如何javaEE通过sessionId获取HttpSession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.MySessionListener</listener-class>
</listener>
根据sessionId获取Session对象：
String sessionId = request.getParameter("sessionId");
HttpSession session = MySessionContext.getSession(sessionId);