I want to access the value of a hidden field (declared in form of a .jsp page in a separate window) and the value needs to be changed from the different window (.jsp page). I dont get how to do it.
If you are trying to access hidden field of parent window (from a popup etc..) you can use parent.document.form.field ... It has nothing to do with jsp, it can be done with javascript...
Can't be done. You can use parent.document or child.document if the "separate window" was a popup of the other or vice versa.