Table of Contents
1. Overview
The tutorial illustrates how to Bootstrap a Web Application with Spring.
We’ll look into the Spring Boot solution for bootstrapping the application and also see a non-Spring Boot approach.
We’ll primarily use Java configuration, but also have a look at their equivalent XML configuration.
2. Bootstrapping Using Spring Boot
2.1. Maven Dependency
First, we’ll need the spring-boot-starter-web dependency:
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
<version>2.4.0</version>
</dependency>
This starter includes:
- spring-web and the spring-webmvc module that we need for our Spring web application
- a Tomcat starter so that we can run our web application directly without explicitly installing any server
2.2. Creating a Spring Boot Application
The most straightforward way to get started using Spring Boot is to create a main class and annotate it with @SpringBootApplication:
@SpringBootApplication
public class SpringBootRestApplication {
public static void main(String[] args) {
SpringApplication.run(SpringBootRestApplication.class, args);
}
}
This single annotation is equivalent to using @Configuration, @EnableAutoConfiguration, and @ComponentScan.
By default, it will scan all the components in the same package or below.
Next, for Java-based configuration of Spring beans, we need to create a config class and annotate it with @Configuration annotation:
@Configuration
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.
Let’s also have a look at a solution using the core spring-webmvc library.
3. Bootstrapping Using spring-webmvc
3.1. Maven Dependencies
First, we need the spring-webmvc dependency:
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-webmvc</artifactId>
<version>5.3.3</version>
</dependency>
3.2. The Java-based Web Configuration
Next, we’ll add the configuration class that has the @Configuration annotation:
@Configuration
@EnableWebMvc
@ComponentScan(basePackages = "com.maixuanviet.controller")
public class WebConfig {
}
Here, unlike the Spring Boot solution, we’ll have to explicitly define @EnableWebMvc for setting up default Spring MVC Configurations and @ComponentScan to specify packages to scan for components.
The @EnableWebMvc annotation provides the Spring Web MVC configuration such as setting up the dispatcher servlet, enabling the @Controller and the @RequestMapping annotations and setting up other defaults.
@ComponentScan configures the component scanning directive, specifying the packages to scan.
3.3. 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.maixuanviet");
container.addListener(new ContextLoaderListener(context));
ServletRegistration.Dynamic dispatcher =
container.addServlet("mvc", new DispatcherServlet(context));
dispatcher.setLoadOnStartup(1);
dispatcher.addMapping("/");
}
}
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.
This class can entirely replace the web.xml file from <3.0 Servlet versions.
4. XML Configuration
Let’s also have a quick look at the equivalent XML web configuration:
<context:component-scan base-package="com.maixuanviet.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
In this article, we looked into two popular solutions for bootstrapping a Spring web application, one using the Spring Boot web starter and other using the core spring-webmvc library.
In the next article on REST with Spring, I cover setting up MVC in the project, configuration of the HTTP status codes, payload marshalling, 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.
