Example of how SpringBoot integrates Kotlin to build Web services

  • 2021-06-29 11:09:32
  • OfStack

Today we are trying to integrate Kotlin with Spring Boot and have decided to build a very simple Spring Boot micro-service using Kotlin as a programming language.

Create a simple Spring Boot application.Here I will use maven to build the project:


<?xml version="1.0" encoding="UTF-8"?>
<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://maven.apache.org/POM/4.0.0"
     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.edurt.ski</groupId>
  <artifactId>springboot-kotlin-integration</artifactId>
  <version>1.0.0</version>
  <packaging>jar</packaging>

  <name>springboot kotlin integration</name>
  <description>SpringBoot Kotlin Integration is a open source springboot, kotlin integration example.</description>

  <parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.1.3.RELEASE</version>
    <relativePath/> <!-- lookup parent from repository -->
  </parent>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
    <java.version>1.8</java.version>
    <!-- plugin config -->
    <plugin.maven.kotlin.version>1.2.71</plugin.maven.kotlin.version>
  </properties>

  <dependencies>
    <!-- spring boot -->
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <!-- kotlin -->
    <dependency>
      <groupId>com.fasterxml.jackson.module</groupId>
      <artifactId>jackson-module-kotlin</artifactId>
    </dependency>
    <dependency>
      <groupId>org.jetbrains.kotlin</groupId>
      <artifactId>kotlin-stdlib-jdk8</artifactId>
    </dependency>
    <dependency>
      <groupId>org.jetbrains.kotlin</groupId>
      <artifactId>kotlin-reflect</artifactId>
    </dependency>
  </dependencies>

  <build>
    <sourceDirectory>${project.basedir}/src/main/kotlin</sourceDirectory>
    <testSourceDirectory>${project.basedir}/src/test/kotlin</testSourceDirectory>
    <plugins>
      <plugin>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-maven-plugin</artifactId>
      </plugin>
      <plugin>
        <artifactId>kotlin-maven-plugin</artifactId>
        <groupId>org.jetbrains.kotlin</groupId>
        <configuration>
          <args>
            <arg>-Xjsr305=strict</arg>
          </args>
          <compilerPlugins>
            <plugin>spring</plugin>
            <plugin>jpa</plugin>
            <plugin>all-open</plugin>
          </compilerPlugins>
          <pluginOptions>
            <option>all-open:annotation=javax.persistence.Entity</option>
          </pluginOptions>
        </configuration>
        <dependencies>
          <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-maven-allopen</artifactId>
            <version>${plugin.maven.kotlin.version}</version>
          </dependency>
          <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-maven-noarg</artifactId>
            <version>${plugin.maven.kotlin.version}</version>
          </dependency>
        </dependencies>
        <executions>
          <execution>
            <id>kapt</id>
            <goals>
              <goal>kapt</goal>
            </goals>
            <configuration>
              <sourceDirs>
                <sourceDir>src/main/kotlin</sourceDir>
              </sourceDirs>
              <annotationProcessorPaths>
                <annotationProcessorPath>
                  <groupId>org.springframework.boot</groupId>
                  <artifactId>spring-boot-configuration-processor</artifactId>
                  <version>${project.parent.version}</version>
                </annotationProcessorPath>
              </annotationProcessorPaths>
            </configuration>
          </execution>
        </executions>
      </plugin>
    </plugins>
  </build>

</project>

Add all required dependencies:

lib Package for kotlin-stdlib-jdk8 kotlin jdk8 kotlin-reflect kotlin Reflection Pack

A simple application class:


package com.edurt.ski

import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication

@SpringBootApplication
class SpringBootKotlinIntegration

fun main(args: Array<String>) {
  runApplication<SpringBootKotlinIntegration>(*args)
}

Add Rest API interface functionality

Create an HelloController Rest API interface, we only provide a simple get request to get hello, kotlin output information:


package com.edurt.ski.controller

import org.springframework.web.bind.annotation.GetMapping
import org.springframework.web.bind.annotation.RestController

@RestController
class HelloController {

  @GetMapping(value = "hello")
  fun hello(): String {
    return "hello,kotlin"
  }

}

Modify the SpringBootKotlinIntegration file to add the following settings to the scan path


@ComponentScan(value = [
  "com.edurt.ski",
  "com.edurt.ski.controller"
])

Add page functionality

Modify the pom.xml file to increase the following page dependencies


<!-- mustache -->
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-mustache</artifactId>
</dependency>

