Q: How do I make a WFS request in my JSP/Java code?

There are a couple of ways to do this.

You could forward to or include another page (in this case a geoserver request) using a servlet (the appropriate methods (forward,include) are on the RequestDispatcher interface. You can also use the jsp:forward and jsp:include tags to do the same thing.

You could make the request from the client using JavaScript/Ajax and include it in your html.

You could do this from java code using a simple http connection. A couple of examples here.

http://javaalmanac.com/egs/java.net/Post.html