Question

One of my projects uses Spring MVC to handle URL mappings and dispatch logic. I have now to use a third party library which uses its own HttpServlet as the main entry point for its functionalities, but as it’s an optional drop-in replacement for another library I can’t just put the <servlet> declaration in the web.xml: I’d rather use a Controller and Spring profiles to switch between such implementations without having to edit the web.xml.

Is there anything offered OOTB by Spring to handle such cases? I don’t seem to find it right away.

Thanks in advance!

Answer 1

Answering my own question here just in case my approach can be useful to others.

There are two key factors I needed to consider:

• the proper initialization of the servlet
• give the servlet full control over the HTTP layer (e.g. setting HTTP headers, etc)

In my specific case there’s no need for properly handling the servlet destruction, as it’s a no-op.

I ended up writing a dedicated Controller, to be instantiated only if a specific Spring profile is activated, which takes care of instantiating and initializing the Servlet. Then, all the requests will be directly handled in a void handler method, as follows:

public class ServletDelegatingController implements ServletConfig {
    private final DelegateServlet delegate = new DelegateServlet();

    public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception { 
        delegate.service(request, response);
    }



    // properly initializes the servlet
    public void setServletConfig(ServletConfig servletConfig) {
        try {
            delegate.init(servletConfig);
        } catch (ServletException e) {
            throw new IllegalStateException("Failure while initializing the servlet", e);
        }
    }
}

The delegating-servlet.xml for the DispatcherServlet looks like the following:

<beans profile="custom">
    <bean id="cmisServiceFactory"
          class="com.foo.ServletDelegatingController"/>
</beans>