Spring Boot WebApplicationType

last modified July 20, 2023

Spring Boot WebApplicationType tutorial presents various types of web applications in a Spring Boot application. The example shows how to set the WebApplicationType.

Spring Boot is a popular application framework for creating enterprise application in Java, Kotlin, or Groovy.

WebApplicationType

The WebApplicationType is an enumeration of possible types of web applications. There are three possible values:

• NONE - the application should not run as a web application and should not start an embedded web server.
• REACTIVE - the application should run as a reactive web application and should start an embedded reactive web server.
• SERVLET - the application should run as a servlet-based web application and should start an embedded servlet web server.

Spring Boot example

In the following application, we define the web application type of a Spring Boot application.

build.gradle 
...
src
├── main
│ ├── java
│ │ └── com
│ │ └── zetcode
│ │ └── Application.java
│ └── resources
└── test
 └── java

This is the project structure of the Spring Boot application.

plugins {
 id 'java'
 id 'org.springframework.boot' version '3.1.1'
 id 'io.spring.dependency-management' version '1.1.0'
}
group = 'com.zetcode'
version = '0.0.1-SNAPSHOT'
java {
 sourceCompatibility = '17'
}
repositories {
 mavenCentral()
}
dependencies {
 implementation 'org.springframework.boot:spring-boot-starter-webflux'
 implementation 'org.springframework.boot:spring-boot-starter-web'
}
test {
 useJUnitPlatform()
}

In the build.gradle file, we have dependencies for a classic servlet and reactive web application.

package com.zetcode;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.WebApplicationType;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.reactive.function.server.RouterFunction;
import org.springframework.web.reactive.function.server.ServerResponse;
import static org.springframework.web.reactive.function.BodyInserters.fromValue;
import static org.springframework.web.reactive.function.server.RequestPredicates.GET;
import static org.springframework.web.reactive.function.server.RouterFunctions.route;
import static org.springframework.web.reactive.function.server.ServerResponse.ok;
@SpringBootApplication
public class Application {
 public static void main(String[] args) {
 new SpringApplicationBuilder(Application.class)
 .web(WebApplicationType.SERVLET)
 .run(args);
 }
}
@RestController
class MyController {
 @GetMapping("/")
 public String hello() {
 return "Home page";
 }
}
@Configuration
class MyRoutes {
 @Bean
 RouterFunction<ServerResponse> about() {
 return route(GET("/about"), request -> ok().body(fromValue("About page")));
 }
}
@Component
class MyRunner implements CommandLineRunner {
 @Override
 public void run(String... args) throws Exception {
 System.out.println("Hello there!");
 }
}

In the Application, we define the Spring Boot application and set up a classic web rest point, a reactive route and a commandline runner.

new SpringApplicationBuilder(Application.class)
 .web(WebApplicationType.SERVLET)
 .run(args);

We define the web application type using the SpringApplicationBuilder. For the WebApplicationType.SERVLET, the reactive route is not available.

$ ./gradlew bootRun

We start the application.

$ curl localhost:8080/
Home page

The classic servlet rest point is active.

In this article we have worked with a Spring Boot WebApplicationType.

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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