HowTo: migrate from traditional web.xml to spring boot?

[mfkenson]

nice to see this great project. wanna switch my projects to spring-based product.
so my 1st question is how to migrate from traditional web.xml to spring boot?

<web-app version="3.0"
  xmlns="http://java.sun.com/xml/ns/javaee"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="
    http://java.sun.com/xml/ns/javaee
    http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
    <display-name>Vaadin Widget Test Application</display-name>
  <listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
  </listener>
  <listener>
    <listener-class>org.springframework.web.context.request.RequestContextListener</listener-class>
  </listener>
  <context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>/WEB-INF/root-context.xml</param-value>
  </context-param>
  <servlet>
    <servlet-name>Gmama</servlet-name>
    <servlet-class>ru.xpoft.vaadin.SpringVaadinServlet</servlet-class>
    <init-param>
      <param-name>beanName</param-name>
      <param-value>myUI</param-value>
    </init-param>
    <init-param>
      <param-name>systemMessagesBeanName</param-name>
      <param-value>DEFAULT</param-value>
    </init-param>
    <async-supported>true</async-supported>
  </servlet>
  <servlet-mapping>
    <servlet-name>Gmama</servlet-name>
    <url-pattern>/*</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>Gmama</servlet-name>
    <url-pattern>/VAADIN/*</url-pattern>
  </servlet-mapping>
  <context-param>
    <description>Vaadin production mode</description>
    <param-name>productionMode</param-name>
    <param-value>false</param-value>
  </context-param>
  <servlet-mapping>
    <servlet-name>default</servlet-name>
    <url-pattern>/static/*</url-pattern>
  </servlet-mapping>
</web-app>

[dsyer]

I'm happy to treat this one as a request for documentation (hence appropriate as an issue) though. If you want to contribute some documentation that would be great. Generally, though, can you post general HOWTO questions on stackoverflow (easier for people to find them for reference in the future), please?

One thing is unusual about your application: it doesn't have a Spring DispatcherServlet. Maybe that's common in Vaadin land (I have no experience with that)., but it isn't common in general. That's not to say that you can't convert you app, but it might not be suitable as a case study for Spring MVC apps in general.

The first thing you have to decide is what the target is. Do you want an executable JAR, or a WAR? If the former, then maybe the latter is a useful first step anyway.

You should be able to just create an application configuration main class (like the samples and guides) and import the XML file to get started. To run as a WAR in a container you will need a SpringBootServletInitializer. That will get you something that runs, but won't be serving your resources yet. Then you can probably start removing stuff from the XML that Boot already provides by autoconfiguration. Without access to the file it's hard to say how smoothly that would go.

A Servlet is added to a Spring Boot standalone application by adding a @Bean of type Servlet (or ServletRegistrationBean for more control of mapping and parameters).

This application only has one servlet. What is the purpose of the /* mapping? Normally this would be a Spring DispatcherServlet in an autoconfigured Boot application, so that will be the only complicated piece. I imagine you can probably just create a @Bean definition for it, but you will have to take steps to disable the default DispatcherServlet. Looking at DispatcherServletAutoConfiguration I'd say you might only be able to do that by declaring your own DispatcherServlet and mapping it to an unused path. (Or if SpringVaadinServlet actually is a DispatcherServlet, forgive my ignorance, then just declaring it with bean id "dispatcherServlet" would be enough.)

I'm happy to work with you to make this easier if it turns out to be hard for no good reason.

[mfkenson]

It's my pleasure to contribute, though I am not familiar with the Spring MVC. I believe Vaadin is great sample for beginner like me who prefer OO user interface instead of complete HTML/CSS. Every UI components are OO in Vaadin and they can be managed by Spring Container!

Since the UI rendering is completely done on server-side (vaadin characteristics), 1 servlet is enough for it.
Though there may be many views
(e.g.
http://vaadin.app.sample/!#login
http://vaadin.app.sample/!#admin
)
,they are handled by the "spring-vaadin" servlet -> ru.xpoft.vaadin.SpringVaadinServlet
I believe this SpringVaadinServlet actually is a DispatcherServlet.

You could take a look here.
https://github.com/xpoft/spring-vaadin/blob/master/src/main/java/ru/xpoft/vaadin/SpringVaadinServlet.java
And the Sample Spring-Vaadin Web Application here.
https://github.com/xpoft/vaadin-samples/tree/master/spring-integration

I wanna have an executable JAR!( One of the major reasons I wanna move to spring boot)

I have just posted the question in stack overflow
http://stackoverflow.com/questions/20240939/how-to-migrate-from-traditional-java-web-application-with-web-xml-to-spring-bo

[dsyer]

I added some general guidelines to the Stackoverflow post and to the Spring Boot docs. I can't make much progress with this particular app unless the source code for all dependencies (in particular Vaadin) is available (it isn't in the Maven repository as far as I can tell).

[mfkenson]

thank you dsyer! i would work on it! btw, vaadin is on maven, isn't it?
you can see the dependency in https://github.com/xpoft/vaadin-samples/blob/master/parent/pom.xml as referred by that sample application. and the source code https://github.com/vaadin/vaadin

[dsyer]

Thanks. I found the vaadin source code (don't know why I couldn't see it before), but the xpoft spring integration code is apparently only available on github which is a pain. My work in progress is here: https://github.com/dsyer/vaadin-samples/tree/feature/bootify, so you can see that it's not a lot of work. It is still broken (even with some changes to Boot that I just pushed). The current problem is eager initialization of Vaadin components that rely on a web request being active. I'll continue to look at that.

[dsyer]

OK, so now the app on my branch is starting and the home page looks OK (hard to say since I don't I don't know what it is supposed to do). The i18n pages don't work, and I don't know enough about Vaadin to know why, so you might have to help with that. Be sure to get the latest Boot snapshots.

[dsyer]

There is generic documentation in https://github.com/spring-projects/spring-boot/blob/master/docs/howto.md now, so I'll leave the Vaadin question to be answered on StackOverflow.

[JLLeitschuh]

That link no longer exists.

[dsyer]

Yeah, and this is a closed issue that is almost 4 years old. Did you try the user guide (e.g. http://docs.spring.io/spring-boot/docs/1.5.2.RELEASE/reference/htmlsingle/#howto-convert-an-existing-application-to-spring-boot) or the Spring guides (e.g. https://spring.io/guides/gs/convert-jar-to-war/)?

[JLLeitschuh]

The link to that issue is useful. Random users may stumble across it now and again searching google for such things.
Thanks for the help!

[mekazu]

Here's a link to the more up-to-date relevant guide: https://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#howto-convert-an-existing-application-to-spring-boot