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.

pom.xml

<?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.

com/zetcode/config/MyWebInitializer.java

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.

com/zetcode/config/WebConfig.java

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.

com/zetcode/controller/MyController.java

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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