session - Java HttpSession timeout not changing from no timeout to 10 minutes timeout doesnt work -

using java code , not in web.xml, need ensure session created @ particular page no time out. once user goes past page, same session needs have timeout of 10 minutes.

//i using set no time limit: session.setmaxinactiveinterval(-1);  //and using same code different value set 10 minute limit: session.setmaxinactiveinterval(ten_minutes); 

however, session never times out.. makes me think once sessions inactive interval set no limit, cannot undone.

i need working described.

thanks...