Using Spring Autowired in Kotlin

This post shows an example of how to use Spring Autowired to inject an service object into controller objects in Kotlin.

Requirements For Spring and Kotlin

These are Software applications used for this post.

IntelliJ IDEA Ultimate 2016.3
- The Community Edition maybe enough, but we have not tried it.
Kotlin Version 1.1
Windows 10
Spring or Spring Boot

First, we need a project that has both Kotlin and Spring working together. The fastest way to create such project is via the Spring Initialzr and explicitly choosing Kotlin as the language.

Service Codes For Kotlin in Spring

Next, we create a service within that Spring project we generated online for Kotlin. In our example, we are using two Spring beans (or components) – ClientRepo and ClientService. To demonstrate how Spring Autowired works with Kotlin, we autowire the ClientRepo in the ClientService.

package com.turreta.service

import com.turreta.domain.Client
import com.turreta.repository.ClientRepo
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.stereotype.Service
import org.springframework.transaction.annotation.Propagation
import org.springframework.transaction.annotation.Transactional

/**
 * Created by Turreta.com on 18/6/2017.
 */
@Service
class ClientService {

    // Our Spring Data repository
    @Autowired
    lateinit private var clientRepo: ClientRepo

    @Transactional(propagation = Propagation.REQUIRED)
    fun createClient(clientName: String) {
        var c = Client()
        c.clientName = clientName
        clientRepo.save(c)
    }
}

package com.turreta.service

import com.turreta.domain.Client

import com.turreta.repository.ClientRepo

import org.springframework.beans.factory.annotation.Autowired

import org.springframework.stereotype.Service

import org.springframework.transaction.annotation.Propagation

import org.springframework.transaction.annotation.Transactional

/**

* Created by Turreta.com on 18/6/2017.

@Service

class ClientService {

// Our Spring Data repository

@Autowired

lateinit private var clientRepo: ClientRepo

@Transactional(propagation = Propagation.REQUIRED)

fun createClient(clientName: String) {

var c = Client()

c.clientName = clientName

clientRepo.save(c)

}

Although the ClientRepo is not available on this post, we could create it as follows.

package com.turreta.repository

import com.turreta.domain.Client
import org.springframework.stereotype.Component

/**
 * Created by Turreta.com on 17/10/2022.
 */
@Component
class ClientRepo {

    fun save(client: Client) {
        // Save client to database
    }
}

package com.turreta.repository

import com.turreta.domain.Client

import org.springframework.stereotype.Component

/**

* Created by Turreta.com on 17/10/2022.

@Component

class ClientRepo {

fun save(client: Client) {

// Save client to database

}

Controller Codes

Then, we use the Spring Autowired annotation in Kotlin to inject the ClientService object in the IndexController.

package com.turreta.controller

import com.turreta.service.ClientService
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.stereotype.Controller
import org.springframework.web.bind.annotation.RequestMapping

@Controller
class IndexController {
    @Autowired
    lateinit var clientService: ClientService

    @RequestMapping("/")
    fun index(): String {

        clientService.createClient("Turreta.com")

        return "index"
    }
}

package com.turreta.controller

import com.turreta.service.ClientService

import org.springframework.beans.factory.annotation.Autowired

import org.springframework.stereotype.Controller

import org.springframework.web.bind.annotation.RequestMapping

@Controller

class IndexController {

@Autowired

lateinit var clientService: ClientService

@RequestMapping("/")

fun index(): String {

clientService.createClient("Turreta.com")

return "index"

}

In summary, we created three objects and let Spring manage them – ClientRepository, ClientService, and IndexController. With the exception of the ClientRepository, the other two objects has dependency to at least one other object. Therefore, IndexController has a dependency to the ServiceClient which has a dependency on the ClientRepository. We used the Spring Autowired annotation to build that chain of dependencies in Kotlin.

Alternatively, we could do away with the Spring Autowired annotation in Kotlin and retrieve the dependencies from the Spring Context.