1. 建立一個自己的SessionContext：

程序代碼：
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.新建一個Session監聽

程序代碼
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

程序代碼
<listener>
    <listener-class>cn.org.jshuwei.session.core.SessionListener</listener-class>
</listener>

4.使用

程序代碼
MySessionContext myc= MySessionContext.getInstance();
HttpSession sess = myc.getSession(sessionId);