付上源码（这是dwr2的src包中的例子JavaChat，我稍做修改）
package org.getahead.dwrdemo.chat;
import java.util.Collection;
import java.util.LinkedList;
import javax.servlet.http.HttpSession;
import org.directwebremoting.WebContext;
import org.directwebremoting.WebContextFactory;
import org.directwebremoting.proxy.dwr.Util;
import org.directwebremoting.util.Logger;
/**
* @author Joe Walker [joe at getahead dot ltd dot uk]
*/
public class JavaChat
{
/**
* @param text The new message text to add
*/
public void addMessage(String text)
{
// Make sure we have a list of the list 10 messages
if (text != null && text.trim().length() > 0)
{
messages.addFirst(new Message(text));
while (messages.size() > 10)
{
messages.removeLast();
}
}
WebContext wctx = WebContextFactory.get();
//这里是自己加入的代码
HttpSession hSn = wctx.getSession();
if(hSn.getAttribute("No")==null){
hSn.setAttribute("No", getID());
}
log.info((Long)hSn.getAttribute("No")+" : " + hSn.getId());
//到这里结束
String currentPage = wctx.getCurrentPage();
// Clear the input box in the browser that kicked off this page only
Util utilThis = new Util(wctx.getScriptSession());
utilThis.setValue("text", "");
// For all the browsers on the current page:
Collection sessions = wctx.getScriptSessionsByPage(currentPage);
Util utilAll = new Util(sessions);
// Clear the list and add in the new set of messages
utilAll.removeAllOptions("chatlog");
utilAll.addOptions("chatlog", messages, "text");
}
//这里取得一个访问者的ID
private synchronized long getID(){
return No++;
}
/**
* The current set of messages
*/
private LinkedList messages = new LinkedList();
/**
* The log stream
*/
protected static final Logger log = Logger.getLogger(JavaChat.class);
private long No = 0;//访问者的ID序号
}
