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? 是或者不是屬于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，對于某一個PORTLET來說，如果有對其的SESSION進行的操作，并沒有真正的在該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，開發人員由于習慣問題，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。然后問題就出在這里，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：這里將獲取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);
????????}

????}

?

Portal開源實現-Liferay的Portlet Session處理(2)