The JXPathContext returned by getPageContext() provides access to all scopes via the PageContext.findAttribute() method. Thus, an expression like "foo" will first look for the attribute named "foo" in the "page" context, then the "request" context, then the "session" one and finally in the "application" context.

If you need to limit the attibute lookup to just one scope, you can use the pre-definded variables "page", "request", "session" and "application". For example, the expression "$session/foo" extracts the value of the session attribute named "foo".

Following are some implementation details. There is a separate JXPathContext for each of the four scopes. These contexts are chained according to the nesting of the scopes. So, the parent of the "page" JXPathContext is a "request" JXPathContext, whose parent is a "session" JXPathContext (that is if there is a session), whose parent is an "application" context.

The XPath context node for each context is the corresponding object: PageContext, ServletRequest, HttpSession or ServletContext. This feature can be used by servlets. A servlet can use one of the methods declared by this class and work with a specific JXPathContext for any scope.

Since JXPath chains lookups for variables and extension functions, variables and extension function declared in the outer scopes are also available in the inner scopes.

Each of the four context declares exactly one variable, the value of which is the corresponding object: PageContext, etc.

The "session" variable will be undefined if there is no session for this servlet. JXPath does not automatically create sessions.