The basic type (int, String, etc.) stored in the session is different from the reference type (object).
1. basic type
session.setAttribute("test"，1)
-------》Object test = session.getAttribute("test")
-------》test = 2
-------》system.out.print( session.getAttribute("test"));
-------" The print result is: 1 (not 2)
2. reference type
Test test = new Test();
test.setName("小明");
session.setAttribute("test"，test)
-------》Object test2 = session.getAttribute("test")
-------》test2.setName(‘xiaoming’);
-------》system.out.print( session.getAttribute("test").getName());
-------" The print result is: xiaoming (the reference type will be automatically updated to the session field)