Spring WebApplicationInitializer tutorial

last modified October 18, 2023

Spring WebApplicationInitializer tutorial shows how to bootstrap Spring web applications programatically with WebApplicationInitializer.

Spring is a popular Java application framework for creating enterprise applications.

WebApplicationInitializer

WebApplicationInitializer is used for booting Spring web applications. WebApplicationInitializer registers a Spring DispatcherServlet and creates a Spring web application context. Mostly, developers use AbstractAnnotationConfigDispatcherServletInitializer, which is an implementation of the WebApplicationInitializer, to create Spring web applications.

Traditionally, Java web applications based on Servlets were using web.xml file to configure a Java web application. Since Servlet 3.0, web applications can be created programatically via Servlet context listeners.

Spring WebApplicationInitializer example

The following application uses WebApplicationInitializer to create a Spring web application.

pom.xml
src
├───main
│ ├───java
│ │ └───com
│ │ └───zetcode
│ │ ├───config
│ │ │ MyWebInitializer.java
│ │ │ WebConfig.java
│ │ └───controller
│ │ MyController.java
│ └───resources
└───test
 └───java

This is the project structure.

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
 http://maven.apache.org/xsd/maven-4.0.0.xsd">
 <modelVersion>4.0.0</modelVersion>
 <groupId>com.zetcode</groupId>
 <artifactId>mockmvcex</artifactId>
 <version>1.0-SNAPSHOT</version>
 <packaging>war</packaging>
 <properties>
 <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
 <maven.compiler.source>17</maven.compiler.source>
 <maven.compiler.target>17</maven.compiler.target>
 <spring-version>5.3.23</spring-version>
 </properties>
 <dependencies>
 <dependency>
 <groupId>ch.qos.logback</groupId>
 <artifactId>logback-classic</artifactId>
 <version>1.4.0</version>
 </dependency>
 <dependency>
 <groupId>javax.servlet</groupId>
 <artifactId>javax.servlet-api</artifactId>
 <version>4.0.1</version>
 <scope>provided</scope>
 </dependency>
 <dependency>
 <groupId>org.springframework</groupId>
 <artifactId>spring-webmvc</artifactId>
 <version>5.3.23</version>
 </dependency>
 </dependencies>
 <build>
 <plugins>
 <plugin>
 <groupId>org.apache.maven.plugins</groupId>
 <artifactId>maven-war-plugin</artifactId>
 <version>3.3.2</version>
 </plugin>
 </plugins>
 </build>
</project>

In the pom.xml file we have the following dependencies: logback-classic javax.servlet-api, and spring-webmvc.

package com.zetcode.config;
import org.springframework.web.WebApplicationInitializer;
import org.springframework.web.context.support.AnnotationConfigWebApplicationContext;
import org.springframework.web.servlet.DispatcherServlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
public class MyWebInitializer implements WebApplicationInitializer {
 @Override
 public void onStartup(ServletContext servletContext) throws ServletException {
 var ctx = new AnnotationConfigWebApplicationContext();
 ctx.register(WebConfig.class);
 ctx.setServletContext(servletContext);
 var servlet = servletContext.addServlet("dispatcher", new DispatcherServlet(ctx));
 servlet.setLoadOnStartup(1);
 servlet.addMapping("/");
 }
}

MyWebInitializer implements the WebApplicationInitializer interface. The bootstrap code is in the onStartup method.

var ctx = new AnnotationConfigWebApplicationContext();
ctx.register(WebConfig.class);
ctx.setServletContext(servletContext);

We create an AnnotationConfigWebApplicationContext and register a web configureation file with register. We bind the application context with the Servlet context.

var servlet = servletContext.addServlet("dispatcher", new DispatcherServlet(ctx));
servlet.setLoadOnStartup(1);
servlet.addMapping("/");

Here we register a Spring DispatcherServlet, which is a front controller for a Spring web application.

package com.zetcode.config;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;
@Configuration
@EnableWebMvc
@ComponentScan(basePackages = "com.zetcode")
public class WebConfig {
}

The WebConfig enables Spring MVC annotations with @EnableWebMvc and configures component scanning for the com.zetcode package.

package com.zetcode.controller;
import org.springframework.http.MediaType;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
@RestController
public class MyController {
 @GetMapping(value = "/", produces = MediaType.TEXT_PLAIN_VALUE)
 public String home() {
 return "This is home page";
 }
}

MyController is a RESTful controller, which has one mapping.

$ curl localhost:8080
This is home page

We connect to the home page with curl tool.

In this article we have created a simple Spring web application with WebApplicationInitializer.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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