Use an ArrayList of the Object 'Integer'.

Integer i1 = new Integer(1);
Integer i3 = new Integer(3);

ArrayList list = new ArrayList();
list.add(i1);
list.add(i3);

session.setAttribute(String, list);

...then...

ArrayList listFromSession = (ArrayList)session.getAttribute(String);

Then listFromSession is the ArrayList of Integer objects.

Actually, I think arrays are Java Objects, so just put your int[] array
into the Session using setAttribute() and when you do getAttribute just
cast to an int array.  I'm pretty sure that will work.

Each array is also an object. So try the following code :

session.setAttribute("intArray", ia);

ia = (int[]) session.getAttribute("intArray");