You can use this code:
Enumeration enumeration = session.getAttributeNames();
while (enumeration.hasMoreElements()) {
String element = (String) enumeration.nextElement();
session.removeAttribute(element);
}
If yo don't have delete any element, you can do this:
Enumeration enumeration = session.getAttributeNames();
while (enumeration.hasMoreElements()) {
String element = (String) enumeration.nextElement();
if(!element.matches("notDeleteElement") )
session.removeAttribute(element);
}

