Tomcat: Change the Virtual hosts programmatically?

You shouldn't change the server environment programmatically and there are no reliable and standard ways to do this. Best is to do and keep it all on the webapp side. To start, a Filter is perfectly suitable for this. Store the names somewhere in a database table or a properties file which you cache in the application scope. Check the HttpServletRequest#getRequestURI() (or the getServerName() if it is a subdomain instead of pathinfo) and do the forwarding task accordingly.

Hope this helps.

Tomcat provides APIs to create new virtual host. To get access to the wrapper object needed for this, you need to implement a ContainerServlet. You can create virtual host like this,

    Context context = (Context) wrapper.getParent();
    Host currentHost = (Host) context.getParent();
    Engine engine = (Engine) currentHost.getParent();

    StandardHost host = new StandardHost();
    host.setAppBase(appBase);
    host.setName(domainName);

    engine.addChild(host);

You need to make sure appBase directory exist and you have to find ways to persist the new host to the server.xml or you lose the host on restart.

However, this approach rarely works. If your users run their own apps, you really want run separate instances of Tomcat so you can sandbox the apps better. e.g. One app running out of memory doesn't kill all other apps.

If you provide the app, you can just use one host (defaultHost). You can get the domain name from Host header and do whatever domain-specific stuff in your code.