根据sessionId获取Session对象

Servlet2.1之后不支持SessionContext里面getSession(String id)方法。

但是，我们可以通过HttpSessionListener监听器和全局静态map自己实现一个SessionContext。

MySessionContext.java:

public class MySessionContext {
    private static HashMap mymap = new HashMap();

    public static synchronized void AddSession(HttpSession session) {
        if (session != null) {
            mymap.put(session.getId(), session);
        }
    }

    public static synchronized void DelSession(HttpSession session) {
        if (session != null) {
            mymap.remove(session.getId());
        }
    }

    public static synchronized HttpSession getSession(String session_id) {
        if (session_id == null) 
        return null;
        return (HttpSession) mymap.get(session_id);
    }
}

MySessionListener.java:

public class MySessionListener implements HttpSessionListener {
    public void sessionCreated(HttpSessionEvent httpSessionEvent) {
    MySessionContext.AddSession(httpSessionEvent.getSession());
    }

    public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
        HttpSession session = httpSessionEvent.getSession();
        MySessionContext.DelSession(session);
    }

}

web.xml添加一个监听器：

<listener> 
<listener-class>listener.MySessionListener</listener-class> 
</listener>

根据sessionId获取Session对象：

String sessionId = request.getParameter("sessionId");

HttpSession session = MySessionContext.getSession(sessionId);