Create the templates folder under the src/main/resources path

Create a page file named hello.mustache under the templates folder


<h1>Hello, Kotlin</h1>

Create Page Converter HelloView


package com.edurt.ski.view

import org.springframework.stereotype.Controller
import org.springframework.ui.Model
import org.springframework.web.bind.annotation.GetMapping

@Controller
class HelloView {

  @GetMapping(value = "hello_view")
  fun helloView(model: Model): String {
    return "hello"
  }

}

Browser access to http://localhost:8080/hello_view will see the page content

Add data persistence

Modifying the pom.xml file adds the following dependencies (we use the h2 in-memory database for testing purposes)


<!-- data jpa and db -->
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
  <groupId>com.h2database</groupId>
  <artifactId>h2</artifactId>
  <scope>runtime</scope>
</dependency>

Create User entity


package com.edurt.ski.model

import javax.persistence.Entity
import javax.persistence.GeneratedValue
import javax.persistence.Id

@Entity
//class UserModel(
//    @Id
//    @GeneratedValue
//    private var id: Long? = 0,
//    private var name: String
//)
class UserModel {

    @Id
    @GeneratedValue
    var id: Long? = 0
        get() = field
        set

    var name: String? = null
        get() = field
        set

}

Create UserSupport dao Database Operations Tool Class


package com.edurt.ski.support

import com.edurt.ski.model.UserModel
import org.springframework.data.repository.PagingAndSortingRepository

interface UserSupport : PagingAndSortingRepository<UserModel, Long> {

}

Create UserService service class


package com.edurt.ski

import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication

@SpringBootApplication
class SpringBootKotlinIntegration

fun main(args: Array<String>) {
  runApplication<SpringBootKotlinIntegration>(*args)
}

0

Create UserServiceImpl implementation class


package com.edurt.ski

import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication

@SpringBootApplication
class SpringBootKotlinIntegration

fun main(args: Array<String>) {
  runApplication<SpringBootKotlinIntegration>(*args)
}

1

Create user UserController to persist data


package com.edurt.ski

import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication

@SpringBootApplication
class SpringBootKotlinIntegration

fun main(args: Array<String>) {
  runApplication<SpringBootKotlinIntegration>(*args)
}

2

Use the console window to execute the following commands to save data


curl -X POST http://localhost:8080/user/save/qianmoQ

Return results received

{"id":1,"name":"qianmoQ"}

Indicates that the data was saved successfully

Add data read rendering

Modify UserService to add the following code


package com.edurt.ski

import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication

@SpringBootApplication
class SpringBootKotlinIntegration

fun main(args: Array<String>) {
  runApplication<SpringBootKotlinIntegration>(*args)
}

4

Modify UserServiceImpl to add the following code


package com.edurt.ski

import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication

@SpringBootApplication
class SpringBootKotlinIntegration

fun main(args: Array<String>) {
  runApplication<SpringBootKotlinIntegration>(*args)
}

5

Modify UserController to add the following code


package com.edurt.ski

import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication

@SpringBootApplication
class SpringBootKotlinIntegration

fun main(args: Array<String>) {
  runApplication<SpringBootKotlinIntegration>(*args)
}

6

Create UserView file to render User data


package com.edurt.ski

import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication

@SpringBootApplication
class SpringBootKotlinIntegration

fun main(args: Array<String>) {
  runApplication<SpringBootKotlinIntegration>(*args)
}

7

Create an user.mustache file to render data (parse the returned data yourself)


{{users}}

Browser access to http://localhost:8080/user_view to see the page content

Add Unit Function

Modify the pom.xml file to add the following dependencies


package com.edurt.ski

import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication

@SpringBootApplication
class SpringBootKotlinIntegration

fun main(args: Array<String>) {
  runApplication<SpringBootKotlinIntegration>(*args)
}

9

Create an UserServiceTest file to test the UserService functionality


package com.edurt.ski

import com.edurt.ski.service.UserService
import org.junit.jupiter.api.AfterAll
import org.junit.jupiter.api.Test
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.context.SpringBootTest
import org.springframework.data.domain.PageRequest

@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
class UserServiceTest(@Autowired private val userService: UserService) {

  @Test
  fun `get all`() {
    println(">> Assert blog page title, content and status code")
    val entity = this.userService.getAll(PageRequest(0, 1))
    print(entity.totalPages)
  }

}

Source address: GitHub


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