1. 建立一个自己的SessionContext：

程序代码：

package cn.org.jshuwei.session.core;

import javax.servlet.http.HttpSession;

import java.util.HashMap;

public class MySessionContext {

private static MySessionContext instance;

private HashMap mymap;

private MySessionContext() {

mymap = new HashMap();

}

public static MySessionContext getInstance() {

if (instance == null) {

instance = new MySessionContext();

}

return instance;

}

public synchronized void AddSession(HttpSession session) {

if (session != null) {

mymap.put(session.getId(), session);

}

}

public synchronized void DelSession(HttpSession session) {

if (session != null) {

mymap.remove(session.getId());

}

}

public synchronized HttpSession getSession(String session_id) {

if (session_id == null) return null;

return (HttpSession) mymap.get(session_id);

}

}

2.新建一个Session监听

程序代码

package cn.org.jshuwei.session.core;

import javax.servlet.http.HttpSessionListener;

import javax.servlet.http.HttpSessionEvent;

import javax.servlet.http.HttpSession;

import java.util.HashMap;

import java.util.Map;

public class SessionListener implements HttpSessionListener {

public static Map userMap = new HashMap();

private   MySessionContext myc=MySessionContext.getInstance();

public void sessionCreated(HttpSessionEvent httpSessionEvent) {

myc.AddSession(httpSessionEvent.getSession());

}

public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {

HttpSession session = httpSessionEvent.getSession();

myc.DelSession(session);

}

}

3.在web.xml中配置

程序代码

cn.org.jshuwei.session.core.SessionListener

4.使用

程序代码

MySessionContext myc= MySessionContext.getInstance();

HttpSession sess = myc.getSession(sessionId);

来源：http://blog.sealyu.com/2011/06/21/java%E6%A0%B9%E6%8D%AEsessionid%E8%8E%B7%E5%8F%96session%E5%AF%B9%E8%B1%A1/