I need to change the serverName of the ServletRequest object in my Grails controller. I'm having trouble figuring out how to do this since the serverName is a read-only property.
The most correct thing to do is probably to set up a clever filter or redirect which "fixes" your request URL before your servlet even gets involved. I know nothing about how to do that; you should ask on serverfault.com if you want to do that.
In java, you can fake it by creating your own subclass of HttpServletRequestWrapper which provides setServerName() and overrides getServerName() while delegating all other methods to the superclass. You can then provide a filter which creates an instance of your request and sends that one down the chain.
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain)
throws IOException, ServletException {
YourHttpServletRequest yourRequest =
new YourHttpServletRequest(request, newServerName);
chain.doFilter(yourRequest, response);
}