Migrating Spring web application to Spring Boot

Question

I have a web project, and I depoly it on tomcat easily. Infact I have a WebAppInitializer class that implements WebApplicationInitializer (this class it's really fat), as you know every application server that supports servlet 3.0, it can easily detect it and try to boot it. Now I wonder that it could be possible to use spring boot starter and without any further configuration, I pass my WebAppInitializer to it and spring boot based on my WebAppInitializer boots my project?

I just want to use the approach of spring-boot to deploy application on Tomcat and I don't want to use other spring-boot's facilities.

Answer 1

From the Spring Boot docs :

Servlet 3.0+ applications might translate pretty easily if they already use the Spring Servlet 3.0+ initializer support classes. Normally all the code from an existing WebApplicationInitializer can be moved into a SpringBootServletInitializer. If your existing application has more than one ApplicationContext (eg if it uses AbstractDispatcherServletInitializer) then you might be able to squash all your context sources into a single SpringApplication. The main complication you might encounter is if that doesn't work and you need to maintain the context hierarchy. See the entry on building a hierarchy for examples. An existing parent context that contains web-specific features will usually need to be broken up so that all the ServletContextAware components are in the child context.

So yes, it's possible but you need to convert it to SpringBootServletInitializer , which seems to be quite similar.

Answer 2

http://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#howto-create-a-deployable-war-file准确地描述了如何做到这一点

Answer 3

Yes, it's an old question. But I do not see an accepted answer and the one closest to a working one only has a link to an external resource. So here it is.

https://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#boot-features-embedded-container-context-initializer

28.4.2 Servlet Context Initialization

Embedded servlet containers do not directly execute the Servlet 3.0+ javax.servlet.ServletContainerInitializer interface or Spring's org.springframework.web.WebApplicationInitializer interface. This is an intentional design decision intended to reduce the risk that third party libraries designed to run inside a war may break Spring Boot applications.

If you need to perform servlet context initialization in a Spring Boot application, you should register a bean that implements the org.springframework.boot.web.servlet.ServletContextInitializer interface. The single onStartup method provides access to the ServletContext and, if necessary, can easily be used as an adapter to an existing WebApplicationInitializer.

Scanning for Servlets, Filters, and listeners

When using an embedded container, automatic registration of classes annotated with @WebServlet, @WebFilter, and @WebListener can be enabled by using @ServletComponentScan.

[Tip] @ServletComponentScan has no effect in a standalone container, where the container's built-in discovery mechanisms are used instead.

I've tried it. It works

In my use case I have project containing a few dozens of webapps, designed to run on Tomcat as WAR. Lots of logics was neatly crafted into WebApplicationInitializers and it seemed there should be an easier way to reuse all this. Adding implements ServletContextInitializer to those initializers and exposing them as beans through @Configuration classes lit my webservers up with SpringBoot's embedded Tomcat.