二、LIFERAY中的實現
LIFERAY在構建ActionRequestImpl和RenderRequestImpl時，會設置PORTLET SESSION，如下代碼所示：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); ... }從蘭色的部分（ _ses = new PortletSessionImpl(_req.getSession(),_portletName, _portletCtx); ）我們可以看到，這個PORTLET SESSION其實就是PORTAL SYSTEM的 SESSION 對象。所以無論request調用getSession()或者getPortletSession()都將獲取Portal 系統的SESSION 對象，而無論該PORTLET 是或者不是屬於PORTAL SYSTEM上下文。而且即使不同PORTAL APPLICATION的PORTLET也將使用同一個SESSION 對象（PORTAL 系統）。也就是說，對於某一個PORTLET來說，如果有對其的SESSION進行的操作，並沒有真正的在該APPLICATION上下文中的SESSION進行操作，而是在PORTAL系統上下文的SESSION中進行操作。
而且LIFERAY提供getPortletSession來獲取PortletSession對象，而不是getSession()方法，所以即使getPortletSession()可以獲取正確的Session對象，開發人員由於習慣問題，也因使用getSession()而得不到。
另外如果調用request.getSession(true)還可能會出現錯誤，因為LIFERAY在包含某一個PORTLET內容是，調用PortletRequestDispatcherImpl.include()方法，該方法將生成PortletServletRequest 和PortletServletResponse，請見如下代碼:
PortletServletRequest portletServletReq = new PortletServletRequest( httpReq, reqImpl, pathInfo, queryString, requestURI, servletPath);
PortletServletResponse portletServletRes = new PortletServletResponse( resImpl.getHttpServletResponse(), resImpl);而PortletServletRequest的構造函數是如下定義的：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系統上下文的。然後問題就出在這裡，PortletServletRequest實現了getSession()方法，但是沒有實現getSession(boolen create)方法，如果用戶在此階段調用getSession(true)的話，在某些情況下就會拋出NullPointerException
原因見如下代碼（請注意我添加的注釋部分）//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()); // 我的注釋：這裡將獲取PORTAL系統的SESSION對象。 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 { // 我的注釋：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(); //我的注釋：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); }
}
