I'm trying to forward a request to another URL which includes the hash symbol ('#'):
request.getRequestDispatcher("/some/path.jsp#somehash").forward(request, response);
Tomcat, however, tells me that "the requested resource is not available". If I remove the hash from the URL, everything works fine. Are hashes not allowed or am I not treating them right?
The # symbol is a browser thing, not a server thing. When you type a URL with a # into the browser, the browser doesn't send that part to the server. It sends the URL without it, then jumps to the named anchor when it gets the page back.
When you ask the container to get that URL for you, it doesn't treat the # any differently to any other URL - it has no special meaning for it, so it looks for a JSP page called /some/path.jsp#somehash, which of course doesn't exist.
You'll need to keep that jump-to-anchor logic on the client somehow. Perhaps you could put some javascript on the resulting page to scroll to that point in the document.
URL fragments are purely client side. The RequestDispatcher#forward() is entirely server-side. The in the forward given URL won't be sent to the client side. You can however redirect to the given URL using HttpServletResponse#sendRedirect(). The URL fragment will then be sent to the client side and reflected in browser address bar as well. Redirecting the request has however the disadvantage that the current request will be garbaged and a brand new one will be created. If that's not affordable, then you'll indeed have to look in the JavaScript corner for the solution.