http client/stress tool

I am trying to create a basic test tool, that hopefully will develop into a bigger project, basically I want to create a simple threaded httpclient that will send multiple requests to a server, record the avg response time, response time etc.  I want to know what would be the best way to modify this using threads and is their anything I have to look out for.  How can I record the response times etc, as I want to create a graph from the results??  Has anyone tried this before?  ANy good links etc?? I have read a lot, I know im capable of doing it, I just want to be put on the right track.

 Some sample code would be great.

import java.net.*;
import java.io.*;
import java.util.*;

public class WebTest
{
    public static void main (String[] args)
    {
        // initialize random seed
        Random randomGen = new Random(new Date().getTime());
        while(true)
        {
            try
           {
               // sleep for a random interval
               Thread.currentThread().sleep(randomGen.nextInt(args.length>1?(new Integer(args[1]).intValue()):10000));
                if(args.length>0)
               {
                   // print the user supplied URL to the console window
                   System.out.println(args[0]);
                   // open URL connection
                   URLConnection urlConn = new URL(args[0]).openConnection();
                   urlConn.setUseCaches(false);
                   // read and print the content to the console window
                   InputStream in = urlConn.getInputStream();
                    byte buf[] = new byte[4096];
                    int nSize = in.read(buf);
                    while(nSize>=0)
                   {
                       System.out.print(new String(buf,0,nSize));
                       nSize = in.read(buf);
                   }
                   System.out.print("\r\n");
               }
                else return;
           }
            catch(Exception e)
           {
               // print error message
               System.out.println("Exception: "+e.getMessage());
           }
        }
    }
}

Thanks,

Paul