int state, i;
res.setContentType ("text/html");
ServletOutputStream out = res.getOutputStream ();
out.println ("<html>");
out.println ("<head><title>Sub</title></head>");
out.println ("<body>");
out.println ("Invoking subprogram...");
out.println (" ");
try
r = Runtime.getRuntime();
p = r.exec ("java -cp .;c:\\Programs\\Apache~1.0\\webapps\\SMain\\WEB-INF\\classes Sub");
out.println ("...invoked ");
oos = new ObjectOutputStream (p.getOutputStream ());
obj = new Obj (5);
oos.writeObject (obj);
oos.flush ();
out.println (" SMain sends to Sub: " + obj.toString () + " ");
try
p.waitFor ();
catch (InterruptedException e)
out.println (" Subprogram was interrupted ");
out.println (" " + e.toString () + " ");
state = p.exitValue ();
out.println (" Subprogram state: " + state + " ");
ois = new ObjectInputStream (p.getInputStream ());
out.print (" Sub sends to SMain: ");
obj2 = (Obj) ois.readObject ();
p.destroy ();
catch (SecurityException e)
out.println (" SecurityException ");
out.println (" " + e.toString () + " ");
catch (IOException e)
out.println (" IOException ");
out.println (" " + e.toString () + " ");
catch (Exception e)
out.println (" Exception ");
out.println (" " + e.toString () + " ");
out.println ("</body>");
out.println ("</html>");
So, as you can see, both application AMain and servlet SMain invoke application Sub and pass it the serializable object Obj. Oddly enough, application AMain works fine whereas servlet SMain throws a StreamCorruptedException exception.
johnpoole said:
�It's hard to guess what would cause the exception without seeing code, but the interaction between the processes would differ from that between two applications, because the servlet process is started with a different class loader. I'm not sure which one the jvm started by the call would use.�
How can I enforce that a System classloader be used in the call to Runtime.getRuntime ().exec () ? (I mean by System classloader a classloader equals to the one applications are launched from console).
johnpoole said
�Is there a reason why you aren't starting the second process manually and then connecting to it on a port?�
The idea is providing a Web interface for an application running in the server. The servlet is used to restrict access to this application but once access is granted (passing the servlet) the application should not be constrained.

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