How to add tomcat virtual hosts instances programatically - spring

Question

I was working for the last 2 years on building a social network for companies using Grails.
A new requirement appeared which is creating separate virtual host for each company that will have it's own database of users, timelines, etc (I would like to avoid rewriting all the service layer)
So initially the application was running on http://www.my-social-network.com for example
Now using an admin console that we will have to develop, companies should be able to create their own subdomain like this : http://company1.my-social-network.com and so on.
The web server that we are using is Apache 2.2 + tomcat 6
Is there someone who has an idea about how to do it?
Ideally I want to have one instance of the application that receives requests with different host names so it can behave differently in order to save resources because Grails consumes too much memory.
For example :
subdomain1.my-social-network.com --> apache 2 --> my-social-network.com (+ specific headers) --> tomcat
If such thing was possible, is there a way to select a datasource depending on a request parameter or header?
Any help is appreciated

Answer 1

There are a number of different options you can take, but first you need to make a decision on how you are going to implement this at the lowest level:
You can take the requests to subdomain1.my-social-network.com and redirect the user to my-social-network.com.
Same as above but use HTTP 302, HTTP 303 or HTTP 307 instead.
Simply show the contents of the site, responding with HTTP 200 (probably the best approach as these domains are meant to be permanent). Further text assumes this option.
Next, you need to have a servlet filter which intercepts all HTTP traffic and has a map {virtual_path -> real_site}. This filter can simply set relevant request attribute (hint: servletRequest.setAttribute(String, Object)) when it detects that requested virtual path is recognized.
If a user creates/renames/deletes a domain/virtual path, you would populate the map accordingly.
Finally, your render component should check that parameter and render relevant site. It is really hard to elaborate further without knowing more details on how your application works.