二、LIFERAY中的实现

LIFERAY在构建ActionRequestImpl和RenderRequestImpl时，会设置PORTLET SESSION，如下代码所示：
public RenderRequestImpl(HttpServletRequest req, Portlet portlet,
        CachePortlet cachePortlet,
        PortletContext portletCtx,
        WindowState windowState, PortletMode portletMode,
        PortletPreferences prefs, String layoutId) {
   ...
  _req = dynamicReq;
  _portlet = portlet;
  _cachePortlet = cachePortlet;
  _portalCtx = new PortalContextImpl();
  _portletCtx = portletCtx;
  _windowState = windowState;
  _portletMode = portletMode;
  _prefs = prefs;
  _ses = new PortletSessionImpl(
   _req.getSession(), _portletName, _portletCtx);
   ...
 }
从兰色的部分（  _ses = new PortletSessionImpl(_req.getSession(),_portletName, _portletCtx);  ）我们可以看到，这个PORTLET SESSION其实就是PORTAL SYSTEM的 SESSION 对象。
所以无论request调用getSession()或者getPortletSession()都将获取Portal 系统的SESSION 对象，而无论该PORTLET  是或者不是属于PORTAL SYSTEM上下文。而且即使不同PORTAL APPLICATION的PORTLET也将使用同一个SESSION 对象（PORTAL 系统）。
也就是说，对于某一个PORTLET来说，如果有对其的SESSION进行的操作，并没有真正的在该APPLICATION上下文中的SESSION进行操作，而是在PORTAL系统上下文的SESSION中进行操作。

而且LIFERAY提供getPortletSession来获取PortletSession对象，而不是getSession()方法，所以即使getPortletSession()可以获取正确的Session对象，开发人员由于习惯问题，也因使用getSession()而得不到。

另外如果调用request.getSession(true)还可能会出现错误，因为LIFERAY在包含某一个PORTLET内容是，调用PortletRequestDispatcherImpl.include()方法，该方法将生成PortletServletRequest 和PortletServletResponse，请见如下代码:

PortletServletRequest portletServletReq = new PortletServletRequest(
    httpReq, reqImpl, pathInfo, queryString, requestURI,
    servletPath);

   PortletServletResponse portletServletRes =
    new PortletServletResponse(
     resImpl.getHttpServletResponse(), resImpl);
而PortletServletRequest的构造函数是如下定义的：
public PortletServletRequest(HttpServletRequest req,
         RenderRequest renderRequest, String pathInfo,
         String queryString, String requestURI,
         String servletPath) {

  super(req);

  _ses = req.getSession();
  _renderRequest = renderRequest;
  _pathInfo = pathInfo;
  _queryString = queryString;
  _requestURI = requestURI;
  _servletPath = servletPath;
 }
所以其SESSION依然是PORTAL系统上下文的。然后问题就出在这里，PortletServletRequest实现了getSession()方法，但是没有实现getSession(boolen create)方法，如果用户在此阶段调用getSession(true)的话，在某些情况下就会抛出NullPointerException

原因见如下代码（请注意我添加的注释部分）
//ApplicationHttpRequest：  

 public HttpSession getSession(boolean create) {

        if (crossContext) {
           
            // There cannot be a session if no context has been assigned yet
            if (context == null)
                return (null);

            // Return the current session if it exists and is valid
            if (session != null)
                return (session.getSession());
     // 我的注释：这里将获取PORTAL系统的SESSION对象。
            HttpSession other = super.getSession(false);
            if (create && (other == null)) {
                // First create a session in the first context: the problem is
                // that the top level request is the only one which can
                // create the cookie safely
                other = super.getSession(true);
            }
            if (other != null) {
                Session localSession = null;
                try {
                    // 我的注释：this context did not have the session with session id. It can just be found in the Portal
                    // context. So here it will return a null value.
                    localSession =
                        context.getManager().findSession(other.getId());
                    localSession.access(); //我的注释：Here, localSession is null. So it throws a NullPointException.
                } catch (IOException e) {
                    // Ignore
                }
                if (localSession == null) {
                    localSession = context.getManager().createEmptySession();
                    localSession.setNew(true);
                    localSession.setValid(true);
                    localSession.setCreationTime(System.currentTimeMillis());
                    localSession.setMaxInactiveInterval
                        (context.getManager().getMaxInactiveInterval());
                    localSession.setId(other.getId());
                }
                session = localSession;
                return session.getSession();
            }
            return null;

        } else {
            return super.getSession(create);
        }

    }