Setting up Undertow with Spring MVC

In case you still don't know about it, Undertow is web server developed under JBoss community, and is praised a lot for its impressive performance. I usually deployed my web application in .war form under some servlet container (mostly Tomcat), but now I wanted to try out embedded servlet container, and Undertow had seemed especially good for that considering its small footprint.

I am also heavy Spring user, so I wanted to integrate this web server with Spring MVC, but only examples so far where I could find Spring-Undertow integration is within Spring Boot project, and for some reason I still use plain Spring Framework, so I set out to do it my own.

Of course, as everything in Spring is a bean, I developed my own UndertowServer bean which was pretty straightforward, and bigger question was how to define my web application deployment in it because there are couple of ways to do it. I decided to use Servlet 3.0+ ServletContainertInitializer (one other option would be to straight use Undertow's API to specify web application deployment).

Here is piece of code from our implementation of this interface:

 public class WebAppServletContainerInitializer implements ServletContainerInitializer, ApplicationContextAware {  
   private ApplicationContext applicationContext;  

   @Override  
   public void onStartup(Set<Class<?>> c, ServletContext ctx) throws ServletException {  
     XmlWebApplicationContext rootWebAppContext = new XmlWebApplicationContext();  
     rootWebAppContext.setConfigLocation("/WEB-INF/applicationContext.xml");  
     rootWebAppContext.setParent(applicationContext);  
     ctx.addListener(new ContextLoaderListener(rootWebAppContext));
  
     FilterRegistration.Dynamic encodingFilter = ctx.addFilter("encoding-filter", CharacterEncodingFilter.class);  
     encodingFilter.setInitParameter("encoding", "UTF-8");  
     encodingFilter.setInitParameter("forceEncoding", "true");  
     encodingFilter.addMappingForServletNames(EnumSet.allOf(DispatcherType.class), false, "admin");  

     FilterRegistration.Dynamic springSecurityFilterChain = ctx.addFilter("springSecurityFilterChain", DelegatingFilterProxy.class);  
     springSecurityFilterChain.addMappingForServletNames(EnumSet.allOf(DispatcherType.class), false, "admin");  
     ServletRegistration.Dynamic dispatcher = ctx.addServlet("admin", DispatcherServlet.class);  
     dispatcher.setLoadOnStartup(1);  
     dispatcher.addMapping("/admin/*");  
 ...  
 ...  

We had to inject our main ApplicationContext (that contains UndertowServer bean) via ApplicationContextAware marker, to be able to use it as parent context for root WebApplicationContext that we put under /WEB-INF/ together with other DispatcherServlet contexts.

Later on, we use this ServletContainertInitializer implementation during startup phase of Undertow server to construct DeploymentInfo object:

 InstanceFactory<? extends ServletContainerInitializer> instanceFactory = new ImmediateInstanceFactory<>(servletContainerInitializer);  
 ServletContainerInitializerInfo sciInfo = new ServletContainerInitializerInfo(WebAppServletContainerInitializer.class, instanceFactory, new HashSet<>());  

 DeploymentInfo deploymentInfo = constructDeploymentInfo(sciInfo);  

FInal result is that we can now readily use this web server bean in our Spring XML deployment descriptors, such as:

 <bean class="vmarcinko.undertow.UndertowServer">  
   <property name="port" value="8080"/>  
   <property name="webAppName" value="myapp"/>  
   <property name="webAppRoot" value="${distribution.dir}/web-app-root"/>  
   <property name="servletContainerInitializer">  
     <bean class="vmarcinko.web.admin.WebAppServletContainerInitializer"/>  
   </property>  
 </bean>  

If you ask me why I still use Spring XML in 2015 instead of Java config - well, I think XML is still nicer DSL for describing deployment than Java, but that's just me :)

Anyway, when you boot the system, this little web server will be up and running under specified port, serving this single web application under given root directory. In the example above, my administration web console (specific DispatcherServlet serving that under '/admin/*') would be available under:

http://localhost:8080/myapp/admin

Whole code for both classes is available at this Gist.