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);  }    }  

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);}}

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

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