[JAVA] Spring with Kotorin ―― 7. Service layer

Overview / Description

I've created a server-side application in Kotlin, but it's not yet properly configured. Create a controller class with "Kotorin and Spring Mone-- 2. RestController and Data Class", and the configuration is still such that data is handled directly. Therefore, we will make changes little by little. First, let's consider the "** service **" layer.

Web applications are roughly divided into the following functions.

--Request / response processing --Processing of application logic --Data processing

Until now, these functions were handled in a single layer. With this configuration, the logic to handle increases and the data model becomes complicated, One class becomes huge and development / maintenance efficiency deteriorates.

Separate each function and divide it into multiple layers.

By the way, the class I was making is RestController, Originally, it is the responsibility to handle request / response. Therefore, the other processing is cut out and it is designated as ** service **.

Assumptions / Environment

Runtime version

• Kotlin : 1.3.0
• SpringBoot : 2.1.0.RELEASE

Spring Dependencies

• Web
• Actuator

Development environment

• OS : Mac
• IDE : IntelliJ IDEA
• Build : Gradle

Procedure / Explanation

Controller class before change

Originally, I was doing things other than request / response processing such as data generation in the controller class as follows.

@RestController
@RequestMapping("/messages")
class SimpleController {

    @GetMapping
    fun getMessages() : List<Message> {
        return listOf(
                Message(
                        UUID.randomUUID().toString(),
                        "First Message",
                        "This is a 1st message on ${getDate()}."
                ),
                Message(UUID.randomUUID().toString(),
                        "Second Message",
                        "This is a 2nd message on ${getDate()}."
                )
        )
    }

    private fun getDate() : String {
        val simpleDateFormat = SimpleDateFormat("yyyy/MM/dd HH:mm:ss")
        return simpleDateFormat.format(Date())
    }
}

Service class

Move the contents originally implemented in the controller class to the service class as follows.

@Service("Message Service")
class MessageService {

    fun getMessages() : List<Message> {
        return listOf(
                Message(
                        UUID.randomUUID().toString(),
                        "First Message",
                        "This is a 1st message on ${getDate()}."
                ),
                Message(UUID.randomUUID().toString(),
                        "Second Message",
                        "This is a 2nd message on ${getDate()}."
                )
        )
    }

    private fun getDate() : String {
        val simpleDateFormat = SimpleDateFormat("yyyy/MM/dd HH:mm:ss")
        return simpleDateFormat.format(Date())
    }
}

Annotate the service class with @Service. This makes it available by Dependency Injection in the controller class.

@Autowired
private lateinit var service: MessageService

Use the lateinit keyword to declare an instance without initializing it.

Changed controller class

In the controller class that uses the service class, only the processing related to the request / response should be handled. Make the following changes to call the process implemented in the service class.

@RestController
@RequestMapping("/messages")
class MessageController() {

    @Autowired
    private lateinit var service: MessageService

    @GetMapping
    fun getMessages() = service.getMessages()
}

Summary / Looking back

Developing applications with separate layers for each responsibility is now a standard. Still, in this state, data processing is performed directly from the service layer, so Next, we will separate that part.

This source

• shinyay/spring-just-rest-kotlin/tree/first-service-layer