This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
Portlet sessions have 2 scopes - portlet and application. The data placed in portlet scope is not accessible to other portlets in the same portlet application. The data placed in application scope is accessible to other portlets and servlets in the same portlet application. The concept of global session scope is specific to portlets, wherein the bean is placed in the application scope, so that it is accessible to all the servlets/portlets in the portlet application.