How to display the response it a different window (a.k.a. How to change form target in action?)
By Frank Zammetti, extracted from StrutsSolutions page.
Simply put, there is no way to do this. Opening a new window is a strictly client-side activity. You have to "fake it". There's two ways to do it...
First, you could simply target your HTML form using the target="_blank" attribute. This will result in whatever response the server sends back appearing in a new window. The down-side to this is you have to know before-hand to do this. If you want a variable solution, you have to get into scripting... You can set the target attribute's value via client-side scripting as appropiate before submitting the form.
The bottom-line here is this: There is no way to direct the browser to open the response in a new window from an Action. You either have to indicate you want this behavior when the form is submitted, or make it happen with scripting once the response is back at the browser. At least, this is true within the confines of plain old HTML... You could always pull an applet out and do something like this!