How to migrate from traditional java web application (with web.xml) to spring boot?

spring, spring-boot, vaadin, web.xml

Solution

This application is not a Spring MVC application as far as I can tell - it would probably be a lot easier to migrate if it was. The goal (per the github issue) is to obtain an executable JAR. The basic plan though might be to migrate first to a WAR using Spring Boot and then to a JAR once that is working. It's a pretty simple app so all we really need to do is look at the `web.xml` and translate it into the relevant Spring Boot features. Here are some general guides:

Create a deployable WAR by extending `SpringBootServletInitializer` (e.g. in a class called `Application`), and add the Spring Boot `@EnableAutoConfiguration` annotation. Example:

    @Configuration
    @EnableAutoConfiguration
    @ComponentScan
    public class Application extends SpringBootServletInitializer {

        @Override
        protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
            return application.sources(Application.class);
        }

Then add some configuration:

A `@Bean` of type `Servlet` or `ServletRegistrationBean` installs that bean in the container as if it was a `<servlet/>` and `<servlet-mapping/>` in `web.xml`

A `@Bean` of type `Filter` or `FilterRegistrationBean` behaves similarly (like a `<filter/>` and `<filter-mapping/>`).

The `ApplicationContext` in this case is rooted in an XML file, so the easiest first step is to `@Import` that into the Spring `Application`. This one is so simple that it can be recreated in a few lines as `@Bean` definitions.

Static resources can be moved to `/public` (or `/static` or `/resources` or `/META-INFO/resources`) in the classpath root

Once the WAR is working we make it executable by adding a `main` method to our `Application`, e.g.

public static void main(String[] args) {
    SpringApplication.run(Application.class, args);
}

See also the Getting Started Guide on Converting a JAR to a WAR.

As I said, the biggest problem with this specific app is that it isn't a Spring MVC app. As the Irishman might say "If I wanted to get to there, sir, I wouldn't be starting from here." This is an interesting question in general, but I recommend anyone else looking to migrate a Spring application to Spring Boot read the general advice here but maybe start another discussion somewhere else.

Anyway, I'll have a bash at converting this specific app (source code jars would be nice), and update this response if I learn anything new.

Problem

Original source