转：Session 管理
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原帖：http://hi.baidu.com/jlh_jianglihua/item/9007f429de1855ff51fd87a5
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最近一个项目中用到了getsession根据sessionid来获取session，但是怎么获取都为空，请教N多人，才发现在servlet的api中有如下：
???????? HttpSession HttpSessionContext.getSession(java.lang.String sessionId)
??????
?????? 不赞成的用法.?? Java Servlet API的版本 2.1中，还没有将之替换掉。该方法必须返回一个空值，且将会在未来的版本中被抛弃掉。
?????? 最新的解决办法是通过实现HttpSessionListener的sessionCreated和sessionDestroyed来实现
?????? 解决步骤：
??????
?????? 1、在web.xml增加监听:
???? <listener>
?????????? <listener-class>com.aceway.util.LoginSessionListener</listener-class>
???? </listener>
?????? 2、LoginSessionListener:??
?????????? LoginSessionListener方法实现了HttpSessionListener,并且重写sessionCreated和sessionDestroyed方法
????????
?????????? public static Map userMap = new HashMap();???????????????????????????????? //创建了一个对象来保存session的
?????????? private?? MySessionContext myc=MySessionContext.getInstance();?? //MySessionContext是实现session的读取和删除增加?? 单例模式
???????? public void sessionCreated(HttpSessionEvent event)
???????? {
???????????? myc.AddSession(event.getSession());
???????? }
???????? public void sessionDestroyed(HttpSessionEvent event)
???????? {
???????? HttpSession session = event.getSession();
???????? myc.DelSession(session);
???????? }
???? 3、session的单例管理
Java代码
package com.aceway.flex;??
import java.util.*;??
import javax.servlet.http.HttpSession;??
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);??
???? }??
}??
4、这样我们就可以单例来获取session
???? private MySessionContext myc=MySessionContext.getInstance();
?????? HttpSession session = myc.getSession(SessionId);
