Servlet with thread

I have this servlet that executes a system cmd (like to run a perl script). Some of the perl scripts can take a very long time to finish and it would hold my servlet would not come back until they are done.

So I'm trying to use Thread, start() and run(). But all the examples I've found are Thread running applet.

Here is what I want to do

public class ExecServlet extends HttpServlet {
...
...
...
private void launchExecution(String runType, int statusID,
HttpServletRequest request,
HttpServletResponse response)
throws ServletException , IOException
{

StringBuffer launchStr = new StringBuffer();
launchStr.append("perl long_running.pl");

String retString = doServerCommand(launchStr.toString(), request);
if (retString.indexOf("Successfully Running") == -1) {
msgBean.setPrimaryMsg("Error Launching execution"
forward("/exec_err_msg.jsp", request, response);
} else {
StringBuffer s = new StringBuffer("Execution Launched!");
int strIdx = retString.indexOf("Log File is");
if (strIdx > -1) {
s.append("<P>" + retString.substring(strIdx) + "<P>");
}
msgBean.setPrimaryMsg(s.toString());
forward("/exec_msg.jsp", request, response);
}


private synchronized String doServerCommand(String cmd, HttpServletRequest request)
{
...
...
Process cmdProc = Runtime.getRuntime().exec(cmd);

// get its output (your input) stream
//
BufferedReader cmdIn = new BufferedReader(new InputStreamReader(cmdProc.getInputStream()));
BufferedReader cmdErr = new BufferedReader(new InputStreamReader(cmdProc.getErrorStream()));
try {
String inStr;
while (( inStr = cmdIn.readLine()) != null) {
cmdStdOutput.append(inStr + "\n");
}
while (( inStr = cmdErr.readLine()) != null) {
cmdErrOutput.append(inStr + "\n");
}
}
...
...