Kotlin을 사용한 Spring Boot 개발기 - Controller (@RequestParam, @PathVariable) Spring Boot with Kotlin - Controller (@RequestParam, @PathVariable)

I’m going to try developing Spring Boot using Kotlin.

I was a bit bored (?) and thought, let’s do another development project with Spring! And since I was making it anyway, I decided to try it with Kotlin.

It might be a bit disorganized, but I’ll organize what I look up while developing.

Spring Boot and Kotlin

I won’t write about setup since many people have already written about it. (Everyone has already done a great job explaining it)

I’m planning to create a project similar to LinkedIn. It’s a demo project, but I want to experience connecting many people.

Writing a Controller in Kotlin

I first wrote a controller related to User.

Within the package containing the base Application.kt, I set up a Controller package and created a Kotlin file below it.

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Since it’s a test, let’s say hello with GetMapping - queryParam

While thinking about what to do with the controller, I thought let’s just do a simple test with GetMapping! I wanted to receive GET requests with GetMapping and wrote code to check incoming queryParams.

The annotation that receives query parameters is @RequestParam.

package com.example.linkwithbackend.controller

import org.springframework.stereotype.Controller
import org.springframework.web.bind.annotation.*
import java.util.*

@Controller
@RestController
@RequestMapping("/user")
class UserController {

    @GetMapping()
    fun getUser(@RequestParam(required = false) name: Optional<String>): String {
        return "Hello ${name.orElse("World")}"
    }
}

I thought the Query Parameter might not always come in, and I wanted it to work well anyway, so I wanted to give it options.

Unlike the previous Java-based Spring, I didn’t just give the option with (required=false), but also gave Optional<T> to the data type of the parameter variable.

I made the return value to show what came in if the variable (query parameter) comes in, and to output World otherwise, to handle each situation.

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Since it’s a test, let’s say hello with GetMapping - PathVariable

Let’s also check the method of putting variables in the url path, not just Query Parameters.

URLs sometimes have variable parameters for the resource to be displayed, like the 1 at the end of http://www.abcd.com/user/1. Since it can be used in many places, not just GET requests, I tried it out briefly.

@GetMapping("/{idx}")
    fun getUserDetail(@PathVariable("idx") idx:Int):String{
        return "Hello User Detail $idx"
    }

I wrote it inside the same controller as before, and set idx as the PathParam. The annotation that receives this variable is @PathVariable, and you just use the saved variable name as is.

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Next Todo

In the next post, I’ll briefly look at POST-related things and try to properly set up the Return object. And now that I have a basic feel for it, I should develop features related to user information.

• Create user table
• User CRUD
• Login