Build a Kotlin Spring Boot Web App in Minutes: Step‑by‑Step Guide

Kotlin, originally popular for mobile development, is increasingly adopted by backend developers due to its seamless interoperability with Java, functional programming features, and strong IDE support from JetBrains.

Author Yuan Kang shares his experience using Kotlin and Spring Boot for backend development and has written the book “Practical Kotlin Spring Boot Microservices”.

The chapter “Kotlin in Common Middleware” demonstrates how to integrate Kotlin with Spring Boot, Redis, JPA, QueryDSL, MongoDB, Spring Security, RocketMQ, Elasticsearch, and Swagger, providing practical examples for each.

Spring Boot, a Pivotal project, simplifies the setup of Spring applications by following the “convention over configuration” principle, offering embedded servers, starter dependencies, and production‑ready features such as health checks and metrics.

To create a Kotlin Spring Boot project, use Spring Initializr to generate a Maven project with the Spring Web dependency, then configure the pom.xml (shown below) to include the appropriate Kotlin and Spring Boot versions.

1  <?xml version="1.0" encoding="UTF-8"?>
 2  <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 3         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
 4    <modelVersion>4.0.0</modelVersion>
 5    <parent>
 6        <groupId>org.springframework.boot</groupId>
 7        <artifactId>spring-boot-starter-parent</artifactId>
 8        <version>2.2.2.RELEASE</version>
 9        <relativePath/><!-- lookup parent from repository -->
10    </parent>
11    <groupId>io.kang.example</groupId>
12    <artifactId>kolinspringboot</artifactId>
13    <version>0.0.1-SNAPSHOT</version>
14    <name>kolinspringboot</name>
15    <description>Demo project for Spring Boot</description>
16    <properties>
17        <java.version>1.8</java.version>
18        <kotlin.version>1.3.61</kotlin.version>
19    </properties>
20    <dependencies>
21        <dependency>
22            <groupId>org.springframework.boot</groupId>
23            <artifactId>spring-boot-starter</artifactId>
24        </dependency>
25        <dependency>
26            <groupId>org.jetbrains.kotlin</groupId>
27            <artifactId>kotlin-reflect</artifactId>
28        </dependency>
29        <dependency>
30            <groupId>org.jetbrains.kotlin</groupId>
31            <artifactId>kotlin-stdlib-jdk8</artifactId>
32        </dependency>
33        <dependency>
34            <groupId>org.springframework.boot</groupId>
35            <artifactId>spring-boot-starter-test</artifactId>
36            <scope>test</scope>
37            <exclusions>
38                <exclusion>
39                    <groupId>org.junit.vintage</groupId>
40                    <artifactId>junit-vintage-engine</artifactId>
40                </exclusion>
41            </exclusions>
42        </dependency>
43    </dependencies>
44    <build>
45        <sourceDirectory>${project.basedir}/src/main/kotlin</sourceDirectory>
46        <testSourceDirectory>${project.basedir}/src/test/kotlin</testSourceDirectory>
47        <plugins>
48            <plugin>
49                <groupId>org.springframework.boot</groupId>
50                <artifactId>spring-boot-maven-plugin</artifactId>
51            </plugin>
52            <plugin>
53                <groupId>org.jetbrains.kotlin</groupId>
54                <artifactId>kotlin-maven-plugin</artifactId>
55                <configuration>
56                    <args>
57                        <arg>-Xjsr305=strict</arg>
58                    </args>
59                    <compilerPlugins>
60                        <plugin>spring</plugin>
61                    </compilerPlugins>
62                </configuration>
63                <dependencies>
64                    <dependency>
65                        <groupId>org.jetbrains.kotlin</groupId>
66                        <artifactId>kotlin-maven-allopen</artifactId>
67                        <version>${kotlin.version}</version>
68                    </dependency>
69                </dependencies>
70            </plugin>
71        </plugins>
72    </build>
73 </project>

Define a main application class annotated with @SpringBootApplication and a simple controller using @RestController and @GetMapping to return “Hello, Kotlin for Spring Boot!!”. The full source files are:

// KotlinSpringbootApplication.kt
@SpringBootApplication
class KotlinSpringbootApplication
fun main(args: Array<String>) {
    runApplication<KotlinSpringbootApplication>(*args)
}

// IndexController.kt
@RestController
class IndexController {
    @GetMapping("/index")
    fun index(): String = "Hello, Kotlin for Spring Boot!!"
}

Running the application and accessing http://localhost:8080/index displays the greeting, demonstrating how quickly a Kotlin‑based web service can be built.