Support @WebServlet, @WebFilter, and @WebListener

[wilkinsona]

ServletContextInitializerBeans finds all beans that are a Servlet and creates a ServletRegistrationBean for each of them. We could perhaps, as this user expected, look for @WebServlet on such a bean to determine, among other things, the url patterns to which the servlet should be mapped.

[philwebb]

There is also @WebFilter to consider. My initial feeling is that it might be confusing to try and support these annotations directly. We already made the decision not to support @HandlesTypes and WebApplicationInitializer and this one feels like it's in a similar category. Perhaps we could add our own equivalent annotations that are also @Component annotated?

[wilkinsona]

I think both @WebServlet and @WebFilter are slightly different. We support both Servlets and Filters so this is about how the user configures them. The ideal, imo, would be able to use @WebServlet and @WebFilter and not have to also use @Component. Failing that, our own @WebServlet and @WebFilter annotations that are @Component-annotated would still be worthwhile, imo.

[dsyer]

I agree with Andy. It's a bit like Spring respecting @Resource without actually being an EJB container. The annotations @WebServlet and @WebFilter are probably not as rich as a *RegistrationBean, but we could respect them if no registration is provided. No need for a new Spring annotation IMO, though, just to save one line of code adding @Component.

[michaelhaessig]

How can one use a third party library that is based on those annoations with Spring Boot without having to search the source code of the library and add each Filter/Servlet manually ? Is there a way to tell the web app container to search for these annotations ?

[wilkinsona]

@miki4you The embedded containers don't perform any scanning for @WebServlet or @WebFilter. Can you point us to some libraries that make use of them and that are causing you a problem?

[joensson]

@miki4you Though not Spring Boot specific it is possible to configure the embedded Tomcat do the scanning for @WebServlet and @webfilter.

See the accepted solution on SO for how to enable it - the accepted solution contains the solution for both embedded Tomcat 7 and embedded Tomcat 8 http://stackoverflow.com/questions/11669507/embedded-tomcat-7-servlet-3-0-annotations-not-working

Based on that answer I think you can achieve the same in Spring Boot by using the TomcatEmbeddedServletContainerFactory - something along these lines (not tested - pseudo code :)):

    @Bean
    public TomcatEmbeddedServletContainerFactory tomcatFactory() {
        return new TomcatEmbeddedServletContainerFactory() {
            @Override
            protected void postProcessContext(Context context) {
                WebResourceSet myCustomResourceSet = new JarResourceSet();
//or DirResourceSet, or FileResourceSet or JarWarResourceSet 
//and add the needed resources to the set, you may need to combine this with context.setAddWebinfClassesResources(true); in order for @WebServlet in jar files to be loaded
                context.getResources().addPreResources(myCustomResourceSet);
            }
        };
    }

[michaelhaessig]

@wilkinsona i wanted to try out https://github.com/stagemonitor/stagemonitor with spring boot , followed the configuration tutorial and when the app started nothing happend. i've taken a look at the source and saw the heavy use of WebFilter/WebServlet.

Then i started searching the web for a solution , tought it was a spring boot problem. But as @joensson pointed out it seems to be related with the embedded web container. Thank you @joensson for the quick answer. i'm going to try it out as soon as possible.

[michaelhaessig]

I 've just tried to get it working with the help form your example. To first thing i noticed is that the call to

 context.getResources()

returns null, which means the WebResource Set can not be added.

In the Stackoverflow example , they are working with a "StandardContext" from de deployed wepapp.
I searched the Embedded Tomcat Documentation to find an example to create a JarStandartContext to code looks like this

    @Bean
    public TomcatEmbeddedServletContainerFactory tomcatFactory() {
        return new TomcatEmbeddedServletContainerFactory() {

            @Override
            protected void postProcessContext(Context context) {

                context.setAddWebinfClassesResources(true);

                WebResourceRoot resources = new StandardRoot();
                WebResourceSet myCustomResourceSet = new JarResourceSet(resources,"/","/","/");
                resources.addPreResources(myCustomResourceSet);
                context.setResources(resources);

            }
        };
    }

But now the app wont start up with the Exception
org.springframework.context.ApplicationContextException: Unable to start embedded container;

[8a8aleo]

As a long time Spring user I am disappointed that I needed to add spring specific code just to get a servlet up and running.

Don't get me wrong though, I really believe spring boot is a great leap forward and I appreciate all the hard work.

[dsyer]

Thank you for your loyalty. How about proposing something concrete, like maybe in a pull request?

[michaelhaessig]

@8a8aleo have you got the automatic scanning of servelt annotations working ? as you said i had to declare every single servelt/weblistener as a bean

Running into the same thing with a dependent jar which contains @webfilter annotations which are not getting picked up by Spring Boot. Was quite difficult to track down why things were not working and while I can work around by registering filters for this jar myself it leaves the door open for breaking things any time I update dependencies if someone adds a new @webfilter or @WebServlet annotation.