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1. Overview

The tutorial illustrates how to Bootstrap a Web Application with Spring. We’ll focus on Java configuration, but also have a look at XML configuration.

Further reading:

Spring Boot Tutorial – Bootstrap a Simple Application

This is how you start understanding Spring Boot.

Read more

Configure a Spring Boot Web Application

Some of the more useful configs for a Spring Boot application.

Read more

Migrating from Spring to Spring Boot

See how to properly migrate from a Spring to Spring Boot.

Read more

2. Maven Dependencies

The main dependency we need for a web application is the spring-webmvc dependency:

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-webmvc</artifactId>
    <version>5.0.0.RELEASE</version>
</dependency>

3. The Java-based Web Configuration

First, we’ll add a WebConfig class that has the @Configuration annotation:

@Configuration
@EnableWebMvc
@ComponentScan(basePackages = "com.baeldung.controller")
public class WebConfig {
   
}

This annotation is the main artifact used by the Java-based Spring configuration; it is itself meta-annotated with @Component, which makes the annotated classes standard beans and as such, also candidates for component-scanning.

The main purpose of @Configuration classes is to be sources of bean definitions for the Spring IoC Container. For a more detailed description, see the official docs.

Next, the @EnableWebMvc annotation provides the Spring Web MVC configuration that enables the @Controller and the @RequestMapping annotations.

Moving on to @ComponentScan – this configures the component scanning directive, specifying the packages to scan.

As of Spring 3.1, the @Configuration are excluded from classpath scanning by default – see this JIRA issue. Before Spring 3.1 though, we needed to exclude these classes explicitly:

excludeFilters = { @ComponentScan.Filter( Configuration.class ) }

The @Configuration classes should not be auto-discovered because they are already specified and used by the container – allowing them to be rediscovered and introduced into the Spring context will result in the following error:

Caused by: org.springframework.context.annotation.ConflictingBeanDefinitionException: Annotation-specified bean name ‘webConfig’ for bean class [org.rest.spring.AppConfig] conflicts with existing, non-compatible bean definition of same name and class [org.rest.spring.AppConfig]

3.1. The Initializer Class

Next, we need to add a class that implements the WebApplicationInitializer interface:

public class AppInitializer implements WebApplicationInitializer {

    @Override
    public void onStartup(ServletContext container) throws ServletException {
        AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
        context.scan("com.baeldung");
        container.addListener(new ContextLoaderListener(context));

        ServletRegistration.Dynamic dispatcher = container.addServlet("mvc", new DispatcherServlet(context));
        dispatcher.setLoadOnStartup(1);
        dispatcher.addMapping("/");   
    }
}

This class can entirely replace the web.xml file from <3.0 Servlet versions.

Here, we’re creating a Spring context using the AnnotationConfigWebApplicationContext class, which means we’re using only annotation-based configuration. Then, we’re specifying the packages to scan for components and configuration classes.

Finally, we’re defining the entry point for the web application – the DispatcherServlet.

4. XML Configuration

Let’s also have a quick look at the equivalent XML web configuration:

<context:component-scan base-package="com.baeldung.controller" />
<mvc:annotation-driven />

We can replace this XML file with the WebConfig class above.

To start the application, we can use an Initializer class that loads the XML configuration or a web.xml file. For more details on these two approaches, check out our previous article.

5. Conclusion

The presented approach shows how we can configure a web application with Spring and how to migrate the Spring configuration from XML to Java, mixing the old and the new. This is important for older projects, which may have a lot of XML based configuration that we can’t migrate all at once.

This way, in a migration, we can port the XML beans in small increments.

In the next article on REST with Spring, I cover setting up MVC in the project, configuration of the HTTP status codes, payload marshaling, and content negotiation.

As always, the code presented in this article is available over on Github. This is a Maven based project, so it should be easy to import and run as it is.

I just announced the new Spring Boot 2 material, coming in REST With Spring:

>> CHECK OUT THE LESSONS

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Chris Beams
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Chris Beams

Hi Eugen,

Note that as of Spring 3.1 RC2, use of [email protected](Configuration.class) is no longer necessary. See https://jira.springsource.org/browse/SPR-8808.

Would you mind updating your examples to depend on RC2 and eliminating this bit from the @ComponentScan definition?

Thanks for a great series of posts!

Eugen Paraschiv
Guest

Thank you for letting me know (as well as for the actual work). The update is now included in the article.

Amol Khanolkar
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Amol Khanolkar

Can you tell me some advantages of using java based configurations over XML based and when to choose which one?

Torben Vesterager
Guest
Torben Vesterager

Simple – you have one file for configuration and functionality – instead of jumping between 2

Eugen Paraschiv
Guest

Type safety is a big one, and ease of use is a close second.

Stephane
Guest
Stephane

And you can use a debugger if needed.

Eugen Paraschiv
Guest

I updated the article – thanks.

Stephane
Guest
Stephane

It’d be nice to also include a showcase on how to replace the web.xml file by a class implementing the WebApplicationInitializer interface.

Eugen Paraschiv
Guest

I am planning to discuss that in an upcoming article.

Stephane
Guest
Stephane

I could in fact do it, and it wasn’t that hard. The only thing that I could not cut is how to move the elements of the log4j config into a Java config. Google was dry on this one. Maybe your next article would shed some light on this 🙂 Thanks again.

Stephane
Guest
Stephane

It’s funny, my comment was automatically closed by a tag.

Anuj Patel
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Anuj Patel

Thanks ! It really helps to clear concepts and will help while doing actual Implementation