[JAVA] Spring with Kotorin --2 RestController and Data Class

Overview / Description

The code I saw in "Spring with Kotorin-- 1. SPRING INITIALIZR" was automatically generated by SPRING INITIALIZR and there is no particular processing. It was a thing.

So this time, I will add the following very simple process.

--Add controller for REST access: ** RestController ** --Adding entities for information to display on access: ** Data Class **

RestController Create a class with ** @ RestController ** annotations to define the RestController class.

RestController

@RestController
class SimpleController { 
  ...
}

By the way, this @RestController is a combination of ** @ Controller ** and ** @ ResponseBody **. Therefore, it behaves in the same way even if it is defined as follows.

Controller

@Controller
@ResponseBody
class SimpleController { 
  ...
}

RequestMapping ** @RequestMapping ** Annotate and map to the request from the client.

Specify the mapping condition using the following attributes.

• value --Write the URL path
• method --Specify methods such as GET and POST
• headers --Specify HTTP header
• params --Specify request parameters

GetMapping The ** @GetMapping ** annotation is an annotation that acts as a shortcut for @RequestMapping (method = RequestMethod.GET).

Data Class A data class is a class that is used to hold only data without processing. The data class is defined in the following format.

-** data ** Add keyword before class --Define the primary constructor

DataClass

data class Data(var id: String, var value: String)

The compiler automatically infers and generates the following processing from the contents defined as the data class.

• equals() / hashCode() --ToString () in "Data (id = foo, value = bar)" format
• copy() --ComponentS () that retrieves the contents in the declared order

Assumptions / Environment

Runtime version

• Kotlin : 1.3.0
• SpringBoot : 2.1.0.RELEASE

Spring Dependencies

• Web

Development environment

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

Procedure / Explanation

Data Class

data class Message(var id: String,
                   var title: String,
                   var message: String)

You can see that the description is simple without getter, setter, toString, and equals that were described when defining the definition of JavaBeans in Java. A similar description was achieved in Java by using ** Lombok **, but Kotlin supports this format at the language level.

RestController

import io.pivotal.syanagihara.simple.data.Message
import org.springframework.web.bind.annotation.GetMapping
import org.springframework.web.bind.annotation.RequestMapping
import org.springframework.web.bind.annotation.RestController
import java.text.SimpleDateFormat
import java.util.*

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

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

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

Using Java API

I am using the ** java.util.Date ** class to print the current date and time. In this way, Java API calls from Kotlin can be made transparently.

Access modifier

I have declared getDate () private, but I will briefly summarize Kotlin's access modifiers.

Summary / Looking back

When accessing this application, the following result is returned.

$ curl http://localhost:8080/simple

[{"id":"2ac2bf0a-8276-43e2-89d2-c0eb70ad38d9","title":"First Message","message":"This is a 1st message on 2018/11/04 20:52:45."},{"id":"04e915e4-f4fb-4920-84c9-f411f7603044","title":"Second Message","message":"This is a 2nd message on 2018/11/04 20:52:45."}]

I find Lombok + Java useful, but I find Kotlin, which offers Lombok-equivalent functionality at the language level, even more useful. Also, this time I made a simple application using RestController. It's very simple and easy with Spring + Kotlin without any unnecessary description.

This source

• spring-just-rest-kotlin/tree/first-rest-get