Hi Marlon,
Session obj is not thread safe:
You may launch two brwosers, and activate two thread of the same servelt1, these two servlet threads can access the same sessionObj. On the other hand,you may have servlet1 and servlet2 access the same sessionObj.
Request Obj is thread safe, as it exists only per request basis. No one else can access it, even you launch two browser to access the same page/servlet, the request obj are different.
David
SCJP/SCWCD/SCEJA