spring-boot-kotlin-app

In this guide, we will be building a Kotlin RESTful web services using Spring Boot and Spring MVC / JAX-RS. Instructions are provided to use either Spring MVC or JAX-RS. We will be adding unit tests and integration tests as well. This guide assumes you have a basic knowledge of Kotlin, Spring Boot and Maven.

Note: Maven is used in the uploaded source code but instructions are provided to use Gradle instead of Maven.

Setup

Create a sample app

• Go to Spring Initializr and generate a Gradle/Maven with Kotlin and Spring Boot project.
• Select Web as dependency to build a Spring MVC RESTful webservice.
• Select Jersey (JAX-RS) as dependency to build a JAX-RS RESTful webservice.
• Fill in the Group and Artifact and click on generate project.

Import to IntelliJ

Import the extracted folder to IntelliJ.

Application Context

Add a Spring Boot application context. This class will be generated by Spring Initializr.

@SpringBootApplication
class HelloApplication

fun main(args: Array<String>) {
    SpringApplication.run(HelloApplication::class.java, *args)
}

Add a REST endpoint class

Add a controller

Spring MVC

@RestController
@RequestMapping("hello")
class HelloController {
    @GetMapping("/string")
    fun helloString() = "Hello string!"
}

Add a JAX-RS endpoint

JAX-RS

@Component
@Path("/hello")
class HelloResource {
    @GET
    @Path("/string")
    fun helloString() = "Hello string!"
}

Add Jersey ResourceConfig

JAX-RS

Note: This is required only for JAX-RS based service. Do not add this for Spring MVC based service.

Add Jersey ResourceConfig class to your Spring context and register the JAX-RS endpoint class. This is commented out in uploaded source code. You have to uncomment it, if you are using JAX-RS.

@Component
class HelloConfig : ResourceConfig() {
    init {
        registerEndpoints()
    }

    private fun registerEndpoints() {
        register(HelloResource())
    }
}

Start the application

Start the application from HelloApplication class and load http://localhost:8080/hello/string

Hello string!

Service

Let's add a service and wire it into our controller / JAX-RS endpoint.

Add a service class

Spring MVC and JAX-RS

@Service
class HelloService {
    fun getHello() = "Hello service!"
}

Add a new REST endpoint

Spring MVC

@Autowired
lateinit var helloService: HelloService

@GetMapping("/service")
fun helloService() = helloService.getHello()

JAX-RS

@Autowired
lateinit var helloService: HelloService

@GET
@Path("/service")
fun helloService() = helloService.getHello()

Restart the application

Restart the application from HelloApplication class and load http://localhost:8080/hello/service

Hello service!

Data class

Let's add a data object to return in our controller / JAX-RS endpoint.

Add a data class

Spring MVC and JAX-RS

data class Hello(val message: String)

Add a new REST endpoint

Spring MVC

@GetMapping("/data")
fun helloData() = Hello("Hello data!")

JAX-RS

@GET
@Path("/data")
@Produces("application/json")
fun helloData() = Hello("Hello data!")

Add the Jackson maven dependency

jackson-module-kotlin is required to support marshaling.

Spring MVC and JAX-RS

Gradle

compile('com.fasterxml.jackson.module:jackson-module-kotlin')

Maven

<dependency>
    <groupId>com.fasterxml.jackson.module</groupId>
    <artifactId>jackson-module-kotlin</artifactId>
</dependency>

Restart the application

Restart the application from HelloApplication class and load http://localhost:8080/hello/data

{
    "message":"Hello data!"
}

Integration test

Spring MVC and JAX-RS

@RunWith(SpringRunner::class)
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
class HelloEndointIntegrationTest {

    @Autowired
    lateinit var testRestTemplate: TestRestTemplate

    @Test
    fun testHelloController() {
        val result = testRestTemplate.getForEntity("/hello/string", String::class.java)
        assertNotNull(result)
        assertEquals(result.statusCode, HttpStatus.OK)
        assertEquals(result.body, "Hello string!")
    }

    @Test
    fun testHelloService() {
        val result = testRestTemplate.getForEntity("/hello/service", String::class.java)
        assertNotNull(result)
        assertEquals(result.statusCode, HttpStatus.OK)
        assertEquals(result.body, "Hello service!")
    }

    @Test
    fun testHelloDto() {
        val result = testRestTemplate.getForEntity("/hello/data", Hello::class.java)
        assertNotNull(result)
        assertEquals(result.statusCode, HttpStatus.OK)
        assertEquals(result.body, Hello("Hello data!"))
    }
}

Unit test

Controller / JAX-RS unit test

Spring MVC

@RunWith(MockitoJUnitRunner::class)
class HelloControllerUnitTest {

    @InjectMocks
    lateinit var helloController: HelloController

    @Mock
    lateinit var helloService: HelloService

    @Test
    fun testHelloController() {
        val result = helloController.helloString()
        assertNotNull(result)
        assertEquals("Hello string!", result)
    }

    @Test
    fun testHelloService() {
        doReturn("Hello service!").`when`(helloService).getHello()
        val result = helloController.helloService()
        assertNotNull(result)
        assertEquals("Hello service!", result)
    }

    @Test
    fun testHelloDto() {
        val result = helloController.helloData()
        assertNotNull(result)
        assertEquals(Hello("Hello data!"), result)
    }
}

JAX-RS

@RunWith(MockitoJUnitRunner::class)
class HelloResourceUnitTest {

    @InjectMocks
    lateinit var helloResource: HelloResource

    @Mock
    lateinit var helloService: HelloService

    @Test
    fun testHelloController() {
        val result = helloResource.helloString()
        assertNotNull(result)
        assertEquals("Hello string!", result)
    }

    @Test
    fun testHelloService() {
        doReturn("Hello service!").`when`(helloService).getHello()
        val result = helloResource.helloService()
        assertNotNull(result)
        assertEquals("Hello service!", result)
    }

    @Test
    fun testHelloDto() {
        val result = helloResource.helloData()
        assertNotNull(result)
        assertEquals(Hello("Hello data!"), result)
    }
}

Service unit test

Spring MVC and JAX-RS

@RunWith(MockitoJUnitRunner::class)
class HelloServiceUnitTest {

    @InjectMocks
    lateinit var helloService: HelloService

    @Test
    fun testHelloController() {
        val result = helloService.getHello()
        assertNotNull(result)
        assertEquals("Hello service!", result)
    }
}

References

• http://www.baeldung.com/spring-boot-kotlin
• https://dzone.com/articles/using-jax-rs-with-spring-boot-instead-of-mvc